A relativistic exact two-component approach for calculation of electronic g-factors with applications to f-element molecules pertinent to search for new physics

An exact two-component (X2C) approach for calculations of electronic g-factors together with applications to heavy metal containing small molecules relevant to search for new physics is presented. A magnetic-field-dependent unitary transformation of the Dirac Hamiltonian is adopted to enable a simple inclusion of the quantum electrodynamics correction to the electron spin g-factor in the four-component formulation. The X2C transformation is subsequently employed to eliminate the positronic degrees of freedom to enhance computational efficiency without significant loss of accuracy compared with the parent four-component theory. To demonstrate the accuracy and usefulness of the present scheme, spin-orbit coupled cluster calculations for g-factors of representative small molecules relevant to precision measurement for search of new physics, including HfF⁺, ThF⁺, and ThO, are presented.