ORTHOGONALITY CONSTRAINED GENERAL VARIATIONAL CALCULATION OF EXCITED-STATE WAVE-FUNCTIONS AND ENERGIES - A NEW STRATEGY

A viable strategy is developed for the general variational calculation of excited state wavefunctions which are constrained to remain orthogonal to all the lower-lying states of the same symmetry. A key element of the strategy is to employ the penalised functional procedure for enforcing the relevant orthogonality constraints and the method of steepest descent to locate the constrained minima with respect to all variables, linear as well as nonlinear. The workability of the algorithm is tested by applying the technique for the optimization of nonlinear parameters in trial functions for the 2 s state of H atom and singlet 1 s2 s states of helium atom and some isoelectronic ions. © 1990 Indian Academy of Sciences.