The role of the kinetic energy density in approximations to the exchange energy

Abstract

Local and gradient corrected functionals for the non-interacting kinetic energy (Ts) are applied to the atomization process. These functionals and a newly developed generalized gradient approximation (GGA) for Ts are not accurate enough for thermochemistry. The limited accuracy of the gradient expansion approximation for Ts is shown to be related to the remaining errors in existing GGAs for the exchange energy Ex. Various new approximation schemes for Ex are developed which attempt to overcome the problems arising from approximations to Ts.