Embedding methods allow a system to be divided into two smaller subsystems, each of which can be treated using a different level of theory. For example, in WF-in-DFT embedding, a WF-level (e.g. HF, MP2, CCSD(T), CASSCF, etc.) calculation is performed on one subsystem, while a DFT-level calculation is performed on the other subsystem. The interactions between the two subsystems are calculated at the DFT level. The primary advantage of WF-in-DFT embedding is that it facilitates the application of an accurate, systematically improvable WF method to regions where such accuracy is required, while a more efficient DFT method is applied to the remainder of the system. The overall strategy for WF-in-DFT embedding is described as follows:
It is possible to replace the WF-level calculation on subsystem A with a DFT-level calculation, which corresponds to DFT-in-DFT embedding. Because the interaction potential between the subsystems is calculated at the DFT level, the result of a DFT-in-DFT embedding calculation is numerically identical to the results of a DFT calculation on the full system. Confirming that the DFT-in-DFT energy is numerically equivalent to the energy of a DFT calculation on the full system can thus be a useful sanity check. Similarly, it is possible to replace the DFT-level calculation with a HF-level calculation, which corresponds to WF-in-HF embedding.
Molpro implements the numerically exact projection-based WF-in-DFT embedding method for open and closed shell systems developed in the following papers:
All publications resulting from the use of this method must acknowledge the above.