Geometry Optimisation with CASTEP

in figure 8 below
Figure 8:The total final energy per supercell atom as a
function of the number of layers of silicon.
We can see that the energy per atom is decreasing almost linearly with the number of layers. We would
need to add very many layers for the energy to not vary by the inclusion of more layers. We will use 9
layers of silicon in future calculations. With 9 silicon layers the vacuum gap was varied from 3 Å to 15 Å
in 2 Å steps. The total final energy as a function of vacuum gap separation is shown below.
Figure 9:The total final energy as a function of the vacuum gap