title: On the origin of the electrostatic potential difference at a liquid-vacuum interface.
abstract: The microscopic origin of the interface potential calculated from computer simulations is elucidated by considering a simple model of molecules near an interface. The model posits that molecules are isotropically oriented and their charge density is Gaussian distributed. Molecules that have a charge density that is more negative toward their interior tend to give rise to a negative interface potential relative to the gaseous phase, while charge densities more positive toward their interior give rise to a positive interface potential. The interface potential for the model is compared to the interface potential computed from molecular dynamics simulations of the nonpolar vacuum-methane system and the polar vacuum-water interface system. The computed vacuum-methane interface potential from a molecular dynamics simulation (-220 mV) is captured with quantitative precision by the model. For the vacuum-water interface system, the model predicts a potential of -400 mV compared to -510 mV, calculated from a molecular dynamics simulation. The physical implications of this isotropic contribution to the interface potential is examined using the example of ion solvation in liquid methane.
authors.affiliation: Department of Biochemistry and Molecular Biology, Center for Integrative Science, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Edward
authors.initials: E
authors.lastname: Harder
authors.forename: Benoît
authors.initials: B
authors.lastname: Roux
mesh_terms: D007477:Ions / Q000737:chemistry; D008697:Methane / Q000737:chemistry*; D008956:Models, Chemical; D012997:Solvents / Q000737:chemistry; D055672:Static Electricity; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D012997:Solvents; D014867:Water; D008697:Methane