Finite-order method to calculate approximate density matrices in the Fock-space multireference coupled cluster theory
An efficient approach to calculate approximate pure-state and transition reduced density matrices in the framework of the multireference relativistic Fock-space coupled cluster (FS CC) theory is proposed. The method is based on the effective operator formalism and consists of the direct substitution...
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Main Authors | , , , |
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Format | Journal Article |
Language | English |
Published |
22.08.2024
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Subjects | |
Online Access | Get full text |
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Summary: | An efficient approach to calculate approximate pure-state and transition
reduced density matrices in the framework of the multireference relativistic
Fock-space coupled cluster (FS CC) theory is proposed. The method is based on
the effective operator formalism and consists of the direct substitution of the
FS CC Ansatz for a wave operator into the effective operator expression with
the subsequent truncation of expansion at the terms quadratic in cluster
amplitudes. The final density matrix is defined by active-space density
matrices of different ranks "dressed" with contributions from cluster
operators. The method gives a connected expression for pure-state density
matrices, provided that the intermediate normalization condition is fulfilled.
Moreover, under some additional assumptions, the connectivity can also be
ensured for calculated transition property matrix elements and natural
transition spinors. The developed technique allows for fast and accurate
calculations of one-particle reduced density matrices for a wide range of
electronic states. A pilot application of the new technique to construct
averaged atomic natural orbital (ANO) basis sets for fully relativistic
electronic structure calculations is presented. |
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DOI: | 10.48550/arxiv.2408.12546 |