The Pole Structure of the Dynamical Polarizability Tensor in Equation-of-Motion Coupled-Cluster Theory

27 August 2018, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

In this Letter, we investigate the pole structure of dynamical polarizabilities computed within the equation-of-motion coupled-cluster (EOM-CC) theory. We show, both theoretically and numerically, that approximate EOM-CC schemes such as, for example, the EOM-CC singles and doubles (EOM-CCSD) model exhibit an incorrect pole structure in which the poles that reflect the excitations from the target state (i.e., the EOM-CC state) are supplemented by artificial poles due to excitations from the coupled-cluster (CC) reference state. These artificial poles can be avoided
by skipping the amplitude response and reverting to a sum-over-states formulation. While numerical results are generally in favor of such a solution, its major drawback
is that this scheme violates size extensivity.

Keywords

Coupled cluster
Equation-of-Motion Coupled-Cluster Methods
Excited-State Polarizabilities
Spurious pole structure
sum-over-states expressions

Supplementary materials

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