Accurate prediction of equilibrium structures for heavy element containing molecules pertinent to laser cooling

Accurate prediction of molecular geometries is a central subject in electronic structure theory. Accurate calculation of vibronic branching ratios for laser coolable molecules requires high-accuracy calculations of molecular geometries for both ground state and excited states. Using exact two-component theory and analytical spin-orbit coupled-cluster gradients, we present calculations of molecular equilibrium structures and vibrational frequencies for molecules containing heavy atoms with essentially quantitative accuracy, e.g., < 0.001 Å for bond lengths and ~ 1 cm^-1 for vibrational frequencies. We demonstrate the accuracy and applicability of these methods using calculations for laser coolable molecules containing heavy atoms.