Electronic spectra of ytterbium fluoride from relativistic electronic structure calculations.

Johann V Pototschnig,Kenneth G Dyall,André Severo Pereira Gomes,Lucas Visscher

doi:10.1039/d1cp03701c

Abstract

We report an investigation of the low-lying excited states of the YbF molecule-a candidate molecule for experimental measurements of the electron electric dipole moment-with 2-component based multi-reference configuration interaction (MRCI), equation of motion coupled cluster (EOM-CCSD) and the extrapolated intermediate Hamiltonian Fock-space coupled cluster (XIHFS-CCSD). Specifically, we address the question of the nature of these low-lying states in terms of configurations containing filled or partially-filled Yb 4f shells. We show that while it does not appear possible to carry out calculations with both kinds of configurations contained in the same active space, reliable information can be extracted from different sectors of Fock space-that is, by performing electron attachment and detachment IHFS-CCSD and EOM-CCSD calculation on the closed-shell YbF+ and YbF− species, respectively. From these calculations we predict Ω = 1/2, 3/2 states, arising from the 4f13σ26s, 4f145d1/6p1, and 4f135d1σ16s configurations to be able to interact as they appear in the same energy range around the ground-state equilibrium geometry. As these states are generated from different sectors of Fock space, they are almost orthogonal and provide complementary descriptions of parts of the excited state manifold. To obtain a comprehensive picture, we introduce a simple adiabatization model to extract energies of interacting Ω = 1/2, 3/2 states that can be compared to experimental observations.

Highlights

A noteworthy finding in our previous work was the sensitivity of coupled cluster calculations to the basis set in use and, indirectly, to the amount of electron correlation recovered in the calculations
As expected from the preceding discussion, no changes are observed for the ground-state, since it is too separated in energy from the other electronic states. In this manuscript we have presented a study of the ground and excited states of the YbF molecule, with 2-component multireference CI, equation-of-motion and Fock space coupled cluster approaches
We have focused on obtaining electronic states up to around 24 000 cmÀ1 arising from configurations which differ in the occupation of the 4f shell (4f14 and 4f13), which are very difficult to treat on the same footing due to a number of subtle correlation and relaxation effects

Summary

Introduction

A noteworthy finding in our previous work was the sensitivity of coupled cluster calculations to the basis set in use and, indirectly, to the amount of electron correlation recovered in the calculations. The same was recently observed by Pasteka et al.[16] for the nuclear quadruple coupling constant This suggests the existence of a low lying perturbing state, which we want to investigate further in the current work. Experimental[17,18] and previous theoretical[19,20,21] investigations suggest that in the ground state the unpaired electron is located in a ss orbital with dominant contributions from the 6s orbital of Yb, corresponding to a Yb(4f14s16s)F configuration. This 2S1/2 state ground state was studied in greater detail by combining microwave and optical spectroscopy for the odd 171Yb isotope.[22]

Objectives

Methods

Results

Conclusion