bluuebunny/crossref_metadata_2025_split huggingface dataset:
The intermolecular vibrations of the bifurcated water dimer: An Ab initio study
Authors: Muguet F. F. , Robinson G. W. , Bassez‐Muguet M.‐P. 
Published: January 2005

AbstractThe intermolecular modes of the bifurcated water dimer are determined at the HF level using an extended basis set. In these computations, the donor libration frequency is found to be real and the bifurcated structure does not collapse toward the linear dimer. This result is contrary to all previous ab initio computations, which have predicted a Hessian with one negative eigenvalue. A good representation of other intermolecular modes, such as the libration of the acceptor, also requires an extended basis set. An interesting infrared active transition is predicted around 444 cm−1. This transition, which corresponds to the donor wag, is found in the low‐temperature spectrum of water in a N2 matrix.
String model for the rate constant of nonadiabatic solvation in the hydration reaction of carbon dioxide
Authors: Tachibana Akitomo , Fueno Hiroyuki , Tanaka Eishi , Murashima Masatoshi , Koizumi Masahiko , Yamabe Tokio 
Published: January 2005

AbstractPerturbation theory for the rate constant of nonadiabatic solvation is presented. Miller's treatment of the RRKM theory is used for the unperturbed rate constant, and thereby the “string model” of chemical reaction is used for the description of the perturbation of solvation. The reaction path under the influence of the external force field is defined as the intrinsic reaction coordinate (IRC) that is treated as a string. The string is thrown in the external static force field that acts as a nonadiabatic source of perturbation. As an application of the present treatment, the effect of the external point charge for hydration reaction of CO2 is calculated as a preliminary model for catalytic activity of the carbonic anhydrase in the tissues and lung capillary vessels.
Aromaticity measured by Kekulé structures
Authors: Hall George G. 
Published: January 2005

AbstractThe total energies, in the Hückel theory, of a large number of polyhex molecules and some containing a four‐membered ring have been calculated and analyzed. The results confirm that within a set of isomers the number of Kekulé structures is the dominant variable. It is proposed that this term should be recognized as the aromatic term. The remaining contributions to the energy can be attributed to local features of the molecule. Comparison with the Hess–Schaad analysis of the same energies indicates that this treatment is simpler, more complete, and closer to the original concept of aromaticity.
Modified virtual orbitals (MVO) in limited CI calculations
Authors: Wasilewski J. 
Published: January 2005

AbstractA modification of virtual orbitals seems to be an inexpensive way of calculating a large part of the correlation energy. Three types of MVOS have been compared in this paper, on the basis of limited valence‐shell CI calculations for some lower states of the H2O molecule: A — orthogonalized eigenfunctions of exchange operators; B — eigenfunctions of one combined exchange operator; C — eigenfunctions of the Fock operator for a highly ionized system. For small virtual spaces (20% of available orbitals used), approach C gives 70% of EcorrCI‐SD, being superior to the two other approaches. When using only 50% of MVOS, all the three types of approaches result in calculating 90% of EcorrCI‐SD, but the ionic orbitals give a better description of the state separations.
Single‐excitations‐adapted molecular orbitals for a simplified description of electronic excited states
Authors: Cioslowski J. 
Published: January 2005

AbstractAn orbital transformation that minimizes the sum of the squares of the off‐diagonal Hamiltonian elements between the singly excited configurations is described. The resulting single‐excitations‐adapted molecular orbitals (SEAMOS) are found to be very suitable for the description of electronic excited states. The test calculations on the singlet and triplet excited states of the N2, CO, and H2CO molecules are presented.
A calculation of the isotropic and anisotropic spectral moments of the dipole oscillator strength distribution of N2
Authors: Diercksen G. H. F. , Oddershede J. , Paidarova I. , Sabin J. R. 
Published: January 2005

AbstractWe calculate a range of isotropic and anisotropic spectral moments of the dipole oscillator strength distribution for N2 in the random phase approximation. The internuclear dependence of, in particular, S∥(k) is nonnegligible and vibrationally averaged moments are reported. The results are compared to other calculations and to experiment when available, and we conclude that the scheme gives reliable results. Based on our results, we predict a 10% anisotropy in the stopping power of oriented N2 molecules.
MNDO calculations on borazine derivatives. The substitution of one [HNBH] fragment for one [HCCH] fragment in benzene to form the azaborines and the nature of the cyclotrimer of the 1,2‐isomer
Authors: Massey Scott T. , Zoellner Robert W. 
Published: January 2005

AbstractThe three azaborine isomers with the formula C4H6BN, 1,2‐, 1,4‐, and 1,3‐azaborine (I, II, and III), have been examined using MNDO (modified neglect of diatomic overlap) calculations. The most stable azaborine was I (heat of formation ‐8.147 kcal/mol), followed by II (+11.60 kcal/mol) and III (+16.64 kcal/mol). Qualitatively, although the π‐ and π*‐orbitals calculated for the azaborines exhibited an ordering similar to that in benzene and borazine, the HOMO/LUMO energy differences (9.27, 9.68, and 8.44 eV, respectively) were smaller than was the difference calculated for borazine (12.81 eV), but of the same magnitude as the difference for benzene (9.76 eV). With the exception of borazine, each molecule had a π‐orbital for the HOMO and a π*‐orbital for the LUMO; borazine's LUMO was a π*‐orbital. The calculated shapes and atomic contributions for the π‐and π*‐orbitals of the azaborines were best described as “hybrids” of the π‐ and π*‐orbitals of benzene and borazine. As was observed for the π‐ and π*‐orbitals of borazine, the azaborines exhibited increased orbital density at the nitrogen atom in the π‐bonding orbitals and at boron in the π‐antibonding orbitals, as would be predicted from electronegativity considerations. Although I and II exhibited significant double‐ and single‐bond localization, all of the ring bonds in III were delocalized. The delocalization in III was not uniform but, rather, resembled two inequivalent fused allyl systems. The cyclotrimer (IV) of 1,2‐azaborine (heat of formation ‐44.07 kcal/mol), based purely on thermodynamic considerations, was predicted to form spontaneously from three monomer molecules with the concurrent loss of three molecules of dihydrogen. The cyclotrimers that could theoretically be produced from 1,2‐azaborine without the loss of dihydrogen (IVc and IVt) were each calculated to be less stable (heats of formation +24.45, and +33.29 kcal/mol, respectively) than was the experimentally observed IV. The carbon molecules triphenylene (TP) and cis‐ and trans‐4a,4b,8a,8b,12a,12b‐ hexahydrotriphenylene (TPc and TPt) (heats of formation +76.79, +101.6, and +103.1 kcal/mol, respectively) were each calculated to be less stable than were the azaborine cyclotrimer analogs, as was observed in comparisons of benzene with the azaborines and borazine.
Approximate density matrices and Husimi functions using the maximum entropy formulation with constraints
Authors: Morrison Robert C. , Parr Robert G. 
Published: January 2005

AbstractThe entropy of an electronic system is defined in terms of the Husimi function, a nonnegative distribution function in phase space. The Husimi function is calculated by maximizing the entropy subject to the constraints that the Husimi function give a Gaussian convolution of the desity when integrating over the momentum coordinates and that its second moment with respect to momentum give a sum of Gaussian convolutions of the density and the kinetic energy density. The result is compared with the Wigner function. Equations are given for calculating the density matrix from the Husimi function. The resulting equation for the exchange energy requires a difficult numerical integration. An alternate method is used to obtain the density matrix from an approximate partially collapsed Husimi matrix that gives the maximum entropy Husimi function as its diagonal. The results are exact for the harmonic oscillator ground state. Exchange energies calculated for H and the He isoelectronic series through C+4 show slight improvements over those calculated using a maximum entropy Wigner function.
Theoretical treatment of chemisorption using an Ab initio SCF Green‐matrix formalism
Authors: Fleck O. , Ladik J. 
Published: January 2005

AbstractWe present a treatment of chemisorption that uses the Green matrix of the surface and the admolecule, as well as a cluster calculation of a small surface cluster. Since full HF‐SCF‐band structures with nonlocal exchange are available now for larger systems for a couple of years, it is possible to treat the substrate surface and the admolecule on equal footing. This offers a natural way to solve the embedding problem. We have applied the formalism to the adsorption of H2 on beryllium and show that in contrast to cluster calculations there appears a binding, which is experimentally verified.
The influence of the solvent on the conformational energy differences due to the anomeric effect
Authors: Montagnani Raffaele , Tomasi Jacopo 
Published: January 2005

AbstractThe solvation free energy ΔGsol of molecules exhibiting the anomeric effect is computed in an approach that considers a continuous distribution for the solvent. A partition of ΔGsol into separately evaluated contributions confirms that changes in the energy of the systems due to changes in conformation of the solute are ruled by the electrostatic contribution. A comparison with the “exact” values indicates that the approximate expression for the electrostatic contribution to ΔGsol are not accurate enough to permit a proper modeling of the solvent influence on the anomeric effect. The systems are composed of methanediol, methoxymethanol, dimethoxymethane, and 2‐methoxytetrahydropyran in carbon tetrachloride, chloroform, acetone, and water. The calculations have been performed at the SCF level with the STO‐3G and 4–31Gbasis sets.
On some relations to wave functions of one‐dimensional Schrödinger equation
Authors: Bakuradze R. Sh. , Stankevich I. V. 
Published: January 2005

AbstractA model problem connected with the investigation of a 2n one‐dimensional Fermion system in a nonhomogeneous well with infinitely high walls is considered in this paper. The one‐particle density ρ(x) is supposed to be known. We show that in terms of ρ(x) and the potential v(x) without using the Schrödinger equation there may be found wave functions and one‐particle energy levels appropriate to the density ρ(x). An integro‐differential equation satisfied by the functions v(x) and ρ(x) is obtained. The problem of satisfying N, v‐representability by a nonnegative function ρ(x) is reduced to the problem of finding conditions for the existence of a solution of a certain equation.
Midgap levels of photoexcited conductive polymers. II. Detailed analysis of trans‐polyacetylene
Authors: Tanaka Kazuyoshi , Yoshizawa Kazunari , Takeuchi Tomonari , Yamabe Tokio 
Published: January 2005

AbstractWe have studied in more detail aspects of the soliton‐antisoliton pair in a trans‐polyacetylene chain based on our previous study of the midgap levels associated with the photogenerated oppositely charged soliton‐antisoliton pair in conductive polymers employing the concept of the molecular orbital interaction (Part I of this study, this issue). The intersoliton distance has been estimated to be about 10 Å from the Pariser–Parr–Pople method. We have found that the energy gap between the midgap levels is estimated to be 0.45 eV, being significantly related to an additional photoinduced absorption.
Ionization potentials, electron affinities, electronegativities, and hardnesses of fractional charged atoms from the density‐functional theory
Authors: Guo Yufei , Whitehead M. A. 
Published: January 2005

AbstractThe electron‐correlation and self‐interaction corrected generalized exchange local‐spin‐density functional theory with the Gopinathan, Whitehead, and Bogdanovic Fermi‐hole parameters has been employed to give self‐consistent field calculations for the quark atoms, the first‐ and second‐order positive ions, and the first‐ and second‐order negative ions of the quark atoms with fractional nuclear charges \documentclass{article}\pagestyle{empty}\begin{document}$ Z = N \pm \frac{1}{3} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ Z = N \pm \frac{2}{3} $\end{document}. A special technique to obtain the converged second‐order negative ions is discussed. The first and second ionization potentials and electron affinities are calculated by the differences of the total energies between the ionized and nonionized systems and compared with the empirical inter‐extrapolation results. The agreement between the present calculations and the inter‐extrapolated results is excellent for the ionization potentials and reasonably good for the electron affinities of the quark atoms. Finally, the calculated ionization potentials and electron affinities are used in obtaining the electronegativities and hardnesses for these quark atoms.
Further investigation of the spatial generalization of Kato's theorem by a variational density‐functional approach
Authors: Csavinszky P. , Kubaska T. 
Published: January 2005

AbstractIn a recent work, Csvinszky formulated a variational density‐functional approach for the investigation of the spatial generalization of Kato's theorem by March. In the previous work, a 10‐electron model system (filled K and L shells) was considered. In the present work, the investigation is extended to two other cases: a 28‐electron model system (filled K, L, and M shells) and a 60‐electron model system (filled K, L, M, and N shells). As in the previous work, several expressions are adapted for the kinetic‐energy functional of the electrons and the intriguing question of identifying the “best” kinetic‐energy functional is raised and discussed.
Ag vibrational levels of cyclobutadiene on a new potential energy surface
Authors: Čársky Petr , Downing John W. , Michl Josef 
Published: January 2005

AbstractGVB/[5s3p1d/3s1p] energies were calculated for 31 geometries of cyclobutadiene in the D2h point group. These geometries differed in the values of the symmetrized internal coordinates for two CC stretching and one CCH bending modes. The data points were fitted to the expansions of in powers of . Variational calculations provided the following energies of the lowest Ag vibrational levels (with respect to the vibrational ground state): 4.4; 1161.2; 1162.3; 1304.0; 1322.8; 1920.3; and 1991.0 cm−1.
Harmonic oscillator tensors. I. The nondegenerate case
Authors: Palting Pancracio 
Published: January 2005

AbstractIt is shown that the Heisenberg Lie algebra of the nondegenerate harmonic oscillator leads to a basis {J+, J0, J−} of LASU(2). The Hamiltonian of the system is proportional to J0, and the basis elements give rise to irreducible tensors in the associative enveloping algebra of the Heisenberg Lie algebra. The construction of these irreducible tensors is studied with special attention being paid to the case in which they act upon a single vector space spanned by the harmonic oscillator basis functions. A tensor coupling rule is developed, and useful application is made of it in the calculation of general expressions for vibrational operators and their matrix elements. Throughout, the value of the additional algebraic quantum numbers (l, m) is emphasized.
MCSCF/MCLR Studies of potential energy surfaces, spectra, and properties of the X1A1 and a3B2 states of ozone
Authors: Nordfors David , Ågren Hans , Jensen Hans Jørgen Aa. 
Published: January 2005

AbstractPotential energy surfaces, properties, and spectra of singlet (X1A1) and triplet (a3B2) ozone are investigated by means of MCSCF/MCLR analytical response theory calculations. MCSCF analytical gradients and Hessians are used to locate equilibrium and transition‐state structures and to obtain associated vibrational and rotational constants, infrared intensities, and dipole moments. By means of MC linear response functions, electronic excitation energies, and oscillator strengths, static and dynamic polarizabilities as well as dispersion (C6) coefficients are obtained. Good agreement is achieved, in some cases within experimental error margins, for properties where experimental data are known. A very low IR intensity for triplet ozone is predicted.
Formulation of N‐ and v‐representable density functional theory. IV. Non‐Born–Oppenheimer approach
Authors: Kryachko Eugene S. , Ludeña Eduardo V. , Mujica Vladimiro 
Published: January 2005

AbstractLocal‐scaling transformations are employed in order to formulate a desity functional theory where both electrons and nuclei are treated quantum mechanically. Because of the properties of these transformations, the ensuing version of density functional theory is N‐ and v‐ representable. In particular, we study the effect of these transformations on both densities and generating wave functions, and as a result, a functional for the energy expressed in terms of the electronic and nuclear densities is constructed. Plausible physical approximations for simplifying this electronic‐nuclear functional are considered, and upon variation of the fuctional with respect to the electronic and nuclear densities, a system of coupled Euler–Lagrange equations is obtained.
Analytic form of Thomas–Fermi–Dirac dielectric function for III–V compound semiconductors
Authors: Gurumurugan K. , Chandramohan D. 
Published: January 2005

AbstractThe nonlinear Thomas–Fermi–Dirac equation is solved variationally for positive and negative point charges in various III–V compound semiconductors. The parameters are presented, and the results are compared with those obtained numerically.
The prism algorithm for two‐electron integrals
Authors: Gill Peter M. W. , Pople John A. 
Published: January 2005

AbstractA new approach to the evaluation of two‐electron repulsion integrals over contracted Gaussian basis functions is developed. The new scheme encompasses 20 distinct, but interrelated, paths from simple shell‐quartet parameters to the target integrals, and, for any given integral class, the path requiring the fewest floating‐point operations (FLOPS) is that used. Both theoretical (FLOP counting) and practical (CPU timing) measures indicate that the method represents a substantial improvement over the HGP algorithm.
Spin‐orbit (core) and core potential integrals
Authors: Pitzer Russell M. , Winter Nicholas W. 
Published: January 2005

AbstractMolecular integral formulas and corresponding computational algorithms are developed for the relativistic spin‐orbit and core potential operators that are obtained from atomic relativistic calculations by means of the effective core potential procedure. Much use is made of earlier work on core potential integrals by McMurchie and Davidson. The resulting computer code has been made part of the ARGOS (Argonne, Ohio State) program from the C⋅OLUMBUS suite of programs, which computes the needed integrals over symmetry‐adapted combinations of generally contacted Gaussian atomic orbitals.
Optimized Gaussian basis sets for use with relativistic effective (core) potentials: LiAr
Authors: Wallace Nora M. , Blaudeau Jean P. , Pitzer Russell M. 
Published: January 2005

AbstractBalanced atomic basis sets, at the double‐zeta level with d functions, have been developed for the elements LiAr within the relativistic effective core potential procedure. The number of primitive functions, their orbital exponents, and the number of contractions were chosen for use in both Hartree–Fock and correlated calculations. Spin‐orbit splittings have been obtained using the approximate operator corresponding to relativistic effective potentials and are compared with experimental values.
Exact and approximate solutions to the one‐center McMurchie–Davidson tree‐search problem
Authors: Johnson Benny G. , Gill Peter M. W. , Pople John A. 
Published: January 2005

AbstractWe have attempted to optimize the cost (the total number of floating‐point operations required) of using the McMurchie–Davidson RNLMj recurrence relation. Rigorous solutions of the tree‐search problem inherent in the cost minimization are given for total angular momentum L ≤ 7. For L ≥ 8, the rigorous search algorithm is prohibitively expensive, and we propose an approximate algorithm that generates highly optimized trees. Cost comparisons demonstrate that the present scheme is consistently superior to two others currently in use.
Conformational preferences of 6‐furfuryl amino purine and 6‐benzyl amino purine
Authors: Tewari Ravindra 
Published: January 2005

AbstractConformational preferences of N6‐furfurylamino purine (kinetin) and N6‐benzyl amino purine (BAP) have been investigated theoretically by the quantum chemical perturbative configuration interaction using localized orbitals method. The predicted most stable conformations for these molecules are quite similar. The N6 substituents in both these molecules are oriented toward N(1) and away from the imidazole moiety of the purine. The furfuryl ring in kinetin as well as the aromatic benzene ring in BAP are not coplanar with the purine ring. Comparison of these results with the preferred conformation of another compound N6‐(Δ2‐isopentenyl) adenine reveals striking similarity in the orientations of the N6 substituents in these cytokinin‐active plant‐growth‐stimulating substances.
Bethe logarithm and Lamb shift for the hydrogen molecular ion
Authors: Bukowski Robert , Jeziorski Bogumił , Moszyński Robert , Kołos Włodzimierz 
Published: January 2005

AbstractA variational method is used to evaluate Bethe logarithm for the ground electronic state of the hydrogen molecular ion. The trial function employed in the calculations analytically represents the singular behavior of the exact solution of the variational problem for high virtual photon energies. This ensures that the accuracy of six significant figures can be obtained with basis sets not exceeding 70 functions. For the equilibrium internuclear separation of 2.0 bohr, the calculated value of the Bethe logarithm, equal to 2.31936, lies outside the bounds 2.35 and 2.56, representing the best previous estimation of this quantity. The accurate values of the Bethe logarithm for internuclear separations ranging from 0.6 to 6.0 bohr are tabulated and used to calculate the radiative corrections to the rovibrational energy levels of H2+, HD+, and D2+. The influence of these corrections on the transition and dissociation energies is also examined.