[Pw_forum] Intermolecular energy of two fragments.

[Valentina Cantatore]

1) Yes
2) Yes
3) Yes

I attach to the mail my three inputs. Thank you, again, for your help.

Valentina Cantatore
PostDoc Researcher @ Università del Piemonte Orientale

2014-09-18 11:26 GMT+02:00 Giovanni Cantele <giovanni.cantele at spin.cnr.it>:

>
> On 18 Sep 2014, at 10:40, Valentina Cantatore <valecantatore at gmail.com>
> wrote:
>
> > Good morning to everyone.
> >
> > I would like to calculate the interaction energy between to molecules
> using QE. What I set up was to fix the dimension of a cubic box at 20 A (I
> think it is big enough to avoid interactions between the other replicated
> molecules), calculate the energy of each of the two fragments (Ea and Eb)
> and then calculate the energy of the two fragments together (Eab). What I
> expect is that interaction energy (Ein) is given by Ein=Eab-(Ea+Eb).
> >
> > I also used the assume_isolated option for all calculations. I sampled
> only gamma points.
> >
> > The results obtained are not of the same order of magnitude of those
> obtained with a gaussian basis set on the same systems.
> >
> > Where am I wrong? Is it possible run this kind of calculation with
> Quantum Espresso? Thank you
> >
> > Valentina Cantatore
> > PostDoc Researcher @ Università del Piemonte Orientale
> >
>
>
> the procedure you describe is correct and this kind of calculations is of
> course possible with QE. Just few questions:
> 1) are you using the same XC approximation with gaussian and plane waves
> runs (e.g. PBE)?
> 2) are you sure that both calculations are converged with respect to the
> respective parameters (in particular basis set size)?
> 3) did you carefully check the energy units used by the two different
> codes?
>
> Otherwise, you should provide more details and/or inputs to understand
> what is going on.
>
> Giovanni
>
> --
>
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it
> Phone: +39 081 676910
> Skype contact: giocan74
>
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> Web page: http://people.na.infn.it/~cantele
>
>
>
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