New tau-dependent correlation functional combined with a modified Becke exchange

A new correlation functional is derived within the Kohn-Sham (KS) Density F unctional Theory (DFT) involving the electron kinetic energy density tau an d the Laplacian of the electron density as key nonlocal variables. The deri vation is based on a direct resolution of the adiabatic connection formula and using an analogy with the local thermodynamic approach in DFT, followin g the Lap3 theory developed previously. Compared to the latter, the new fun ctional involves higher order tau -dependent energy terms in a form suggest ing a possible resummation procedure that could be used for further develop ment. It is combined with the nonlocal exchange functional of Becke, by mod ifying the latter in an empirical fashion to achieve better synchronization between the two energy components. The resulting exchange-correlation sche me (named "Bm tau1") is validated on several test systems known as difficul t for DFT, at least at the Local Spin Density and Generalized Gradient Appr oximation levels. The recent nonempirical hybrid scheme PBE1PBE ("PBE0") is included in the comparative tests as a parameter-free benchmark for the hy brid HF-KS DFT approach. Improved results for relative energies, activation barriers and equilibrium geometries are obtained with the Bm tau1 function al, particularly concerning aromatic compounds, systems with weak hydrogen bonds, proton transfer processes and transition-metal carbonyls. (C) 2000 A merican Institute of Physics. [S0021-9606(00)30645-1].