On the calculation of high-spin states in the full configuration-interaction formalism

A modified electronic Hamiltonian that allows the calculations of high-spin eigenfunctions in the Sz=0 manifold, is presented. In this formalism the low-spin states are shifted in energy while all the states having a multiplicity larger than a given value are kept untouched. This formalism has been applied to a test calculations of the lowest quintet state of the helium dimer and of the quintet state of the tetrahedral Li4 cluster.