bluuebunny/crossref_metadata_2025_split huggingface dataset:
Third‐order many‐body perturbation theory for the ground state of the carbon monoxide molecule
Authors: Bartlett Rodney J. , Wilson Stephen , Silver David M. 
Published: December 2004

AbstractMany‐body perturbation calculations have been performed for the ground state of the carbon monoxide molecule at its equilibrium internuclear separation. The calculations are complete through third order within the algebraic approximation; i.e., the state functions are parameterized by expansion in a finite basis set. All two‐, three‐, and four‐body terms are rigorously determined, and many‐body effects are found to be very important. A detailed comparison is made with a previously reported configuration interaction study. Padé approximants to the energy expansion are constructed. The many‐body perturbative wave function is used in the Rayleigh quotient to produce upper bounds to the electronic energy.
Electronic absorption spectra of V2O5
Authors: Lazukova N. I. , Gubanov V. A. , Mokerov V. G. 
Published: December 2004

AbstractMO calculations of electronic structure and optical transitions for [VOn]5 −; 2n (n = 4, 5, 6) clusters in V2O5 monocrystals have been carried out by means of the semiempirical CNDO CI method. Using the calculated results, a complete analysis of V2O5 optical data as available in the literature and as obtained in the electroreflectivity experiments presented in this paper is performed. An identification of optical transitions in a wide energy range is presented. The optical properties of vanadium pentoxide are shown to be due to the localized charge transfer electronic transitions in the clusters. The fine structure of optical spectra is connected with the covalent splittings of the vanadium 3d and oxygen 2p atomic levels.
A simplified model for the predissociation of diatomic molecules
Authors: Berrondo M. , Flores‐Riveros A. 
Published: December 2004

AbstractA model consisting of a harmonic oscillator well and a repulsive inverse square potential, coupled by a delta function, is solved. We find the S‐function for this case and study its poles as a function of the coupling strength. These poles show how the harmonic levels shift and broaden as the two potential curves couple and predissociation occurs. A “new state” is found when the energy threshold is just below the first excited state of the harmonic oscillator.
Stationarity of resonant pole trajectories in complex scaling
Authors: Canuto Sylvio , Goscinski Osvaldo 
Published: December 2004

AbstractA reciprocity theorem relating the real parameters η and α that define the complex scaling transformation r →η reiα in the theory of complex scaling for resonant states is demonstrated. The virial theorem is used in connection with the stationarity of the pole trajectory. The Stark broadening in the hydrogen atom using a basis set generated by Rayleigh–Schrödinger perturbation theory is treated as an example.
Complex coordinates and the Stark effect
Authors: Cerjan C. , Hedges R. , Holt C. , Reinhardt W. P. , Scheibner K. , Wendoloski J. J. 
Published: December 2004

AbstractThe theories of the dilatation, r → r eiθ, and translation, x → x + iq, transformations as related to the Stark problem are reviewed, and new results obtained. Results for the hydrogen atom n = 1 and n = 2 levels and the 1P0, 2s2p H− shape resonance in dc fields are presented, and the extension to the ac Stark effect made. Spectral estimates are made using the technique of the numerical range and via discussion of several model problems, using both coordinate rotation and coordinate translation.
Refined AMOS for some organic semiconductors
Authors: Roustan J. , Dugay M. 
Published: December 2004

AbstractFor a few organic semiconductors we present calculations performed on a simple model by means of the field‐theoretical formulation of the “different‐orbitals‐for‐different‐spins” method. The numerical methods are extensively described and the results are discussed in comparison with other methods existing in the same domain.
Ab initio valence bond calculations. X. Vertical valence ionization potentials of allene and butatriene
Authors: Tantardini Gian Franco , Simonetta Massimo 
Published: December 2004

AbstractThe ground and vertical valence ionized states of allene and butatriene have been studied in the ab initio valence bond framework using the 6–31G basis set after contraction and introducing the core–valence shell separation. The final wave functions have been analyzed in terms of VB structures by means of population analysis.
Dependence of approximate ab initio molecular loge sizes on the quality of basis functions
Authors: Mezey Paul G. , Daudel Raymond , Csizmadia Imre G. 
Published: December 2004

AbstractSize and shape parameters for the core, bonding, and lone electron pairs of the ten‐electron hydrides (CH4, NH3, H2O, HF) were determined from ab initio MO wave functions using various Gaussian basis sets. The fundamental features of approximate electron pair loge representation are somewhat more sensitive to the quality of the basis functions than the molecular total energy. The total size of the molecular electron distribution is less affected by basis set variations than its components: the core, bonding, and lone pair sizes. There is an apparent tendency to “preserve” the total size of molecular distribution.
Comments on the exclusion‐principle‐violating diagrams cancellation in correlations energy calculation by many‐body Rayleigh–Schrödinger perturbation theory
Authors: Hubač Ivan 
Published: December 2004

AbstractWhen calculating the correlation energy where the effect of higher than double excitations is included by means of many‐body Rayleigh–Schrödinger perturbation theory (MB‐RSPT) through fourth order the problem of cancellation of exclusion‐principle‐violating (EPV) diagrams arises. The cancellation of EPV diagrams in fourth order of MB‐RSPT is demonstrated for diagrams which include the effect of tetraexcitations.
Resonances in the elastic electron‐SF6 molecule scattering
Authors: Gyemant I. , Varga Zs. , Benedict M. G. 
Published: December 2004

AbstractIn agreement with previous calculations by the authors, three definite resonances in the elastic electron‐SF6 molecule scattering in the energy range 5–40 eV have been obtained with a multiple scattering method, elaborated originally for molecular bound states and modified here for scattering states. Results with various more‐reliable one‐electron potentials have been compared with previous calculations and available experimental data.
Use of the Hiller–Sucher–Feinberg identity for spin‐density calculations
Authors: Harriman John E. 
Published: December 2004

AbstractThe identity recently presented by Hiller, Sucher, and Feinberg relating the expectation value of a δ‐function operator to that of another operator is rederived for the case of the Fermi contact interaction and the required expectation values expressed in terms of the spin‐density and conditional spin‐density matrices. The ground state of the H atom is considered as an example and it is shown that, for approximation by a linear combination of Gaussian orbitals, use of the identity improves the estimate of spin density at the nucleus by an order of magnitude or more.
Model potential Xα method for the electronic structure calculations
Authors: Katsuki Shinichi , Taketa Hiroshi 
Published: December 2004

AbstractA new method is presented for the electronic structure calculations with use of Bonifacic and Huzinaga's model potential and Slater's Xα local‐statistical‐exchange potential. The density of the valence electrons and its cube root are least‐square fitted to ls‐type Gaussians to evaluate the Coulomb potential and the Xα potential analytically. Preliminary results of the applications of the method to molecules consisting of the second‐row atoms are given. Agreement with experimental ionization energies is satisfactory.
Ab initio unrestricted Hartree–Fock (UHF) and UHF–natural orbital CI studies of ozone
Authors: Yamaguchi Kizashi 
Published: December 2004

AbstractThe electronic structures of both the ground and excited states of ozone (O3) are investigated by the ab initio unrestricted Hartree–Fock (UHF) and UHF‐natural orbital (NO) CI methods. It is found that the ab initio UHF‐NO CI method provides reasonable descriptions of both the states of O3.
Ab initioLCAO MO SCF calculation of potential surface of the NO2 molecule
Authors: Morita Keiko , Sato Hiroshi , Ishiguro Eiichi 
Published: December 2004

AbstractThe SCF potential surface of the ground state for NO2 was calculated by using program JAMOL 3. The McLean–Loew–Berkowitz CGTO's were used as basis functions. One of the two NO distance R is fixed to 2.25 a.u. and the other one r and the ONO angle θ are varied from 2.25 to 5.0 a.u. and from 0° to 180°, respectively. The potential surface has the minimum around r = 2.50 a.u. and θ = 120°, where the energy is found to be −203.954 a.u.
Novel sign‐alternation rule for the triplet state in aromatic systems
Authors: Gondo Yasuhiko , Kanda Yoshiya 
Published: December 2004

AbstractWithin the framework of the LCAO‐MO theory, a novel sign‐alternation rule has been found empirically for the lowest excited ππ* triplet state in the alternant aromatic system. This rule can be applied to identify the phosphorescent state.
Theory of the Bose particle representation for geminals
Authors: Okido Sadao , Tanimoto Osamu 
Published: December 2004

AbstractAn electron pair in a molecule is a complex entity and is incompletely described by the independent particle picture. Electron pairs are treated as Bose particles to include correlation of intrapair interaction effectively by the use of the Dyson transformation. The use of a Bose‐type Hamiltonian permits a straight forward interpretation for geminals and facilitates the calculation of electronic energies. A Bose‐type representation method is applied to the calculation of electronic energies of a lithium hydride molecule.
ESCA peak intensities for small molecules in the sudden approximation
Authors: Palma A. , González E. , Goscinski O. 
Published: December 2004

AbstractA simple transition probability formula is applied to the core hole ionization in CO, satisfactorily predicting the ratio between the intensity of the two inner‐shell peaks. The formula is also applied to the full ESCA spectra of water and methane; the theoretical results agree reasonably well with the experiment.
Electron distribution in water by high‐energy electron scattering
Authors: Shibata S. , Hirota F. , Kakuta N. , Muramatsu T. 
Published: December 2004

AbstractThe differential cross‐sections for high‐energy electrons scattered from water have been measured over a wide range of momentum transfers. The effect of chemical binding was seen from the comparison between the experiment and the calculation for an independent‐atom model. The ab initio calculation using SCF MO was carried out with respect to the elastic scattering. It was in a good agreement with the experiment and thus a reliable electron distribution in water was obtained.
INDO Studies on the structure of benzosemiquinone radicals
Authors: Shinagawa Yoshiya , Shinagawa Yasuko , Uyesaka Nobuhiro , Fukuda Kohji 
Published: December 2004

AbstractThe spin densities of the radical anions from 4‐methylcatechol, 4‐carboxylic catechol, and 3‐methylcatechol were calculated by means of the INDO method with the geometrical parameter adjusting method. The observed protion hyperfine coupling constants were exactly reproduced.
Nuclear distortion of the equidistant arrangement in trans‐polyacetylene, (CH)x
Authors: Kertész M. , Koller J. , Ažman A. 
Published: December 2004

AbstractThe occurrence of broken‐symmetry Hartree‐Fock solutions may indicate instability of the lattice depending on the symmetry of the charge‐density wave (CDW). In case of polyacetylene, (CH)x, we have found such solutions having an off‐diagonal CDW. It is pointed out that this sort of instability is principally different from the Peierls instability. The importance of correct (symmetrical) cutoff of interactions in direct space (“finite neighbor's approximation”) is emphasized. A basic difference in the potential‐energy curve of trans‐(CH)x and the isoelectronic (HCN)x around the equidistant configuration is shown.
Dynamique moléculaire du cristal ammoniac. Calcul ab initioSCF de l'energie electronique
Authors: Et S. Odiot J. Bridet , Fliszar S. 
Published: December 2004

AbstractThe wave function and total energy of ammonia crystal are determined from the results of a totally optimized STO‐3G ab initio calculation of the tetramer, pattern of the crystal. The crystal electronic energy is expressed in terms of the interatomic distances and charge density matrix elements. The geometry obtained from optimization of the tetramer energy on geometric parameters is in very good agreement with the experimental data of the crystal.
Role of CA2+ ion in the abortifacient action of prostaglandins. II. Molecular orbital and conformation energy calculations of PGA1
Authors: Kothekar V. , Dutta S. 
Published: December 2004

AbstractThis paper reports some theoretical studies of PGA1 using conformational and molecular orbital techniques. The conformation energy (CE) calculations, using empirical potential‐energy functions, for intrinsic torsional rotations around C12C13 (θ), C7C8 (Ψ), and C14C15 (ϕ) show a number of energy minima. The relative value of the CE for these minima ranges from 4.09 to 8.01 kcal/mol. An additional rotation around C4C5 (χ) giving “twist” to the carboxyl chains lowers the CE value by 2–3 kcal/mol and a conformation with CE value 2.39 kcal/mol less than crystallographic one is obtained. The interchain interaction energy showed changes with conformations. No significant change in the interchain interaction energy was observed due to “twist” in the carboxyl chain. The isopotential mapping study demonstrated the probable ionic binding site near the carboxyl and the ring (O9) oxygens. Conformational and molecular orbital results are discussed in the light of the reduced abortifacient potency of PGA1 with respect to PGF2α and the possible role of Ca2+ ions in this action.
Geometry of a quantal system
Authors: García‐Sucre Máximo , Bunge Mario 
Published: December 2004

AbstractClassically every physical thing has some geometry or other, but in the quantum theory the notions of spatial structure, shape, and size seem to become hazy if not outright inapplicable. In particular, elementary entities are by definition structureless and seem to have no size or shape other than those imposed by their environmént—as represented, e.g., by the boundary conditions. However, this does not entail that systems of interacting components, such as molecules, lack a geometry as well, as has been argued in recent times. The purpose of this paper is to investigate this claim. Since the solution to the problem whether a quantum‐mechanical system possesses a geometry depends critically upon the definition of the latter, we elucidate the notions of extension, shape, and spatial configuration of a system. We do so first classically in terms of the energy density, then quantum mechanically in terms of a suitably constructed position distribution function that depends upon the spatial coordinates (and is thus a field quantity) rather than on the particle coordinates. In this way we construct both classical and quantal concepts of the geometry of a system. We also define the notions of spatial structure and chemical structure of a quantal system. Our quantum‐mechanical concepts are quite general and constitute smooth extensions of the corresponding classical concepts. The upshot of this investigation is that a quantal system does have a geometry, albeit not as clearcut a one as a classical system, that is primarily determined by the interactions among its components. (Thus, physics determines geometry of physical systems, not the other way around.) This conclusion is obtained within nonrelativistic quantum mechanics without adding any extra assumptions. Our result vindicates the ball‐and‐spoke models of molecules and thus shows once again that quantum chemistry, although different from classical chemistry, stays close to the chemist's work bench.
Application of the strong‐coupling correspondence principle to atom–triatom collinear collisions
Authors: Farantos S. C. , Murrell J. N. 
Published: December 2004

AbstractThe strong‐coupling correspondence principle has been used to calculate the T–V transition probabilities in the collinear collision of He and Kr with CO2. For a harmonic CO2 potential the results for He agree well with published quantum mechanical probabilities. For Kr the agreement is less satisfactory but at worst the ratio of quantum to semiclassical transition probability is approximately 0.2. Introduction of anharmonicity in the CO2 potential was found to increase the semiclassical transition probabilities but this may just be due to the lowering of the vibration frequencies.
Quantum mechanical calculations of vibrational transition probabilities in collinear atom–triatom collisions
Authors: Erkoç S. , Murrell J. N. 
Published: December 2004

AbstractQuantum mechanical calculations have been made of vibrational transition probabilities in the collinear collision of an inert gas atom with either CO2 or OCS. The dependence of the transition probability on the relative translational energy and the reduced mass is similar to that found for atom–diatom collisions. The transition P00 → 10 (excitation of the first stretching mode) is much greater than P00 → 01 (the second stretching mode). This is largely due to the difference in frequencies but it has been shown that there is an independent mass factor responsible for this difference.
Steady states and quasienergies of a system in an oscillating field within the perturbation configuration interaction method
Authors: Dmitriev J. , Lochmann R. , Weller Th. 
Published: December 2004

AbstractA perturbation configuration interaction method is formulated for a system in an external oscillating field (PCILOSC). It is closely connected with the static PCILO method and can be used for the conformational analysis of molecules and molecular crystals with localized bonds in external fields.
Exact solutions for interacting finite potential wells
Authors: Heffernan Daniel M. , Liboff Richard L. 
Published: December 2004

AbstractExact wave functions and eigenenergy relations are obtained for a biwell potential as a function of interwell displacement and single well parameters. The proliferation of energies is shown explicitly as the wells are brought into close proximity. The model is compared with the opaque division‐wall model. These results find important application in laser and nuclear physics.
Dynamic nonlinear Jahn–Teller effect of the type E ⊗ ϵ
Authors: Singh Jai 
Published: December 2004

AbstractBy applying the projection operator method it is shown that the complicated Hamiltonian of a E ⊗ ϵ JT system with nonlinear coupling coefficients can be written in terms of two Hamiltonians which are simple to handle and transform according to irreducible representations E, A1, and A2 of C3v point group. A variational approach is then used to calculate the ground state energy, using the Hamiltonian that transforms according to E, as an explicit function of the linear and nonlinear coupling parameters. The energies calculated in the strong coupling limit are finally compared with the corresponding previously calculated energies.
Atomic calculations with an effective one‐body potential
Authors: Daudey J. P. , Berrondo M. 
Published: December 2004

AbstractThe accuracy of a new effective one‐body potential is assessed by the study of the electronic structure of atoms from He to Kr. The exchange part of this potential is obtained from a local approximation. Several simplified representations of the electronic density which lead to analytic Coulomb potentials are tested. It is shown that the introduction of the shell structure of the density is necessary, at least for third row atoms. The screening parameters of the potential are variationally optimized with respect to the total energy of the atom. With the most elaborate form of the Coulomb potential which contains one screening parameter for each shell, the comparison of the results with exact Hartree–Fock calculations is very promising. The relative difference is on the order of 10−5 for the total energy and on the order of 10−2 for the orbital energies. Multiplet splitting is reproduced accurately and F− is predicted to be stable (in contrast some others local potentials) by an amount of 0.046 a.u., compared with 0.050 a.u. for an exact Hartree–Fock calculation.
Structure and function of propranolol: A β‐adrenergic blocking drug
Authors: Phadke Ratna S. , Kumar N. Vasanth , Hosur R. V. , Saran Anil , Govil Girjesh 
Published: December 2004

AbstractIn our earlier studies using quantum chemical methods we had proposed that propranolol has an extended structure. These results were confirmed using proton NMR. We have now carried out extensive magnetic resonance and model building studies to examine the interaction of this drug with model membranes. The effect of propranolol on organization of lipid bilayers has been studied using ESR spin labeling technique. Spin label Tempo and spin labeled stearic acid (5 SASL) have been used to monitor changes in the fluidity of model membranes. Presence of the drug is found to fluidize the lipids. In case of 0.2M dipalmitoyl phosphatidyl choline (DPPC), presence of drug (0.1M) is found to decrease the gel‐liquid crystalline phase transition temperature by about 10°C. The order parameter measured from the spectrum of 5 SASL shows a 4% decrease on incorporation of the drug in membranes. 13C spin lattice relaxation time (T1) measurements have been carried out for different nuclear sites of the drug. The aromatic moiety shows a high degree of molecular rigidity when the drug is bound to the lipid bilayers. The oxypropanolamine group is however relatively flexible. It appears from these studies that the aromatic group binds strongly to the hydrophobic regions of the lipid bilayer, while the oxypropanolamine moiety remains relatively free and lies in the hydrophilic region. The 13C chemical shifts indicate the involvement of the β‐hydroxyl group in hydrogen bonding with the lipids. The NH group may be involved in electrostatic interactions with the negatively charged phosphate group of the lipid bilayers.
Cholesterol and phospholipids in membranes: The hydrogen bonding problem
Authors: Lala Anil K. 
Published: December 2004

AbstractCholesterol and phospholipids are major components of biological membranes. The role of cholesterol in membranes is not metabolic and is known to be a regulator of membrane fluidity which in turn regulates various biological phenomena. We have studied the nature of cholesterol and phospholipid interaction in artificial membranes using 13C NMR spectroscopy. This involved preparation of phospholipids specifically labeled with 13C in the ester carbonyl group. Though the chemical shift data did not provide very useful information the T1 and T2 measurements indicated that previously proposed H bonding between the ester carbonyl group and hydroxyl group of cholesterol seems unprobable.