Calculation of nuclear magnetic shielding constants by the method of gauge-invariant atomic orbitals using Gaussian functions

It has been shown that the using of the gauge-invariant atomic orbitals together with Gaussian expansion of orbitals allows one to obtain satisfactory results for the proton magnetic shielding constants without an average excitation energy approach, the wave functions being obtained by any MO LCAO method. It is necessary to employ a more complicated variation function for the calculations of 13C shielding constants. The proton and 13C shielding constants have been calculated for a number of molecules (CH4, C2H6, CH3NH2, CH3OH, CH3F). The simple functions, obtained by extended Hückel and INDO methods have been used as unperturbed solutions. Comparison with ab initio calculations and experimental data have been carried out. © 1979