The vicinal indirect nuclear spin-spin coupling constant (SSCC) between the two ¿uorine atoms in di¿uoroethyne has been reinvestigated. This coupling has previously proved dif¿cult to calculate accurately. In this study we have therefore systematically investigated the dependence of this coupling on the choice of one-electron basis set, the choice of correlated wave function method and the inclusion of zero-point vibrational and temperature corrections. All terms of the SSCC have been evaluated at the second-order polarization propagator, SOPPA and SOPPA(CCSD), and coupled cluster singles and doubles (CCSD) levels of theory and for the most correlation dependent term, the paramagnetic spin-orbit contribution (PSO), also at the very accurate CC3 level. We ¿nd that in order to get results that are well converged with respect to the basis set, one needs to use special SSCC optimized basis sets of at least quadruple zeta quality and with added diffuse functions. Furthermore, the PSO term is not yet converged at the CCSD level as shown by the CC3 calculations. Finally, it is shown that vibrational effects are very important, as they are in this case of the same order of magnitude as the equilibrium geometry value of the coupling constant. Only by using a converged basis set and including both vibrational and higher order correlation effects can we obtain agreement with the experimental value for this coupling.
Physical Chemistry Chemical Physics, 2012, Vol 14, Issue 47, p. 16440-16447
NMR; spin-spin coupling constants; difluoroethyne; vibrational correction; quantum chemistry; Computational Chemistry; The Faculty of Science