Classical fluctuating charge theories: The maximum entropy valence bond formalism and relationships to previous models

We explore the relationship between grand canonical (GC) ensemble and charg e equilibration (CE), also known as electronegativity equalization, theorie s for describing charge flow in molecules. We introduce a new unifying appr oach to classical charge transfer theories based on valence bond (VB) theor y and the maximum entropy (ME) method, which we call MEVB. We show how MEVB reduces to GC and CE theories with different choices for the definition of atomic partial charge. We believe that the MEVB approach provides a rigoro us framework within which both improved classical models of charge transfer can be developed and a well-defined procedure for interfacing classical el ectrostatic models with quantum chemistry can be established.