Effects from Spin–Orbit Coupling on Electron–Nucleus Hyperfine Coupling Calculated at the Restricted Active Space Level for Kramers Doublets

Abstract

Calculations of electron-nucleus hyperfine coupling were implemented at the restricted active space state interaction (RASSI) level to treat spin-orbit (SO) coupling, based on scalar relativistic restricted active space wave functions. The current implementation is suitable for light atomic systems, for light ligand atoms in heavy metal complexes, and for spin-orbit coupling-induced hyperfine coupling of heavy atoms if the unpaired electrons are described by orbitals with high angular momentum. Spin polarization is reasonably well treated by allowing one hole and one electron in a window of active orbitals ('ras1', 'ras3') surrounding the principal active space ('ras2'). A benchmark set of Kramers doublet states of molecules with light and heavy atoms is used to evaluate the approach and verify the implementation. For NpF6, the impact of SO coupling on the Np and F hyperfine coupling tensors is investigated in detail. It is demonstrated that the Np hyperfine coupling is strongly dominated by SO effects, that there is a large SO effect on the F hyperfine tensor components, and that SO coupling causes the fluorine dipolar term to acquire an isotropic component.

A Nonorthogonal State-Interaction Approach for Matrix Product State Wave Functions

“…Assume an ONV for L spin-orbitals as it was given in Eq. (12). Recalling that annihilation of the vacuum state is impossible, …”

“…Similarly, calculating magnetic properties 6 such as molecular g-factors and electron-nucleus hyperfine coupling, which are central parameters in electron paramagnetic resonance (EPR) spectroscopy, requires spin-orbit coupled wave functions 7,8 . To this end, correlated two-and four-component ab initio wave function [9][10][11][12] , and density functional theory approaches [13][14][15] . In the present study we focus on EPR g-tensors for testing purposes, but it should be noted that the underlying novel method of gaining access to wave functions that include the effects from SOC has a vast range of applications.…”

Four-Component Relativistic Density Functional Theory Calculations of EPRg- and Hyperfine-Coupling Tensors Using Hybrid Functionals: Validation on Transition-Metal Complexes with Large Tensor Anisotropies and Higher-Order Spin–Orbit Effects

“…21 Similar limitations apply to restricted active space state interaction (RASSI)-based calculations of HFCs. 22 Recent density matrix renormalization group (DMRG) calculations of hyperfine couplings 23 have so far also been limited to small molecules, and to scalar relativistic levels. 24 Coupled-cluster and configuration-interaction calculations of g-tensors [25][26] and relativistic coupled-cluster calculations of HFC tensors 27 suffer from the same limitations.…”

Hyperfine Coupling Constants from Internally Contracted Multireference Perturbation Theory

“…10,[17][18][19][20][21] These approaches have been generalized to relativistic analogues to account for the scalar relativistic and spin-orbit effects. [22][23][24][25][26] Recently, Lan et al 27,28 has used the CASSCF method with the density-matrix renormalization group (DMRG) algorithm to show that it is capable of reproducing experimental results when used with very large active spaces (up to 36 orbitals). Though the work by Lan et al 27,28 has clearly shown that the DMRG-CASSCF method provides benchmark accuracy for small systems, the use of such large active spaces severely limits the scope of applications; the necessity of such large active spaces originates from the fact that the DMRG-CASSCF model is not designed to efficiently capture dynamical electron correlation, the importance of which has been emphasized in the previous studies based on the coupled cluster theory.…”