[CP2K-user] Problem with geometry optimization using LS_SCF
Torstein Fjermestad
tfjer... at gmail.com
Mon May 25 10:34:25 UTC 2020
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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