Influence of the choice of projection manifolds in the CASPT2 implementation. (17th September 2017)

• Record Type: Journal Article
• Authors: Yanai, Takeshi; Kurashige, Yuki; Saitow, Masaaki; Chalupský, Jakub; Lindh, Roland; Malmqvist, Per-Åke
• Is Part Of: Molecular physics. Volume 115:Number 17/18(2017)
• Page Start: 2077
• Page End: 2085
• Publication Date: 2017-09-17
• Subjects: Multireference theory -- CASPT2 -- MOLCAS -- computer-aided programming; Molecules -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Molécules -- Périodiques; Chimie physique et théorique -- Périodiques; 539.6.05
• DOI: 10.1080/00268976.2016.1271152
• Languages: English
• ISSNs: 0026-8976

Abstract

ABSTRACT: 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 themolcas 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 ofmolcas (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 intomolcas has been carried out, which is available in the version 8sp1 . Abstract :