The relativistic four-component coupled cluster method for molecules: spectroscopic constants of SnH4

The relativistic coupled cluster method is applied to SnH4. Starting from Dirac-Fock four-components spinors, correlation is incorporated at the second-order perturbation theory and coupled cluster singles and doubles levels. Eighteen electrons are correlated to include any core polarization effects. Both correlation and relativity shorten the bond length of the molecule. The two effects are of comparable magnitude. The correlated relativistic results are in good agreement with experiment: Re is 1.702 Å (experimental 1.701 Å) and ωe for the breathing (a1) mode is 2019 cm−1 (experimental 1955 cm−1).