 Some surfaces also experience relaxations in the lateral direction as well as the normal, so that the upper layers become shifted relative to layers further in, in order to minimize the positional energy.Reconstruction refers to a change in the two-dimensional structure of the surface layers, in addition to changes in the position of the entire layer.For example, in a cubic material the surface layer might re-structure itself to assume a smaller two-dimensional spacing between the atoms as lateral forces from adjacent layers are reduced.