Diagonal and off-diagonal hyperfine structure matrix elements in KCs within the relativistic Fock space coupled cluster theory

TL;DR

This paper employs a relativistic coupled cluster method to calculate magnetic hyperfine interactions in KCs molecules, revealing weak R-dependence at large separations and notable deviations near equilibrium.

Contribution

It introduces a detailed relativistic Fock space coupled cluster approach to compute both diagonal and off-diagonal hyperfine matrix elements in KCs molecules.

Findings

Matrix elements are nearly R-independent beyond 8 Å.

Deviations from atomic values reach 15% near equilibrium.

The level of core correlation affects hyperfine coupling results.

Abstract

The four-component relativistic Fock space coupled cluster method is used to describe the magnetic hyperfine interaction in low-lying electronic states of the KCs molecule. Both diagonal and off-diagonal matrix elements as functions of the internuclear separation $R$ are calculated within the finite-field scheme. The resulting matrix elements exhibit very weak dependence on $R$ for the separations exceeding 8 \AA , whereas in the vicinity of the ground-state equilibrium the deviation of molecular HFS matrix elements from the atomic values reaches 15\%. The dependence of the computed HFS couplings on the level of core correlation treatment is discussed.