Determination of molecular hyperfine-structure constant using the second-order relativistic many-body perturbation theory

Abstract

The spin-rotational Hamiltonian parameters ${A}_{\ensuremath{\parallel}}$ and ${A}_{\ensuremath{\perp}}$ for the BaF molecule are calculated using four-component relativistic spinors at the second-order many-body perturbation theory (MBPT) level via the Z-vector technique. The second-order MBPT is applied to assess the accuracy of the computed hyperfine-structure constants before studying the problem with the state-of-the-artcoupled cluster with single and double excitations (CCSD) method which is highly accurate but computationally more expensive than MBPT. The hyperfine-structure constants $A$ and ${A}_{d}$ resulted from these calculations agree favorably well with experimental findings and with other correlated calculations. The convergence behavior of $A$ and ${A}_{d}$ with respect to the number of active orbitals used in the perturbative calculations suggests that our estimated $A$ and ${A}_{d}$ values should be accurate.