John Perdew’s research in the Hohenberg-Kohn-Sham density-functional theory of electronic structure has helped to establish this theory as the most widely-used method to predict the properties of atoms, molecules, and solids from the principles of quantum mechanics. A density functional is a formula that expresses the energy of a many-electron system in terms of its electron density, facilitating the easy computer calculation of both. Perdew and his collaborators have discovered some unexpected properties of the exact density functional, including its derivative discontinuity and scaling properties, and more recently a strongly-tightened lower bound on the exchange energy. They have also constructed a ladder of nonempirical approximations to the exact functional, on which higher rungs are more complex and more accurate. In essence, they have been making educated guesses at the rule for “nature’s glue” that binds electrons into atoms and atoms into molecules and solids. They seek functionals that are rooted in physical principles and work reliably for atoms, molecules, solids, surfaces, and molecules on surfaces. Their functionals are built into standard computer codes, and are widely used by both physicists and chemists. Current research includes the development of better meta-generalized gradient approximations from a dimensionless ingredient that can recognize and assign appropriate descriptions to covalent, metallic, and weak bonds.
