  The development of semilocal models for the kinetic energy density (KED) is
an important topic in density functional theory (DFT). This is especially true
for subsystem DFT, where these models are necessary to construct the required
non-additive embedding contributions. In particular, these models can also be
efficiently employed to replace the exact KED in meta-Generalized Gradient
Approximation (meta-GGA) exchange-correlation functionals allowing to extend
the subsystem DFT applicability to the meta-GGA level of theory. Here, we
present a two-dimensional scan of semilocal KED models as linear functionals of
the reduced gradient and of the reduced Laplacian, for atoms and weakly-bound
molecular systems. We find that several models can perform well but in any case
the Laplacian contribution is extremely important to model the local features
of the KED. Indeed a simple model constructed as the sum of Thomas-Fermi KED
and 1/6 of the Laplacian of the density yields the best accuracy for atoms and
weakly-bound molecular systems. These KED models are tested within subsystem
DFT with various meta-GGA exchange-correlation functionals for non-bonded
systems, showing a good accuracy of the method.
