ISSN:0192-8651    

DOI:10.1002/jcc.540140102

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractAs probed byab initiocalculations at SCF and MCSCF levels, the rotational barrier of the PC double bond in the title compound is similar in magnitude to the corresponding one in methylenephosphane. The transition state for rotation is dipolaric in nature. On this basis, a combination of electron releasing and electron accepting substituents reduces the magnitude of the rotational barrier in phosphatriafulvene. It is supported by experimental investigations. © 1993 John Wiley&Sons, Inc

ISSN:0192-8651    

DOI:10.1002/jcc.540140103

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA data compression algorithm for packing/unpacking floating point numbers is presented. The method has been used to compress large volumes of data commonly generated inab initioquantum mechanical calculations. To retain an accuracy of 10−6Hartree on the final energy, the required file space needed is approximately half its original size whereas the CPU time required to solve the Hartree–Fock self‐consistent field equations increases with 30–60%. © 1993 John Wiley&S

ISSN:0192-8651    

DOI:10.1002/jcc.540140104

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe principles of an efficient, fast algorithm for the calculation of diagrams appearing in Green function and many‐body perturbation methods are discussed and timing examples are given. Within the suggested algorithm, the third order‐diagrams required in the Green function approach are evaluated by arranging computations in such a way that the most inner loops contain only simple scalar products and multiplication of vector by scalar operations. The molecular symmetry is taken into account for abelian groups. © 1993 John Wiley&Sons,

ISSN:0192-8651    

DOI:10.1002/jcc.540140105

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA method is proposed to perform computer simulations of protein dynamics in the long‐time regime. The method is based upon a Monte Carlo technique. The only molecular degrees of freedom considered are bond rotations. All other degrees of freedom including the amide plane torsions are kept rigid. These constraints approximately account for all interactions related to chemical bonding. An individual Monte Carlo step adopts the Go and Scheraga algorithm where local conformational changes in a small window of the protein backbone are performed. By using correlated rotations, the conformation of residues outside the window remains invariant. To test the reliability of the method, the nonbonded interactions are turned off in the present application. Exact statistical averages are compared with values obtained from data of computer simulation involving 2 × 106scans of the window along the protein backbone. Time is related to the number of scans of the window along the protein backbone. End‐to‐end distance autocorrelation functions decay to 1/eof its initial value in about 103–104scans of the window algorithm. Time decay follows a stretched exponential Kohlrausch decay law. © 1993 John Wiley&

ISSN:0192-8651    

DOI:10.1002/jcc.540140106

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractWe consider the tree search problem for the recurrence relation that appears in the evaluation of molecular integrals over Cartesian Gaussian basis functions. A systematic way of performing tree search is shown. By applying the result of tree searching to the LRL2 method of Lindh, Ryu, and Liu (LRL) (J. Chem. Phys.,95, 5889 1991), which is an auxiliary function‐based method, we obtain significant reductions of the floating point operations (FLOPS) counts in the K4region. The resulting FLOPS counts in the K4region are comparable up to [dd|dd] angular momentum cases to the LRL1 method of LRL, currently the method requiring least FLOPS for [dd|dd] and higher angular momentum basis functions. For [ff|ff], [gg|gg], [hh|hh], and [ii|ii] cases, the required FLOPS are 24, 40, 51, and 59%, respectively, less than the LRL1 method in the K4region. These are the best FLOPS counts available in the literature for high angular momentum cases. Also, there will be no overhead in either the K2or K0region in implementing the present scheme. This should lead to more efficient codes of integral evaluations for higher angular momentum cases than any other existing codes. © 1993 John Wiley&Sons, I

ISSN:0192-8651    

DOI:10.1002/jcc.540140107

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractMNDO parameters for helium are derived from an optimization that employs only atomic and diatomic reference data. Comparisons with published high‐levelab initioresults indicate that MNDO correctly predicts the existence of covalently bonded helium compounds and normally reproduces the geometries of these small charged molecules reasonably well. Endohedral fullerene–helium complexes and the transition states for their formation are studied for C60, C60, and C 602+. The calculated barriers are discussed and compared with those for the passage of helium through C6H6, C6H 6+, and C6H 62+. © 1993 John Wiley

ISSN:0192-8651    

DOI:10.1002/jcc.540140108

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe antitumor drugcis‐diamminedichloroplatinum(II) (cisplatin) binds preferentially to GpG and ApG sequences of DNA, forming N7,N7 intrastrand chelates. Molecular modeling of the intrastrand adducts have been handicapped, so far, by the lack of force‐field data describing the Pt–guanine and Pt–adenine binding. We usedab initiocalculations with relativistic pseudopotentials to evaluate three important parameters for the platinum–adenine model complex [Pt(NH3)3(Ade)]2+: (1) the force constant for the PtN7 bond bending out of the adenine plane; (2) the energy profile for the torsion about PtN7; (3) a set of fractional atomic charges that reproduce theab initiopotential for a number of space points placed around the adduct. A population analysis and comparative study on the tetrammine complex [Pt(NH3)4]2+have shown that for platinum adenine is a better σ‐donor than NH3, but its capacity as a π‐acceptor is weak. © 1993

ISSN:0192-8651    

DOI:10.1002/jcc.540140109

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractEnergy optimization calculations have been carried out to determine the variability of optimump,d, andfpolarization function exponents in molecules containing first‐ and second‐row elements and in normal valency and hypercoordinate species. Optimum exponents were determined for single sets of higher‐order functions at both Hartree–Fock and correlated (Moller–Plesset) levels of theory using the Dunning–Hay double zeta and the McLean–Chandler triple zeta basis sets. More detailed calculations were used to test the response to nonoptimumdandffunction exponents of the total energy, the optimum geometry, and harmonic stretching frequencies. The variability in optimum exponents and the size of the energy penalties incurred by adopting nonoptimum values reduces the utility of standard exponents forp,d, andfpolarization functions. © 1993 John W

ISSN:0192-8651    

DOI:10.1002/jcc.540140110

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe CO, CO2, CS, CIF, and SO2molecules were used to test the dependence of supplementarydandffunction exponents to changes in bond lengths and bond angles in MO calculations utilizing Gaussian basis sets in Hartree–Fock and Moller–Plesset calculations. Using Dunning–Hay double zeta basis sets, optimizations were performed at internuclear separations from 100–200 pm and beyond. The energy cost of not reoptimizingdfunction exponents when bonds are stretched or compressed is much smaller for correlated calculations than for those at the Hartree–Fock level and is greatest at the lower end of the range of internuclear distances. The problem is much less serious at all levels when multiple sets ofdfunctions are used. © 1993 John Wiley

ISSN:0192-8651    

DOI:10.1002/jcc.540140111

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY