  Generally, the first step in modeling molecular magnets involves obtaining
the low-lying eigenstates of a Heisenberg exchange Hamiltonian which conserves
total spin and belongs usually to a non-Abelian point group. In quantum
chemistry, it has been a long standing problem to target a state which has
definite total spin and also belongs to a definite irreducible representation
of the point group. Many attempts have been made over years, but unfortunately
these have not resulted in methods that are easy to implement, or even
applicable to all point groups. Here we present a general technique which is a
hybrid method based on VB basis and constant Ms basis, which is applicable to
all types of point groups, easy to implement on computer. We illustrate the
power of the method by applying it to the molecular magnetic system, Cu6Fe8,
with cubic symmetry. We emphasize that our method is applicable to spin
clusters with arbitrary site spins and is easily extended to Fermionic systems.
