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arXiv · 2602.24236

Relativistic Complete Active Space Self-consistent-Field Method with a Hierarchy of Exact Two-Component Hamiltonians

Xubo Wang·Sen Wang·Yixuan Wu·Lan Cheng
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Abstract

The development of a novel exact two-component (X2C) scheme with the inclusion of the picture-change correction for the fluctuation potential, the X2Ccorr scheme, is reported, hereby establishing a hierarchy of X2C schemes with systematic improvement for the treatments of relativistic two-electron contributions. Using benchmark X2C complete active space self-consistent-field (CASSCF) calculations for zero-field splittings in chalcogen diatomics, the contributions of two-electron spin-orbit coupling, electron spin-spin coupling, and quantum electrodynamics are carefully analyzed. The capability of the new Cholesky decomposition-based implementation for relativistic two-component CASSCF method using super-configuration-interaction algorithms is further demonstrated with calculations for the low-lying electronic states of neodymium aqua-ions with up to the second coordination shells.

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Xubo Wang, Sen Wang, Yixuan Wu, Lan Cheng. 2026-02-27. Relativistic Complete Active Space Self-consistent-Field Method with a Hierarchy of Exact Two-Component Hamiltonians. https://arxiv.org/abs/2602.24236

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