A Density-Based Approach to Decompose Interaction Energies and Generate Descriptors in Periodic Systems

We discuss the use of a density-based energy decomposition analysis (EDA) scheme, which we call the pawEDA approach, for partitioning interaction energies computed in periodic chemical systems. The method requires the use of the projector augmented wave (PAW) scheme to treat the behavior of the variational electron orbitals near the atomic nuclei, and it functions by generating a "promolecule" whose (smoothed) valence pseudoorbitals reproduce the same valence electron density as the superposition of the underlying fragments. This construction mimics the behavior of some previously published EDA schemes, particularly that of the DEDA method, which was the first scheme to build a promolecule from density-based constraints. The pawEDA scheme effectively creates a two-step transformation from the fragments to the final system, where the electron density generally shifts smoothly through and/or near the fragment boundaries within each step, and its simplicity complements well other more well-established (and more elaborate) EDA schemes, especially when it is used to compare two or more chemically related systems. It also allows for the construction of two-state "Δ-functions" that accompany the steps, which can be built from the likes of the electron density (Δρ), the electrostatic potential ("ΔESP"), and the electron localization function (ΔELF).