bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of level-spacing statistics in chaotic graphene billiards
Authors: Huang Liang , Lai Ying-Cheng , Grebogi Celso
Published: March 2011

A fundamental result in nonrelativistic quantum nonlinear dynamics is that the spectral statistics of quantum systems that possess no geometric symmetry, but whose classical dynamics are chaotic, are described by those of the Gaussian orthogonal ensemble (GOE) or the Gaussian unitary ensemble (GUE), in the presence or absence of time-reversal symmetry, respectively. For massless spin-half particles such as neutrinos in relativistic quantum mechanics in a chaotic billiard, the seminal work of Berry and Mondragon established the GUE nature of the level-spacing statistics, due to the combination of the chirality of Dirac particles and the confinement, which breaks the time-reversal symmetry. A question is whether the GOE or the GUE statistics can be observed in experimentally accessible, relativistic quantum systems. We demonstrate, using graphene confinements in which the quasiparticle motions are governed by the Dirac equation in the low-energy regime, that the level-spacing statistics are persistently those of GOE random matrices. We present extensive numerical evidence obtained from the tight-binding approach and a physical explanation for the GOE statistics. We also find that the presence of a weak magnetic field switches the statistics to those of GUE. For a strong magnetic field, Landau levels become influential, causing the level-spacing distribution to deviate markedly from the random-matrix predictions. Issues addressed also include the effects of a number of realistic factors on level-spacing statistics such as next nearest-neighbor interactions, different lattice orientations, enhanced hopping energy for atoms on the boundary, and staggered potential due to graphene-substrate interactions.
Heteronuclear proton assisted recoupling
Authors: Paëpe Gaël De , Lewandowski Józef R. , Loquet Antoine , Eddy Matt , Megy Simon , Böckmann Anja , Griffin Robert G.
Published: March 2011

We describe a theoretical framework for understanding the heteronuclear version of the third spin assisted recoupling polarization transfer mechanism and demonstrate its potential for detecting long-distance intramolecular and intermolecular 15N–13C contacts in biomolecular systems. The pulse sequence, proton assisted insensitive nuclei cross polarization (PAIN-CP) relies on a cross term between 1H–15N and 1H–13C dipolar couplings to mediate zero- and/or double-quantum 15N–13C recoupling. In particular, using average Hamiltonian theory we derive effective Hamiltonians for PAIN-CP and show that the transfer is mediated by trilinear terms of the form N±C∓Hz (ZQ) or N±C±Hz (DQ) depending on the rf field strengths employed. We use analytical and numerical simulations to explain the structure of the PAIN-CP optimization maps and to delineate the appropriate matching conditions. We also detail the dependence of the PAIN-CP polarization transfer with respect to local molecular geometry and explain the observed reduction in dipolar truncation. In addition, we demonstrate the utility of PAIN-CP in structural studies with 15N–13C spectra of two uniformly 13C,15N labeled model microcrystalline proteins—GB1, a 56 amino acid peptide, and Crh, a 85 amino acid domain swapped dimer (MW = 2 × 10.4 kDa). The spectra acquired at high magic angle spinning frequencies (ωr/2π > 20 kHz) and magnetic fields (ω0H/2π = 700–900 MHz) using moderate rf fields, yield multiple long-distance intramonomer and intermonomer 15N–13C contacts. We use these distance restraints, in combination with the available x-ray structure as a homology model, to perform a calculation of the monomer subunit of the Crh protein.
Electron attachment to POCl3. III. Measurement and kinetic modeling of branching fractions
Authors: Shuman Nicholas S. , Miller Thomas M. , Viggiano A. A. , Troe Jürgen
Published: March 2011

Electron attachment to POCl3 was studied in the bath gas He over the pressure range 0.4–3.1 Torr and the temperature range 300–1210 K. Branching fractions of POCl3−, POCl2−, Cl−, and Cl2− were measured. The results are analyzed by kinetic modeling, using electron attachment theory for the characterization of the nonthermal energy distribution of the excited POCl3−* anions formed and chemical activation-type unimolecular rate theory for the subsequent competition between collisional stabilization of POCl3−* and its dissociation to various dissociation products. Primary and secondary dissociations and/or thermal dissociations of the anions are identified. The measured branching fractions are found to be consistent with the modeling results based on molecular parameters obtained from quantum-chemical calculations.
Self-irradiation enhanced tritium solubility in hydrogenated amorphous and crystalline silicon
Authors: Liu Baojun , Chen Kevin P. , Kherani Nazir P. , Kosteski Tome , Leong Keith R. , Zukotynski Stefan
Published: March 2011

Experimental results on tritium effusion, along with the tritium depth profiles, from hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) tritiated in tritium (T2) gas at various temperatures and pressures are presented. The results indicate that tritium incorporation is a function of the material microstructure of the as-grown films, rather than the tritium exposure condition. The highest tritium concentration obtained is for a-Si:H deposited at a substrate temperature of 200°C. The tritium content is about 20 at. % on average with a penetration depth of about 50 nm. In contrast, tritium occluded in the c-Si is about 4 at. % with penetration depth of about 10 nm. The tritium concentration observed in a-Si:H and c-Si is much higher than the reported results for the post-hydrogenation process. β irradiation appears to catalyze the tritiation process and enhance tritium dissolution in the silicon matrix. The combination of tritium decay and β-induced ionizations results in formation of reactive species of tritium (tritium atoms, radicals, and ions) that readily adsorb on silicon. The electron bombardment of the silicon surface and subsurface renders it chemically active thereby promoting surface adsorption and subsurface diffusion of tritium, thus leading to tritium occlusion in the silicon matrix. Gaussian deconvolution of tritium effusion spectra yields two peaks for a-Si:H films tritiated at high temperature (250°C), one low temperature (LT) peak which is attributed to tritiated clusters and higher order tritides, and another high temperature peak which is attributed to monotritides. Activation energy of 2.6–4.0 eV for the LT peak was found.
Correlation between structural and luminescent properties of Eu3+-doped ZnO epitaxial layers
Authors: Badalawa Wasanthamala , Matsui Hiroaki , Osone Takamasa , Hasuike Noriyuki , Harima Hiroshi , Tabata Hitoshi
Published: March 2011

We have studied the epitaxial growth and photoluminescent (PL) properties of Eu3+-doped ZnO layers in correlation with structural analyses. Incorporation of Eu3+ ions into a ZnO host resulted in deterioration in crystal quality and lattice distortion. The spectral structure of Eu3+ emission revealed that Eu3+ ions were located at site symmetries lower than the original C3v of the Zn2+ ion sites in a hexagonal wurtzite structure of ZnO, which allowed for efficient red luminescence based on the electric dipole transitions. Moreover, we have found an anticorrelation of PL intensity between the excitonic and Eu3+ emissions, related to energy transfer from the ZnO host to the Eu3+ ions. The excitonic structure at the band edge was obscured upon doping with Eu3+ ions due to the formation of a band tail around 3.2 eV. This correlated with a reduction in excitonic emissions, leading to enhancement of Eu3+ emission. Strong PL emission from Eu3+ ions was only observed at low temperatures, and was remarkably suppressed with increasing temperature due to two types of nonradiative energy transfer paths. For the energy transfer process to Eu3+ ions, we suggest that the recombination energy of an electron–hole pair at the band tail near the band edge is close to that of high-lying excited levels in the Eu3+ 4f shell, providing an efficient energy pathway for the excitation of Eu3+ ions in the ZnO system.
Conduction electron scattering and spin-flipping at sputtered Al/Cu Interfaces
Authors: Sharma A. , Theodoropoulou N. , Loloee R. , Pratt W. P. , Bass J. , Zhang J. M. , Crimp M. A. , Cullen D. A. , Smith David. J. , Liu Kai , Wang Shuai , Xia Ke
Published: March 2011

We use two different techniques to derive the two parameters describing conduction electron scattering and spin-flipping at sputtered Al/Cu interfaces in the current-perpendicular-to-plane (CPP) geometry. These parameters are: 2ARAl/Cu, twice the interface specific resistance, where A is the area through which the CPP current flows; and δAl/Cu, which gives the probability P of spin-flipping from P = 1 – exp(−δ). A technique involving simple multilayers, and sample temperature not exceeding room temperature, gives 2ARAl/Cu = 2.3 ± 0.2 fΩm2. A technique involving exchange-biased spin-valves (EBSVs), where the sample is annealed briefly to 453 K, gives 2ARAl/Cu = 2.0 ± 0.15 fΩm2. Averaging the two values, but increasing the uncertainty for reasons explained, gives the best estimate of 2ARAl/Cu = 2.15 ± 0.4 fΩm2. This average is comparable to, but smaller than, the published value of 2ARAl/Cu = 3.6 ± 1 fΩm2 derived from thermal conductance measurements, and larger than our calculated values for interface thicknesses up to 6 monolayers (ML). However, it is similar to our calculated values for an interface thickness of 8 ML. Combining extrapolation of higher temperature bulk diffusion data for Al in Cu and vice-versa, with x-ray and transmission electron microscope (TEM) studies of similarly sputtered multilayers, indicates that such interface thicknesses are possible, especially for annealed multilayers. CPP-magnetoresistance (MR) measurements of the EBSV samples give only very small spin-flipping at the Al/Cu interface—δAl/Cu = 0.05−0.05+0.02. Such a small value is consistent with expected small spin-orbit interactions in both Al and Cu. Supplementary studies of CPP-MR of Permalloy (Py)-based EBSVs containing [Cu/Al/Cu] trilayers, show unusual behavior when the central Al layer is at least 10 nm thick, giving a CPP-MR like that for Py/Al, independent of Cu layer thicknesses from 0 to 10 nm. MR, x-ray, and TEM results give some clues as to the origins of this behavior, but a completely satisfactory explanation is not yet available.
On the derivation of the magnetocaloric properties in ferrimagnetic spinel Mn3O4
Authors: Thota Subhash , Guillou Francois , Hardy Vincent , Wahl Alexandre , Prellier Wilfrid , Kumar Jitendra
Published: March 2011

Large magnetocaloric effect has been observed in Mn3O4 around its ferrimagnetic transition at TN = 42.75 K. Field-induced isothermal entropy changes (ΔS) were derived from both magnetic and calorimetric techniques. The maximum |ΔS| and adiabatic temperature change (ΔTad) at TN are 11 J kg−1 K−1 and 1.9 K, respectively, for a magnetic field change of 20 kOe. Moreover, it is found that the complex magnetic phase transitions taking place below TN produce additional—but smaller—features on ΔS(T).
On the isobaric thermal expansivity of liquids
Authors: Troncoso Jacobo , Navia Paloma , Romaní Luis , Bessieres David , Lafitte Thomas
Published: March 2011

The temperature and pressure dependence of isobaric thermal expansivity, αp, in liquids is discussed in this paper. Reported literature data allow general trends in this property that are consistent with experimental evidence to be established. Thus, a negative pressure dependence is to be expected except around the critical point. On the other hand, αp exhibits broad regions of negative and positive temperature dependence in the (T, p) plane depending on the nature of the particular liquid. These trends are rationalized here in terms of various molecular-based equations of state. The analysis of the Lennard-Jones, hard sphere square well and restricted primitive model equations allows understanding the differences in the αp behavior between liquids of diverse chemical nature (polar, nonpolar, and ionic): broader regions of negative temperature and positive pressure dependencies are obtained for liquids characterized by larger ranges of the interparticle potential. Also, using the statistical associating fluid theory (SAFT) allowed the behavior of more complex systems (basically, those potentially involving chain and association effects) to be described. The effect of chain length is rather simple: increasing it is apparently equivalent to raise the interaction range. By contrast, association presents a quite complex effect on αp, which comes from a balance between the dispersive and associative parts of the interaction potential. Thus, if SAFT parameters are adjusted to obtain low association ability, αp is affected by each mechanism at clearly separate regions, one at low temperature, due to association, and the other to dispersive forces, which has its origin in fluctuations related with vapor–liquid transition.
Analysis of the forward and reverse bias I-V characteristics on Au/PVA:Zn/n-Si Schottky barrier diodes in the wide temperature range
Authors: Taşçıoğlu İlke , Aydemir Umut , Altındal Şemsettin , Kınacı Barış , Özçelik Süleyman
Published: March 2011

In this study, the forward and reverse bias current-voltage (I-V) characteristics of Au/Zinc acetate doped polyvinyl alcohol/n-Si Schottky barrier diodes (SBDs) have been investigated over the temperature range of 80-400 K. The values of zero-bias barrier height evaluated from forward and reverse bias I-V data, (ФBFo) and (ФBRo), increase with increasing temperature, and a discrepancy is observed between the values of ФBFo and ФBRo. Because the apparent barrier height (BH) seen from metal to semiconductor is higher than the one seen from semiconductor to metal, the obtained value of ФBFo is always greater than ФBRo value. The difference between them is almost the same as the Fermi energy level. The crossing of the experimental forward bias semilogarithmic ln I-V plots appears as an abnormality when compared to the conventional behavior of ideal SBDs. This behavior was attributed to the lack of free charge at a low temperature and could be expected in the temperature region where there is no carrier freezing out, which is non-negligible at low temperatures. Prior to intersection, the voltage dependent value of resistance (Ri) obtained from Ohm’s law decreases with increasing temperature, but it begins to increase after this intersection point. Such an increase in ФBo and series resistance (Rs) with temperature corresponding to high voltage region is in obvious disagreement with the reported negative temperature coefficients. However, the value of shunt resistance (Rsh) corresponding to a low or negative voltage region decreases with increasing temperature. In addition, the temperature dependent energy density distribution profiles of interface states (Nss) were obtained from forward bias I-V measurements by taking into account the bias dependence of the effective barrier height (Фe) and Rs of the device, and the values of Nss without considering Rs are almost one order of magnitude larger than Nss when considering Rs value.
Phase behavior of hard colloidal platelets using free energy calculations
Authors: Marechal Matthieu , Cuetos Alejandro , Martínez-Haya Bruno , Dijkstra Marjolein
Published: March 2011

We investigate the phase behavior of a model for colloidal hard platelets and rigid discotic molecules: oblate hard spherocylinders (OHSC). We perform free energy calculations using Monte Carlo simulations to map out the phase diagram as a function of the aspect ratio L/D of the particles. The phase diagram displays a stable isotropic phase, a nematic liquid crystal phase for L/D ⩽ 0.12, a columnar phase for L/D ≲ 0.3, a tilted crystal phase for L ≲ 0.45, and an aligned crystal phase for L/D ≳ 0.45. We compare the results to the known phase diagram of hard cut spheres. Thin cut spheres are almost cylinder-shaped, while the interactions between real discotic mesogens and colloidal platelets are more consistent with the toroidal rims of the OHSC. Since the shapes of the OHSC and the cut spheres are otherwise similar, the phase diagrams of the two types of particles are quite akin. However, the tilted crystal phase for OHSC, which is of a crystal type that is frequently found in experiments on disklike molecules, has not been found for hard cut spheres. Furthermore, although we have found a cubatic phase, it was shown to be definitely unstable, whereas the stability of the cubatic phase of cut spheres is still disputed. Finally, we also show that the phase boundaries differ significantly from those for cut spheres. These are remarkable consequences of a subtle change in particle shape, which show that for a detailed comparison with the phase behavior of experimental particles, the OHSC should be used as a model particle.
Exponentially and pre-exponentially correlated Gaussians for atomic quantum calculations
Authors: Sharkey Keeper L. , Adamowicz Ludwik
Published: March 2011

Explicitly correlated, n-electron, one-center s Gaussian (ECG) functions that depend on the interelectron distances in the exponent are combined with s ECGs which also depend on the interelectron separations through pre-exponential \documentclass[12pt]{minimal}\begin{document}$r_{ij}^2$\end{document}rij2 multipliers. The pre-exponentially \documentclass[12pt]{minimal}\begin{document}$r_{ij}^2$\end{document}rij2-dependent ECGs are included in the basis to better describe the interelectron correlation and the interelectron cusps. The basis set is tested in the calculations of the ground state of the beryllium atom (9Be).
Determination of molecular vibrational state energies using the ab initio semiclassical initial value representation: Application to formaldehyde
Authors: Wong Stephanie Y. Y. , Benoit David M. , Lewerenz Marius , Brown Alex , Roy Pierre-Nicholas
Published: March 2011

We have demonstrated the use of ab initio molecular dynamics (AIMD) trajectories to compute the vibrational energy levels of molecular systems in the context of the semiclassical initial value representation (SC-IVR). A relatively low level of electronic structure theory (HF/3-21G) was used in this proof-of-principle study. Formaldehyde was used as a test case for the determination of accurate excited vibrational states. The AIMD-SC-IVR vibrational energies have been compared to those from curvilinear and rectilinear vibrational self-consistent field/vibrational configuration interaction with perturbation selected interactions-second-order perturbation theory (VSCF/VCIPSI-PT2) and correlation-corrected vibrational self-consistent field (cc-VSCF) methods. The survival amplitudes were obtained from selecting different reference wavefunctions using only a single set of molecular dynamics trajectories. We conclude that our approach is a further step in making the SC-IVR method a practical tool for first-principles quantum dynamics simulations.
Determination of the temperature of bremsstrahlung photon generated by ultraintense laser using various thickness attenuators
Authors: Hasegawa Shuichi , Takashima Ryuta , Todoriki Masaru , Kikkawa Satoshi , Soda Keita , Takano Kei , Oishi Yuji , Nayuki Takuya , Fujii Takashi , Nemoto Koshichi
Published: March 2011

We evaluate the simplified method using the Lambert–Beer law to measure the temperature of bremsstrahlung photon generated by an ultraintense laser. Analytical values are compared to the results of the Monte Carlo calculation of GEANT4 and they agreed very well on the condition of the appropriate distance between the attenuator and the detector. We performed the experiment to measure the temperature of bremsstrahlung x-ray emitted from a metal target irradiated by a Ti:sapphire laser with 76 mJ, 72 fs, 2.2 × 1018 W/cm2. For a Cu target of 30 μm thick, the photon temperature was reasonably determined to be 0.18 MeV, which is in good agreement with previous studies.
Effect of Coulomb interaction on nonlinear (intensity-dependent) optical processes and intrinsic bistability in a quantum well under the electric and magnetic fields
Authors: Karabulut İbrahim
Published: March 2011

The effect of the electrostatic Coulomb interaction on the line shape related to the intensity-dependent intersubband optical processes in a Si δ-doped quantum well is studied using the density matrix formalism. The electronic structure of the quantum well is calculated from the self-consistent numerical solution of the coupled Schrödinger–Poisson equations. The line shape function is considerably modified by the optical intensity and the electric and magnetic fields. Moreover, we demonstrate the existence of the optical bistability for appropriate values of the optical intensity and also the control of the optical bistability with the electric and magnetic fields. It is also found that the intersubband relaxation time plays an important role in determining the optical bistability region.
Local ab initio methods for calculating optical band gaps in periodic systems. I. Periodic density fitted local configuration interaction singles method for polymers
Authors: Lorenz Marco , Usvyat Denis , Schütz Martin
Published: March 2011

We present a density fitted local configuration interaction singles (CIS) method for calculating optical band gaps in 1D-periodic systems. The method is based on the Davidson diagonalization procedure, carried out in the reciprocal space. The one-electron part of the matrix–vector products is also evaluated in the reciprocal space, where the diagonality of the Fock matrix can be exploited. The contraction of the CIS vectors with the two electron integrals is performed in the direct space in the basis of localized occupied (Wannier) and virtual (projected atomic) orbitals. The direct space approach allows to utilize the sparsity of the integrals due to the local representation and locality of the exciton. The density fitting approximation employed for the two electron integrals reduces the nominal scaling with unit cell size to \documentclass[12pt]{minimal}\begin{document}${\cal O(N}^4)$\end{document}O(N4). Test calculations on a series of prototypical systems demonstrate that the method in its present stage can be used to calculate the excitonic band gaps of polymers with up to a few dozens of atoms in the cell. The computational cost depends on the locality of the exciton, but even relatively delocalized excitons occurring in the polybiphenyl in the parallel orientation, can be routinely treated with this method.
Spatially optimized gene transfection by laser-induced breakdown of optically trapped nanoparticles
Authors: Arita Yoshihiko , Torres-Mapa Maria Leilani , Lee Woei Ming , Čižmár Tomáš , Campbell Paul , Gunn-Moore Frank J. , Dholakia Kishan
Published: March 2011

We demonstrate laser-induced breakdown of an optically trapped nanoparticle with a nanosecond laser pulse. Controllable cavitation within a microscope sample was achieved, generating shear stress to monolayers of live cells. This efficiently permeabilize their plasma membranes. We show that this technique is an excellent tool for plasmid-DNA transfection of cells with both reduced energy requirements and reduced cell lysis compared to previously reported approaches. Simultaneous multisite targeted nanosurgery of cells is also demonstrated using a spatial light modulator for parallelizing the technique.
Flexible, ab initio potential, and dipole moment surfaces for water. I. Tests and applications for clusters up to the 22-mer
Authors: Wang Yimin , Huang Xinchuan , Shepler Benjamin C. , Braams Bastiaan J. , Bowman Joel M.
Published: March 2011

We report full-dimensional, ab initio potential energy and dipole moment surfaces, denoted PES and DMS, respectively, for arbitrary numbers of water monomers. The PES is a sum of 1-, 2-, and 3-body potentials which can also be augmented by semiempirical long-range higher-body interactions. The 1-body potential is a spectroscopically accurate monomer potential, and the 2- and 3-body potentials are permutationally invariant fits to tens of thousands of CCSD(T)/aug-cc-pVTZ and MP2/aug-cc-pVTZ electronic energies, respectively. The DMS is a sum of 1- and 2-body DMS, which are covariant fits to tens of thousands MP2/aug-cc-pVTZ dipole moment data. We present the details of these new 2- and 3-body potentials and then extensive applications and tests of this PES are made to the structures, classical binding energies, and harmonic frequencies of water clusters up to the 22-mer. In addition, we report the dipole moment for these clusters at various minima and compare the results against available and new ab initiocalculations.
What makes ionic fluids characteristically ionic? A corresponding-states analysis of the surface tension of an ionic model fluid with variable dispersion interactions
Authors: Leroy Frédéric , Weiss Volker C.
Published: March 2011

Inorganic molten salts, such as NaCl, are known to show characteristically lower values of Guggenheim's corresponding-states surface tension γred at a given reduced temperature T/Tc than simple or aprotic polar fluids. Recently, the corresponding values of γred for (some) room temperature ionic liquids (RTILs) were found in the same region as those for weakly polar fluids, that is, markedly above the values typical of inorganic molten salts despite the ionic character of RTILs. Here, we present the results of simulations of an ionic model fluid in which the strength of attractive dispersion interactions among the ions is varied relative to the Coulomb interactions. For weak dispersive interactions, the behavior known for real inorganic molten salts is found. If the attractive dispersion energy of two unlike ions at contact exceeds 20% of the Coulombic attraction in such an isolated ion pair, γred increases markedly and approaches the region of values for simple and polar fluids. Rough theoretical estimates of the relative strengths of dispersive and Coulombic attractions in molten inorganic salts and in RTILs support our conclusion that the dispersion interactions in RTILs are strong enough for their corresponding-states surface tension to behave regularly and, thus, to deviate from the values one would expect for strongly ionic systems.
Modeling of low-voltage oxide-based electric-double-layer thin-film transistors fabricated at room temperature
Authors: Dai Mingzhi , Wu Guodong , Yang Yue , Jiang Jie , Li Li , Wan Qing
Published: March 2011

The room-temperature-made low-voltage electric-double-layer (EDL) thin-film transistors (TFTs) are reported previously with good performance including a huge EDL gate capacitance above 1 μF/cm2. We report a two-dimensional simulation of the carrier transport and subgap density of states (DOS) in low-voltage indium tin oxide EDL TFTs. The simple model with a constant mobility and two-step subgap DOS reproduces well the characteristics of EDL TFTs. A nice fitting to the experimental data was obtained with a changeable effective conduction band DOS and valence band DOS model, which is reasonable to EDL electrostatic modulation mechanism. The EDL TFTs show much lower DOS than the InGaZnO4 TFTs.
Inverted micelle formation of cell-penetrating peptide studied by coarse-grained simulation: Importance of attractive force between cell-penetrating peptides and lipid head group
Authors: Kawamoto Shuhei , Takasu Masako , Miyakawa Takeshi , Morikawa Ryota , Oda Tatsuki , Futaki Shiroh , Nagao Hidemi
Published: March 2011

Arginine-rich peptide and Antennapedia are cell-penetrating peptides (CPPs) which have the ability to permeate plasma membrane. Deformation of the plasma membrane with CPPs is the key to understand permeation mechanism. We investigate the dynamics of CPP and the lipid bilayer membrane by coarse-grained simulation. We found that the peptide makes inverted micelle in the lipid bilayer membrane, when the attractive potential between the peptide and lipid heads is strong. The inverted micelle is formed to minimize potential energy of the peptide. For vesicle membrane, the peptide moves from the outer vesicle to the inner vesicle through the membrane. The translocation of the peptide suggests inverted micelle model as a possible mechanism of CPPs.
Accurate ab initio determination of the adiabatic potential energy function and the Born–Oppenheimer breakdown corrections for the electronic ground state of LiH isotopologues
Authors: Holka Filip , Szalay Péter G. , Fremont Julien , Rey Michael , Peterson Kirk A. , Tyuterev Vladimir G.
Published: March 2011

High level ab initio potential energy functions have been constructed for LiH in order to predict vibrational levels up to dissociation. After careful tests of the parameters of the calculation, the final adiabatic potential energy function has been composed from: (a) an ab initio nonrelativistic potential obtained at the multireference configuration interaction with singles and doubles level including a size-extensivity correction and quintuple–sextuple ζ extrapolations of the basis, (b) a mass–velocity-Darwin relativistic correction, and (c) a diagonal Born–Oppenheimer (BO) correction. Finally, nonadiabatic effects have also been considered by including a nonadiabatic correction to the kinetic energy operator of the nuclei. This correction is calculated from nonadiabatic matrix elements between the ground and excited electronic states. The calculated vibrational levels have been compared with those obtained from the experimental data [J. A. Coxon and C. S. Dickinson, J. Chem. Phys. 134, 9378 (2004)]. It was found that the calculated BO potential results in vibrational levels which have root mean square (rms) deviations of about 6–7 cm−1 for LiH and ∼3 cm−1 for LiD. With all the above mentioned corrections accounted for, the rms deviation falls down to ∼1 cm−1. These results represent a drastic improvement over previous theoretical predictions of vibrational levels for all isotopologues of LiH.
Quantum mechanical simulation of electronic transport in nanostructured devices by efficient self-consistent pseudopotential calculation
Authors: Jiang Xiang-Wei , Li Shu-Shen , Xia Jian-Bai , Wang Lin-Wang
Published: March 2011

We present a new empirical pseudopotential (EPM) calculation approach to simulate the million atom nanostructured semiconductor devices under potential bias using periodic boundary conditions. To treat the nonequilibrium condition, instead of directly calculating the scattering states from the source and drain, we calculate the stationary states by the linear combination of bulk band method and then decompose the stationary wave function into source and drain injecting scattering states according to an approximated top of the barrier splitting (TBS) scheme based on physical insight of ballistic and tunneling transports. The decomposed electronic scattering states are then occupied according to the source/drain Fermi-Levels to yield the occupied electron density which is then used to solve the potential, forming a self-consistent loop. The TBS is tested in a one-dimensional effective mass model by comparing with the direct scattering state calculation results. It is also tested in a three-dimensional 22 nm double gate ultra-thin-body field-effect transistor study, by comparing the TBS-EPM result with the nonequilibrium Green’s function tight-binding result. We expected the TBS scheme will work whenever the potential in the barrier region is smoother than the wave function oscillations and it does not have local minimum, thus there is no multiple scattering as in a resonant tunneling diode, and when a three-dimensional problem can be represented as a quasi-one-dimensional problem, e.g., in a variable separation approximation. Using our approach, a million atom nonequilibrium nanostructure device can be simulated with EPM on a single processor computer.
Thermoelectric and bulk mobility measurements in pentacene thin films
Authors: Kim G.-H. , Shtein M. , Pipe K. P.
Published: March 2011

Low-noise thermoelectric and electrical measurements were used to derive the dependences of Seebeck coefficient and hole mobility on carrier concentration and grain size in the “bulk” regions of thermally evaporated pentacene thin films (in contrast to the channel field-effect mobility typically measured using thin-film transistor geometries). Distinct charge transport regimes were observed for larger (0.5 and 0.8 μm) and smaller (0.2 μm) grain sizes, attributed to carrier-dopant scattering and percolation, respectively.
Direct evidence of dopant segregation in Gd-doped ceria
Authors: Li Zhi-Peng , Mori Toshiyuki , Auchterlonie Graeme John , Zou Jin , Drennan John
Published: March 2011

Microstructures and segregations of dopants and associated oxygen vacancies in gadolinium-doped ceria (GDC) have been characterized by high-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM). Diffuse scattering was detected in 25 at. % GDC (25GDC) in comparison to 10GDC, which is ascribed to nanodomain formation in 25GDC. HRTEM, dark-field, and STEM Z-contrast imaging investigations all provide direct evidence for dopant segregation in doped ceria. It is illustrated that dopant cations cannot only segregate in grain interior forming larger nanodomains but also at grain boundary forming smaller ones. Detailed analyses about nanodomain formation and related dopant segregation behaviors are then elucidated.
Numerical analysis of Ostwald ripening in two-dimensional systems
Authors: Dubrovskii V. G. , Kazansky M. A. , Nazarenko M. V. , Adzhemyan L. T.
Published: March 2011

This work addresses theory of Ostwald ripening based on the continuum second order kinetic equation for the size distribution of embryos over sizes. Numerical studies are performed with two-dimensional condensing systems having different growth laws of islands, using different forms of kinetic equation. The material influx into the system is terminated to enable the Ostwald ripening process. We obtain numerical solutions for the size distributions with and without fluctuation effects described by the second derivative in the kinetic equation. We show that fluctuations lead to a considerable broadening of size distribution at the early Ostwald ripening step in the diffusion limited growth of islands. Comparison of our numerical distributions with the deterministic Lifshitz–Slezov shape shows that the latter in principle withstands fluctuations. However, the correspondence between the numerical large time asymptotes and the Lifshitz–Slezov spectra is not perfect, particularly in the diffusion-induced growth regime, and becomes worse when the fluctuations are included.
Mass changes of microparticles in a plasma observed by a phase-resolved resonance method
Authors: Carstensen Jan , Jung Hendrik , Greiner Franko , Piel Alexander
Published: March 2011

The influence of a plasma environment on melamine formaldehyde particles is studied. High-precision measurements of the vertical confinement frequency with a phase-resolved resonance method indicate that the particle mass is affected in two ways: the deposition of sputtered material at the particle leads to a mass gain, whereas the outgassing of water causes a mass loss.
Structures and photoelectron spectroscopy of Cun(BO2)m− (n, m = 1, 2) clusters: Observation of hyperhalogen behavior
Authors: Feng Yuan , Xu Hong-Guang , Zheng Weijun , Zhao Hongmin , Kandalam Anil K. , Jena Puru
Published: March 2011

The electronic structures of CuBO2−, Cu(BO2)2−, Cu2(BO2)−, and Cu2(BO2)2− clusters were investigated using photoelectron spectroscopy. The measured vertical and adiabatic detachment energies of these clusters revealed unusual properties of Cu(BO2)2 cluster. With an electron affinity of 5.07 eV which is larger than that of its BO2 superhalogen (4.46 eV) building-block, Cu(BO2)2 can be classified as a hyperhalogen. Density functional theory based calculations were carried out to identify the ground state geometries and study the electronic structures of these clusters. Cu(BO2) and Cu(BO2)2 clusters were found to form chainlike structures in both neutral and anionic forms. Cu2(BO2) and Cu2(BO2)2 clusters, on the other hand, preferred a chainlike structure in the anionic form but a closed ringlike structure in the neutral form. Equally important, substantial differences between adiabatic detachment energies and electron affinities were found, demonstrating that correct interpretation of the experimental photoelectron spectroscopy data requires theoretical support not only in determining the ground state geometry of neutral and anionic clusters, but also in identifying their low lying isomers.
Benchmark calculations for dissipative dynamics of a system coupled to an anharmonic bath with the multiconfiguration time-dependent Hartree method
Authors: López-López S. , Martinazzo R. , Nest M.
Published: March 2011

In this paper, we present benchmark results for dissipative dynamics of a harmonic oscillator coupled to an anharmonic bath of Morse oscillators. The microscopic Hamiltonian has been chosen so that the anharmonicity can be adjusted as a free parameter, and its effect can be isolated. This leads to a temperature dependent spectral density of the bath, which is studied for ohmic and lorentzian cases. Also, we compare numerically exact multiconfiguration time-dependent Hartree results with approximate solutions using continuous configuration time-dependent self-consistent field and local coherent state approximation.
Coarse-graining errors and numerical optimization using a relative entropy framework
Authors: Chaimovich Aviel , Shell M. Scott
Published: March 2011

The ability to generate accurate coarse-grained models from reference fully atomic (or otherwise “first-principles”) ones has become an important component in modeling the behavior of complex molecular systems with large length and time scales. We recently proposed a novel coarse-graining approach based upon variational minimization of a configuration-space functional called the relative entropy, Srel, that measures the information lost upon coarse-graining. Here, we develop a broad theoretical framework for this methodology and numerical strategies for its use in practical coarse-graining settings. In particular, we show that the relative entropy offers tight control over the errors due to coarse-graining in arbitrary microscopic properties, and suggests a systematic approach to reducing them. We also describe fundamental connections between this optimization methodology and other coarse-graining strategies like inverse Monte Carlo, force matching, energy matching, and variational mean-field theory. We suggest several new numerical approaches to its minimization that provide new coarse-graining strategies. Finally, we demonstrate the application of these theoretical considerations and algorithms to a simple, instructive system and characterize convergence and errors within the relative entropy framework.
Transport, phase transitions, and wetting in micro/nanochannels: A phase field/DDFT approach
Authors: Mickel Walter , Joly Laurent , Biben Thierry
Published: March 2011

While the flow of a liquid in a macroscopic channel is usually described using hydrodynamics with no-slip boundary conditions at the walls of the channel, transport phenomena in microchannels involve physics at many different scales due to the interplay between the micrometric section of the channel and the micro- or nanometric roughness of the boundaries. Roughness can have many different effects such as increasing the friction between the liquid and the walls (leading to the macroscopic no-slip boundary condition) or on the contrary reduce it thanks to the Wenzel–Cassie–Baxter wetting transition induced by capillarity. Here we detail a phase-field/dynamic density functional theory model able to account for the wetting transitions, the resulting friction between the wall and the fluid, and compressible hydrodynamics at high viscosity contrast.
Novel pentagonal silicon rings and nanowheels stabilized by flat pentacoordinate carbon(s)
Authors: Zdetsis Aristides D.
Published: March 2011

It is predicted by accurate density functional and coupled-cluster theory that planar [Si5C]2− and [Si5C]1− rings can be stabilized by flat pentacoordinate carbon–silicon bonds. The energy difference of the [Si5C]2− dianion from the lowest energy three-dimensional isomer is about 12.2 kcal/mol at the level of the density functional theory using the Becke 3-parameter (exchange), Lee, Yang and Parr functional, and the triple-ζ doubly polarized basis sets. Stable composite [Si5C]2 structures are formed either as nanowheels with axial C–C bonds of 1.51 Å or as isoenergetic pentagonal graphiticlike layers with double C–C distance (3.02 Å) and almost double aromaticity index, based on nucleus independent chemical shifts. Both of these structures are at least 12 kcal/mol lower in energy than the lowest energy Si10C2 structure reported in the literature, but about 5 kcal/mol higher than the lowest energy structure found here.
Assembly of CdSe nanoparticles on graphene for low-temperature fabrication of quantum dot sensitized solar cell
Authors: Sun Shengrui , Gao Lian , Liu Yangqiao , Sun Jing
Published: March 2011

Quantum dot sensitized solar cell (QDSSC) was fabricated in a low-temperature process based on graphene-CdSe composite, which was prepared by the procedures of immobilizing CdSe on graphene oxide (GO) and reduction in GO. It was found that the charge separation between excited CdSe and graphene could be tapped to generate photocurrent from photocurrent measurements, which established the ability of graphene to collect and transport electrons. By optimizing the CdSe-to-GO ratio at 4.5:1, the obtained graphene-CdSe-based cells exhibited significantly higher short-circuit photocurrent and energy conversion efficiency (5.8 mA/cm2 and 0.72%, respectively) than the reported values of the C60 or carbon nanotube related QDSSC, demonstrating that the graphene-CdSe composite is an attractive candidate in energy conversion devices.
A cluster expansion approach to renormalization group transformations
Authors: Yin Mei
Published: March 2011

The renormalization group (RG) approach is largely responsible for the considerable success which has been achieved in developing a quantitative theory of phase transitions. This work treats the rigorous definition of the RG map for classical Ising-type lattice systems in the infinite volume limit at high temperature. A cluster expansion is used to justify the existence of the partial derivatives of the renormalized interaction with respect to the original interaction. This expansion is derived from the formal expressions, but it is itself well-defined and convergent. Suppose in addition that the original interaction is finite-range and translation-invariant. We will show that the matrix of partial derivatives in this case displays an approximate band property. This in turn gives an upper bound for the RG linearization.
Transition-metal dioxides: A case for the intersite term in Hubbard-model functionals
Authors: Kulik Heather J. , Marzari Nicola
Published: March 2011

Triatomic transition-metal oxides in the “inserted dioxide” (O–M–O) structure represent one of the simplest examples of systems that undergo qualitative geometrical changes via subtle electronic-structure modulation. We consider here three transition-metal dioxide molecules (MO2 where M = Mn, Fe, or Co), for which the equilibrium structural (e.g., bent or linear geometry) and electronic (e.g., spin or symmetry) properties have been challenging to assign both theoretically and experimentally. Augmenting a standard density-functional theory (DFT) approach with a Hubbard term (DFT+U) occasionally overlocalizes the 3d manifold, leading to an incorrect bond elongation and, in turn, poor equilibrium geometries for MO2 molecules, while preserving good spin-state splittings. Proper description of both geometry and energetics for these molecules is recovered; however, through either calculating DFT+U relaxations at fixed M–O bond lengths or by inclusion of an intersite interaction term V that favors M(3d)–O(2p) interactions. In this latter case, both U and V are calculated fully from first-principles and are not fitting parameters. Finally, we identify an approach that more accurately determines the Hubbard U over a coordinate in which the covalent character of bonding varies.
Radiationless decay in the region of the 2t2g and 4eg resonances in SF6
Authors: Bolognesi P. , Kivimäki A. , O’Keeffe P. , Feyer V. , Tarantelli F. , Storchi L. , Avaldi L.
Published: March 2011

The S 2p Auger spectrum of SF6 has been studied in the region of the 2t2g and 4eg resonances. The partial Auger spectra due to the ionization of the 2p spin–orbit components and of a shake-up satellite state have been measured selectively by tuning the photon energy and using the Auger electron–photoelectron coincidence technique. A detailed analysis of the Auger spectrum has also been performed using the Green's function-based second-order algebraic diagrammatic construction method.
Dispersion relations for a general anisotropic distribution function represented as a sum over Legendre polynomials
Authors: Shaisultanov Rashid , Eichler David
Published: March 2011

The dielectric tensor is obtained for a general anisotropic distribution function that is represented as a sum over Legendre polynomials. The result is valid over all of k-space. We obtain growth rates for the Weibel instability for some basic examples of distribution functions.
Extraction of effective ion pair interactions in warm dense beryllium and helium plasmas within integral equation theory
Authors: Ye Jingxin , Zhao Bin , Zheng Jian
Published: March 2011

Under hypernetted chain (HNC) approximation, effective ion pair interaction potentials for the warm dense matter are extracted by using available radial distribution functions (RDFs). The effective ion pair potentials extracted from first-principles simulation results are found containing the short-ranged attraction (SRA) component for both warm dense helium and beryllium plasmas. The SRA potentials can be well represented by Gaussian functions in both cases and then the extracted effective ion potentials are well fitted. As an application, the well fitted potentials are used to describe ion-ion interactions in classical molecular dynamics simulations. The yield RDFs are in excellent agreement with those computed by HNC equations and first-principles simulations, respectively.
Transport limited interfacial carrier relaxation in a double-layer device investigated by time-resolved second harmonic generation and impedance spectroscopy
Authors: Zhang Le , Taguchi Dai , Li Jun , Manaka Takaaki , Iwamoto Mitsumasa
Published: March 2011

The interfacial carrier relaxation in an indium tin oxide/polyimide/pentacene/Au double-layer device was studied in both time and frequency domains by using time-resolved second harmonic generation (TR-SHG) and impedance spectroscopy (IS), respectively. Although both hole and electron injection into the pentacene layer and their accumulation at the pentacene/polyimide interface were revealed in TR-SHG, it was only observed in IS under the hole injection condition. The “contradiction” between the two methods for the same carrier relaxation process was explained on the basis of a model, transport limited interfacial carrier relaxation, in which the quasistatic state governs the one-directional carrier transport.
Abnormal temperature dependence of interband electronic transitions in relaxor-based ferroelectric (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (x=0.24 and 0.31) single crystals
Authors: Zhu J. J. , Li W. W. , Xu G. S. , Jiang K. , Hu Z. G. , Zhu M. , Chu J. H.
Published: March 2011

The transmittance spectra of (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (x=0.24 and 0.31) single crystals have been studied in the temperature range of 5.3–300 K. It was found that the direct band gap Egd is 3.150±0.016 eV, indirect band gap Egi is 2.939±0.014 eV, and the phonon energy Ep is 0.098±0.014 eV for the PMN-0.24PT crystal at 300 K. With increasing the temperature, the Egd of the PMN-0.24PT crystal decreases from 3.263±0.017 to 3.150±0.016 eV while the Egd of the PMN-0.31PT crystal increases from 3.050±0.015 to 3.101±0.016 eV. The peculiar characteristic can be ascribed to the monoclinic and rhombohedral multiphase coexistence in the PMN-0.31PT crystal.