A formulation and an implementation of analytic energy gradients for coupled-cluster singles and doubles augmented with noniterative triples [CCSD(T)] method with spin-orbit (SO) coupling included at the orbital level is reported. The standard density-matrix formulation for analytic CC gradient theory adapted to complex algebra has been used. The orbital-relaxation contributions from frozen core, occupied, virtual, and frozen virtual orbitals to analytic SO-CCSD(T) gradients are fully taken into account and treated efficiently, which is of importance to calculations of heavy elements. Benchmark calculations of first-order properties using the corresponding exact two-component property integrals are presented for heavy-element containing molecules to demonstrate the applicability and usefulness of the present analytic scheme.

Analytic energy gradients for spin-orbit coupled-cluster singles and doubles augmented with noniterative triples method

ACS Fall 2021

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