DFT tutorial 8: Vacancy formation energy

We demonstrate how to calculate vacancy formation energy in aluminum bulk with two methods. For the first method, the system is fully relaxed. The second method follows Gillan's work [J. Phys.: Condens. Matter 1 689 (1989)], in which the vacancy system's lattice parameter is obtained from re-scaling. Tutorial PDF is at this link: https://sites.google.com/site/huangfsu/dft-tutorials