RELEVANT SPACE WITHIN THE SPIN-ADAPTED REDUCED HAMILTONIAN THEORY .2.STUDY OF THE PI-CLOUD IN BENZENE AND NAPHTHALENE

The properties of the spin-adapted reduced Hamiltonian (SRH) matrices and of their eigenvectors permit in many cases a projection of the two -electron matrices, which amounts to an effective truncation of the ba sis at the stage of the calculations which are time and as memory cons uming. besides this effective truncation of the basis, another simplif ication can be introduced by segregating an n-electron cloud from the N electrons of the system. Thus, the energy and the elect-ron distribu tion of a smaller electronic cloud, for instance, the pi or the sigma cloud in aromatic systems, can be calculated; their separability being subsequently analyzed. Different relevant spaces have been examined i n the study of the pi-electron cloud in benzene and naphthalene. (C) 1 997 John Wiley & Sons, Inc.