Mixed-valence complexes are potential candidates for the molecular quantum-dot cellular automata (QCA) approach, which encodes binary information using the configuration of localized and mobile charges. In the Robin-Day classification of mixed-valence complexes, charge localization/delocalization is determined by the ratio of the nuclear reorganization energy and the electron transfer (ET) matrix element. We point out that the driving force for charge localization in molecular QCA is the Coulomb interaction between neighboring molecules rather than nuclear relaxation. This suggests a different criterion for the relevant charge localization, one based on the ET matrix element and the driving bias of a neighboring molecule. (C)2015 Elsevier B.V. All rights reserved.