# [molpro-user] BSSE with ECP potential/basis

Kirk Peterson kipeters at wsu.edu
Sat May 7 16:53:20 CEST 2016

```Hi Amit,

as far as I know, one doesn’t have to treat ECP-based calculations any differently compared to those without.  It is a little surprising  you get the same CP corrected binding energies with these two basis sets, but DZ results can be strange sometimes.

regards,

-Kirk

> On May 6, 2016, at 5:21 AM, Amit Sharma <greifsw at gmail.com> wrote:
>
> Hi all,
> I want to calculate BSSE where one of the atoms has an ECP potential basis on it. Should BSSE be computed differently for ECP? There is some discussion in the literature about switching off the core but I am not sure how to do that in molpro.
>
> As a test I compute BSSE for two noble gas atoms with AVDZ basis and get a BSSE of about 47 cm-1. Then I switch the basis on one of the atoms to be def2-SVPD and I get BSSE which is twice that of the AVDZ result (about 97 cm-1).
>
> However, the CP corrected interaction energy is approximately the same between the two calculations. 400 cm-1 vs 403 cm-1, so maybe nothing special needs to be done. Can anyone please help clarify this for me.
> Thanks
> Amit
>
> ***, Ar + he bsse
>
> geometry={Ar
> He Ar Rx}
>
> Rx=5.0
>
> !basis=avdz,he=avdz
> basis=def2-SVPD,he=avdz
>
>
>  text,calculation for complex
>  hf                            !RHF for total system
>  ccsd(t)
>  e_Arhe=energy                 !save energy in variable e_Arhe
>
>  text,cp calculation for HE
>  dummy,Ar                      !make Ar a dummy
>  hf                           !RHF for He
>  ccsd(t)
>  e_he=energy                   !save energy in variable e_he
>
>  text,cp calculation for Ar
>  dummy,he                      !make he dummy
>  hf
>  ccsd(t)
>  e_Ar=energy                   !save energy in variable e_Ar
>
>  text,separate calculation for he
>  symmetry,x,y
>  geometry={he}                 !geometry for he alone
>  hf                            !RHF for He
>  ccsd(t)
>  e_he_inf=energy               !save energy in variable e_he_inf
>
>  text,separate calculation for Ar
>  symmetry,x,y
>  geometry={Ar}                 !geometry for Ar alone
>  hf                            !scf for Ar
>  ccsd(t)
>  e_Ar_inf=energy               !save energy in variable e_Ar_inf
>
> de(i)=(e_Arhe-e_he_inf-e_Ar_inf)*tocm    !compute uncorrected interaction energy
> de_cp(i)=(e_Arhe-e_he-e_Ar)*tocm         !compute counter-poise corrected interaction energy
> bsse_he(i)=(e_he-e_he_inf)*tocm          !BSSE for he
> bsse_Ar(i)=(e_Ar-e_Ar_inf)*tocm          !BSSE for Ar
> bsse_tot(i)=bsse_he(i)+bsse_Ar(i)              !total BSSE
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