Exchange-correlation functionals from ab initio electron densities

We describe a procedure for developing new exchange-correlation functionals. For a training set of selected first-row molecules we compute Zhao, Morrison, Parr exchange-correlation potentials from ab initio Brueckner Doubles or MP2 electron densities, and use them to least-squares refine the functional derivatives of chosen exchange-correlation functional forms. The resulting potentials reproduce the characteristic shell structure in the Zhao, Morrison, Parr potentials, and yield Kohn-Sham orbitals with accurate asymptotic behaviour. For a set of 22 closed-shell first-row molecules we obtain optimised geometries which are comparable to those from the BLYP functional. Total energies are significantly in error unless terms are added to account for the derivative discontinuity in the exact exchange-correlation potential.