Fourth-order perturbative extension of the singles-doubles coupled-cluster method
Abstract
Fourth-order many-body corrections to matrix elements for atoms with one valence electron are derived. The obtained diagrams are classified using coupled-cluster-inspired separation into contributions from n-particle excitations from the lowest-order wavefunction. The complete set of fourth-order diagrams involves only connected single, double, and triple excitations and disconnected quadruple excitations. Approximately half of the fourth-order diagrams are not accounted for by the popular coupled-cluster method truncated at single and double excitations (CCSD). Explicit formulae are tabulated for the entire set of fourth-order diagrams missed by the CCSD method and its linearized version, i.e. contributions from connected triple and disconnected quadruple excitations. A partial summation scheme of the derived fourth-order contributions to all orders of perturbation theory is proposed.
Cite
@article{arxiv.physics/0204056,
title = {Fourth-order perturbative extension of the singles-doubles coupled-cluster method},
author = {Andrei Derevianko and Erik D. Emmons},
journal= {arXiv preprint arXiv:physics/0204056},
year = {2009}
}
Comments
12 pages, 6 figures