Multi-reference coupled cluster theory using the normal ordered exponential ansatz
Chemical Physics
2024-10-02 v2
Abstract
Properly spin-adapted coupled-cluster theory for general open-shell configurations remains an active area of research in electronic structure theory. In this contribution we examine Lindgren's normal-ordered exponential ansatz to correlate specific spin states using spin-free excitation operators, with the aid of automatic equation generation software. We present an intermediately normalised and size-extensive reformulation of the unlinked working equations, and analyse the performance of the method with single and double excitations for simple molecular systems in terms of accuracy and size-consistency.
Cite
@article{arxiv.2403.05389,
title = {Multi-reference coupled cluster theory using the normal ordered exponential ansatz},
author = {Alexander Gunasekera and Nicholas Lee and David P. Tew},
journal= {arXiv preprint arXiv:2403.05389},
year = {2024}
}