  In quantum/classical (QM/CM) partitioning methods for multi-scale modeling,
one is often forced to introduce uncontrolled phenomenological effects of the
environment (CM) in the quantum (QM) domain as ab initio quantum calculations
are computationally too intensive to be applied to the whole sample. We propose
a method, in which two qualitatively different components of the information
about the state of the CM region are incorporated into the QM calculations.
First, pseudoatoms constructed to describe the chemistry of the nearest
neighbor exchange interactions replace the atoms at the boundary of the CM and
the QM regions. Second, the remaining effect of the CM bulk environment due to
long-range Coulombic interactions is modeled in terms of dipoles. We have
tested this partitioning method in a silica nanorod and a 3-membered silica
ring for which ab initio quantum data for the whole system is available to
assess the quality of the proposed partitioning method.
