[CP2K-user] [CP2K:13145] CELL Optimization - Energy not decreasing

[Jan Elsner]

Dear all, 

I thought I should post an update on this. 

It seems that there is a problem with using PW92 as the local correlation 
part of XC functional. When I use VWN instead, the analytical and numerical 
forces are equal. I attach input and output files for DEBUG runs on a 
single H20 molecule using optPBE in combination with PW92 and VWN. In the 
case of PW92, there is a mismatch between analytical and numerical forces. 

I note that the same applies for the some of the other functionals listed 
here: https://github.com/cp2k/cp2k/tree/master/data/xc_section (at least, I 
can confirm that optB88 and C09 also give a mismatch between numerical and 
analytical forces using the settings listed here). 

Best wishes, 

Jan




On Friday, April 24, 2020 at 10:43:00 AM UTC+1, Jan Elsner wrote:
>
> Dear Juerg, 
>
> Many thanks for the quick response! Unfortunately, decreasing EPS_SCF (all 
> the way to 1.0E-10) does not solve the problem. 
>
> I have done a DEBUG run which results in the following error (see end of 
> attached file debug.out): *'Abort: A mismatch between the analytical and 
> the numerical stress tensor has been detected. Check the implementation of 
> the stress tensor'*. I'm not entirely sure how I should proceed from here 
> / what the problem is exactly - any insight would be very much appreciated. 
>
> If it helps shed some light on the problem, I also attach a figure showing 
> Total Energy, RMS Gradient and Cell Volume as a function of optimization 
> step (plotted from the original cell.out file I sent). The optimiser seems 
> to overshoot the minimum energy configuration. 
>
> One other question which comes to mind is whether it's ok to use GTH-PBE 
> or GTH-PADE pseudopotentials with optPBE-vdW?
>
> Best wishes, 
>
> Jan
>
>
>
>
>
> On Monday, April 20, 2020 at 10:20:34 AM UTC+1, jgh wrote:
>>
>> Hi 
>>
>> I don't know how well a setup as this is tested. However, from 
>> your output I would guess the problem could be related to your 
>> SCF convergence. With the methods you are using you have to set 
>> the convergence criteria much tighter in order to get converged 
>> energy and forces. I would suggest to use at least 1.E-8. 
>>
>> The ultimate test would be to do a DEBUG run in order to verify 
>> forces and stress tensor for the setting of options. 
>>
>> regards 
>>
>> Juerg Hutter 
>> -------------------------------------------------------------- 
>> Juerg Hutter                         Phone : ++41 44 635 4491 
>> Institut für Chemie C                FAX   : ++41 44 635 6838 
>> Universität Zürich                   E-mail: h... at chem.uzh.ch 
>> Winterthurerstrasse 190 
>> CH-8057 Zürich, Switzerland 
>> --------------------------------------------------------------- 
>>
>> -----c... at googlegroups.com wrote: ----- 
>> To: "cp2k" <c... at googlegroups.com> 
>> From: "Jan Elsner" 
>> Sent by: c... at googlegroups.com 
>> Date: 04/18/2020 08:33PM 
>> Subject: [CP2K:13145] CELL Optimization - Energy not decreasing 
>>
>> Dear all, 
>>
>> I am trying to run a Cell Optimisation on a periodic molecular crystal 
>> (beta-resorcinol: C6H6O2, 4 molecules in unit cell) using K-points and BFGS 
>> as optimiser. I am using the vdW-DF-optPBE functional (
>> https://github.com/cp2k/cp2k/commit/74ef05b96a46523a0daf7da04e75804420b5cd5e). 
>> After 83 optimisation steps, my system does converge to the required MOTION 
>> thresholds, however from step 7 onwards the total energy increases at every 
>> step i.e.: 
>>
>> --------  Informations at step =     7 ------------ 
>>   Optimization Method        =                 BFGS 
>>   Total Energy               =      -280.1489665596 
>>   Internal Pressure [bar]    =     -2667.4573178334 
>>   Real energy change         =         0.0001037473 
>>   Predicted change in energy =        -0.0001063956 
>>   Scaling factor             =         0.0000000000 
>>   Step size                  =         0.0124910496 
>>   Trust radius               =         0.4724315332 
>>   Decrease in energy         =                   NO 
>>   Used time                  =               60.978 
>>
>>   Convergence check : 
>>   Max. step size             =         0.0124910496 
>>   Conv. limit for step size  =         0.0010000000 
>>   Convergence in step size   =                   NO 
>>   RMS step size              =         0.0029192108 
>>   Conv. limit for RMS step   =         0.0010000000 
>>   Convergence in RMS step    =                   NO 
>>   Max. gradient              =         0.0034738629 
>>   Conv. limit for gradients  =         0.0001000000 
>>   Conv. for gradients        =                   NO 
>>   RMS gradient               =         0.0006857738 
>>   Conv. limit for RMS grad.  =         0.0001000000 
>>   Conv. for gradients        =                   NO 
>>   Pressure Deviation [bar]   =     -2668.4705678334 
>>   Pressure Tolerance [bar]   =       200.0000000000 
>>   Conv. for  PRESSURE        =                   NO 
>>  --------------------------------------------------- 
>>
>> The resulting cell-optimised structure is therefore not a minimum in 
>> energy. I've attached the input and output files. Some points which may (or 
>> may not) be relevant: 
>> I did not encounter this problem when using a different functional (PBE + 
>> D3 instead of optPBE-vdW as used here), but otherwise identical settings. 
>> I encountered the same issue (energy increasing at every step) using 
>> CUTOFF/REL_CUTOFF = 800/60 
>> I initially tried to converge CUTOFF and REL_CUTOFF as in the tutorial ( 
>> https://www.cp2k.org/howto:converging_cutoff), however my single point 
>> calculations did not converge quite as nicely as in the tutorial - instead 
>> oscillating with an amplitude of order ~ e-4 Ha (I've attached a figure 
>> showing this). This is why I use such large CUTOFF/REL_CUTOFF values. I 
>> note that this was also the case when I ran PBE + D3 calculations, however 
>> in the latter case my cell optimisation did work. 
>>
>> Any input would be greatly appreciated. 
>>
>> Best wishes, 
>>
>> Jan 
>>
>>
>>   
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>>
>>   
>>
>> [attachment "cell.inp" removed by Jürg Hutter/at/UZH] 
>> [attachment "cell.out" removed by Jürg Hutter/at/UZH] 
>> [attachment "E_vs_cutoff.png" removed by Jürg Hutter/at/UZH] 
>> [attachment "subsys.include" removed by Jürg Hutter/at/UZH] 
>>
>
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