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A two-step method of calculation of the electronic structure of molecules with heavy atoms: Theoretical aspect

✍ Scribed by A. V. Titov

Publisher: John Wiley and Sons
Year: 1996
Tongue: English
Weight: 839 KB
Volume: 57
Category: Article
ISSN: 0020-7608
DOI: 10.1002/(sici)1097-461x(1996)57:3<453::aid-qua19>3.0.co;2-4

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✦ Synopsis

An approach for a space-separated calculation of the wave function in the valence and core regions of a molecule is proposed. As the first step, the calculation of the orbitals (or two-component spinors in the relativistic case) in the valence region by the effective core potential (ECP) method is performed. Then, it is followed by a restoration of orbitals (four-component spinors) expanded on spherical harmonics in the core regions of heavy atoms. Theoretical questions of the variational calculation of the molecular orbitals are considered in some core region limited by a sphere. Inclusion from the electronic cloud outside this region is reduced by the necessity of taking into account the orthonormality and boundary conditions together with an effective external field in respect to the selected core region.

This method may be used for calculation of matrix elements of operators that are singular near nuclei (P, T-odd interactions, hyperfine structure, etc.). A substantial computational saving can be reached because the method enables, by the most optimal way, to combine the advantages of two well-developed approaches: molecular ECP calculations in the Gaussian basis set and one-center numerical atomic calculations with an external field. It is especially important when the relativistic effects are taken into account. 0 1996 John Wiley & Sons, Inc.

is not widely used yet because of theoretical and technical difficulties 171. HFD calculations have been done for the "small" molecules only (see [6] and references therein).

In its turn, the relativistic effective core potential (RECP) method [8,9] has been successfully applied for the calculation of chemical properties of a considerable variety of molecules. There are a few

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