I: METHODOLOGY

Since standard molecular simulations use different energy expressions for charge and gradient calculations, there are severe problems such as incompleteness in the optimization and simulation of the system with electrostatic (ES) interaction. Here, a new concept is proposed to solve this problem. The consistent charge equilibration (CQEq) equation has been derived which uses the same energy expression for both charge and gradient calculations. The ES energy is given by the atomic partial charge shielded with a nuclear charge described by a normalized S type Slater function located at each atomic site. The partial charge is determined by the variational principal for the ES energy with a constraint that the total sum of the partial charges is constant. Also the first derivative has been determined for the ES energy to the internal coordinates from the same ES energy expression. Although the CQEq is a little heavier than the original QEq for the charge calculation, the CQEq completely satisfies the variational principle for the ES energy of a set of partial charge, and satisfies the consistency requirement in the optimization of the system with ES interaction. A new code has been created and applied to test cases.