Thomas-Fermi-Dirac-Weizsacker model

The minimization of this functional, which includes second order gradient corrections leads to the relativistic analogous of the Thomas-Fermi-Dirac-Weizsacker model and constitutes the state of the art in relativistic semiclassical approaches for many-electron systems. 

It seems that this variational method should be the method of choice for generating the Fukui function. Unfortunately, accurate determination of the hardness kernel is complicated by the lack of an accurate explicit kinetic energy functional, T[p]. Nonetheless, Eq. (40) has been applied to the Hiickel model [49] and Eq. (42) has been applied to the Thomas-Fermi-Dirac-Weizsacker approximation of F[p] [47]. 

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