Ab initio spin-orbit coupling SCF calculation of parity-violating energy of chiral molecules

The spin-orbit coupling SCF (SOC-SCF) wavefunction was obtained on the basis of Breit-Pauli Hamiltonian and generalized spin-orbitals and was used to calculate the parity-violating energy, E-pv, of chiral molecules. For the twisted HOOH molecule, the magnitude of SOC-SCF E, is comparable with those of RPA, MC-LR, and DHF methods, and 2 or 3 times as large as that calculated by sum-over-state perturbation theory (SOS-PT). Moreover, the SOC-SCF method gave a reliable variation in the E-pv value for the conformational change of L-alanine zwitterion (L-ALAZ), indicating that the SOC was introduced appropriately into the SOC-SCF wavefunction. Calculations for several chiral molecules have suggested that the [5s2p/3s] basis set was acceptable for the SCF-SCF E-pv calculation of large molecules. The contribution of one- and two-electron spin-orbit coupling terms to E-pv was analyzed by dividing the E-pv values in parts. It was confirmed that only one-center terms of the spin-orbit coupling integrals are sufficient in the SOC-SCF E-pv calculation, although both one- and two-electron terms should be included. The SOC-SCF method with the [5s2p/3s] basis set was applied to L-ALAZ in aqueous solution, and the E-pv map was created as a function of two torsion angles, phi for the NH3 group and theta for the CO2 group. In the (phi, theta) map of E-pv, the positive E-pv area is wider than the negative one, and the averaged E-pv value was +2.1 x 10(-20) hartree, indicating that L-ALAZ is more unstable than D-ALAZ in aqueous solution due to the parity-violating weak neutral current interaction. (C) 2002 Elsevier Science B.V. All rights reserved.