In order to use different GGA approximations of the non-additive
kinetic potential, the flag `-k`

*string* must be used.
Here *string* is the acronym used to identify a given GGA
kinetic energy approximation, that can be selected among the following
functionals:

*string*=`revapbek`

: generalized gradient approximation with a PBE-like enhancement factor, obtained using the asymptotic expansions of the semiclassical neutral atom as reference [152,153] (revAPBEk). This is the default choice;*string*=`lc94`

: Perdew-Wang (PW91) exchange functional reparametrized for kinetic energy by Lembarki and Chermette [154] (LC94);*string*=`t-f`

: gradient expansion truncated at the zeroth order (GEA0), corresponding to the Thomas-Fermi functional.

For example, the command

FDE -p 3 -k lc94approximates the non-additive kinetic contribution to the embedding potential through the functional derivative of LC94 kinetic energy functional.

A pure electrostatic embedding can be also performed with `FDE`

script, where the embedding potential required by a subsystem A
to account for the presence of the B one will be merely:

with

FDE -p 3 -k electroand can be performed for both Kohn-Sham (only for LDA/GGA exchange-correlation functionals) and Hartree-Fock methods.

The electrostatic embedding is implemented only for testing purpose. It resembles an electrostatic embedding with external point-charges and/or point-dipoles, but it is ``exact'' as it is based on the whole densities (i.e. it considers all multipole moments of the density and the polarizabilies at all orders).

Equivalent command: `--kin`

*string*

`fde.input`

option: `kin=`

*string*