  The large surface density changes associated with the (100) noble metals
surface hex-reconstruction suggest the use of non-particle conserving
simulation methods. We present an example of a surface Grand Canonical Monte
Carlo applied to the transformation of a square non reconstructed surface to
the hexagonally covered low temperature stable Au(100). On the other hand,
classical Molecular Dynamics allows to investigate microscopic details of the
reconstruction dynamics, and we show, as an example, retraction of a step and
its interplay with the surface reconstruction/deconstruction mechanism.
