Molecular crystals show well ordered motifs and can be described by a unit cell or super cell as desribed above. On the other hand, description of liquids or amorphous phases is possible, too. In these cases, the cell vectors need to be chosen large enough. Often these cells are referred to as simulation cells instead of unit cells. While a wealth of structural data of diverse compounds is available under ambient pressure, obtaining structural data under elevated pressure requires increased experimental effort. In such scenarios, simulations yield valuable information. For example, crystal structure prediction (CSP) plays an important role in discovering novel materials. Zurek and Grochala as well as Wang and Ma reviewed various techniques for CSP under pressure, and the interested reader is referred to these reviews for further information on high-pressure CSP.