UNSPECIFIED. (2004) Calibration of the n-electron valence state perturbation theory approach. JOURNAL OF CHEMICAL PHYSICS, 120 (10). pp. 4619-4625. ISSN 0021-9606

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Abstract

Extensive tests have been performed to benchmark and to compare with second-order perturbation theory based on a complete active space self-consistent field reference function (CASPT2), the recently developed n-electron valence state perturbation theory at second order (NEVPT2). Test calculations included the group fifteen diatomic molecules X-2 (X=N, P, As, and Sb) and the S-4/D-2 and S-4/P-2 splittings for the corresponding atoms, the (1)A(1)-B-3(1) splittings for CH2 and SiH2, and the absorption spectra of pyrrole and of Cu(Imidazole)(2)(SH)(SH2)(+), which is a model for plastocyanin. Comparisons with full configuration-interaction calculations and experimental data show that the accuracy of NEVPT2 is in most cases even better than CASPT2. Where intruder states hamper the CASPT2 calculations, NEVPT2 performs significantly better. Care is needed in the choice of active orbitals, for example in the calculation of the S-4/D-2 and S-4/P-2 splittings for the group fifteen atoms. This is due to the different treatment of orbitals belonging to the inactive or active spaces, making the NEVPT2 not invariant for the choice of active space, even in cases where the multiconfiguration self-consistent field energy is invariant. (C) 2004 American Institute of Physics.

Item Type:	Journal Article
Subjects:	Q Science > QC Physics
Journal or Publication Title:	JOURNAL OF CHEMICAL PHYSICS
Publisher:	AMER INST PHYSICS
ISSN:	0021-9606
Date:	8 March 2004
Volume:	120
Number:	10
Number of Pages:	7
Page Range:	pp. 4619-4625
Identification Number:	10.1063/1.1645243
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/8686

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