A gradient method for very general valence bond (VB) wavefunctions is prese
nted. This method introduces the electronic energy as a Lagrange multiplier
, and evaluates the contributions of the derivatives of the normalisation a
nd of the first- and second-order cofactors present in the VB energy expres
sion. The correctness of the method is illustrated with classic and breathi
ng-orbital VB calculations on the HF molecule. (C) 1999 Elsevier Science B.
V. All rights reserved.