If you can assume that only two-body interactions between the various fragment pairs are relevant, what Stefano suggests is perfectly appropriate. If you cannot or do not want to make such assumption, you may choose a model and extract the parameters for your model by fitting it to a few (or many) first-principle energies.
P. On Sun, 2014-01-19 at 15:58 +0200, Manuel Fernandes wrote: > Dear Stefano, > > > Many thanks for your response. The issue is that I would like to know > this answer when the molecules are within a crystal environment so > that they are interacting with many neighbours and not just > interacting with each other. > > > Kind regards, > > > Manuel > > Date: Fri, 17 Jan 2014 15:39:49 +0100 > From: stefano de gironcoli <degironc at sissa.it> > Subject: Re: [Pw_forum] Interaction energies between molecules > To: PWSCF Forum <pw_forum at pwscf.org> > Message-ID: <52D940B5.8080704 at sissa.it> > Content-Type: text/plain; charset="iso-8859-1" > > the way to compute the interaction energy between two fragments is to > compute the two fragments together and compare with the energy of the > two separated fragments. > > stefano > > On 01/17/2014 10:32 AM, Manuel Fernandes wrote: > > Hi everyone, > > > > Is there anyway to do a lattice energy calculation on an organic > > crystal and then extract the interaction energy between pairs of > > molecules of interest from that? What I would like to know for > example > > is how strongly a molecule as a whole interacts with its neighbours > in > > particular directions in a crystal environment. > > > > Thanking you in advance, > > > > Manuel Fernandes > > > > > > > > ______________________________ > _________________ > > Pw_forum mailing list > > Pw_forum at pwscf.org > > http://pwscf.org/mailman/listinfo/pw_forum > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum -- Paolo Giannozzi, Dept. Chemistry&Physics&Environment, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222