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 charge equilibration (CE), also known as electronegativity equalization, theories for describing charge flow in molecules. We introduce a new unifying approach to classical charge transfer theories based on valence bond (VB) theory 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 rigorous framework within which both improved classical models of charge transfer can be developed and a well-defined procedure for interfacing classical electrostatic models with quantum chemistry can be established.