11 Molecules in Complex Environments: Solvent Models, QM/MM and QM/EFP Features, Density Embedding

11.6 Projector-Based Density Embedding

The exact density embedding method adapted from the method of Manby, Miller, and coworkersManby:2012 allows embedding calculations to extend beyond electrostatic embedding. This embedding scheme allows for the fragmentation of a system into two interacting subsystems that are treated at two different levels of quantum mechanics (QM/QM), for example coupled cluster embedded in DFT. This type of embedding fully accounts for polarization as well as quantum mechanical exchange, as calculated from the super-molecular embedding density and the exchange correlation functional used. The goal of this embedding theory is to perform a higher-level QM (DFT or WFT) calculation in an environment described by a lower-level QM theory.