Local and Gradient-Corrected Density Functionals
نویسندگان
چکیده
The generalized gradient approximation (GGA) corrects many of the shortcomings of the local spin-density (LSD) approximation. The accuracy of GGA for ground-state properties of molecules is comparable to or better than the accuracy of conventional quantum chemical methods such as second-order Møller-Plesset perturbation theory. By studying various decompositions of the exchange-correlation energy EXC, we show that the real-space decomposition of EXC facilitates the most detailed understanding of how the local spin-density approximation and the Perdew-Wang 1991 GGA work. The real-space decomposition shows that the near universality of the on-top value for the exchange-correlation hole connects the homogeneous electron gas to inhomogeneous systems such as atoms and molecules. The coupling-constant decomposition shows that the exchange-correlation energy at full coupling strength EXC,λ=1 is ap proximated more accurately by local and semi-local functionals than is the coupling-constant average EXC. We use this insight both to critique popular hybrid functionals and to extract accurate energies from exact electron densities by using functionals for the exchange -correlation energy at full coupling strength. Finally, we show how a reinterpreted spin density functional theory can be applied to sys tems with static correlation.
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