THE RELATIVISTIC 4-COMPONENT COUPLED-CLUSTER METHOD FOR MOLECULES - SPECTROSCOPIC CONSTANTS OF SNH4

The relativistic coupled cluster method is applied to SnH4. Starting f rom Dirac-Fock four-component spinors, correlation is incorporated at the second-order perturbation theory and coupled cluster singles and d oubles levels. Eighteen electrons are correlated to include any core p olarization effects. Both correlation and relativity shorten the bond length of the molecule. The two effects are of comparable magnitude. T he correlated relativistic results are in good agreement with experime nt: 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) ).