Boundary based on exchange symmetry theory for multilevel simulations, 1; Basic theory

Shiga, Motoyuki   ; Masia, M.*

In this paper we lay the foundations for a new method that allows multilevel simulations of a diffusive system, i.e. a system where a flux of particles through the boundaries might disrupt the primary region. The method is based on the use of flexible restraints that maintain the separation between inner and outer particles. It is shown that, by introducing a bias potential that accounts for the exchange symmetry of the system, the correct statistical distribution is preserved. Using a toy model consisting of non-interacting particles in a asymmetric potential well, we prove that the method is formally exact. A real-world test is then made by considering an hybrid MM/MM calculation of cesium ion in water.