摘要:

AbstractA model is proposed which assumes that the pseudorotational potential in five‐membered rings is given by the combination of contributions from the unsubstituted ring, from the individual substituents and from interactions between pairs of substituents. The application of this model to the potentials calculated by the MM2 force field for thecisandtrans‐2,5‐dimethoxytetrahydrofuran shows that the contributions from the individual substituents explain the main features of the potentials of these disubstituted rings. The pseudorotational analysis from vicinal proton spin‐spin coupling constants3JHHconfirms the realibility of the MM2 pot

ISSN:0192-8651    

DOI:10.1002/jcc.540090302

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effect of scaling the molecular velocities to a fixed total energy in molecular dynamics simulations within the (N,V,E) ensemble has been investigated. The effect of using different time steps is also discussed. It is found that, even for small time steps, velocity scaling has a substantial influence on the resulting molecular trajectories, velocities, and forces. Furthermore, velocity rescaling and larger time step seem to have an additive effect on the calculated trajectories, but not on the average thermodynamic properties, such as temperature, pressure, and energy.

ISSN:0192-8651    

DOI:10.1002/jcc.540090303

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe computer code developed previously (K. Balasubramanian,J. Computational Chem.,5, 387 (1984)) for the characteristic polynomials of ordinary (nonweighted) graphs is extended in this investigation to edge‐weighted graphs, heterographs (vertex‐weighted), graphs with loops, directed graphs, and signed graphs. This extension leads to a number of important applications of this code to several areas such as chemical kinetics, statistical mechanics, quantum chemistry of polymers, and unsaturated systems containing heteroatoms which include bond alternation. The characteristic polynomials of several edgeweighted graphs which may represent conjugated systems with bond alternations, heterographs (molecules with heteroatoms), directed graphs (chemical reaction network), and signed graphs and lattices are obtained for the first t

ISSN:0192-8651    

DOI:10.1002/jcc.540090304

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe conformational potential energy surface as a function of the two internal torsion angles inC‐nitrosomethanol has been obtained using the semiempirical AM1 method. Optimized geometries are reported for the local minima on this surface and also for the corresponding points on the HF/6‐31G, 6‐31G*, and 6‐31G** surfaces. All methods predict cis and trans minima which occur in degenerate pairs, each pair being connected by a transition state ofCssymmetry. The AM1 structures are found to compare well with the correspondingab initiostructures.Ab initioHF/6‐31G and HF/6‐31G* harmonic vibrational frequencies are reported for the cis and trans forms of nitrosomethanol. When scaled appropriately the calculated frequencies are found to compare well with experimental frequencies. Theab initiocalculations predict the energy barrier for cis → trans isomerization to be between 5.8 and 6.5 kcal/mol with the trans → cis isomerization barrier lying between 2.3 and 6.5 kcal/mol. The corresponding AM1 energy barriers are around 1 kcal/mol lower in energy. Theab initiocalculations predict the barrier to conversion between the two cis rotamers to be very small with the AM1 value being around 1 kcal/mol. Both AM1 andab initiocalculations predict interconversion between trans rotamers to require between 1.2 a

ISSN:0192-8651    

DOI:10.1002/jcc.540090305

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractAn algorithm to solve the two‐dimensional Schrödinger equation based on the finite‐element method is proposed. In our scheme, the molecular Hamiltonian with any arbitrary internal coordinate system can be solved as easily as with the Cartesian coordinate system. The efficient computer program based on the algorithm was developed on the HITAC S‐810 supercomputer. The performance of the program is examined in the following test problems; (1) free particle in a box, (2) linear triatomic molecule with two equal force constants, (3) coupled Morse oscillators, (4) Henon‐Heiles potential, (5) H3O+symmetric vibrational modes. The algorithm is demonstrated to be very suited for the vector‐type sup

ISSN:0192-8651    

DOI:10.1002/jcc.540090306

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractIn this article we describe a novel approach to the application of graph theory in structure–activity relationship studies. An information–theoretical topological index for the vertices of a molecular graph has been used for the qualitative evaluation of the mutagenic activity of a series of nonfused ring aromatic compounds. The use of a vertex index contrasts with the conventional approach of using a topological index for the entire molecule. The idea is to identify regions, or substructures in the molecules (molecular graphs) which may be used to determine certain biological activity of chemical compounds. The results obtained in this paper indicate that the present approach is capable of classifying the mutagenic activity of the compounds under consideration and may find useful application in structure–activity relationship studies of diverse bioactive comp

ISSN:0192-8651    

DOI:10.1002/jcc.540090307

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractA previously published scheme for the calculation of partial atomic charges has been extended to include silicon, and has been parameterized for a range of SiX bonds (XC,H,O,F,Cl,Br). For the silicon–halogen and silicon–oxygen bonds, a comparison is made between charges calculated with and without the inclusion of π‐bonding. An extensive data set consisting of experimental geometries and dipole moments for the silicon compounds considered is presented and this leads to the selection of standard SiX bond lengths. The calculated dipole moments for the above compounds are in good agreement with those obtained experimentally only when the π charges are included. A comparison has also been made between the partial charges from this scheme and those obtained from computational methods using the Mulliken population analysis. There is considerable disagreement between the methods. Finally, the implications of the charges and structural data are considered in terms of application to ze

ISSN:0192-8651    

DOI:10.1002/jcc.540090308

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractAn efficient algorithm for solving eigenvalue problems of type HC = SCe or FC = SCe is described. This algorithm is generally faster than conventional algorithms. That is to say, this algorithm is more than 1.8 times faster than Gram‐Schmidt orthogonalization and about 8 times faster than Löwdin's S−1/2method. This algorithm is beneficial for large molecules and molecules having a high degree of symmetry. In addition, this algorithm is more compact than conventional algori

ISSN:0192-8651    

DOI:10.1002/jcc.540090309

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractYETI, an interactive molecular mechanics program for drug‐design applications on small‐molecule protein complexes, is described. To model short‐range interactions in better agreement with experimental data, its force‐field energy expression includes directional potential functions for H‐bonds, salt linkages, and metal ligand interactions. The program works on an internal coordinate concept and uses a conjugate‐gradient minimizer. YETI is available for distribution through the author. The program has been used to model details of small‐molecule binding to the enzyme human carbonic anhydrase I. The impact of the directional potential functions on the geometry of H‐bonds and metal‐ligand interact

ISSN:0192-8651    

DOI:10.1002/jcc.540090310

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

ISSN:0192-8651    

DOI:10.1002/jcc.540090301

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY