You can do DFT calculations now. You can predict several properties of crystals, using quantum physics only. Yet, how reliable are your predictions? This question covers two other questions: (1) are your predictions technically/numerically correct? (2) and how close or how far is DFT expected to be from the true experimental value?
In this chapter, we will examine some answer to these questions. Going thoroughly through this chapter will take you about 1h30m.