Thank you very much for all your answers.. I will run calculations again using your suggestions.
Valentina Cantatore PostDoc Researcher @ Universit? del Piemonte Orientale 2014-09-18 14:47 GMT+02:00 Giovanni Cantele <giovanni.cantele at spin.cnr.it>: > You should carefully check the input geometries and compare them to those > used in Gaussian. > > Using plane waves, what is usually done is to build the supercell with > A+B, then remove either A or B, > to calculate E_A and E_B, so that you single out the interaction energy > (no contribution coming from > geometry relaxation). > > Using your inputs: > E_A = -52.58144317 Ry > E_A+B = -1680.87808274 Ry > E_B = -1628.42761473 Ry > > interaction energy: -0.1309 Ry ~ -41 kcal/mol > > but the I-Pb-I angle is 126.13 degrees in the A+B system and 103.109 in > the isolated B system. > If you use the above prescription (so that the PbI2 fragment has the same > geometry as in the interacting system), > you get > E_B=-1628.29372424 > which corresponds to an interaction energy of ~ +1kcal/mol. > > This does not completely solve your issue (e.g. in the former case I find > a negative interaction energy, whereas in the latter > a positive one), but should help you in finding the discrepancy with > respect to the localised basis set calculation. > > Giovanni > > > PS within the pseudo potential files you can find suggested values of > ecutwfc and ecutrho, the ones you use are > much larger (120Ry/720Ry), maybe rendering the calculation uselessly > expensive. I used 50Ry/300 Ry, and found > no variations after increasing those values to 60Ry/360 Ry. > > > On 18 Sep 2014, at 11:44, Valentina Cantatore <valecantatore at gmail.com> > wrote: > > 1) Yes > 2) Yes > 3) Yes > > I attach to the mail my three inputs. Thank you, again, for your help. > > Valentina Cantatore > PostDoc Researcher @ Universit? 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 @ Universit? 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 >> >> >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > <MA_20.inp><MAPbI2_20.inp><PbI2_20.inp> > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > > > -- > > 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 > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140918/19a71408/attachment.html
