Computer program for optimization of a molecular basis in the calculation of excited state energies in the single-determinant approximation

An important step in variational calculations of excited state (ES) energies is the choice of a test function orthogonal to wave functions which describe the lower-lying states of the same symmetry. We describe an attempt to calculate the ES energy in the single-determinant approximation, but with the Roothaan basis tuned to the corresponding ES. The problem reduces to minimization of the energy functional with respect to nonlinear parameters of the basis set,with an additional condition that the states be orthogonal