Transition properties from the Hermitian formulation of the coupled cluster polarization propagator

TL;DR

This paper develops a Hermitian formulation of the coupled cluster polarization propagator to compute transition properties, achieving results comparable to existing methods and validated against experimental data.

Contribution

It introduces a Hermitian formulation of transition density matrices within coupled cluster theory, providing an alternative to linear response methods with comparable accuracy.

Findings

Good agreement with experimental transition probabilities.

Equivalent accuracy to linear response coupled cluster theory.

Identified optimal approximation balancing accuracy and efficiency.

Abstract

Theory of one-electron transition density matrices has been formulated within the time-independent coupled cluster method for the polarization propagator [R. Moszynski, P. S. \.Zuchowski, and B. Jeziorski, Coll. Czech. Chem. Commun. {\bf 70}, 1109 (2005)]. Working expressions have been obtained and implemented with the coupled cluster method limited to single, double, and linear triple excitations (CC3). Selected dipole and quadrupole transition probabilities of the alkali earth atoms, computed with the new transition density matrices are compared to the experimental data. Good agreement between theory and experiment is found. The results obtained with the new approach are of the same quality as the results obtained with the linear response coupled cluster theory (LRCC). The one-electron density matrices for the ground state in the CC3 approximation have also been implemented. The dipole moments for a few representative diatomic molecules have been computed with several variants of the new approach, and the results are discussed to choose the approximation with the best balance between the accuracy and computational efficiency.