Relativistic second-order many-body and density-functional theory for the parity-violation contribution to the C-F stretching mode in CHFCIBr

Relativistic four-component electronic structure theory using both wave-function (Dirac-Coulomb-Hartree-Fock and second-order many-body perturbation-theory) and density-functional based methods (local density, hybrid, and generalized gradient approximations) is applied to discuss the current status on the accuracy of parity-violation calculations for molecules. As a test case we choose the C-F stretching mode of CHFClBr, which is currently, being investigated by molecular-beam spectroscopy. We show that electron correlation effects are important and cannot. be neglected anymore for the parity nonconservation contribution to the total electronic energy. However, electron correlation contributions to parity violation in vibrational transitions of the C-F stretching mode are less important. The density functionals tested give somewhat different results, but the Becke three-parameter Lee-Yang-Parr functional agrees quite well with the second-order many-body perturbation-theory values. The calculations suggest that electron correlation effects have to be considered for future investigations in parity-violation effects in electronic transitions. The performance of density-functional based methods for this property needs further statistics.