functions and functionals

Computational Materials Physics density functional theory functions and functionals

Without understanding what a functional is, you’ll not be able to understand what density functional theory is:

In your education, you quite likely met examples of functionals — perhaps without calling them by that name. Search your memory for a functional you met before in chemistry, physics, mathematics or engineering and describe in which situation you encountered it or what its purpose was. If you can’t find one, then create an example of a functional yourself. (Post the answer on the forum, and feel free to comment to other answers if you feel like.)