bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gaussian molecular orbital calculations of the barrier to internal rotation in the ethyl cation
Authors: Massa L. J. , Ehrenson S. , Wolfsberg M. 
Published: December 2004

AbstractExtended Gaussian orbital basis set calculations have been carried out on an assumed staggered and eclipsed classical geometrical configuration of C2H. The best total energies obtained for these geometries were −78.170692 a.u. and −78.170674 a.u. respectively, corresponding to a barrier to internal rotation of 1.8 × 10−5 a.u. or 11 kcal/mole. An analysis of the charge density matrix indicates that charge is distributed in these molecules in a manner consistent with the concept of hyperconjugation.
Gaussian expansion method for molecular integrals of molecular properties
Authors: Matsuoka Osamu 
Published: December 2004

AbstractThe finite Gaussian Expansion method for molecular integrals proposed by Taketa, O‐ohata and Huzinaga has been extended to the integrals of molecular properties. The integral formulas of so‐called moment, field and field gradient integrals have been derived. It has been numerically shown that in order to evaluate the field and the field gradient integrals based on Slater type orbitals, eight‐ or ten‐term Gaussian expansions are sufficient but this method fails to attain sufficient effective numbers for the moment integrals.
Configuration interaction study of X‐ray and fast electron scattering factors for light atomic systems
Authors: Tanaka Kiyoshi , Sasaki Fukashi 
Published: December 2004

AbstractA study of X‐ray and fast electron scattering by light atoms and ions has been carried out in the first Born approximation. Coherent and incoherent scattering factors calculated with configuration interaction wave functions are compared with those obtained with Hartree–Fock wave functions. These configuration interaction wave functions involve only L‐shell correlation. It is shown that the changes in the coherent scattering factors due to configuration interaction are not negligible and that the electron correlation effects on the incoherent scattering factors are important. Tables of coherent and incoherent scattering factors for light atomic systems are given.
Irreducible tensor operator methods in strong‐field coupling
Authors: König E. , Kremer S. 
Published: December 2004

AbstractThe algebra of irreducible tensor operators is developed in the strong‐field coupling case. The method is of general applicability to any symmetry group G including nonsimply reducible groups and mixed configurations. The Wigner–Eckart theorem is given for irreducible tensor operators as well as for their Kronecker and scalar products. The expressions required for the calculation of ligand field splitting, Coulomb repulsion, spin–orbit interaction, and Zeeman effect are given in detail. Applications to problems in the spectroscopy and magnetism of transition metal compounds are referred to.
A comparison of geometric methods with other methods for the characterization of density matrices
Authors: Harriman John E. 
Published: December 2004

AbstractSome recently developed geometric methods for characterizing the subset of density matrices within the space of Hermitian matrices are compared with methods commonly used for the approximate characterization of reduced density matrices. The decomposition of a density matrix into components in terms of the reducing basis set is compared with decomposition in terms of representations of U(r).
Transition moment closure tests for ethylene
Authors: Martin Richard L. , McMurchie Larry E. , Davidson Ernest R. 
Published: December 2004

AbstractThe completeness of a basis set for ethylene is examined relative to its ability to describe transition moments. The double zeta (Dunning contraction) plus polarization plus Rydberg Cartesian Gaussian set does much better for length than for velocity moments. An attempt is made to interpret the transition moment sums for the occupied orbitals.
Electronic structure of excimer molecular lasers
Authors: Michels H. H. , Hobbs R. H. , Wright L. A. , Connolly J. W. D. 
Published: December 2004

AbstractThe electronic structure, potential energy curves, and radiative transition probabilities of excimer systems have been examined using quantum mechanical methods. These molecules are characterized by repulsive or weakly bound ground state potential curves and by bound, strongly ionic, or Rydberg, excited states. They constitute a very interesting class of molecules which offer the possibility for high power, high efficiency UV laser operation. Calculations have been carried out using the density functional SCF‐Xα method, modified extensively to correct for well known errors arising from approximations to the potential and exchange terms. A limited number of ab initio calculations were also carried out for comparison purposes. For the ArF system we find that the lowest excited ionic state has symmetry 2∑, and that the dominant laser transition observed at 1933 Å should be assigned to B 2∑ → X 2∑. The C 2Π3/2 → X 2∑ transition is calculated to be two orders of magnitude smaller in emission intensity than the dominant transition, thus ruling out this assignment for the observed laser line in ArF. Preliminary calculations carried out for Ar2F indicate that the bound upper ionic state has 2B2 symmetry and that the most probable ground state also has 2B2 symmetry. This polyatomic system is predicted to exhibit a broadband emission spectrum with a relatively long radiative lifetime.
Hartree‐like methods in electronic structure theory
Authors: Harris Frank E. 
Published: December 2004

AbstractWe consider the “Hartree Problem,” here defined as the problem of finding the orthogonal one‐electron states which in a single determinant minimize the electronic energy, excluding exchange contributions. These states may provide a useful basis for correlation‐energy studies. It is shown how the “Hartree Problem,” although superficially not of pseudoeigenvalue form, can nevertheless be cast in such a form and solved by an iterative diagonalization process.
Automatic geometry optimization for molecules with d orbitals. I. General analytic formulas for derivatives of slater orbitals
Authors: Beran S. , Slanina Z. , Zidarov D. C. 
Published: December 2004

AbstractGeneral analytic formulas for derivatives of real Slater orbitals with respect to the Cartesian coordinates x and y have been derived. The application of this result to molecular geometry optimization or to the construction of a force constant matrix is briefly discussed.
Study of correlation holes. I. Number–sum rules and infinite system
Authors: Resta Raffaele 
Published: December 2004

AbstractThe correlation holes in a finite system of any size are known to satisfy integral number–sum rules directly related to the N‐representability of the reduced density matrices. In regard to infinite systems, the same rules are known to be satisfied in the electron gas. It is shown that the number–sum rules are not generally satisfied in any infinite system, and that this happens independently of the kind of boundary conditions assumed in the N → ∞ limit. A violation is explicitly found within the alternant molecular orbital formalism. The apparent paradox is explained in terms of surface effects (end effects in a linear system), which are present in a large, but finite system. In other words the N‐representability does not imply the number–sum rules. In the N → ∞ limit the rules are satisfied only in physical systems having short‐range correlation.
Biorthonormal basis sets and the interaction between one‐electron atoms
Authors: Dahl Jens Peder 
Published: December 2004

AbstractThe properties of biorthonormal sets and their use in quantum chemistry are discussed. A theoretical description of the interaction between one‐electron atoms is presented. The description is based on a single orbital per electron but is otherwise complete. Structurally simple relations are derived for the energy of interaction, and theoretical justifications for the London equation and the diatomics‐in‐molecules method are presented. Some comments on the stability of spin‐coupling‐optimized methods are made.
Ab initio Hartree–Fock and configuration‐interaction treatment of the interaction between two nickel atoms
Authors: Shim Irene , Dahl Jens Peder , Johansen Helge 
Published: December 2004

AbstractThe interaction between two nickel atoms in the configurations (3d)8(4s)2 and (3d)9 (4s)1 has been calculated using ab initio methods (Hartree–Fock and configuration interaction). The results of the calculations compare favorably with the optical spectrum. The discrepancy between the calculated and the experimental dissociation energy is discussed, and a new estimate of the dissociation energy is given. The configuration‐interaction calculations show that the interaction between the two nickel atoms is of a very complex nature. In spite of this the binding can be interpreted in a simple way. The bond is minly due to the 4sσg molecular orbital while the 3d orbitals of the two nuclei are exchange coupled.
A dynamical theory describing superconductant DNA
Authors: Paine Douglas A. , Pensinger William L. 
Published: December 2004

AbstractA dynamical model describing DNA as superconductant is proposed. The status of superconductivity is described as being represented by a radiation‐induced harmonic oscillation of a parcel of π electrons between the reference level and critical temperatures. A set of field equations is used to describe the information exchange process mediated by a coherent wave phenomenon.
Correlation problems in atomic and molecular systems. VII. Application of the open‐shell coupled‐cluster approach to simple π‐electron model systems
Authors: Saute M. , Paldus J. , C̆íz̆ek J. 
Published: December 2004

AbstractThe coupled‐cluster variational‐like direct approach to the calculation of ionization and electron attachment energies and of excitation energies is applied to several π‐electron model systems, using the PPP Hamiltonian with various parametrizations. A simple approximation, which represents the triexcited clusters in terms of disconnected W1T2 terms, is employed. All the necessary diagrams for both excitation energy and ionization potential (electron affinity) calculations are given in the compact Hugenholtz nonoriented form. The results of the calculations for benzene, trans‐butadiene, all‐trans‐hexatriene, and fulvene are compared with the corresponding full CI results, and the conclusions about the validity and efficiency of this approach are drawn.
Role of Ca+2 ion in the abortifacient action of prostaglandins. I. Molecular‐orbital and conformation‐energy calculations of PGF2α
Authors: Kothekar V. , Dutta S. 
Published: December 2004

AbstractThe paper reports the study of a possible mechanism of Ca+2 activation of prostaglandin PGF2α on the basis of molecular‐orbital and conformation‐energy calculations. The electronic charges on various atoms of the molecule have been evaluated from the available crystallographic data by the extended Hückel theory (EHT). Conformation energies were calculated for intrinsic torsional rotations around the C11C12, C7C8, and C14C15 bonds. The minimum energy conformation was found to differ from the crystallographic conformation by 9.3 kcal/mol. Some additional local energy minima are also reported within this range. The calculation of the long‐range interchain interaction energy between the α and ω chains shows variation with conformation. The binding site for the Ca+2 ion has been estimated on the basis of the molecular electrostatic potentials. Such a binding site was found near the carboxyl group, which agrees with the current chemical thinking. Changes in the electronic charge distribution due to Ca+2 complexation were studied by EHT method using the supramolecular approach. Calcium complexation decreases the conformation energy by 2–3 kcal/mol and has a small effect on the interchain interaction energy.
Nonbonded interactions in membrane‐active cyclic biopolymers. III. Analogs of valinomycin
Authors: Sundaram K. , Tyagi R. S. 
Published: December 2004

AbstractSeveral analogs of valinomycin have been simulated. These are analogs obtained by changing the configuration of the amino acid and hydroxy acid residues one at a time. Nonbonded interactions have been calculated for three conformations of each analog. The electrostatic and polarization contributions to the energy are conformation selective, whereas the Pauli repulsion is the only component which is isomer selective. For the ring chirality considered here the analog of valinomycin having all the three L‐valyl residues replaced by D‐valyl residues is predicted to be frozen in a “top open” conformation.
Note on the Fermi–Amaldi correction for the Thomas–Fermi theory of atoms
Authors: Csavinszky P. 
Published: December 2004

AbstractThe aim of this note is to ascertain the importance of the Fermi–Amaldi (FA) correction for the Thomas–Fermi (TF) theory of atoms. For this purpose, an analytic trial electron density has been chosen and the Thomas–Fermi–Amaldi (TFA) energy expression has been minimized by the Ritz method for the closed‐shell atoms Ne, Ar, Kr, Xe, and Rn. The variationally obtained electron densities have then been used for calculating the diamagnetic susceptibilities of these atoms. The calculated values show only a very small improvement over values calculated by Jensen by an analogous procedure from the TF energy expression.
Configuration‐Interaction study of lower excited states of O2: Valence and rydberg characters of the two lowest 3Σu− states
Authors: Tatewaki Hiroshi , Tanaka Kiyoshi , Sasaki Fukashi , Obara Shigeru , Ohno Kimio , Yoshimine Megumu 
Published: December 2004

AbstractConfiguration‐interaction calculations, with an extended basis, are carried out on the ground and lower excited states of O2 and O2+ at and near the equilibrium internuclear distance (R = 2.3 a.u.) of the ground state of O2. Particular attention has been paid to the two lowest 3Σu− states, and the mixing of the valence and Rydberg characters in these states are studied. The lowest 3Σu− state is a Rydberg‐type state for R < 2.3 a.u., but becomes valence‐type for R ≳ 2.3 a.u. The second 3Σu− state, which is 1.6 eV above the lowest 3Σu− at R = 2.3 a.u., changes its character from Rydberg to valence, valence to Rydberg, and then to valence again when R increases from 1.9 to 3.1 a.u. Satisfactory agreement between the calculated and experimental vertical excitation energies is obtained.
Density functionals for coulomb systems
Authors: Lieb Elliott H. 
Published: December 2004

AbstractThis paper has three aims: (i) To discuss some of the mathematical connections between N‐particle wave functions ψ and their single‐particle densities ρ (x). (ii) To establish some of the mathematical underpinnings of “universal density functional” theory for the ground state energy as begun by Hohenberg and Kohn. We show that the HK functional is not defined for all ρ and we present several ways around this difficulty. Several less obvious problems remain, however. (iii) Since the functional mentioned above is not computable, we review examples of explicit functionals that have the virtue of yielding rigorous bounds to the energy.
Ab initio quantum‐mechanical characterization of the electronic states of anthraquinone, quinizarin, and 1,4‐diamino anthraquinone
Authors: Petke J. D. , Butler Paul , Maggiora Gerald M. 
Published: December 2004

AbstractThe ground and excited singlet and triplet states of 9,10‐anthraquinone and its 1,4‐dihydroxy and 1,4‐diamino derivatives are investigated by ab initio configuration interaction calculations, using a floating Gaussian basis. For anthraquinone the calculated electronic absorption spectrum is consistent with previous experimental and theoretical results. The possible mechanisms of intersystem crossing and intensity borrowing in phosphorescence are discussed in terms of first‐ and second‐order spin‐orbit and vibronic perturbations of the computed singlet and triplet states. The calculated spectra of the 1,4‐disubstituted derivatives are more complex than previously suggested from low‐resolution polarized absorption studies. The principal effect of 1,4‐substitution by electron donating groups is shown to be a powerful conjugative effect which significantly modifies selected molecular orbitals of anthraquinone; the resultant effect on the absorption spectra is the creation of two new substituent‐induced π → π* transitions, one of which corresponds to the intense visible absorption band of these systems.
Electronic structure of DNA dimer units, d(AA) · d(TT), d(TA)2, and d(AT)2, in A and B conformations by DV‐Xα cluster calculations
Authors: Shinoda Takako , Shima Nobuyuki , Tsukada Masaru 
Published: December 2004

AbstractThe electronic structure of d(AA) · d(TT), d(TA)2 and d(AT)2, which are stacked base pairs in the DNA double helix, is elucidated for both A and B conformations in detail by DV–Xα cluster calculations. The results are compared with those of a previous study on the electronic structure of d(GG) · d(CC), d(CG)2, and d(GC)2. A hexanucleotide −10 sequence of the promoters in DNA transcription initiation, TATAAT, can be interpreted as the best sequence for the strong promoters by using the S̃r values of the O2 of each phosphate. The reactivity of polymerization at neighboring thymines in the AA/TT unit is discussed from the electronic structure. © 1993 John Wiley & Sons, Inc.
Electron correlation effects in the Rydberg‐like 33D and 31D states of helium‐like ions
Authors: Cann Natalie Mary , Boyd Russell J. , Thakkar Ajit J. 
Published: December 2004

AbstractThe small and subtle effects of electron correlation in the Rydberg‐like 31D and 33D states of the helium‐like ions are studied using very accurate explicitly correlated wave functions. In particular, the effects of electron correlation on one‐electron densities, probability distributions for the interelectronic distance, and their moments are examined with the help of density and Coulomb holes. Statistical electron correlation is examined with radial and angular correlation coefficients. The different methods of analysis provide complementary insight. © 1993 John Wiley & Sons, Inc.
Eigenvalues of single‐cycle class‐sums in the symmetric group. II
Authors: Katriel Jacob , Pauncz Ruben 
Published: December 2004

AbstractExplicit expressions for the eigenvalues of the single‐cycle class‐sums [(p)(1)n–p]n of the symmetric group (Sn), with p ≤ 20, are constructed. A new algorithm is used that makes no use of representation‐theoretic data. The expressions obtained consist of polynomials in the symmetric power‐sums over the “contents” of the Young diagram specifying the irreducible representation, with coefficients that are polynomials in n. On the basis of the results obtained for p ≤ 20, a conjecture is proposed concerning the general form of the four leading terms in these polynomials. © 1993 John Wiley & Sons, Inc.
Stable electronic energy levels in the presence of off‐diagonal disorder
Authors: László István 
Published: December 2004

AbstractIt is demonstrated that the topological arrangement of atoms can guarantee the existence of stable electronic eigenvalues. These levels are stable in the presence of off‐diagonal disorder. Graph theory is used to describe the topological structure of the Hamiltonian. The actual applications are presented in tight‐binding approximation. It was found that graph theory can be used even if the atoms have more than one atomic orbital. Also, the localization properties of the topologically determined eigenvalues are studied. © 1993 John Wiley & Sons, Inc.
Antiaromaticity in relation to 1,3,5,7‐cyclooctatetraene structures
Authors: Politzer Peter , Murray Jane S. , Seminario Jorge M. 
Published: December 2004

AbstractAn isodesmic energy analysis has been carried out at the MP2/6–31G*//HF/3–21G level for the nonplanar ground state (1) of 1,3,5,7‐cyclooctateraene and for two planar forms, one having complete π delocalization (2) and the other having alternating single and double bonds (3). 1 is found to have a considerable degree of stabilization, which is attributed to limited π delocalization. The polyene 3 is the more stable of the two planar forms; it is a transition state in the inversion between two possible nonplanar structures. 2 is found to be a triplet at the Hartree–Fock level and is a critical point on an alternate pathway between the two possible arrangements of alternating single and double bonds in 3. Both 2 and 3 have negative isodesmic energies, indicating the presence of stabilizing factors. Our results for 3 show that an “antiaromatic” system need not necessarily show a net destabilization. © 1994 John Wiley & Sons, Inc.
Search for stationary points of arbitrary index by augmented Hessian method
Authors: Khait Yu. G. , Panin A. I. , Averyanov A. S. 
Published: December 2004

AbstractConvergence properties of the augmented Hessian (AH) method when searching for stationary points of an arbitrary fixed index are investigated. It is shown that the displacement vector of this method is proportional to one of the Hessian eigenvectors if the current point is far from a stationary one of the required index. A simple and reliable criterion for nearness of the current point to a stationary one of the desired index is proposed. The efficiency of a new one‐dimensional optimization scheme that uses this criterion is studied. The case of coincidence of Hessian eigenvalues, which is a bottleneck of the standard AH method, is analyzed. A relation of the AH method to those by Poppinger and Wales is outlined. The correctness of the results obtained is illustrated on an example of a model surface. © 1995 John Wiley & Sons, Inc.
Matrix elements for Ĵ2 and Ĵz operators over explicitly correlated Cartesian Gaussian functions
Authors: Kozlowski Pawel M. , Adamowicz Ludwik 
Published: December 2004

AbstractGeneral formalism for evaluation of multiparticle integrals involving J̌2 and J̌z operators over explicitly correlated Cartesian Gaussian functions is presented. The integrals are expressed in terms of the general overlap integrals. An explicitly correlated Cartesian Gaussian function is a product of spherical orbital Gaussian functions, powers of the Cartesian coordinates of the particle, and exponential Gaussian factors, which depend on interparticular distances. This development is relevant to both adiabatic and nonadiabatic calculations of energy and properties of multiparticle systems. © 1995 John Wiley & Sons, Inc.
Ab initio studies of the electronic structure of Be93, Be105, Be111, and Be123 clusters
Authors: Ross R. B. , Kern C. W. , Pitzer R. M. , Ermler W. C. 
Published: December 2004

AbstractAb initio self‐consistent‐field calculations are reported for electronic states of beryllium clusters comprised of 93, 105, 111, and 123 atoms. The respective clusters correspond to coordination shells 12‐15 of a central Be atom with internuclear separations derived from the lattice constants of the bulk metal. Ab initio effective core potentials have been employed to replace the 1 s electrons, thereby reducing the complexity of the calculations. In addition, use of the full D3h point group symmetry of the clusters results in a substantial reduction of the numbers of two‐electron integrals that must be computed and processed. Binding energies, orbital energies, electric field gradient, nuclear‐electrostatic potential, diamagnetic shielding constant, second moments, and Mulliken populations are calculated for selected electronic states. Calculated binding energies when compared among the different clusters as well as to smaller and larger fragments from earlier studies provide evidence for the onset of convergence to the Hartree–Fock limit of the bulk. Lowest‐state ionization potentials are consistently above and agree to within 14% of the experimental workfunction. The net charge on the central beryllium atom decreases toward zero. The variability of observed bulklike behavior for the different properties indicates that the transition between cluster and bulklike behavior is not sharp and depends on the quantity of interest. © 1995 John Wiley & Sons, Inc.