Found the culprit! When I turned off the dipole correction, the system converged. Digging deeper, I found the underlying problem.
I had been reckless and used the 'emaxpos' value unchanged from a different set of calculation, inadvertently setting it to too close to the edge of the vacuum. A change from 0.70 to 0.50 solved the problem. Thanks for the all contributions! As for the dispersion correction, the discussion is still open :-) Matej -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Ilya Ryabinkin Sent: Tuesday, November 24, 2015 8:03 PM To: PWSCF Forum <[email protected]> Subject: Re: [Pw_forum] bfgs optimization not going anywhere Colleagues, to summarize: what would be 'the best' DFT correction on to of *existing* functionals, e.g. PBE for molecule-metal-interaction? As far as I understood, vdw-DF must be used with the corresponding pseudopotential (BTW, where one can get them?). -- I. On Tue, Nov 24, 2015 at 8:30 AM, Giuseppe Mattioli <[email protected]> wrote: > > Dear Matej (and all) > >> As for DFT-D2, I admit I am a bit in the dark here. How 'wrong' is >> it? Or to put differently, is it more wrong that not using dispersion >> correction at all? > > Regarding the dispersion correction(s) this is the Stephan Grimme's > paper which indicates that DFT-D2 doubles the DFT-D3 interaction energy > between molecules and metal surfaces: > > J. Chem. Phys. (2010) 132, 154104 > > In my experience of phthalocyanine/metal interactions (but if I > remember well Ari has also performed calculations on > porphyrin/phthalocyanine molecules adsorbed on metal surfaces and he > can add his own knowledge), adsorption geometries and energies are > very different, so that the results are also quite different. See for > example this paper (Cu phthalocyanine interacting with Ag (100) with > DFT-D2) > > PRL 105, 115702 (2010) > > And my paper (TiO phthalocyanine interacting with Ag (100) with > vdW-DF) > > J. Phys. Chem. C 2014, 118, 5255 > > And, yes, of course: if you use no dispersion correction you badly > underestimate the interaction between the molecule and the surface... > > 2 more hints: > > 1) In the case of molecule/metal systems, ab initio functionals > modeling long distance correlation between electrons should be (in my > opinion) preferred to semiempirical functional with add pairwise > forces based on tabulations (or partial calculations) of C6 > coefficients. There is a nice perspective written by J. L. Bredas > which addresses the issue > > Nature Nanotechnology > 8, > 230–231 > (2013) > > 2) Regarding lattice parameters, Ari is right in the case of vdwdf. > But I've tried to simulate gold (bulk and) surfaces in contact with > molecules by using the reparametrized vdwdf-c09 functional: lattice parameter > of gold is ok, and also molecule-surface interactions are expected to be > improved with respect to vdwdf! > >> Also, if I change/switch off the dispersion correction, then I will >> have to re-optimize all already converged structures (metal, isolated >> molecules, adsorbed intermediates), right? Looks rather tedious > > Yes, you should recalculate everything...:-( > > HTH > Giuseppe > > On Tuesday, November 24, 2015 11:37:45 AM Matej Huš wrote: >> Thanks for very useful comments. >> >> Yes, vacuum region is indeed too low in this example (whoops, seems >> like I've attached an old input file). I also ran a calculation with >> 10 A of vacuum without any improvement. Open shell is unnecessary as >> it quickly converges to a closed shell solution. I've just wasted >> some CPU time with that. >> >> Ectuwfc, ecutrhc are large enough (converged). I believe K points >> should also not be the source of a problem. >> >> As for DFT-D2, I admit I am a bit in the dark here. How 'wrong' is >> it? Or to put differently, is it more wrong that not using dispersion >> correction at all? How about vdw-DF, how do I turn it on and does it >> perform better? Where can I find more important about that? >> >> Also, if I change/switch off the dispersion correction, then I will >> have to re-optimize all already converged structures (metal, isolated >> molecules, adsorbed intermediates), right? Looks rather tedious >> >> >> Matej >> >> >> >> -----Original Message----- >> From: [email protected] [mailto:[email protected]] >> On Behalf Of Ari P Seitsonen >> Sent: Tuesday, November 24, 2015 11:22 AM >> To: PWSCF Forum <[email protected]> >> Subject: Re: [Pw_forum] bfgs optimization not going anywhere >> >> >> Dear Matej Hus, >> >> Adding to the previous comments (I think that it is ok to use the >> k points, even though you might gain some CPU time by first indeed >> using Gamma-only and then increasing, as your cell is quite large), >> have you checked the length of your vacuum/lattice vector along the surface >> normal? >> If I see correctly, you have only about six Ångströms, which is >> already very >> (too) little, plus the DFT-D2 (Grimme-D2) adds quite strong an >> interaction through the vacuum at such distances I believe, plus the >> dipole correction... >> >> Greetings from Peaceful Montrouge/France, >> >> apsi >> >> PS My personal opinion of the vdW-DF* is, yes, they might be better, >> but first check the literature about a "suitable empirical choice of >> the particular mixture" of the functional, as some of the choices >> give quite large lattice constants already (4-5 % larger than >> experimental, which, of course, is not necessarily the target, rather >> a good adsorption geometry and energy). And often the best agreement >> is found by tuning the exchange functional, which naturally should >> have not nothing to do with the vdW/London dispersion, which is pure >> correlation... So much about "ab initio". ;) The good news of the >> day is that it seems that seldomly things seem to go completely >> wrong, no matter which choice of the vdW-DF* you take, but still, I >> would study a bit the literature first. If any one has a reference >> for a good review on the vdW-DF* et co applied to surfaces and >> adsorption, I would also be very thankful! :) >> >> -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=- >> =*=-=*= >> - >> Ari Paavo Seitsonen / [email protected] / http://www.iki.fi/~apsi/ >> Ecole Normale Supérieure (ENS), Département de Chimie, Paris >> Mobile (F) : +33 789 37 24 25 (CH) : +41 79 71 90 935 >> >> On Tue, 24 Nov 2015, Matej Huš wrote: >> > Dear PW community >> > >> > I have a problem when trying to find optimized geometry of an >> > adsorbed intermediate in "benzene" hydrogenation on Ru surface (see input >> > below). >> > >> > I believe I am fairly close to optimised structure since I'm only >> > adding one hydrogen atom to an already optimised reactant and only >> > slight displacing the adjacent atoms. >> > >> > >> > >> > The problem is that BFGS doesn't seem to go anywhere. Energy only >> > fluctuates, which to my understanding is a sign of being close to a >> >> minimum. >> >> > However, forces remain large. >> > >> > >> > >> > I've switched to the damp algorithm and the problem persists. I've >> > searched through the forum and the usual approaches of tackling >> > this issue do not seem to work. >> > >> > >> > >> > Any ideas? Thank you! >> > >> > Matej Hus >> > >> > Laboratory of Catalysis and Chemcial Reaction Engineering >> > >> > National Institute of Chemistry >> > >> > Ljubljana, Slovenia >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum > > ******************************************************** > - Article premier - Les hommes naissent et demeurent libres et ègaux > en droits. Les distinctions sociales ne peuvent être fondèes que sur > l'utilitè commune > - Article 2 - Le but de toute association politique est la > conservation des droits naturels et imprescriptibles de l'homme. Ces > droits sont la libertè, la propriètè, la sùretè et la rèsistance à > l'oppression. > ******************************************************** > > Giuseppe Mattioli > CNR - ISTITUTO DI STRUTTURA DELLA MATERIA > v. Salaria Km 29,300 - C.P. 10 > I 00015 - Monterotondo Stazione (RM), Italy > Tel + 39 06 90672836 - Fax +39 06 90672316 > E-mail: <[email protected]> > http://www.ism.cnr.it/english/staff/mattiolig > ResearcherID: F-6308-2012 > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum -- ******************************************************* Ilya Ryabinkin Postdoctoral Scholar Physical and Environmental Sciences University of Toronto Scarborough http://www.utsc.utoronto.ca/~aizmaylov/Members.html ******************************************************* _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
