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** Next:** 37.5 Density fitting
** Up:** 37 SYMMETRY-ADAPTED INTERMOLECULAR PERTURBATION
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##

37.4 High order terms

It has been found that third and higher-order terms become quite important if
one or both monomers are polar. As no higher than second-order terms are
currently implemented in SAPT, one may use a non-correlated estimation of
those terms by using supermolecular Hartree-Fock (see e.g. [7]). This can be
done by adapting the following template:

!dimer
hf
edm=energy
!monomer A
dummy,<monomer2>
{hf; save,$ca}
ema=energy
sapt;monomerA
!monomer B
dummy,<monomer1>
{hf; start,atdens; save,$cb}
emb=energy
sapt;monomerB
!interaction contributions
sapt,sapt_level=2;intermol,ca=$ca,cb=$cb
esup=(edm-ema-emb)*1000. mH
dHF=esup-e1pol-e1ex-e2ind-e2exind

which stores the resulting (HF) term in `dHF`

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molpro@molpro.net 2018-01-18