Density functional theory (DFT) is a method to calculate the electronic structure and electronic properties of a system. Theoretically, this should give very accurate results. Yet, in computational sciences, some approximations need to be made due to the limited time and space resources. The exchange-correlation term between electrons is often approximated, with more or less accuracy depending on the functionals. Here, we will compare several functionals on different systems, in order to see which kind of approximation is better for a given system. This worksheet uses the Maple Quantum Chemistry Toolbox.