Implementation of Z-vector method in the relativistic coupled cluster framework to calculate first order energy derivatives: Application to SrF molecule

TL;DR

This paper implements the Z-vector method within relativistic coupled cluster theory to accurately compute first-order energy derivatives, specifically applied to the SrF molecule's dipole moment and hyperfine structure constants, achieving high accuracy.

Contribution

The paper introduces the implementation of the Z-vector method in relativistic coupled cluster theory for first-order property calculations, improving accuracy over previous methods.

Findings

Achieved molecular dipole moment accuracy of ~0.5%.

Provided the most accurate theoretical value for SrF to date.

Demonstrated the Z-vector method's effectiveness in near and far nuclear regions.

Abstract

The molecular dipole moment and magnetic hyperfine structure constant demand an accurate wavefunction far from the nucleus and in near nuclear region, respectively. We, therefore, employ the so-called Z-vector method in the domain of relativistic coupled cluster theory to calculate the first order property of molecular systems in their open-shell ground state configuration. The implemented method is applied to calculate molecular dipole moment and parallel component of the magnetic hyperfine structure constant of SrF molecule. The results of our calculation are compared with the experimental and other available theoretically calculated values. We are successful in achieving good accordance with the experimental results. The result of our calculation of molecular dipole moment is in the accuracy of ~? 0.5 %, which is clearly an improvement over the previous calculation based on the expectation value method in the four component coupled cluster framework [V. S. Prasannaa et al, Phys. Rev. A 90, 052507 (2014)] and it is the best calculated value till date. Thus, it can be inferred that the Z vector method can provide an accurate wavefunction in both near and far nuclear region, which is evident from our calculated results.