Dear Giuseppe, I think your reply reached also the PW-forum, since I've received it twice, so everyone should have been able to read it.
Il giorno 23/mar/2011, alle ore 10.48, giuseppe.mattioli at mlib.ism.cnr.it ha scritto: > Dear Gabriele > >> is there any concrete evidence that "ab initio" van der Waals >> vdW-DF is systematically better than Grimme's vdW? > > Yes, at least in the case of molecule-surface interactions. Maybe graphite is another story... with PBE-D2 you should get an interlayer spacing just 3.4% smaller than the experimental value, which is not so bad considering the much larger PBE error. > There is a > recent (2010) Grimme paper (I'm sorry, I cannot be more accurate > today...) Maybe this one: THE JOURNAL OF CHEMICAL PHYSICS 132, 154104 (2010) which is the paper introducing the D3 method (and a comparison with its predecessor D2) > that reports an overestimate of the above interactions when > using DFT-D2, currently implemented in QE. I've performed comparative > tests (classical MM, DFT-D2, vdW-DF) on several molecules interacting > with the non-polar 10-10 ZnO surface and I've obtained the best > results (some of them comparable with experimental data, i.e., the > thiophene ring) by using the vdW-DF approach. The DFT-D2 setup, > however, is quite good for molecules in my experience, and can be > tuned by changing the C6 coefficients by hand > (QE/Modules/mm_dispersion.f90), following one of the available force > fields (AMBER, CHARMM, ...). > Maybe DFT-D3 and vdW-DF would converge to > similar results... I can't tell this, but I know that DFT-D3 should include some notable improvements with respect to the D2 version, since it now takes into account some kind of local coordination of the atoms, atom-pair specific coefficients (from ab initio), and should also separate better the long range regime from the short range one. I know there is someone who offered to look at implementing the extension to D3, maybe it will be available in a few months time. > What about cp? No clear idea here. However I believe it should not be difficult to port DFT-D2 to CP, since it requires only atomic positions and the cell setup. These should be handled in a similar way in PW and CP. Gabriele > > Yours > > G. > > Quoting Gabriele Sclauzero <sclauzer at sissa.it>: > >> Dear Giuseppe, >> >> is there any concrete evidence that "ab initio" van der Waals >> vdW-DF is systematically better than Grimme's vdW? >> Are you aware of any paper comparing the latest version of the two >> methodologies (or "phisolophies", if you want), i.e. vdW-DF2 vs >> DFT-D3? >> >> Cheers, >> >> GS >> >> >> Il giorno 23/mar/2011, alle ore 10.12, >> giuseppe.mattioli at mlib.ism.cnr.it ha scritto: >> >>> >>> Dear all >>> You can do better than the semiempirical "Grimme" correction. There is >>> a new ab initio van der Waals correlation functional implemented in QE >>> 4.3a. Try input_dft='vdW-DF', in the &sysytem list. >>> By the way, what about a (semiempirical or ab initio) vdW scheme in >>> cp.x? Is there any project going on? >>> >>> Yours >>> >>> Giuseppe >>> >>> Quoting Masoud Nahali <masoudnahali at gmail.com>: >>> >>>> Dear Eric >>>> >>>> Try london="true" to get improved answer; as you should know DFT is weak >>>> to calculate dispersion forces and by using the keyword one can include >>>> these forces semi-empirically. I hope it helps. >>>> >>>> Best Wishes >>>> >>>> Masoud >>>> -------------- >>>> Masoud Nahali, Sharif University of Technology >>>> >>>> >>>> Eric Wrote: >>>> >>>> Dear all, >>>> >>>> I'm trying to optimize unit cell parameter of graphite. >>>> The problem is the c axis gets too long. >>>> Starting from published data my initial parameters are a=4.59203 Bohr >>>> and c=12.513 Bohr. >>>> The final values are 4.664 and 15.829 respectively. >>>> I need someone to explain to me what I did wrong, I've attached my input >>>> file. >>>> That's a basic calculation so it's very frustrating to not make it done. >>>> I thank you in advance, >>>> >>>> Eric. >>>> >>>> -- >>>> /Be the change you wish to see in the world >>>> / --- Mahatma Gandhi --- >>>> >>>> Dr. ?ric Germaneau <mailto:germaneau at gucas.ac.cn >>>> <http://www.democritos.it/mailman/listinfo/pw_forum>> >>>> >>>> College of Physical Sciences >>>> Graduate University of Chinese Academy of Sciences >>>> Yuquan Road 19A >>>> Beijing 100049 >>>> China >>>> >>> >>> Giuseppe Mattioli >>> ISM-CNR >>> Italy >>> >>> >>> >>> >>> _______________________________________________ >>> Pw_forum mailing list >>> Pw_forum at pwscf.org >>> http://www.democritos.it/mailman/listinfo/pw_forum >> >> >> ? Gabriele Sclauzero, EPFL SB ITP CSEA >> PH H2 462, Station 3, CH-1015 Lausanne >> >> > > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum ? Gabriele Sclauzero, EPFL SB ITP CSEA PH H2 462, Station 3, CH-1015 Lausanne -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110323/89586cbb/attachment.htm
