Much of computational science in physics, chemistry, and biology requires finding the ground-state energy and electron density of a many-electron system such as an atom, molecule, liquid, or solid.  The orbital-based density functional theory of Kohn and Sham, which combines computational efficiency with useful accuracy, is the most widely-used approach to this problem.  It can also be the basis for the construction of effective potentials for molecular dynamics.  Until recently, it has not been possible to find a computationally-efficient semilocal  density functional with satisfactory simultaneous per-formance for covalent, metallic, and weak (van der Waals) bonds.  The key to the solution lies in identifying the right dimensionless ingredient combining the electron density, its gradient, and the orbital kinetic energy density [1].

[1] J. Sun, B. Xiao, Y. Fang, R. Haunschild, P. Hao, A. Ruzsinszky, G.I. Csonka, G.E. Scuseria, and J.P. Perdew, arXiv:1303.5688 and Phys. Rev. Lett., to appear.