Affiliation:
1. Chemistry Department, Moscow State University 1 , Leninskie Gory 1-3, Moscow 119991, Russia
2. Independent Researcher 2
Abstract
Methods based on the multireference perturbation theory (MRPT) with the one-electron zeroth-order Hamiltonian are widely used for the description of excited states, for example, due to their relatively low computational cost. However, current methods have a common drawback—use of a model space with low size. In this article, we propose the MRPT method with the model space extended to the complete active space. The one-electron zeroth-order Hamiltonian suitable for this extension is formulated. The proposed method was applied to common models, such as LiF, ethylene, and trans-butadiene. It was shown to have accuracy superior to XMCQDPT2 in most cases, especially in the case of the small active space.
Funder
Ministry of Science and Higher Education of the Russian Federation