where H o and H so are the kinetic/potential potential energies for the system electrons and the spin-orbit coupling operator, respectively; and the superscripts refer to qualities that are evaluated at the equilibrium nuclear configuration. For cases where the spin-orbit coupling matrix elements are much smaller than the non-adiabatic coupling matrix elements, such as for internal conversion, spin-orbit coupling may be safely ignored. Interestingly, this infers that there are cases where spin-orbit coupling may be required to correct mis-estimated vibronic couplings. Valiev and co-workers do not consider the spinorbit coupling contribution, and cast the Herzberg-Teller-type internal conversion matrix element V HT m0,n{s1,s2,s3,...,s 3N -6 }