Paramagnetism in Closed-Shell Molecules

Proofs that closed-shell molecules must be diamagnetic are shown to be restricted to two-electron systems. An exact nonrelativistic ground-state wave function having four or more electrons is shown to possess a nodal structure which arises from the Pauli principle. These nodes cause the proofs that a closed-shell molecular wave function is necessarily diamagnetic to be invalid when more than one pair of electrons is present. The physical situation is examined with special reference to the diatomic BH molecule.