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-component 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: R(e) is 1.702 Angstrom (experimental 1.701 Angstrom) and omega(e) for the breathing (a(l)) mode is 2019 cm(-1) (experimental 1955 cm(-1)).