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arXiv · 2204.05425

Transition-Potential Coupled Cluster II: Optimization of the Core Orbital Occupation Number

Megan Simons·Devin A. Matthews
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Abstract

The issue of orbital relaxation in computational core-hole spectroscopy, specifically x-ray absorption, has been a major problem for methods such as equation-of-motion coupled cluster with singles and doubles (EOM-CCSD). The transition-potential coupled cluster (TP-CC) method is utilized to address this problem by including an explicit treatment of orbital relaxation via the use of reference orbitals with a fractional core occupation number. The value of the fractional occupation parameter $\lambda$ was optimized for both TP-CCSD and XTP-CCSD methods in an element-specific manner due to the differences in atomic charge and energy scale. Additionally, TP-CCSD calculations using the optimized parameters were performed for the K-edge absorption spectra of gas-phase adenine and thymine. TP-CCSD reproduces the valence region well and requires smaller overall energy shifts in comparison to EOM-CCSD, while also improving on the relative position and intensities of several absorption peaks.

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Megan Simons, Devin A. Matthews. 2022-04-11. Transition-Potential Coupled Cluster II: Optimization of the Core Orbital Occupation Number. https://doi.org/10.1080/00268976.2022.2088421

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