Laplacian-dependent models of the kinetic energy density: Applications in subsystem density functional theory with meta-generalized gradient approximation functionals

摘要

The development of semilocal models for the kinetic energy density (KED) isan important topic in density functional theory (DFT). This is especially truefor subsystem DFT, where these models are necessary to construct the requirednon-additive embedding contributions. In particular, these models can also beefficiently employed to replace the exact KED in meta-Generalized GradientApproximation (meta-GGA) exchange-correlation functionals allowing to extendthe subsystem DFT applicability to the meta-GGA level of theory. Here, wepresent a two-dimensional scan of semilocal KED models as linear functionals ofthe reduced gradient and of the reduced Laplacian, for atoms and weakly-boundmolecular systems. We find that several models can perform well but in any casethe Laplacian contribution is extremely important to model the local featuresof the KED. Indeed a simple model constructed as the sum of Thomas-Fermi KEDand 1/6 of the Laplacian of the density yields the best accuracy for atoms andweakly-bound molecular systems. These KED models are tested within subsystemDFT with various meta-GGA exchange-correlation functionals for non-bondedsystems, showing a good accuracy of the method.