Density and Potential Functional Embedding: Theory and Practice

This chapter presents a general introduction to orbital-free embedding theories (OFETs) and density functional embedding theory (DFET). DFET is formally exact and the embedding potential replacing the interaction between the subsystems is determined at the density functional theory (DFT) level. Once obtained, the embedding potential is used for highly accurate embedded correlated wavefunction (CW) calculations on the subsystems of most interest, to either improve upon the DFT description or access electronically excited states. The chapter discusses theoretical and algorithmic details of DFET and explains how to use the resulting embedding potential in embedded CW calculations. It also discusses potential functional embedding theory (PFET), allowing a self-consistent mutual polarization between subsystems described at different levels of theories. PFET improves upon DFET, as the latter keeps the embedding potential fixed at the DFT/DFT level during the embedded CW calculation, neglecting mutual polarization effects at the CW/DFT level.