Induced charges in a Thomas–Fermi metal: insights from molecular simulations

Abstract

We study the charge induced in a Thomas–Fermi metal by an ion in vacuum, using an atomistic description employed in constant-potential molecular dynamics simulations, and compare the results with the predictions from continuum electrostatics. Specifically, we investigate the effects of the Thomas–Fermi screening length l TF and the position d of the ion with respect to the surface on the induced charge distribution in a graphite electrode. The continuum predictions capture most of the features observed with the atomistic description (except the oscillations due to the atomic sites of the graphite lattice), provided that d and l TF are larger than the inter-atomic distances within the electrode. At large radial distance from the ion, the finite l TF case can be well approximated by the solution for a perfect metal using an effective distance d + l TF . This requires a careful definition of the effective interface between the metal and vacuum for the continuum description. Our atomistic results support in particular an early analytical prediction (Vorotyntsev and Kornyshev, Sov. J. Exp. Theor. Phys. 51, 509 (Mar., 1980)) for a single charge at the interface between a Thomas–Fermi metal and a polarisable medium, which remains to be tested in atomistic simulations with an explicit solvent.