Regensburg 2025 – scientific programme
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O: Fachverband Oberflächenphysik
O 85: New Methods: Theory
O 85.8: Talk
Thursday, March 20, 2025, 12:15–12:30, H25
Assessment of the Accuracy of Equation-of-motion Coupled- cluster band gaps in the Bulk Limit — •Evgeny Moerman1, Alejandro Gallo2, Andreas Irmler2, Andreas Grüneis2, and Matthias Scheffler1 — 1The NOMAD Laboratory at the FHI- MPG, Berlin — 2Institute for Theoretical Physics, TU Wien, Vienna
As a highly regarded theoretical framework in molecular quantum chemistry, coupled-cluster (CC) theory is expected to yield reliable and systematically improvable results for both ground-state and ex cited state properties of materials. One major obstacle to obtaining converged CC results for periodic solids is the often slow convergence with respect to system size. We have investigated the finite-size convergence behaviour of band gaps in equation-of-motion CC (EOM-CC) theory and revealed a direct relation to the GW approximation [1]. Based on these findings, a GW-aided scheme to reliably estimate the size-converged EOM-CC band gap has been developed and tested [2], allowing to assess the true accuracy of the widely used EOM-CCSD method in the periodic case. We find that the accuracy of EOM-CCSD band gaps sensitively depends on the magnitude of orbital relaxation effects, suggesting that such low-order truncation methods as EOM- CCSD may not be sufficiently accurate even for simple materials and that higher orders of correlations seem to be necessary. - This work received support from the European Union's Horizon 2020 research and innovation program under Grant Agreement No.740233.
[1] Moerman et al., arXiv:2409.03721 (2024)
[2] Moerman et al., to be published
Keywords: quantum chemistry; coupled-cluster theory; band gap; GW; finite-size