  We present dynamic Monte Carlo simulations of a lattice-gas model for bromine
electrodeposition on single-crystal silver (100). This system undergoes a
continuous phase transition between a disordered phase at low electrode
potentials and a commensurate c(2X2) phase at high potentials. The lattice-gas
parameters are determined by fitting simulated equilibrium adsorption isotherms
to chronocoulometric data, and free-energy barriers for adsorption/desorption
and lateral diffusion are estimated from ab initio data in the literature.
Cyclic voltammograms in the quasi-static limit are obtained by equilibrium
Monte Carlo simulations, while for nonzero potential scan rates we use dynamic
Monte Carlo simulation. The butterfly shapes of the simulated voltammograms are
in good agreement with experiments. Simulated potential-step experiments give
results for the time evolution of the Br coverage, as well as the c(2X2) order
parameter and its correlation length. During phase ordering following a
positive potential step, the system obeys dynamic scaling. The disordering
following a negative potential step is well described by random desorption with
diffusion. Both ordering and disordering processes are strongly influenced by
the ratio of the time scales for desorption and diffusion. Our results should
be testable by experiments, in particular cyclic voltammetry and surface X-ray
scattering.
