Electron Pair Localization Function (EPLF) for Density Functional Theory and <italic>ab Initio</italic> Wave Function-Based Methods: A New Tool for Chemical Interpretation

We present a modified definition of the Electron Pair Localization Function (EPLF), initially defined within the framework of quantumMonteCarlo approaches [Scemama, A.; Caffarel,M.; Chaquin, P. J. Chem. Phys. 2004, 121, 1725] to be used in Density Functional Theories (DFT) and ab initiowave-function-based methods. This modified version of the EPLF—while keeping the same physical and chemical contents—is built to be analytically computable with standard wave functions or Kohn-Sham representations. It is illustrated that the EPLF defines a simple and powerful tool for chemical interpretation via selected applications including atomic and molecular closed-shell systems, σ and π bonds, radical and singlet open-shell systems, and molecules having a strongmulticonfigurational character. Some applications of the EPLF are presented at various levels of theory and compared to Becke and Edgecombe’s Electron Localization Function (ELF). Our open-source parallel software implementation of the EPLF opens the possibility of its use by a large community of chemists interested in the chemical interpretation of complex electronic structures.