Journal Article FANCI JSON schema Kullback-Leibler Python Research Support, Non-U.S. Gov't ab initio atoms in molecules basis set conversion chemical bonding chemistry software development computational chemistry conceptual density functional theory data parsing ehrenfest force electron density electronic structure energy decomposition analysis file format conversion hirshfeld partitioning information-theoretic fitting input file generation interaction energy least squares linear response function method development molecular mechanics partitioning probabilty density fitting quantum chemistry