Influence of the choice of projection manifolds in the CASPT2 implementation

0478552 - ÚOCHB 2018 RIV GB eng J - Článek v odborném periodiku
Yanai, T. - Kurashige, Y. - Saitow, M. - Chalupský, Jakub - Lindh, R. - Malmqvist, P. A.
Influence of the choice of projection manifolds in the CASPT2 implementation.
Molecular Physics. Roč. 115, 17/18 (2017), s. 2077-2085. ISSN 0026-8976. E-ISSN 1362-3028
Grant CEP: GA ČR GA15-19143S
Institucionální podpora: RVO:61388963
Klíčová slova: multireference theory * CASPT2 * MOLCAS * computer-aided programming
Obor OECD: Physical chemistry
Impakt faktor: 1.704, rok: 2017

The Complete Active Space Second-Order Perturbation Theory (CASPT2) is well-established as a high-accuracy electronic structure method. It was originally implemented in the early 1990s to an efficient computer code in the molcas program suite, and this implementation has been extensively used as a standard tool. Here, we report a comparison of it against two independent computer-aided implementations of the CASPT2 method, revealing that the CASPT2 energies provided by the original code of molcas (version 8 or earlier) are inconsistent with the predictions of the lately developed computer-aided implementations. It is shown that this error is associated with the projections of the first-order equation onto the fully internally contracted multireference bases which are partially inconsistent between the left- and right-hand sides. The degree of the errors is assessed by performing illustrative CASPT2 calculations. The errors in total CASPT2 energies are demonstrated to be negligible relative to chemical accuracy in many cases, while there is a difficult case where they may substantially alter chemical description. The incorporation of the consistent projections into molcas has been carried out, which is available in the version 8 sp1.
Trvalý link: http://hdl.handle.net/11104/0274648