  We test Laplacian-level meta-generalized gradient approximation (meta-GGA)
non-interacting kinetic energy functionals based on the fourth-order gradient
expansion (GE4). We consider several well known Laplacian-level meta-GGAs from
literature (bare GE4, modified GE4, and the MGGA functional of Perdew and
Constantin [Phys. Rev. B \textbf{75},155109 (2007)]), as well as two newly
designed Laplacian-level kinetic energy functionals (named L0.4 and L0.6).
First, a general assessment of the different functionals is performed, testing
them for model systems (one-electron densities, Hooke's atom and different
jellium systems), atomic and molecular kinetic energies as well as for their
behavior with respect to density-scaling transformations. Finally, we assess,
for the first time, the performance of the different functionals for Subsystem
Density Functional Theory (DFT) calculations on non-covalently interacting
systems. We find that the different Laplacian-level meta-GGA kinetic
functionals may improve the description of different properties of electronic
systems but no clear overall advantage is found over the best GGA functionals.
Concerning Subsystem DFT calculations, the here proposed L0.4 kinetic energy
functional is competitive with state-of-the-art GGAs, whereas all other
Laplacian-level functionals fail badly. The performance of the Laplacian-level
functionals is rationalized thanks to a two-dimensional reduced-gradient and
reduced-Laplacian decomposition of the non-additive kinetic energy density.
