摘要:

AbstractA parallel algorithm is developed for the first time based on Frame's method to compute the characteristic polynomials of chemical graphs. This algorithm can handle all types of graphs: ordinary, weighted, directed, and signed. Our algorithm takes only linear time in the CRCW PRAM model withO(n3) processors whereas the sequential algorithm takesO(n4) time. Especially when the number of vertices of the graph is large this method will be more efficient than the recently developed vectorized Frame and Givens–Householder method

ISSN:0192-8651    

DOI:10.1002/jcc.540120702

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA computational method for the evaluation of dispersion and repulsion contributions to the solvation energy is here presented in a formulation which makes use of a continuous distribution of the solvent, without introducing additional assumptions (e.g., local isotropy in the solvent distribution). The analysis is addressed to compare the relative importance of the various components of the dispersion energy (n= 6, 8, 10) and of the repulsion term, to compare several molecular indicators (molecular surface and volume, number of electrons) which may be put in relation to the dispersion‐repulsion energy, and to define simplified computational strategies. The numerical examples refer to saturated hydrocarbons in water, treated with thehomogeneous approximationof the distribution function which for this type of solution appears to be acceptabl

ISSN:0192-8651    

DOI:10.1002/jcc.540120703

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe possible use of a half‐projected Hartree–Fock (HPHF) wavefunction correlating a single pair of electrons is investigated in relation with the computation of potential energy hypersurfaces associated to pericyclic reactions of systems with an even number of electrons, in which the orbital configuration of the lowest‐energy singlet state is not conserved during the course of the reaction. The results of calculations, within the framework of the MINDO/3 Hamiltonian, for eleven stationary points on the potential energy hypersurfaces of three prototypical thermally “forbidden” pericyclic reactions indicate that, in general, the HPHF model provides a geometrical and energetical description that is equivalent to that obtained from a conventional two‐configuration self‐consistent

ISSN:0192-8651    

DOI:10.1002/jcc.540120704

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe local‐density functional (LDF) theory does not accurately predict the total energy and the orbital energy of an atom, because of the incomplete cancellation of the self‐interaction in the Coulomb integral by that in the exchange integral. Recent investigations showed that the agreement of the total energy and one‐electron eigenvalue of an atom in the LDF and Hartree–Fock (HF) theories are remarkably improved by introducing a self‐interaction correction in the LDF theory. An alternative self‐interaction correction (ASIC) in the generalized exchange local‐density functional (GX‐LSD) theory is developed by equalizing the one‐electron eigenvalue with the ionization potential of the corresponding orbital. The ASIC is subsequently applied to some closed‐shell atoms and shown to give numerically better results than both the self‐interaction corrected (SIC) exchange‐only local‐spin‐density functional theory (SIC‐XO‐LSD) and the self‐interaction cor

ISSN:0192-8651    

DOI:10.1002/jcc.540120705

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA new program has been developed for the implementation of the self‐consistent nonorthogonal group function (NOGF) approximation for the calculation of wavefunctions between interacting systems. The NOGF approach is based on the reformulation of a single‐determinental, closed shell wavefunction into an antisymmetrized product of nonorthogonal group functions, each of which is a single determinant of doubly occupied orbitals. The group product form of the wavefunction combined with the relaxation of the orthogonality constraints and the structure of the orbital equations allows each group's orbitals to be expanded in a local basis set, and makes it possible to modify the orbital expansions or iterative process to simplify the computation. Three models for approximating the full single‐determinental wavefunction are tested: (1) different quality basis sets for orbitals belonging to different groups, (2) variation of the types of intergroup interactions included in the wavefunction, and (3) the use of frozen orbitals which have been predetermined in a subsystem and are subsequently transferred to the system of interest. These approximations are applied to the calculation of protonation energies of formate, ammonia, imidazole, and guanidine with part of the first hydration shell being represented by two water molecules hydrogen bonded to each species. The results from different basis sets are compared. Then interaction potentials between the acid and ammonia are calculated for both neutral and charged forms, again with inclusion of part of the first hydration shell. The results show that these techniques can yield reliable wavefunctions of the same quality as obtained with the standard supermolecule approach. The effect of the basis set superposition error in the NOGF approach is briefly considered, and the reduction in computing effort resulting from the three models is disc

ISSN:0192-8651    

DOI:10.1002/jcc.540120706

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

Abstractφ – ψ maps have been calculated by the MM2(87) potential for theNα‐acetyl derivatives of Gly, Ala, Val, and Tle methylamides and theirNα‐methyl substituted derivatives to interpret the1H NMR and CD spectra of these compounds. From the critical examination of the available theoretical and experimental evidence it follows that in the series ofNαunsubstituted Ala, Val, and Tle derivatives the importance of the second lowest energy conformation (C5) is increased and that eventually it becomes the lowest energy conformation instead ofC 7eq. With theNα‐methyl substituted Ala and Val derivatives, the lowest energy conformation seems to beC 7eq. Performance of MM2(87) was tested for the φ – ψ map of the Ala derivative by comparing it with other theoretical data availa

ISSN:0192-8651    

DOI:10.1002/jcc.540120707

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe calculated result obtained with MM2(87) for the rotation of the isopropyl group in 3‐methyl‐1‐butene is not in agreement with experimental data. In order to reparametrize the Csp2‐Csp3‐Csp‐Csp3 torsional angle, 3‐methyl‐1‐butene and 1‐butene have been studied by molecular mechanics (MM2(87)) andab initio(MP2/6‐31G* and MP3/6‐31G*) calculations. The reparametrization of the torsional angle gives calculated results from MM2(87) in agreement with experimental data andab initiocalculations for both 3‐methyl‐1‐butene and 1‐butene. The calculated barriers for the rotation of alkyl groups in alkylbenzenes are imp

ISSN:0192-8651    

DOI:10.1002/jcc.540120708

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractApplication of Allinger's MM2/MM3 force fields to molecules of real interest is frequently hindered by the lack of parameters for various heterocyclic systems and for poly‐functionalized molecules. A common approach to this problem is to manually choose missing parameters “by analogy” with those that are part of the force field's internal parameter set. Naturally, this is generally attempted only by those possessing extensive experience with force fields. In order to use the MM2/MM3 force fields to study herbicides, an algorithm has been developed to automate this process for the non MM2 specialist. Using a set of “relative cost” criteria for atom type replacement, the algorithm searches the force field parameter set and selects the most appropriate parameters for a given molecule whose MM2 output file contains “missing parameter” errors. The program selects parameter error messages from a standard MM2 output file, finds analogous parameters, asks the user to verify their appropriateness and creates a standard MM2 parameter deck for the molecul

ISSN:0192-8651    

DOI:10.1002/jcc.540120709

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractMolecular orbital calculations with geometry optimization in the 3‐21G(*) basis set were carried out for the acylimino (A,1a) and the isoimino (E,1b) tautomers of the free base form of amiloride, and for the protonated form (F,1c) of amiloride. The results showed theE1 tautomer to be 16.8 kcal/mol higher in energy than theAconformer of lowest energy,A1. The protonation energy of theA1 species was found to be 269.4 kcal/mol. Similar results were obtained using the AM1 method. These results are in agreement with the NMR results of Smith et al. which show theAandFspecies to be predominant in solution. The 3‐21G(*) rotational barrier for the acylimino tautomer was found to be 19.0 kcal/mol, with theA4 conformer 2.50 kcal/mol higher in energy than th

ISSN:0192-8651    

DOI:10.1002/jcc.540120710

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractSemiempirical SCFMO computations of the MNDO and AM1 varieties have been employed to model possible interaction processes for cocaine with the biological substrate glycine. It was found for the gas‐phase species that the most likely interactions occurred as nucleophilic attack of the nitrogen lone pair of glycine on the two carbonyl groups of cocaine. These reactions led to intermediates which further decomposed exothermically to amide and alcohol species. The activation enthalpies for the gas‐phase reactions were predicted to be high (39–46 kcal/mol), but it is believed that such processes could possibly occur by reaction pathways with considerably lower activation energies in the liquid state in the presence of mucus containing olfactory binding protein in vertebrate olfactory rece

ISSN:0192-8651    

DOI:10.1002/jcc.540120711

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY