Diamagnetic contributions to the nuclear spinndash;spin coupling constants of several small molecules. An application of Monte Carlo integration methods to molecular onehyphen;electron properties

摘要

A numerical Monte Carlo integration procedure has been developed for calculation ofJ1a, the diamagnetic contribution to the nuclear spinndash;spin coupling constant from an arbitrary molecular charge density. The method is applied first to the HD molecule where several previous values ofJHD1aare refined and corrected. A test of Brillouinrsquo;s theorem for this unusual sum of onehyphen;electron operators is made and the extensive cancellations from different regions of space are examined in detail. Values ofJ1aare then given for HF, BF, CO, and HCN. It appears thatJ1amay be the onehyphen;electron property most sensitive to the quality of the wavefunction which has been considered to date. Monte Carlo integration may be employed for the calculation of onehyphen;electron properties when alternatives to analytic integral evaluation are sought.