  FEMSIM, a Fortran code, has been developed to simulate the fluctuation
electron microscopy signal, the variance, V(k), from a model atomic structure.
FEMSIM has been incorporated into a hybrid-reverse Monte Carlo code that
combines an embedded atom or Finnis-Sinclair potential with the deviation
between simulated and experimental V(k) data to refine an atomic model with
structure constrained by both the potential and experimental data. The
resulting models have experimentally-derived medium-range order.
