bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the conditions for physical admissibility of Schrödinger wave functions
Authors: Hui‐Yun Pan , Sen Zhao Zu 
Published: January 2005

AbstractIt is shown that the dispute about the conditions for physical admissibility of Schrödinger wave functions may be settled if the following two questions are clarified: (a) Are these condittions rooted in the foundations of quantum mechanics or invoked only for particular physical models? (b) Do we consider either the position‐space wave function or the momentum‐space wave function? Both the case of closed states and scattering states are considered. Some general remarks about these conditions are made in the Conclusion.
Pauling's criterion of bond strength and the relative bond lengths in molecule MLk
Authors: Zhan Chang‐Guo 
Published: January 2005

AbstractIn this paper, the bond strengths, defined by Pauling, for a series of molecules in the type of MLk have been calculated by using the generalized method obtained from the maximum overlap method in a preceding paper and by using Pauling's pair–defect–sum approximation. A number of geometrical bonding situations are investigated. It is demonstrated why a previous study purporting to use of Pauling's criterion of bond strength to find that the axial bonds in trigonal bipyramidal ML5 are stronger than the equatorial bonds is incorrect. The results obtained from the two methods approach each other and are in good agreement with the experimental bond lengths, which show that Pauling's criterion is viable and that the pair–defect–sum approximation is indeed an excellent one that agrees with the maximum overlap method.
Variational calculation of vibrational energies of triatomic molecules using SCF optimized modes
Authors: Hidalgo Antonio , Zúñiga José , Francés José M. , Bastida Adolfo , Requena Alberto 
Published: January 2005

AbstractA self‐consistent field optimization of the vibrational coordinates for nonlinear triatomic molecules is presented. The optimal coordinates are obtained by making a three‐dimensional rotational transformation of the normal modes and determining the rotation angles as those for which the SCF energy is stationary. The utility of the optimized coordinates in full variational calculations of vibrational energies is studied for the molecules of H2O, O3, H2D+, H2T+, and D2T+. For H2O and O3, the optimization procedure leads to the local mode representation. It is shown that the use of the optimal coordinates in variational calculations allows a large reduction of the dimension of the Hamiltonian matrix to be diagonalized in order to reach convergence.
Transforming Gaussians into Wannier functions using inversion of cyclic matrix
Authors: Iyakutti K. , Thiagarajan M. , Kumarasamy K. 
Published: January 2005

AbstractOne‐dimensional Gaussians are transformed into orthonormalized atomic orbitals (OAOS) using the inverse of the cyclic overlap matrix. During that process it was found that these OAOS are nothing but the Wannier functions and have properties similar to the Wannier functions obtained by Wannier himself from Gaussians using a different method. The present method gives rise to a better Wannier function with less distortion.
Normalized irreducible tensorial matrices and the Wigner–Eckart theorem for unitary groups: A superposition hamiltonian constructed from octahedral NITM
Authors: Ellzey M. L. 
Published: January 2005

AbstractThe concepts of normalized irreducible tensorial matrices (NITM) are extended to all finite and compact unitary groups by a development that clarifies their relationship to group theory and matrix algebra. NITM for a unitary group G are shown to be elements of a basis obtained by symmetry adapting to G the matrix basis of a matrix space M(α1 × α2). Elements [X] ∈ M(α1 α2) transform under Ga ∈ G according to [Ga] [X][G−1a], where [Ga] and [G−1a] belong to irreducible representations of G. The usual properties of NITM and the Wigner–Eckart theorem follow from these results, which are valid for both finite and compact unitary groups. The NITM span M(α1 × α2) are orthonormal under the trace and transform irreducibly with respect to G. This NITM basis of M(α1 × α2) is said to be simple. A compound NITM basis of a matrix space results when the space is partitioned into two or more subspaces, each spanned by a simple NITM basis. NITM determined from Griffith's V coefficients for the octahedral group are tabulated and used to construct a six‐coordinate superposition Hamiltonian.
Valence and hypervalence in compounds with second‐row elements
Authors: Jug Karl , Fasold Eckhard 
Published: January 2005

AbstractA recently introduced concept of charge and valence for ab initio wave functions is applied to molecules with second‐row elements. Mulliken and Löwdin charges and their valence counterparts by Mayer and Gopinathan‐Jug are calculated for selected molecules with 4‐31G and 6‐31G* wave functions and compared with results derived from the new valence concept. It is concluded that the term hypervalence can be reasonalby used in phosphorus compounds PF5 and PCl5 and sulfur compounds SO3 and SF6.
Molecular equilibrium geometries and vibrational frequencies by maximum overlap symmetry molecular orbital method
Authors: Zhan Chang‐Guo 
Published: January 2005

AbstractIt is demonstrated that the maximum overlap symmetry molecular orbital method can be used for optimization of molecular geometries and calculation of vibrational frequencies by adding a two‐body repulsive energy term and a modification of the Wolfsberg–Helmholz formula. The obtained equilibrium geometries and vibrational frequencies are on the whole in good accordance with experimental data, which shows that the basic idea using the method to optimize molecular geometries and to calculate vibrational frequencies is reasonable.
Vibronic dressed electronic states and nonadiabatic effects in polyacetylene
Authors: Lü Tian‐xiong , Tachibana Akitomo , Yamabe Tokio 
Published: January 2005

AbstractThe nonadiabatic effects in the dynamic Fock equation (DFE) have been studied for the model system, polyacetylene, within the Hückel framework. The validity of the perturbation treatment of DFE has been investigated. It is followed by a proposed iterative procedure for solving the DFE. With this procedure, the self‐consistent vibronic dressed electronic states (VDS) of polyacetylene have been obtained and described. It has been shown that (1) the pairing theorem for an alternant chain remains in the VDS of polyacetylene; (2) the modification of orbital energy due to the nonadiabatic effects decreases with the decreasing of absolute value of adiabatic orbital energy, implying that the energy gap originating from the nonadiabatic effects is too small to be significant; (3) the nonadiabatic mixing happens only for those adiabatic states having the same symmetry; and (4) a dynamic resonance exists between the starred and unstarred atoms, which contributes a dynamic delocalization to the polyacetylene. The size‐dependence of the nonadiabatic effects in polyacetylene has been shown throughout the discussion.
The evaluation of the hybrid one‐center integrals used in the semiempirical NDDO‐type methods for d‐elements from spectra
Authors: Zilberberg I. L. , Filatov M. J. , Zhidomirov G. M. 
Published: January 2005

AbstractFor semiempirical SCF MO methods based on the NDDO assumption, the so‐called one‐center hybrid integrals of the type (ab/cd) are required. These integrals are expressed in terms of the Slater–Condon parameters (SCP) Rk(abcd) with different radial functions. The SCPs from atomic spectra are evaluated by taking into account configurational interaction (CI). As an example, the R1(sdpp), R2(sdpp), and R2(sddd) SCPs for Ti I, Ti II, and Ti III have been evaluated and the values of these parameters are compared with those calculated with Slater‐type orbitals.
Investigation on the intermolecular electrostatic interactions of some polar molecules with cumulative potential‐derived atomic multipole method
Authors: Kong Jing , Yan Ji‐Min 
Published: January 2005

AbstractIn this paper, we propose a systematic method to include cumulatively atomic dipole moments and quadrupole moments in the fitting procedures of the potential‐derived method to derive a set of atomic parameters to calculate the intermolecular electrostatic energy. This method is examined both qualitatively and quantitatively. The description of the charge distributions in polar molecules HF, H2O, and NH3 is agreeable to intuitions and the inverted lone‐pair sites in H2O are explained naturally. It is also shown that atomic dipole moments and quadrupole moments should be included if one wants to calculate the electrostatic energy between molecules precisely. We also use Buckingham's model to calculate the orientations of some H‐bonded complexes and explain the sources of nonlinear forces in terms of atomic dipole moments and quadrupole moments.
A three‐dimensional finite element approach towards molecular SCF computations
Authors: Murakami H. , Sonnad V. , Clementi E. 
Published: January 2005

AbstractFully three‐dimensional, SCF ground‐state computations for the Hartree equation are carried out by a finite element approach that completely avoids forming or storing the Fock matrix. A combination of strategies is used to reduce storage and computational requirements by orders of magnitude over the traditional finite element approach, which makes three‐dimensional molecular orbital computations feasible. Results using the three‐dimensional formulation and computer program are shown for one‐electron systems: He+ and H2+, and for two‐electron systems: He and H2. The best results are within about 30–100 micro‐Hartrees of the exact values of the total energies for the ground states of these systems, indicating that our three‐dimensional approach has been correctly implemented in the computer code.
On the calculation of Rys polynomials and quadratures
Authors: Sagar Robin P. , Smith Vedene H. 
Published: January 2005

AbstractA discretized Stieltjes procedure is used to generate Rys polynomials from a three‐term recurrence relationship. We show that this process is numerically stable in contrast to the evaluation from the moments of the system and polynomial coefficients, i.e., the Stieltjes procedure, where numerical instabilities arise. Rys quadratures may thus be calculated in an accurate manner from the Rys polynomials generated via this discretized Stieltjes procedure.
Photochromic spironaphthoxazines: A theoretical study
Authors: Malatesta V. , Ranghino G. , Romano U. , Allegrini P. 
Published: January 2005

AbstractPhotochromic spironaphthoxazines and their open merocyanine forms were studied via semiempirical Hartree–Fock SCF quantum chemical calculations. The most stable of the merocyanine isomers were found to have a cis–trans–cis conformation and the zwitterionic form is, generally, more stable than is the quinoidal tautomer. The calculated activation energy for the thermal bleaching reaction is in good agreement with the experimental one.
Electronic structure of poly(pyrrole–thiophene) copolymers: Design of polymeric quasi‐one‐dimensional superlattices
Authors: Bakhshi A. K. , Ladik J. 
Published: January 2005

AbstractAb initio band structure results of polypyrrole (PPY) and polythiophene (PTP) obtained with a double‐zeta basis set are reported. The electronic density of states (DOS) of the various quasione‐dimensional copolymers (superlattices) of the type (AmBn)x (A = pyrrole; B = thiophene) have been calculated numerically within the ab initio SCF tight‐binding approximation. These copolymers on the basis of the band positions of PPY and PTP are found to belong to the class of type II (staggered) superlattices. The trends in their electronic properties as a function of (i) composition (m/n), (ii) block sizes m and n, and (iii) arrangement of blocks in the copolymer chain are discussed.
A quantum chemical study of the interaction of carbenes with 2‐alkenylfurans and thiophenes
Authors: Ermolaeva L. V. , Vul'fson S. G. , Shostakovsky V. M. , Nefedov O. M. 
Published: January 2005

AbstractThe study of the interaction mechanism of monoalkenyl‐substituted furans and thiophenes with carbenes was performed by AM1 and MNDO methods. The energy profiles of two pathways were calculated, one leading to ylide formation and the second to cyclopropanation species. The insertion of methyl groups into the vinyl fragment does not change the energetic parameters of path 1. The reactivity of the exocyclic double bond was shown to depend on the degree of substitution. The calculations prove the presence of the intermediate ylide formation, based on experimental data. The stability of the ylides is determined by the heights of the cycloaddition barrier and the one of the reversed reaction 1 as shown by calculations.
Calculation of quadratic hyperpolarizabilities for organic π electron chromophores: Molecular geometry sensitivity of second‐order nonlinear optical response
Authors: Kanis David R. , Marks Tobin J. , Ratner Mark A. 
Published: January 2005

AbstractThis contribution explores the sensitivity of computed quadratic hyperpolarizabilities to the choice of chromophore molecular geometry. The nonlinear optical response of 25 organic π‐electron molecular chromophores is calculated for four different types of input geometries using the ZINDO‐SOS formalism. The calculated nonlinear optical susceptibilites are found to be surprisingly sensitive to certain key alternations in molecular structure; this is understandable in terms of modifications in the conjugation strength through the π system. We also describe an efficient, a priori prescription for constructing chromophore input geometries that yield accurate quadratic hyper‐polarizabilities within the ZINDO‐SOS formalism. The first optical absorption maxima, the dipole moments, and the second‐order nonlinear optical responses computed from these idealized geometries are essentially identical to those derived from MOPAC‐optimized structures and correspond well with available experimental data.
Nonlinear optical properties of conjugated polymers from ab initio finite oligomer calculations
Authors: Kirtman Bernard 
Published: January 2005

AbstractA review of our own work on ab initio calculation of nonlinear optical properties by the finite oligomer method is presented. Various computational considerations such as geometry determination and choice of basis set are discussed as well as extrapolation to the long‐chain limit. For cases where the extrapolation is problematic, two potential solutions are suggested. We also analyze several important areas ripe for investigation including the frequency‐dependence, the effect of vibrational distortion, and the role of electron correlation.
Quantum molecular study of sulfur mustard
Authors: Broch H. , Viani R. , Vasilescu D. 
Published: January 2005

AbstractThe sulfur mustard, HD, a chemical warfare agent, has been studied by ab initio quantum molecular computations (HF/6‐31G* and 6‐31G) on its various forms (neutral, ethylene sulfonium, and free carbonium ions). The geometries of these molecules have been completely optimized and the minimal energy conformations determined with their associated charge distributions. We discuss these results on electrostatic properties with respect to the mechanism of DNA alkylation by HD and compare them with our previous study of the nitrogen mustard mechlorethamine.
Ab initio MO calculations on the stability of the CF, PF, SF, and MoF ions with the F1s core hole
Authors: Falaleyev A. G. , Andreyev V. A. , Vovna V. I. 
Published: January 2005

AbstractFor the CF, PF, SF, and MoF ions appearing after the F1s photoionization, the possibility of dissociation has been shown by the ab initio MO LCAO method within the Z + 1 core equivalent model. According to the calculations, the decay channel AF → AF + F(1s12p6) is energetically open for the ions. So the interpretation of the gas‐phase emission FKα spectra, in which the bands are assigned to the discrete transition energies, can be unacceptable for these ions. The conditions and signs of such failure are discussed.
Polystyrene models. II. Ab initio study of isobutylbenzene
Authors: Lagowski J. B. , Csizmadia I. G. , Vancso G. J. 
Published: January 2005

AbstractThe structure and stability of the various conformations of isobutylbenzene are studied using ab initio molecular orbital theory. The calculations show that coupling between the structural units is important. The results indicate that complete geometry optimization of the stable and transition structures of isobutylbenzene produce significant changes in geometrical parameters and charge distributions of this molecule when compared with the corresponding results obtained using the rigid‐rotor approximation. These changes are particularly noticeable in one of the gauche conformations and in transition structures of isobutylbenzene generated by the phenyl group rotation. For polystyrene, these results present evidence that there is a strong coupling between the chain‐backbone folding and the rotation of the phenyl group. Multidimensional potential energy surfaces are displayed using a topological representation. © 1992 John Wiley & Sons, Inc.
Intermolecular interactions of methyl acetate, β‐propiolactone, ethyl acetate, and γ‐butyrolactone: An AM1 semiempirical study
Authors: Bodor Nicholas , Huang Ming‐Ju 
Published: January 2005

AbstractClosely related structures, like esters and lactones, have vastly different physical properties. This is apparently due to differences in the intermolecular interactions. The intermolecular interactions of methyl acetate, β‐propiolactone, ethyl acetate, and γ‐butyrolactone have been studied using the AM1 semiempirical method. Some of the “arranged clusters” were also compared to possible covalently bound trimers and tetramers of β‐propiolactone and γ‐butyrolactone. © 1992 John Wiley & Sons, Inc.
Maximum overlap symmetry molecular orbital model
Authors: Zhan Chang–Guo 
Published: January 2005

AbstractThis paper provides a brief and systematic presentation of the basic principle and method of the maximum overlap symmetry molecular orbital (MOSMO) model and its application to simplification of molecular orbital calculation and to calculation of molecular structures and properties, together with some new results about the MOSMO calculation and new insights concerning the further extension of the principle and method. It has been shown that the theoretical method of the MOSMO model is very simple, reliable, and useful and can be employed to study the structure–property relation in even very large molecular systems. The numerical results obtained from the MOSMO calculation on various semiempirical molecular orbital approximation levels show that when the same parametrization, such as one of those employed in EHMO, CNDO/2, and HMO methods, is adopted, the MOSMOS are very close to the canonical molecular orbitals obtained from the customary LCAO method and the MOSMO calculation requires less computing time than does the LCAO method. The MOSMO calculation can be used for rapidly obtaining reasonably good molecular geometries, vibrational frequencies, and other properties of molecules by employing a simple improved semiempirical parametrization. Equilibrium geometries, vibrational frequencies, and other results are in good agreement with the experimental data and the results obtained from ab initio molecular orbital calculation. The basic calculational procedure of the MOSMO model can be extended further and has been employed to give some new results, to propose some new theoretical schemes and principles, and to introduce some new interesting theoretical problems that deserve to be studied further.
Role of axial ligand in the electronic structure of model compound I complexes
Authors: Du Ping , Loew Gilda H. 
Published: January 2005

AbstractA quantum chemical study of the two low‐lying quartet states of seven model compound I iron–porphyrin complexes with varying axial ligands has been carried out using the INDO method. The varying axial ligands included in this study are five that are models for those in the intact enzymes: imidazole and imidazolate (model peroxidase HRP and CCP), CH3CONH2 (Gln175 mutant of CCP), PhO−1 (catalase), CH3S−1 (P450), and two that have been used in biomimetics of these enzymes: Cl−1 (hemin) and PhS−1 (model P450s). The purpose of these studies was to determine the role of the axial ligands in determining (i) the relative energies of the two nearly degenerate quartet electronic states of compound I, involved either as an a1u or a2u porphyrin π cation radical and (ii) the electron and spin distributions in the a1u and a2u radical cations of compound I. For most of the model complexes, including both HRP‐I and CAT‐I, a moderate effect of the axial ligand on the relative energy of these two states was observed and the a1u radical cation was found to be the ground state. The energy order of these two radical cations, however, was reversed in the P450‐I model complexes, indicating an association of the unique property of the FeO bond breaking with an a2u radical cation. The symmetry‐allowed overlap between the FeO and 3a2u orbitals may lower the activation energy for the FeO bond cleavage in P450‐I. However, the calculated electronic and spin properties, including the unpaired spin and net charge on the oxygen and the FeO bond overlap density, important determinants of the reactivity of this complex in the ligand–FeO region, are very similar for all complexes and in both cation states. © 1992 John Wiley & Sons, Inc.
Peptide conformational analysis using the TRIPOS force field
Authors: Wall Craig G. , Healy Eamonn F. , Fox Marye Anne 
Published: January 2005

AbstractTo explain observed electron transfer rates between the terminal aromatic moieties in the arylsubstituted alanine dimer 1, a conformational analysis of the dipeptide was performed using a standard molecular mechanics force field. The resulting low‐energy conformers could conveniently be grouped into two families with an average energy difference of ca. 2 kcal mol−1 and populations of 64% and 30%, respectively. These results correlate well with the 78:22 ratio of the two experimentally distinguishable decay processes for the radical anion of 1. © 1992 John Wiley & Sons, Inc.
NDDO/MC: A new semiempirical SCFMO method for transition metal complexes
Authors: Filatov Michael J. , Zilberberg Igor L. , Zhidomirov George M. 
Published: January 2005

AbstractA new semiempirical SCF MO procedure available for prediction of the transition‐metal complexes' binding energy and molecular geometry is developed. The features of the method are (i) an explicit account of the orthogonality of the basis set; (ii) use of a new formula for the resonance integral; and (iii) an effective account of the Coulomb correlation of electrons in the calculation of the two‐electron integrals based on approach of a model Coulomb hole function. The parameterization for H, C, N, O, Co, and Ni atoms is presented. The results of NDDO/MC (NDDO for Metal Compounds) calculations of molecular geometries and binding energies for a number of organic compounds and more than 30 cobalt and nickel complexes are compared with the available experimental and ab initio data. The average absolute errors for the binding energies of organic molecules and metal complexes are 8.8 and 5.0 kcal/mol, respectively. © 1992 John Wiley & Sons, Inc.
Prototropic changes in cationic base‐pair adducts. I. Guanine protonation
Authors: Ford George P. , Wang Bingze 
Published: January 2005

AbstractAM1 calculations have been used to study the effects of protonation on the structures, energies, and, in some cases, proton transfer reactions of guanine cytosine base pairs. Protonation at the guanine O6‐position, or at various ring sites, leads to a relatively facile conversion to a surprisingly stable complementary base pairs following proton transfer to the cytosine 3‐position. In the case of O6‐protonation, this constitutes a direct route to guanine enolization. It is suggested that the spontaneous formation of apyrimidinic sites in nucleic acids take place via prior protonation of guanine moieties in the opposite strand. © 1992 John Wiley & Sons, Inc.