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

[Kanka Ghosh]

Dear Lorenzo, 

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? 

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. 

BQ_BEGIN




"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? 

BQ_END


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 

BQ_BEGIN









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" [ mailto:paulatz at gmail.com | <paulatz at gmail.com> ] ​_ 
To: "users" [ mailto:users at lists.quantum-espresso.org | <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 
BQ_BEGIN

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" 


BQ_END





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 


BQ_BEGIN


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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BQ_END

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BQ_END

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