Calculation of second-order properties with improved virtual orbitals

¹³C---H nuclear spin coupling and ¹³C shielding constants of CH₄, C₂H₆, C₂H₄, C₂H₂ are calculated by means of the second-order perturbation theory and MO LCAO wavefunctions. The aim of this paper is to test the ability of the recently proposed virtual orbitals to accelerte the convergence of the sum over states, compared to the calculation with canonical MO's. The ¹³C---H nuclear spin coupling constants show a significant improvement, the changes of the ¹³C shielding are insignificant.