RELEVANT SPACE WITHIN THE SPIN-ADAPTED REDUCED HAMILTONIAN THEORY .1.STUDY OF THE BH MOLECULE

The algorithm for evaluating the elements of the spin-adapted reduced Hamiltonian (2-SRH) involves the whole basis set of molecular orbitals . However, under a specific condition, its eigenvectors are very spars e. These two properties lead us here to propose a projection of the 2- SRH matrix, which is equivalent to an effective truncation which facil itates considerably the applicability of the SRH method. The criteria for performing this truncation, amounting to the determination of a re levant space are discussed. The results obtained for the BH molecule a re analyzed here. (C) 1997 John Wiley & Sons, Inc.