Application of SAP-X2C to Spectroscopy and Comparison to Screened Nuclear Spin-Orbit Approximations
Abstract
Recently, Surjuse and Valeev [J. Chem. Theory Comput. 22, 3443-3452 (2026).] suggested to use a simple superposition of atomic potentials to account for the two-electron picture-change error in one-electron exact two-component (SAP-X2C) theory. Herein, we generalize this ansatz to analytical derivative theory and apply SAP-X2C to molecular spectroscopy. The accuracy is assessed for NMR, EPR, Mössbauer, UV/vis, as well as X-ray absorption spectroscopy. A thorough comparison with four-component results and the even simpler screened nuclear spin-orbit (SNSO) approximation reveals that both SNSO-X2C and SAP-X2C perform excellently for spectroscopic properties, with SAP-X2C yielding slightly lower errors. Another major advantage is its well defined thermodynamic limit and less empirical nature. Therefore, SAP-X2C may be expected to become the default choice to mitigate the two-electron picture-change error in density functional theory approaches for spectroscopy thanks to its accuracy, simplicity, and efficiency. More complicated approaches to account for this error based on atomic mean-field ansätze may still be relevant for high-level correlated methods and highly accurate thermochemistry.
Versions
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BibTeX
@misc{franzke2026application,
title = {{Application of SAP-X2C to Spectroscopy and Comparison to Screened Nuclear Spin-Orbit Approximations}},
author = {Yannick J. Franzke and Christof Holzer},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2607.03814},
eprint = {2607.03814},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.03814},
}
RIS
TY - UNPB
TI - Application of SAP-X2C to Spectroscopy and Comparison to Screened Nuclear Spin-Orbit Approximations
AU - Yannick J. Franzke
AU - Christof Holzer
PY - 2026
DA - 2026/08/13
PB - arXiv
DO - 10.48550/arxiv.2607.03814
UR - https://arxiv.org/abs/2607.03814
AB - Recently, Surjuse and Valeev [J. Chem. Theory Comput. 22, 3443-3452 (2026).] suggested to use a simple superposition of atomic potentials to account for the two-electron picture-change error in one-electron exact two-component (SAP-X2C) theory. Herein, we generalize this ansatz to analytical derivative theory and apply SAP-X2C to molecular spectroscopy. The accuracy is assessed for NMR, EPR, Mössbauer, UV/vis, as well as X-ray absorption spectroscopy. A thorough comparison with four-component results and the even simpler screened nuclear spin-orbit (SNSO) approximation reveals that both SNSO-X2C and SAP-X2C perform excellently for spectroscopic properties, with SAP-X2C yielding slightly lower errors. Another major advantage is its well defined thermodynamic limit and less empirical nature. Therefore, SAP-X2C may be expected to become the default choice to mitigate the two-electron picture-change error in density functional theory approaches for spectroscopy thanks to its accuracy, simplicity, and efficiency. More complicated approaches to account for this error based on atomic mean-field ansätze may still be relevant for high-level correlated methods and highly accurate thermochemistry.
ER -