Variational formulation of the bond capacity charge polarization model

We present an alternative energy formulation of the bond capacity charge polarization model to be used in molecular dynamics simulations. The energy expression consists of a Coulombic charge-charge interaction contribution as well as a quadratic Coulomb potential term, which can be seen as the electrostatic energy stored in the system's bond capacities. This formulation is shown to be variational in the potential space, although, it shares the same set of charges with the original non-variational formulation of the model. This variational formulation is compared with the non-variational one in terms of few selected observables showing the underlying distinctiveness of the two approaches. Being variational, this formulation allows for the computation of forces by invoking the classical analog of the Hellmann-Feynman theorem, which makes this approach two times faster than the non-variational one.