摘要:

AbstractVibrational transition dipole moments and absorption band intensities for the ground state of formaldehyde, including the deuterated isotopic forms, are calculated. The analysis is based onab initioSCF and CI potential energy and dipole moment surfaces. The formalism derives from second‐order perturbation theory and involves the expansion of the dipole moment in terms of normal coordinates, as well as the incorporation of point group symmetry in the selection of the dipole moment components for the allowed transitions. Dipole moment expansion coefficients for the three molecule‐fixed Cartesian coordinates of formaldehyde are calculated for internal and normal coordinate representations. Transition dipole moments and absorption band intensities of the fundamental, first overtone, combination, and second overtone transitions are reported. The calculated intensities and dipole moment derivatives are compared to experiment and discussed in the context of molecular orbital and bond polarization the

ISSN:0192-8651    

DOI:10.1002/jcc.540090202

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThis article is concerned with the improvement of convergence of the iterative procedure for solving the Hartree–Fock–Roothaan equations by the dynamic “level shift”

ISSN:0192-8651    

DOI:10.1002/jcc.540090203

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractMolecular mechanics methods are applied to the study of neutral molecule complexation with crown ethers. Protocols for the development of parameters necessary to describe these molecule‐molecule interactions are presented. Application of these methods to the study of 1:1 and 2:1 (guest:host) complexation between acetonitrile (1), nitromethane (2), malononitrile (3) and dimethylsulfone (4) reveals positive cooperativity in formation of the 2:1 complexes in isolatio

ISSN:0192-8651    

DOI:10.1002/jcc.540090204

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractIntermediate water structures in a solution of Nα‐acetyl‐N‐methylphenylalaninamide[Phe(amide)2] were investigated by the energy minimization method. The results show that ninety‐eight water molecules hydrate Phe(amide)2and several kinds of cyclic structures are observed. The distribution of water molecules around Phe(amide)2agrees with the results of molecular dynamics and monte carlo studies. The distribution of cyclic structures shows that the six‐membered ones are distributed mainly at the outside of the first hydra

ISSN:0192-8651    

DOI:10.1002/jcc.540090205

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractWe present here a protocol for the determination of oligosaccharide solution conformation from a combination of molecular mechanics calculations and NMR distance constraints treated as pseudoenergies. As an illustration of our methodology we have chosen the determination of the solution conformation of the tetrasaccharide headgroup of the glycolipid globoside. In order to test the ability of our methodology to avoid becoming trapped in local minima, we have chosen three starting structures, well displaced from one another in conformational space. The structures obtained upon convergence of the calculations with distance constraint pseudoenergies were quite similar to one another. For two of the three glycosidic linkages in globoside, the results from the calculations were virtually identical for each of the three starting structures. We also apply our protocol to a model which allows for the existence of multiple conformers in an effort to explore the possibility of conformational flexibility in the oligosaccharide headgroup of globoside.

ISSN:0192-8651    

DOI:10.1002/jcc.540090206

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractCompression of two‐electron integral data is used to reduce integral storage and I/O requirements with FPS M64 Series (formerly FPS‐X64) processors. Schemes are developed and implemented in assembly language to compress floating‐point values to a fixed‐point accuracy, and unsigned integer numbers. The floating‐point scheme stores only the significant bits of the mantissa and a short, biased exponent. The unsigned integers are packed into fixed‐length fields just long enough to hold the largest value. The packing procedures are tested on FPS‐164 and FPS‐264 processors (since renamed M64/145 and M64/60 by FPS) and incorporated into HONDO to compress two‐electron integral files. Reduction factors of 0.2–0.4 are obtained for floating‐point compression and 0.3–0.5 for index packing, with typical overall factors around one‐third. The advantages of improved I/O and storage efficiency are accompanied by a small increase in processor time to perform the packing and unpacking. Timing changes for HONDO are presented, and both packing schemes dramatically reduce SCF elapsed times with FPS‐264 processors. It is concluded that compression effectively extends external storage capacities, improves I/O efficiency, and can reduce the elapsed tim

ISSN:0192-8651    

DOI:10.1002/jcc.540090207

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractWe report herein, the implementation of a second‐order Moller–Plesset perturbation theory (MP2) program on the IBM LCAP parallel supercomputers. The LCAP systems comprise IBM 308X hosts and 10 FPS‐X64 attached processing units (APs). The APs are interconnected by a 512 Mbyte shared memory which allows rapid interprocessor communication. All the computationally demanding steps of the MP2 procedure execute efficiently in parallel. Parallel computation of two‐electron integrals is accomplished by distributing the loop over shell blocks among the APs. Parallel Fock matrix formation is achieved by having each AP evaluate the contribution of its own integral sublist to the total Fock matrix. The contributions are added together on the host, and the sum diagonalized either on the host or on a single AP. The parallel implementations of the integral transformation and the MP2 calculation are less straightforward. In each case, the use of the shared memory is essential for an efficient implementation. Details of the implementations and performance data ar

ISSN:0192-8651    

DOI:10.1002/jcc.540090208

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractA method is presented for the rigorous computation of the electric potential of molecules of arbitrary shape, under the assumption of continuous linear dielectric media. The computational technique involves finding the distribution ofinduced polarization chargeon the molecular surface, and proceeds by an application of the method ofboundary elements.The surface, which separates the molecular interior (of low dielectric constant) from the highly polar solvent, is given a piece‐wise analytic representation as a collection of curvilinear elements. Given a set of internal fixed charges, the distribution of polarization‐charge is found as a continuous function over the surface elements, and the electric potential (including all polarization effects) is then easily computed at any point. The method is applied to a spherical interface, and to several small molecules of biological interest, including a hexapeptide. The resulting potentials show good convergence in all cases. The future application of the method to macromolecules is discus

ISSN:0192-8651    

DOI:10.1002/jcc.540090209

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

ISSN:0192-8651    

DOI:10.1002/jcc.540090210

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

ISSN:0192-8651    

DOI:10.1002/jcc.540090201

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY