##

37.5 Density fitting

In order to be able to study interactions between extended
monomers one can use density fitting to approximate the
integrals in SAPT [7]. For this one may use the input:

{sapt;intermol,ca=$ca,cb=$cb,fitlevel=3
dfit,basis_coul=jkfit,basis_exch=jkfit,basis_mp2=mp2fit,cfit_scf=3}

with in the basis section defined `jkfit`

and `mp2fit`

fitting
basis sets (see section 15).

Currently only the ALDA xc-kernel is implemented for the
case `SAPT_LEVEL`=3 and `SAPT_FITLEVEL`=3. This means that
a corresponding SAPT calculation would be uncompatible with
hybrid-DFT monomer orbitals/orbital energies. Therefore it is
recommended to use nonhybrid functionals in the
case the dispersion/exchange-dispersion energy terms are requested
in a DF-DFT-SAPT run. Another possibility is to localise the
xc-potential via, e.g., the OEP method (see also example in
section 37.7.3).

molpro@molpro.net 2019-06-16