The main problem with the use of plain quantum physics to treat solids lies in the need of efficient algorithms to solve the Schroedinger equation and the need of very powerful hardware to run the calculations using these algorithms. In other words we’re facing and trying to solve a problem of both mathematical and technological nature. Also, one cannot just blindly run QM calculation. Indeed, it is necessary to understand the physical and mathematical concepts implemented in computational softwares and have a solid understanding of the nature of the problem we want to treat in order to be able to run meaningful calculations and to interpret their results at the end. Understanding the whole machinery behind also allows to wisely choose the right balance between computational resources and needed accuracy.