[CP2K:8719] Comparison between CP2K and Quantum Espresso

[Tommaso Francese]

Dear Apsi,
thanks for the reply. I will take into considerations also your suggestions!
Best,
Tommaso
> Il giorno 18 feb 2017, alle ore 16:49, Ari Paavo Seitsonen <ari.p.s... at gmail.com> ha scritto:
> 
> Dear Tommaso and David,
> 
>   I would definitely _not_ call using Vanderbilt pseudo potentials as having "minimal basis set", usually the precision is better than with norm-conserving pseudo potentials (due to several reference energies/projectors). The reduction of cut-off is due to a good reason. So lowering the basis set in CP2K would be unfair, as the results are of lower precision. Rather using GAPW (instead of GPW) would have kind-of the same effect, as this would allow a lower cut-off energy being used in the plane wave part of QuickStep.
> 
>   The idea of shifting the k point might refer to the scheme of Baldereschi's special point (I do not know much, I was just told that this is the "best" point if using a single point; since most people do not know it and Monkhorst-Pack is so "black box"-convenient, younger generations have probably not become users of it). Just my guess.
> 
>     Greetings from Paris,
> 
>        apsi
> 
> 2017-02-08 11:28 GMT+01:00  <tfran... at gmail.com <mailto:tfran... at gmail.com>>:
> Dear David,
> first of all thanks a lot for your very useful comments.
> 
> I will benchmark my system in CP2K with a lower basis sets, in order to test again the parameters and to have better reference with respect to QE. 
> 
> Regarding the compilation of the program in our cluster, I think that it is the pitfall and that our technician missed something. He told me ( because I am not allowed to install anything, but only the technician ) that he compiled the precompiled version of CP2K. But I am pretty sure he missed some of the libraries you listed above. Indeed I am insisting in a more "serious" compilation of the program, that we wanna massively exploit for our dynamics. 
> 
> Regarding the single point shift from the gamma point in QE, that was suggested by one of my old Professors. At that time ( almost three years ago) he told us that the shift is recommended. 
> I always used that setting, without honestly taking care too much about the change in performances. By the way, thanks a lot for the really useful hints. Now I will re-benchemark the new machine testing several levels of theory as you suggested.
> 
> Best Regards,
> Tommaso Francese
> 
> Il giorno mercoledì 8 febbraio 2017 11:09:16 UTC+1, David T ha scritto:
> Hi Tommaso
> 
> as you I am more expert on QE and only recently moved on CP2K.
> On my experience CP2K is much more quicker and allows to work with bigger systems that planewave code could not afford. On the other hand it is true that this is really system depended so the fact that for nano-porous material CP2K is more efficient could not be true for other systems.
> After having read the inputs a comment I can give to you is that you are probably not making a fair comparison. 
> I've see you use ultrasoft pseudo which allows a very low cut-off and can be "though" as minimal basis-set. So you should probably use some corresponding low basis-set in CP2K (for instance a dobule zera instead of triple zeta).
> 
> Probably more important another thing I can tell you is that I've seen that if CP2K is not properly compiled, its performance can be slow. For instance my own version with mpi, mkl, libxsmm and elpa is about 30% faster than the standard one I found on our cluster. 
> Moreover the speediness of the code can be further boosted if you use also GPU and hybrid openMP-MPI.
> 
> P.S. a curiosity, in QE why are you using a single point shifted from gamma? if there is not a major reason using the gamma algorithm on QE can accelerate you calc up to 30%
> 
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>   Ari Paavo Seitsonen / Ari.P.S... at iki.fi <mailto:Ari.P.S... at iki.fi> / http://www.iki.fi/~apsi/ <http://www.iki.fi/~apsi/>
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