Nudged Elastic Band (NEB, BAND): understanding and improving efficiency

[S. Ling]

Hi Daniele,

4) Fixed cell for NEB is a serious constraint: are you developing a 
variable-cell-neb in the next version? An alternative seems to be USPEX 
which is interfaced with cp2k but not properly documented for it (in my 
opinion). Do you have any input example to share?

For flexible cell NEB (or solid-state NEB) calculations, you may consider 
to use the TSASE tool by the Henkelman group at UT Austin, 
see http://theory.cm.utexas.edu/tsase/. If you download the package, you 
will find a few examples there. Just set the ASE calculator to CP2K (see 
https://www.cp2k.org/tools:ase), then you should be able to run a 
solid-state NEB calculation for your MOF in which the cell parameters of 
the transition state are optimised together with the atomic coordinates. 
The solid-state NEB method is discussed in this paper, 
see http://scitation.aip.org/content/aip/journal/jcp/136/7/10.1063/1.3684549.

SL


On Wednesday, July 27, 2016 at 2:48:15 PM UTC+1, Daniele Ongari wrote:
>
> Dear cp2k developers, 
> I'm working with BAND algorithm in cp2k, to explore phase transition in 
> metal organic frameworks.
>
> I'm using a starting configuration and a final configuration (sometimes I 
> also add an intermediate configuration to avoid strange geometry 
> interpolations) to generate 20 replicas.
>
> Using a DFT/PBE+D3 calculation on ~300 atoms efficiency is very important 
> to me and I'm asking your help to understand better how to chose the best 
> input:
>
> 1) If i use a total of 400 cpus to run 20 replicas, I know that with 
> "NPROC_REP 100" the SCF of 4 replicas are done in parallel and is better 
> for scalability issues. But I found out that BAND starts with replica 1 2 3 
> 4 and move to 5 6 7 8 only when the last SCF is terminated, making lots of 
> cpus waiting for nothing. Am I right or I misunderstood something? Is there 
> an option to avoid this nonsense?
>
> 2) Why starting and final configuration need a SCF for each BAND cycle? 
> The configuration and the energy appear to be always the same, so why run a 
> SCF more than once?
>
> 3) In an old post (
> https://groups.google.com/forum/#!topic/cp2k/_icaeFBVnZ4) I found that 
> for each BAND cycle there are more than one SCF running without geometry 
> change, and this is related to NO_LS and NP_ LS (=2 by default). What is 
> the scope of this? Can NO_LS be safely used? Does NO_LS=T correspond to 
> NP_LS=1?
>
> 4) Fixed cell for NEB is a serious constraint: are you developing a 
> variable-cell-neb in the next version? An alternative seems to be USPEX 
> which is interfaced with cp2k but not properly documented for it (in my 
> opinion). Do you have any input example to share?
>
> Thanks for your help and for your continuous effort to improve this 
> wonderful software.
>
> Daniele Ongari
> PhD candidate, LSMO, EPFL Switzerland
>
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