KLD: A Program to Elucidate the Localization of the Fermi and Coulomb Holes in Molecular Systems

The present paper contains a detailed description of the design and implementation of the program KLD, which was primarily developed to elucidate electron localization in molecular systems by evaluating the information content of electron-pair density functions. In our method, the electron-pair conditional density is compared with the electron density by means of the Kullback-Leibler divergence. After briefly introducing the importance of possessing appropriate means to study electron localization and providing some theoretical background, the algorithm and code are thoroughly described. A subsequent section describes a recent implementation of the program aimed at reducing computational costs. Moreover, results on the time scaling and speedup obtained for a set of simple molecules are thoroughly discussed. The obtained data show that our most recent version of our code computes electron localization approximately an order of magnitude faster compared to older versions.