EXCITED-STATE GRADIENTS VIA CPHF EQUATIONS

A detailed derivation of the equations for the energy gradients for ex cited-state wave functions is presented. These excited states are gene rated by singles-only CI (CIS) from the Hartree-Fock ground-state wave function. The gradients are obtained from direct differentiation of t he CIS energy expression. Since this expression contains explicit term s involving the derivative of the Hartree-Fock orbital coefficients, c oupled perturbed Hartree-Fock (CPHF) equations are used to eliminate t he need to evaluate these terms. The final equations are then transfor med to the atomic orbital basis to avoid costly AO-to-MO transformatio ns. (C) 1995 John Wiley & Sons, Inc.