Foundation 3: What is covered in this review?
For the rest of this tutorial review, we will use research articles published in the past decade to extract some simple representative calculation that focus on different undervalued aspects of DFT. We collected all calculations in the form of a series of experiments in a laboratory notebook provided in the Supporting Information (SI). We invite the readers to try all experiments on their own and to compare their answers with the ones provided as a key. All calculations can be performed on desktop computers or even on a laptop, and they should take at maximum just a few hours. Mirroring the structure of this essay, we collected the experiments into three groups, the first dealing with the foundations of the theory, where we mainly test the knowledge of the acronyms used in the computational chemistry community. The second group deals with the choice of the method (where method refers to the combination of a functional and a basis set), and the third deals with the technical issues. The three groups have a total of 12 activities, plus an additional final self-assessment test/questionnaire. The experiments and their take-home messages are summarized in Table 1 .
Given the vastness of the topic, it was necessary for us to make some choices on the material to either include or exclude. For example, we have decided to concentrate exclusively on molecular calculations in gas-phase based on Gaussian basis functions and Kohn–Sham DFT, because of their importance in chemistry and related fields of molecular science. We will not consider orbital-free DFT methods, projector-augmented wave and related methods, and several flavors of plane-waves and periodic boundary conditions-based KS-DFT calculations, despite their importance in the solid state and material science community. For some of those topic, we refer the reader to recent reviews57–67
Even on the chemical side, we will not discuss some of the important corollary aspects of molecular calculations, such as solvation models, calculation of partial atomic charges, use and interpretation of molecular orbitals, calculations with effective core potentials, as well as calculations of associated properties (such as prediction of spectra, polarizabilities, magnetic properties, etc). We left these topics out because they are not strictly bound to KS-DFT itself, since they equally apply to most of quantum chemical calculation methods, including wave-function-theory–based ones. Each of these subjects deserves a thorough treatment, for which we refer to specific field studies and reviews, such as Baik et al.68 for solvation models. Finally, for investigating the state-of-the-art in DFT research development and application, we refer the readers to the recent reviews and perspectives.16,19,22,25,26,36,43,69