Question on exercises:2016_summer_school:geometry_and_cell_optimization

[Chris K. Lee]

Dear all CP2K users,


I'm doing some exercises by following 
"exercises:2016_summer_school:geometry_and_cell_optimization(
https://www.cp2k.org/exercises:2016_summer_school:geometry_and_cell_optimization
)".

What I want to know from this optimazation calculation is the functional 
that fits with the experimental data.

Now here are some questions.

1.
On the example page, there are 3steps.
1) Geometry optimize with Fist(MM Force Field) with each "NREP" for 
"MULTIPLE_UNIT_CELL ${NREP} ${NREP} ${NREP}"
2) Energy calculation with QS(DFT) with each "SCALING_FACTOR" for "ABC 
5.620*${SCALE_FACTOR} 5.620*${SCALE_FACTOR} 5.620*${SCALE_FACTOR}"
3) Cell optimization with QS(DFT)

>From the results, 1) shows no big defferences with 
MULTIPLE_UNIT_CELL. Should I do  this?
Would doing it with QS(DFT) not with Fist(MM Force Field) works?

I just used the input on the page and fixed it to do the 3) CELL_OPT 
calculation. It contains the KEEP_SYMMETRY option.
But the result shows that the length of the each nearest atoms are not 
equal.
What happened? Did I do something wrong? (input and output files are 
attached)

>From 2) I can get the proper scaleing factor by caculating energy of the 
unitcell with various lattice parameter.
But I'm not sure that this scaled structure is same as the optimized 
structure because of the bad results of 3).
How can I check it?



2.
I tried with 2) Energy calculation and 3) Cell optimization with both 
optimizer BFGS and LBFGS.
>From the output, BFGS and LBFGS run times were very similar.
Does optimizer have no effects on calculating energy and cell optimization?
Followings are the runtime of the Energy calculation.
----------------------------------------------------------------------------------------------------------------------------
OPTIMIZER : BFGS, NREP : 1, SCALE_FACTOR : 1, CUTOFF : 400
  **** **** ******  **  PROGRAM STARTED AT               2017-09-25 
15:28:03.704
  **** **** ******  **  PROGRAM ENDED AT                 2017-09-25 
15:28:13.963
   0:10
OPTIMIZER : BFGS, NREP : 2, SCALE_FACTOR : 1, CUTOFF : 400
  **** **** ******  **  PROGRAM STARTED AT               2017-09-25 
15:28:21.649
  **** **** ******  **  PROGRAM ENDED AT                 2017-09-25 
15:29:04.595
   0:37
OPTIMIZER : BFGS, NREP : 3, SCALE_FACTOR : 1, CUTOFF : 400
  **** **** ******  **  PROGRAM STARTED AT               2017-09-25 
15:29:13.594
  **** **** ******  **  PROGRAM ENDED AT                 2017-09-25 
15:32:48.711
   3:35
OPTIMIZER : BFGS, NREP : 4, SCALE_FACTOR : 1, CUTOFF : 400
  **** **** ******  **  PROGRAM STARTED AT               2017-09-25 
15:33:49.742
  **** **** ******  **  PROGRAM ENDED AT                 2017-09-25 
15:47:38.693
   13:89
OPTIMIZER : LBFGS, NREP : 1, SCALE_FACTOR : 1, CUTOFF : 400
  **** **** ******  **  PROGRAM STARTED AT               2017-09-25 
16:15:59.167
  **** **** ******  **  PROGRAM ENDED AT                 2017-09-25 
16:16:11.632
   0:12
OPTIMIZER : LBFGS, NREP : 2, SCALE_FACTOR : 1, CUTOFF : 400
  **** **** ******  **  PROGRAM STARTED AT               2017-09-25 
16:16:14.969
  **** **** ******  **  PROGRAM ENDED AT                 2017-09-25 
16:17:20.282
   1:06
OPTIMIZER : LBFGS, NREP : 3, SCALE_FACTOR : 1, CUTOFF : 400 
  **** **** ******  **  PROGRAM STARTED AT               2017-09-25 
16:20:41.212
  **** **** ******  **  PROGRAM ENDED AT                 2017-09-25 
16:24:30.740
   3:49
OPTIMIZER : LBFGS, NREP : 3, SCALE_FACTOR : 1, CUTOFF : 400
  **** **** ******  **  PROGRAM STARTED AT               2017-09-25 
16:25:31.836
  **** **** ******  **  PROGRAM ENDED AT                 2017-09-25 
16:39:20.152
   13:49
----------------------------------------------------------------------------------------------------------------------------

3. Can I calculate the bandgap of the bulk material  from the unitcell 
information with CP2K?
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