摘要:

AbstractAnalysis of a Gaussian potential function suitable for modeling degenerate bending vibrations in weakly bound molecular complexes is presented. Approximate eigenvalues and eigenvectors are obtained by application of perturbation theory. Comparison to the “exact” eigenvalues obtained via a numerical solution shows that the first‐ and higher‐order perturbation corrections are consistent with variational pri

ISSN:0192-8651    

DOI:10.1002/jcc.540050202

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe geometries of several conformations of propanal and butanal have been refined by geometrically unconstrainedab initiogradient relaxation on the 4‐21G level. Both compounds possess energy minima at OCCC torsional angles of 0° and in the 120° region, and energy maxima in the 70° region and at 180°. The structure of the aldehyde functional group is found to be relatively invariant both when different systems or when different conformations of the same system are compared. Conformationally dependent geometrical trends in propanal and butanal are discussed and found to be subtle yet

ISSN:0192-8651    

DOI:10.1002/jcc.540050203

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractWe present an approach for deriving net atomic charges fromab initioquantum mechanical calculations using a least squares fit of the quantum mechanically calculated electrostatic potential to that of the partial charge model. Our computational approach is similar to those presented by Momany [J. Phys. Chem.,82, 592 (1978)], Smit, Derissen, and van Duijneveldt [Mol. Phys.,37, 521 (1979)], and Cox and Williams [J. Comput. Chem.,2, 304 (1981)], but differs in the approach to choosing the positions for evaluating the potential. In this article, we present applications to the molecules H2O, CH3OH, (CH3)2O, H2CO, NH3, (CH3O)2PO 2−, deoxyribose, ribose, adenine, 9‐CH3adenine, thymine, 1‐CH3thymine, guanine, 9‐CH3guanine, cytosine, 1‐CH3cytosine, uracil, and 1‐CH3uracil. We also address the question of inclusion of “lone pairs,” their lo

ISSN:0192-8651    

DOI:10.1002/jcc.540050204

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractCompact, contracted Gaussian basis sets for halogen atoms are generated and tested inab initiomolecular calculations. These basis sets have similar structure to that of Huzinaga and co‐workers' (HTS) sets; however, they give both better atomic total energies and better properties of atomic valence orbitals. These sets, after splitting of valence orbitals and augmenting with polarization functions, provide molecular results that agree well with those given by extended calculations. Basis set superposition error (BSSE) is calculated using the counterpoise method.BSSEhas only slight influence on calculated equilibrium geometry, shape of potential curve, and electric properties (dipole and quadrupole moments) of molecules. However, atomization energies may be significantly changed by theBSS

ISSN:0192-8651    

DOI:10.1002/jcc.540050205

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA collection of programs which aid in the use of group theory has been developed for the Apple II. The programs automate much of the tedious algebra necessary to generate character tables and representation matrices from the properties of the operators chosen to generate the group. At the same time, the presentation of intermediate results provides a schematic guide to the procedures by which groups are constructed. The choice of generators is not limited to the reflections, rotations, and inversions, which are the familiar features of chemical group theory. Any generator representable as a permutation may be treated; thus general permutation groups and Longuet‐Higgins groups may be studied. As an illustration we describe the states of beryllium borohydride, which require a form of Longuet‐Higgins group the

ISSN:0192-8651    

DOI:10.1002/jcc.540050206

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractAn algorithm is described for generating atomic Cartesian coordinates of conformations of macrocyclic molecules possessing exact rotational or rotation‐reflection symmetries. A fragment representing the asymmetric unit of the molecule is suitably oriented in space, and then a symmetry operator is applied to generate the initial coordinates of the molecule. An empirical force field of interatomic interactions is used to generate equilibrium conformations. Results of calculations performed on two cyclic polylactones and one crown ether using this approach are given. They reveal that symmetric conformations of these molecules are often preferred. Since the latter conformations are probably responsible for the specialized properties of these molecules, this method should facilitate doing theoretical studies on these kinds of compound

ISSN:0192-8651    

DOI:10.1002/jcc.540050207

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe geometries of several conformations of ethyl and isopropyl formate were optimized by theab initiogradient method on the 4‐21G level. The calculations are in agreemnt with the existence of two conformers of ethyl formate of nearly equal energy. The COCC torsional angle in one is anti (180°) and in the other is gauche (about 80°). The equilibrium configuration of the isopropyl group in the formate is found to be unsymmetrical, with a COCH torsional angle of about 40°. A second minimum of torsional energy, at COCH = 180°, is 1.2 kcal/mol less stable than the unsymmetrical form. The calculations demonstrate the tranferability of internal rotational‐potential parameters and of conformationally dependent geometrical trends between ethyl and isopropyl formate. There is good agreement between the calculated results and empirical potential‐energy functions and rotational constants determined from microwave spe

ISSN:0192-8651    

DOI:10.1002/jcc.540050208

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe principles of a new method, the method of zero determinants, are described which can be used for the determination of the number of exponentials in accurate, multiexponential decay curves, as well as for the smoothing of multiexponential experimental data. It is based on the idea that the determinant of an overdetermined data matrix for accurate data is zero. The method is not limited by mathematical approximations, and thus uncovers the decay curve hidden in the data set.

ISSN:0192-8651    

DOI:10.1002/jcc.540050209

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA computational procedure, developed from the power series method, is used to investigate oscillating systems. In addition to its great accuracy and reduced computer time, the method is very easily programmable since the algorithm is provided by the reaction mechanism itself.

ISSN:0192-8651    

DOI:10.1002/jcc.540050210

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractAb initioself‐consistent‐field molecular orbital calculations have been carried out for the CnH2n(n= 3 to 6) cycloalkanes and various conformers of their protonated forms. The calculated protonation energies for the sequence of conformers of the protonated forms follow the experimentally observed trend. Correlations between optimum CCC bond angles at the protonation site and the calculated protonation energies have been observed, and these correlations may be of some use in estimating protonation energy‐bond angle relations in other (strained) cyclic compounds when the central carbon atom of a CCC moiety

ISSN:0192-8651    

DOI:10.1002/jcc.540050211

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY