Mastodon

ChemRxivThe Bond Capacity Electronegativity Equilibration Charge Model (EEQBC) for the Elements Z=1–103The accurate and efﬁcient assignment of atomic partial charges is crucial for many applications in theoretical and computational chemistry, including polarizable force ﬁelds, dispersion corrections, and charge-dependent basis sets. Classical charge models struggle to distinguish between neutral and zwitterionic fragments because, unlike quantum mechanical methods, there are no discrete electronic states. This limitation can lead to either reduced or additional artiﬁcial charge transfer (CT) at different interfragment distances. To address this issue, we propose a new version of a bond capacity electronegativity equilibration (EEQBC) model, which limits artiﬁcial CT between distant fragments in the simple EEQ framework. EEQBC offers excellent agreement with DFT-based reference charges for elements up to lawrencium (Z = 103) with mean absolute errors as low as 0.02 and 0.07 e− for random PubChem molecules and "mindless" molecules (MLMs), respectively. Thanks to its computational efﬁciency for both atomic charges and their analytical nuclear gradients, EEQBC is highly suitable as an initial charge guess for next-generation tight-binding methods. For seamless accessibility, EEQBC is implemented in the freely available multicharge program at: github.com/thfroitzheim/multicharge/tree/eeq-bc.