Bug? The conserved quantity is NOT conserved after flexible cell MD is restarted

Rustam rusta... at gmail.com
Sun Aug 14 03:41:28 UTC 2016

Hi Matthias,

Thanks for the great advice! I tried changing the basis set to the one 
compatible with Mg q2 and low cutoff. Unfortunately, the problem remains as 
shown in the new figure.

On a different note, what basis sets would you recommend for solid state 
systems? All-electron basis sets? Or do you think I should generate a pair 
of potential/basis for the problem at hand?

Thanks again,

PS. The input file is also attached.

On Saturday, August 13, 2016 at 2:34:04 AM UTC-4, Matthias Krack wrote:
> Hi Rustam
> in the first place I would suggest to use a compatible pair of basis set 
> and potential for Mg. The Mg TZV2P-GTH basis set was generated for a Mg 
> GTH-*-q10, but a GTH-BLYP-q2 is employed. Unfortunately, the GTH_BASIS_SET 
> file provides only generic labels. I will fix that. Please, run the case 
> with a valid combinations of potential and basis set and report if the 
> error persists. Note, that the Mg q10 potential requires a very large 
> cutoff and for the Mg q2 potential there is only a DZVP basis set available 
> in the file BASIS_SET.
> Best regards
> Matthias
> PS: The basis sets in GTH_BASIS_SETS are usually not well suited for 
> (dense) solid state systems as they have been generated mainly for 
> molecular systems.
> On Saturday, 13 August 2016 07:56:39 UTC+2, Rustam wrote:
>> Hi guys,
>> As Amandine Chouanard mentioned in a recent post  
>> <https://groups.google.com/forum/#!topic/cp2k/mwieBkpEjns>the conserved 
>> quantity shows discontinuities when a flexible cell MD simulation is 
>> restarted. I used her input file and found that restart works fine with NVT 
>> and NPT_I simulations, but NOT with NPT_F (see attached figure). The 
>> discontinuities in NVT_F the conserved quantity are larger if restarts are 
>> less frequent (i.e. trajectory pieces are longer).
>> It seems that the conserved quantities in NPT_I and NPT_F simulations are 
>> computed by the same subroutine in motion/md_conserved_quantities.F:390. So 
>> it seems that the restart file contains ALL data on the current state of 
>> the barostat and thermostat to ensure a smooth restart.
>> Is it possible that this has something to do with the CELL_REF setting? 
>> Something along the lines that the grids before and after the restart are 
>> different? I tried printing the GRID info but it seems to keep the number 
>> of points constant...
>> I will appreciate any suggestions/comments,
>> Rustam
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