The biorthogonal method for optimizing modern valence bond wavefunctions

An implementation of a biorthogonal approach to modern valence bond calculations is presented, emphasizing the problems associated with larger numbers of active electrons. A full treatment of up to 20 active electrons seems feasible within this strategy. A restricted-step second-order algorithm is proposed which may be of use also for other non-symmetrical optimization problems. Applications to the ground states of methylene and naphthalene are presented, highlighting the difference between a biorthogonal approach and the analogous variational calculations.