A fragment-based approximation of the Pauli kinetic energy

The Pauli kinetic energy is expressed via a non-analytical functional, which, here, is a bifunctional of the Pauli potential and the electron density. This type of functionals allows to approximate directly the functional derivative and subsequently evaluate the energy functional. In this work, the molecular Pauli kinetic energy is approximated using the atomic fragment approach. The energetic performance of the resultant fragment kinetic energy is comparable to the ones of the kinetic energy functional from Tran and Wesolowski while being a completely parameter-free approximation.