  In simulations of metallic interfaces, a critical aspect of metallic behavior
is missing from the some of the most widely used classical molecular dynamics
force fields. We present a modification of the embedded atom method (EAM) which
allows for electronic polarization of the metal by treating the valence density
around each atom as a fluctuating dynamical quantity. The densities are
represented by a set of additional fluctuating variables (and their conjugate
momenta) which are propagated along with the nuclear coordinates. This
``density readjusting EAM'' (DR-EAM) preserves nearly all of the useful
qualities of traditional EAM, including bulk elastic properties and surface
energies. However, it also allows valence electron density to migrate through
the metal in response to external perturbations. We show that DR-EAM can
successfully model polarization in response to external charges, capturing the
image charge effect in atomistic simulations. DR-EAM also captures some of the
behavior of metals in the presence of uniform electric fields, predicting
surface charging and shielding internal to the metal. We further show that it
predicts charge transfer between the constituent atoms in alloys, leading to
novel predictions about unit cell geometries in layered L$1_0$ structures.

Materials Science;Chemical Physics;Computational Physics