[CP2K-user] [CP2K:13369] Problem with geometry optimization using LS_SCF

[Thomas Kühne]

Dear Torstein, 

apparently you are not exploiting the WF guess in your LS_SCF run, as you have guessed. 
Without an input I can only speculate, but by default EXTRAPOLATION_ORDER is 4 within 
LS_SCF and 3 for all other methods. Regarding test 3, did you also restart the Hessian matrix? 

Cheers, 
Thomas

> Am 25.05.2020 um 12:34 schrieb Torstein Fjermestad <tfjer... at gmail.com>:
> 
> Dear all, 
> 
> First some background for my question:
> I got computing hours on a cluster with GPUs. I did some tests with single point calculations, and I found that linear scaling SCF ran about 5 times faster than "normal" SCF for my system on that cluster. The total energy between SCF and LS_SCF differed only by about 0.04 kJ mol-1; and I therefore found the results encouraging. 
> 
> I then went on to compare LS_SCF and "normal" SCF for geometry optimizations on a machine without GPUs. I did three tests:
> Test 1: Single point calculation
> Test 2: Geometry optimization starting from the geometry in Test 1
> Test 3: Geometry optimization starting from the optimized geometry in Test 2
> 
> I used the following keywords in the LS_SCF section. 
> 
> &LS_SCF
>   EPS_FILTER 1.0E-7
>   EPS_SCF    1.0E-7
> &END
> 
> At the beginning of the attached output files the complete input is echoed. 
> 
> I now describe the results of the tests.
> 
> Test 1: Single point calculation. The total energy differs by 0.05 kJ mol-1
> 
> entry
> Total energy/ Ha
> wall time / s
> LS_SCF?
> 1
> -3499.00767
> 309
> yes
> 2
> -3499.00768
> 380
> no
> 
> 
> Test 2: Geometry optimization starting from the geometry in Test 1. SCF_GUESS ATOMIC is used 
> 
> entry
> Total energy, first geom / Ha
> max. grad of first step
> # geometry steps
> Total energy, optim geom / Ha
> wall time, s
> wall time / geom. step, s
> LS_SCF?
> 1
> -3499.00767
> 0.03493
> 54
> Did not converge within the requested wall time
> 7260 a
> 134
> yes
> 2
> -3499.00769
> 0.03613
> 123
> -3499.11153
> 4386
> 36
> no
> a Requested wall time in submit script
> 
> In Test 2, the wall time per geometry step is much longer when LS_SCF is used than when "normal" SCF is used. This is in spite of Test 1 showing that LS_SCF is notably faster for a single point calculation. 
> Am I doing something wrong here?
> Is the start guess of the wavefunction at each geometry step perhaps not adequate in the case of LS_SCF?
> How should I change the LS_SCF parameters in order to improve the calculation?
> 
> Test 3: Re-optimization of the optimized structure in Test 2 (entry 2). SCF_GUESS ATOMIC is used 
>  
> entry
> Total energy, first geom / Ha
> max.grad of first step
> # geometry steps
> Total energy, optim geom / Ha
> wall time
> wall time / geom step
> LS_SCF?
> 1
> -3499.11150
> 0.00016
> 1
> -3499.11153
> 396
> 396
> no
> 2
> -3499.11147
> 0.00183
> 19
> Did not converge within the requested wall time
> 7260a
> 382
> yes
> a Requested wall time in submit script
> 
> Not unexpectedly, in Test 3,  the geometry optimization with "normal" SCF converges after 1 geometry step. 
> However, the geometry optimization with LS_SCF did not converge within two hours and took only 19 geometry steps.
> I see that the max. gradient of the first geometry step is much higher in the case of LS_SCF than in the case of "normal" SCF. 
> Are there some LS_SCF parameters I should adjust to check if the gradient has converged?
> 
> I would really appreciate help in this matter, because in the current situation, I am not able to use LS_SCF for geometry optimizations. 
> 
> Thanks and regards,
> Torstein Fjermestad
> 
>   
> 
>  
> 
> 
> 
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==============================
Thomas D. Kühne
Dynamics of Condensed Matter
Chair of Theoretical Chemistry
University of Paderborn
Warburger Str. 100
D-33098 Paderborn
Germany
tdku... at mail.upb.de
+49/(0)5251/60-5726

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