AB-INITIO CALCULATION OF MOLECULAR-ENERGIES INCLUDING PARITY-VIOLATING INTERACTIONS

We present a new approach towards electroweak quantum chemistry includ ing the parity violating weak nuclear force. After introducing the gro und work of electroweak quantum chemical perturbation theory to calcul ate parity violating potentials, E-pv, we present specifically a CIS-R HF method (configuration interaction singles-restricted Hartree-Fock). The method is compared to the previously established and widely used SDE-RHF method for calculations of E-pv [single determinant excitation s-restricted Hartree-Fock, R. A. Hegstrom, D. W. Rein, and P. G. H. Sa ndars, J. Chem. Phys. 73, 2329 (1980)]. It is demonstrated that the ne w CIS-RHF method can lead to values of E-pv which are more than an ord er of magnitude larger than those obtained with SDE-RHF (for example i n H2O2, where the new maximum value is E-pv= 3.7 x 10(-19)E(h)), Furth ermore, the importance of the tensor character of E-pv is outlined by showing that the components of the trace of this tensor E-pv(xx) + E-p v(yy) + E-pv(zz) = E-pv evolve essentially independently from each oth er in magnitude and sign as functions of molecular structure and compu tational method. The total Epv results thus as a remainder after subst antial mutual cancellation of these components. This finding explains the phenomenon of zero total Epv at chiral geometries, whereas the ind ividual tenser components remain nonzero. We present systematic invest igations of parity violating potentials as a function of structure for H2O2, H2S2, N2O4, C2H2, C2H4, C2H6, CH4, and alanine. The effect of n uclear charge Z is investigated for the pair H2O2 and H2S2 and a power law Z(3+delta) (delta approximate to 1.5) for the enhancement of E-pv (ii) can be established with significance for the individual tenser co mponents (i = x,y, or z), whereas just considering the total E-pv woul d be misleading in analyzing the Z dependence. Contributions of hydrog en atoms to E-pv are estimated and found to be orders of magnitude low er than those of the heavier atoms mentioned. The results are discusse d in relation to a possible spectroscopic experiment to measure Delta E-pv = 2E(pv) in enantiomers of chiral molecules and in relation to va rious hypotheses for the origin of nature of homochirality in chemical evolution. (C) 1998 American Institute of Physics. [S0021-9606(98)303 32-3].