Ab initio calculation of parity-violating potential energy hypersurfaces of chiral molecules

We introduce the explicit concept of parity-violating potential energy hypersurfaces which govern the rotation-vibration tunneling dynamics as well as the time-dependent parity violation in chiral molecules. Calculations are reported for sections of the hypersurfaces of H2O2 and H2S2 at various levels of electroweak quantum chemistry, including CIS-RHT, CIS-LR, and CASSCF-LR. Important findings concern the observed increase of the parity-violating potentials (E-pv) with increasing bond lengths r(OO) and r(SS), which is to some extent physical and partly a consequence of the only approximate electronic wavefunction and perturbational treatment, the confirmation of lines and surfaces of "accidentally" zero E-pv. at chiral geometries, and the absence of a precise, simple scaling law for observables such as the measurable parity-violating energy difference between enantiomers DeltaE(pv). The latter is due to the complicated geometry dependent E-pv, although a rough scaling on the order of Z((5+/-1)) with nuclear charges of the two heavy centers can be confirmed. The results are discussed in relation to possible experiments on molecular parity violation. (C) 2004 Wiley Periodicals, Inc.