Since its inception in the 1920s, computational chemistry has had a revolutionary impact on the way chemists perform research. Once limited to describing the bonding interactions of the hydrogen molecule, 2 modern computational chemistry can accurately predict a multitude of molecular properties for systems containing hundreds or thousands of atoms, including molecular orbitals and their energies, molecular vibrations, electronic excited states, transition states, nuclear magnetic resonance (NMR) shielding and coupling constants, and reaction pathways. Much of this explosion in scale was driven by the seminal works of Hohenberg, Kohn, and Sham, building upon the works of many others, in developing the fast but accurate methodology that is known as density functional theory (DFT). Today, a plethora of computational models are available to the theoretician.