New method of incorporating nonhorizontal AO in semiempirical quantum-chemical calculations

Autor: V. A. Tikhomirov, M. V. Bazilevskii, A. G. Shamov
Rok vydání: 1988
Předmět:
Zdroj: Theoretical and Experimental Chemistry. 23:359-367
ISSN: 1573-935X
0040-5760
DOI: 10.1007/bf00536351
Popis: A previously proposed semiempirical method has been developed for calculating the molecular electron structures and geometries, which explicitly incorporates AOnonorthogonality. The integrals are parametrized in an atomic basis, and then a transfer is made to an orthogonal basis, in which the zero differential overlap approximation is used. The electron-repulsion integral matrix Г is transformed by a method in which one uses only the Coulomb part. The performance has been evaluated from the number of elementary operations, which is proportional to N3, where N is the basis size. The method is implemented as two schemes that differ in the method of specifying Г in the atomic basis: λ-CNDO and λ-NDDO. Calculations are presented on hydrocarbons by means of the λ-CNDO scheme, which enables one to calculate the heats of formation and the geometry with an accuracy comparable with that in MINDO/3. The performance is higher in calculations on transitional states, as is demonstrated for the model of nucleophilic substitution (CH5− anion). The λ-NDDO scheme has been examined at the level of electron-interaction integral transformation and has considerable advantages over the λ-CNDO one.
Databáze: OpenAIRE
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