Just an observation: there are constrained atoms. I am not sure how well current convergence criteria for BFGS deal with this case.
Paolo On Tue, Nov 24, 2015 at 11:37 AM, Matej Huš <[email protected]> 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 > -- Paolo Giannozzi, Dept. Chemistry&Physics&Environment, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
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