Coupled-Cluster Calculations of Indirect Nuclear Coupling Constants: TheImportance of Non-Fermi Contact Contributions

摘要

Electron correlation effects to the four coupling mechanisms which contribute tothe isotropic nuclear spin-spin coupling constant, the Fermi contact (FC), paramagnetic spin-orbit (PSO), spin-dipole (SD), and diamagnetic spin-orbit (DSO) are studied using the equation of motion coupled-cluster (EOM-CC) method. The second-order properties are expressed as a sum-over state (SOS) using EOM-CC intermediate state wave functions. This formulation is simple, accurate, computationally convenient, and involves no truncation. Several molecules, HF, CO, N2, H2O, NH3, and HCl which have been previously shown to have large noncontact contributions are investigated using the EOM-CC method and the results are compared with experiment and other theoretical methods, including polarization propagator and finite-field MBPT(2) methods. Using fairly large basis sets, the EOM-CCSD provides results which agree with experimental indirect nuclear spin-spin coupling constants to within an average error of 13%.