To do

1. Silicon  is an important material which finds many application as semi-conductor in electronics.  Repeat the calculation previously proposed for MgO and compare the results with the MgO ones. Results can be interpreted in  the same way. 
2. Be is a simple metallic solid. The Fermi energy must be computed by integration: the value of the Gilat shrinking factor, ISP  must be set to 2*IS (shrinking factor Pack-Monkhorst net).  Repeat the calculation proposed for MgO and Si and compare results with the previous ones. Note that Be bulk structure has two lattice parameters to be optimized. In this case, the geometry optimization of the cell may be performed by fixing the c/a ratio at its experimental value (1.5677) and by plotting the total energy vs the volume of the cell.