[QE-users] D3Q code stopped due to davcio error

[Lorenzo Paulatto]

>
> Yes it took little more than 5 days to compute only the first q-point. 
> anyway it seems that I should use 1x1x1 grid instead of 2x2x2. But are 
> you suggesting to do the single mode calculation with 1x1x1 grid or 
> the "mode=full" using the 1x1x1 grid?

Yes, but no need to do it: you have done it already. You can just call 
d3_qq2rr and specify "1 1 1" as the grid size:

ls anh*| d3_qq2rr.x 1 1 1

and it will automatically compute the force constants from the 
calculation at (0,0,0). This way you can immediately test how it works.

If you want to try the 2x2x2 grid, I would use 10 pools and maybe try 
with *fewer* CPUs per pool: at the moment you are using 128 which 
requires a lot of communications. If the calculation fits in RAM, I 
would recommend keeping each pool on a single computing node.

You may try to use some local scratch in order to avoid running out of 
disk space (ask the cluster managers what to use).

Finally, if you manage to get everything running, you can run al the 
q-points triplet simultaneously as different batch jobs by setting 
"first" and "last". You can have the same outdir and prefix, as long as 
they work on different triplets, they will not interfere (this is true 
for d3q, but not in general for other linear response codes)

hth

>
> Regards,
> Kanka
>
> Kanka Ghosh
> Postdoctoral Researcher
> I2M-Bordeaux
> University of Bordeaux, CNRS UMR 5295
> Site: Ecole Nationale Supérieure des Arts et Métiers
> Bordeaux-Talence 33400
>
> ------------------------------------------------------------------------
> *From: *"Lorenzo Paulatto" <paulatz at gmail.com>
> *To: *"users" <users at lists.quantum-espresso.org>
> *Sent: *Friday, December 4, 2020 9:09:50 AM
> *Subject: *Re: [QE-users] D3Q code stopped due to davcio error
>
>     Thanks for pointing out the storage issue. Yes, I am running it at
>     the French computing centre (University of Bordeaux's cluster
>     system (curta, mcia)). Here I am attaching the d3q output file.
>     Indeed, it was in the process of computing the second q-point triplet.
>
> I do not have access to  Bordeaux cluster, but I could ask it if you 
> need that I look at the code. That said, I see that to compute the 
> first q-point it took about 5 days, it will take at least a month to 
> do the second point ! Because it has less symmetry the code needs to 
> compute 2x more k-points and 3x more perturbations.
>
>
>     "Maybe for such a large system you can get some decent
>     force-constants already from (0,0,0) alone"
>
>
>     In that case, you mean to implement the "mode=gamma-only" tag?
>
> Not really, the triple (0,0,0) is in itself the 1x1x1 grid, and you 
> can threat it as such. Thanks to some Fourier interpolation trickery, 
> you can use it to get the D3 matrices at any point. Also, the d3_qq2rr 
> code is not particularly optimized, and is not parallelized I'm not 
> sure you would manage to compute the Fourier transform of the 2x2x2 
> grid anyway.
>
> You have to keep in mind that the 3-body force constant become huge 
> very quickly with the number of atoms and the size of the grid: each 
> D3 matrix has (3*nat)^3 complex elements, and a grid n x n x n  
> contains n^6 power triplets
>
> In your case, the 2x2x2 grid would use about 2.2GB of RAM, which is 
> probably still feasible, but i would try the 1x1x1 first.
>
>
> cheers
>
>
>
>     Regards,
>
>     Kanka
>
>
>
>
>
>     Kanka Ghosh
>     Postdoctoral Researcher
>     I2M-Bordeaux
>     University of Bordeaux, CNRS UMR 5295
>     Site: Ecole Nationale Supérieure des Arts et Métiers
>     Bordeaux-Talence 33400
>
>     ------------------------------------------------------------------------
>     *From: *"Lorenzo Paulatto" <paulatz at gmail.com>​_
>     *To: *"users" <users at lists.quantum-espresso.org>
>     *Sent: *Thursday, December 3, 2020 11:23:58 PM
>     *Subject: *Re: [QE-users] D3Q code stopped due to davcio error
>
>          task #        71
>
>              from davcio : error #      5011
>              error while writing from file
>         ".//D3_Q1.0_0_0_Q2.0_0_-1o2_Q3.0_0_1o2/scf.d1.dq1pq1.72"
>
>
>     I guess it may have run out of space, d3q uses a ton of disk space
>     and there is not easy way to avoid this. If you are running on any
>     of the French computing centers I can try to have a look directly.
>
>     I do not think the change in number of CPUs could cause this
>     problem, but if you provide the full output I can check. Also, 44
>     atoms is a lot for the d3q code, it seems like you're running the
>     second q-point triplet, which is of kind (0,q,-q), it takes much
>     more time and disk space than the triplet (0,0,0). Maybe for such
>     a large system you can get some decent force-constants already
>     from (0,0,0) alone
>
>     cheers
>
>
>         Kanka Ghosh
>         Postdoctoral Researcher
>         I2M-Bordeaux
>         University of Bordeaux, CNRS UMR 5295
>         Site: Ecole Nationale Supérieure des Arts et Métiers
>         Bordeaux-Talence 33400
>
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