Practical criterion for the determination of translation factors. IV. Simplified norm method

Closing the series on the use of the norm method as a practical criterion to determine translation factors, we report a considerable simplification of the computational effort involved in our method. We study the speed of convergence of the sum-over-states expression giving the norms, and the possible use as criteria of rough approximations obtained by truncating this sum to a few states. Our main conclusion is that the rough-approximation method would yield the same translation factors as the exact one, while involving a minimal additional programming effort to that of the evaluation of molecular energies and couplings, and being applicable to semianalytical as well as variational wave functions, state-dependent as well as common translation factors, and package as well as ad hoc molecular programs.