Relativistic unitary coupled-cluster method for ground-state molecular properties.

Area of Science:

• Quantum Chemistry
• Relativistic Calculations
• Atomic Physics

Background:

• Coupled-cluster methods are essential for accurate electronic structure calculations.
• Relativistic effects become significant for heavy elements, influencing their properties.
• Calculating first-order properties requires sophisticated theoretical frameworks.

Purpose of the Study:

• To develop and apply a relativistic unitary coupled-cluster expectation-value approach.
• To compute ground-state properties of heavy-element systems.
• To assess the performance of perturbative and non-perturbative formulations.

Main Methods:

• Relativistic unitary coupled-cluster (UCC) theory.
• Expectation-value approach for first-order properties.
• Perturbative and non-perturbative commutator-based formulations.
• Calculations of permanent dipole moment, magnetic hyperfine structure constant, and electric field gradient.

Main Results:

• The non-perturbative commutator-based UCC approach showed superior agreement with experimental data and the UCC Z-vector method.
• Both perturbative and non-perturbative methods were applied to calculate key properties.
• The non-perturbative method, truncated at singles and doubles, demonstrated improved accuracy.

Conclusions:

• The non-perturbative relativistic UCC expectation-value method is a reliable tool for heavy-element systems.
• This approach offers better accuracy than perturbative variants due to improved relaxation effect treatment.
• The findings provide a more accurate way to compute properties of heavy elements.