Nobel Lecture: Electronic structure of matter—wave functions and density functionals

In the intervening more than six decades enormous progress has been made in finding approximate solutions of Schrodinger's wave equation for systems with several electrons, decisively aided by modern electronic com- puters. The outstanding contributions of my Nobel Prize co-winner John Pople are in this area. The main objec- tive of the present account is to explicate DFT, which is an alternative approach to the theory of electronic struc- ture, in which the electron density distribution n(r), rather than the many-electron wave function, plays a central role. I felt that it would be useful to do this in a comparative context; hence the wording ''Wave Func- tions and Density Functionals'' in the title. In my view DFT makes two kinds of contribution to the science of multiparticle quantum systems, including problems of electronic structure of molecules and of condensed matter. The first is in the area of fundamental understanding. Theoretical chemists and physicists, following the path of the Schrodinger equation, have become accustomed to think in terms of a truncated Hilbert space of single-