Spin-spin coupling constants in HC≡CXH3 molecules; X=C, Si, Ge, Sn and Pb.

The nuclear spin-spin coupling constants in a series of acetylene derivatives HC≡CXH3<inline-graphic></inline-graphic>, where X is C, Si, Ge, Sn, Pb, have been calculated employing both coupled-cluster theory (CC) and density functional theory (DFT), the latter in nonrelativistic and relativistic four-component approach with different exchange-correlation functionals and basis sets. In addition, property derivatives with respect to molecular geometry parameters have been computed with nonrelativistic and relativistic Hamiltonians in order to evaluate the usefulness of the calculated nonrelativistic vibrational corrections. Generally, the CC method reproduces the experimental values somewhat better than DFT. In the case of the latter, the performance of B3LYP functional was the most satisfactory. The relativistic effects become noticeable for the couplings including heavy atom in tin- and lead-containing molecules. The calculations of the derivatives of the coupling constants indicate that these derivatives are even more sensitive to the relativistic effects than the corresponding coupling constants. [ABSTRACT FROM AUTHOR]