state selective equation of motion coupled cluster theory some preliminary results国家选择性运动方程耦合的集群理论的一些初步结果.pdf

Int. J. Mol. Sci. 2002, 3, 656-675 International Journal of Molecular Sciences ISSN 1422-0067 © 2002 by MDPI /ijms/ State Selective Equation of Motion Coupled Cluster Theory: Some Preliminary Results Marcel Nooijen Department of Chemistry, Princeton University, Princeton NJ 08544. E-mail: Nooijen@ Received: 21 December 2001 / Accepted: 19 March 2002 / Published: 30 June 2002 Abstract: A multireference variant of coupled cluster theory is described that applies to systems that can qualitatively be described by deleting two electrons from a closed shell determinant, for example biradicals, single bond breaking processes, or valence excited states. The theory can be generalized to arbitrary open-shell systems and takes a form that is akin to equation-of-motion coupled cluster theory, but where all wave function parameters are explicitly optimized for the state of interest. The implementation of the present methods was accomplished in an automated fashion using the recently developed Automatic Program Generator (APG). We present benchmark results for the O2 and F2 molecules and investigate the behaviour of a number of closely related variants within the same general framework. Keywords: Multireference electronic structure; Coupled cluster; Electronically excited states; Automatic code generation