Representing molecules as atomic-scale electrical circuits with fluctuating-charge models

Fluctuating-charge models (FCMs), also known as chemical potential equilibration models, can describe charge transfer in molecular mechanics (MM). Examples of FCMs are QEq [1], \textit{fluc}-q (FQ) [2], and our recently proposed PE-CC-QVB2 [3] and QTPIE [4]. FCMs describe the accumulation and depletion of atomic charges with electronegativities and chemical hardnesses. We show that this description of atoms maps molecular systems onto electrical circuits. Unlike other models [1, 2], our models correctly model a diatomic molecule in the dissociation limit; we explain how this is reflected in its circuit representation. FCMs hence establish a new connection between the statistical mechanics of molecular electronic structure [5] and classical circuit theory. [1] A. K. Rappe, and W. A. Goddard III, \textit{J. Phys. Chem.} \textbf{95}, 3358 (1991). [2] S. W. Rick, S. J. Stuart, and B. J. Berne, \textit{J. Chem. Phys.} \textbf{101}, 6141 (1994). [3] J. Morales, and T. J. Mart\'{\i}nez, \textit{J. Phys. Chem.} \textbf{108A}, 3076 (2004). [4] J. Chen, and T. J. Mart\'{\i}nez, \textit{Chem. Phys. Lett.} submitted (2006). [5] J. Morales, and T. J. Mart\'{\i}nez, \textit{J. Phys. Chem.} \textbf{105A}, 2842 (2001).