The Density Functional Theory (DFT) is the most popular first-principles computational method to describe many-electron systems in condensed-matter physics, quantum chemistry and nanoscience. However, its accuracy depends on the approximation of the exchange-correlation (XC) energy functional, which contains all the electron-electron interaction effects beyond the classical Coulomb repulsion. Reference model systems, which can be solved exactly, are of utmost importance for the current quest for the exact XC functional.
We propose to use the non-relativistic semi-classical neutral atom with an infinite number of electrons as a reference system to construct a non-empirical generalized gradient approximation (GGA) for the XC functional. In this work, published in Physical Review Letters, we showed that this new functional, named APBE, is among the most accurate GGAs for molecular systems, it is non-empirical and perform well also for solid state.