Charge and current densities for approximate molecular wavefunctions

The charge and current densities for variational molecular wavefunctions in finite basis spaces are examined, and the consequences of their failure to satisfy a continuity equation, and the local charge generation and annihilation, are discussed. The current can be used to compute observables even though it might not satisfy the continuity equation. When approximate wave-functions are used charge is not conserved locally, but is conserved globally, and the details of the structure of the charge sources and sinks are discussed in the case of benzene. A valence bond technique for the calculation of current density is described and applied to benzene. Valence bond and molecular orbital methods are compared.