ISSN:
0192-8651
Keywords:
Computational Chemistry and Molecular Modeling
;
Biochemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Computer Science
Notes:
The complete set of second-order Gaussian functions (6D) includes a totally symmetric second-order Gaussian function (3s-type) in addition to the five d-type functions. This 3s-type function in the 3-21G(*) basis set for the sulfur atom is described (1) in terms of its geometric and electronic effects observed in the sulfur atom and in four sulfur-containing molecules and (2) by the ability of a single zero-order 1s-type Gaussian function (with various exponents) to replace it in ab initio Hartree-Fock calculations. The geometry of the molecules (dihydrogen sulfide, dihydrogen thioketone, dihydrogen disulfide, and methanesulfonamide) were obtained using various semiempirical and ab initio methods. It is found that the 3s-type function lowers the energy relative to that calculated with the 3-21G(*) basis set with only five second-order Gaussian functions by ca. 46-48 kcal/mol per sulfur atom. Only small changes in geometry are observed when the latter basis set is augmented with a 3s or 1s function. When the exponent of the 1s replacement function is chosen so that the resulting function has a location similar to that of the 3s function as measured by the degree of overlap or the coincidence of radial distribution maxima, the corresponding drop in energy is less than 8 kcal/mol per sulfur atom. However, when the shape of the radial distribution of the 1s function is similar to that of the 3s, i.e., when the value of the 1s exponent is ca. equal to that of the 3s function (a local maximum in the 1s energy profile), the energy lowering is similar to that produced with the 3s function. The electronic effects observed in the molecules differ from those in the atom, the largest deviations being found in the methanesulfonamide calculations.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcc.540100508
