Very high forces on (experimentaly) relaxed geometries

Daniele Fontanari danielef... at gmail.com
Sun Nov 13 19:32:02 CET 2016


Dear CP2K users

I'm very new to the software and DFT in general.
Hope this is the right place to ask this question.

I'd like to use CP2K to find structures of solids through geometry 
optimization runs.
I thought that a good strategy for preliminary calculations was to take a 
known structure (a crystal whose atom positions are known) and run a 
geometry optimization on it.
My hope would be that it is possible to judge the "goodness" of the used 
parameters by finding a relaxed structure close to the experimental.

I tried to work with As2S3 (on a cell counting 8 atoms of As and 12 atoms 
of S). My first optimization run managed to decrease a lot the energy but 
completely destroyed the structure of the molecule, to understand what is 
going on I tried to compute the forces on the atoms in my experimental 
configuration and it appears that the total force is close to 0, the forces 
on almost all the atoms are close to 0 except on 2 couples As As and S S 
where there are enormous (but with 0 resultant) forces. Might this be an 
anomaly source of the issue? 

Is there someone that can help me? Did I use bad potentials/basis/xc 
functional? Not fine enough grids? bad scf algorithms for this system?

Thanks in advance.



Here it is the cp2k code, I tried to keep it simple, a thing might be 
useful to know is that without the OT method the SCF run oscillates and 
apparently doesn't converge.

 &GLOBAL
  PROJECT As2S3_forces_calc
  RUN_TYPE ENERGY_FORCE
  PRINT_LEVEL LOW
&END GLOBAL
&FORCE_EVAL
  METHOD QS
  &SUBSYS
    &CELL
      ABC 11.475 9.577 4.256
      ALPHA_BETA_GAMMA 90.0 90.68 90.0
    &END CELL
    &TOPOLOGY
      COORD_FILE_FORMAT XYZ
      COORD_FILE_NAME As2S3.xyz
    &END TOPOLOGY
    &KIND S
      BASIS_SET TZV2P-GTH
      POTENTIAL GTH-PADE
    &END KIND
    &KIND As
      BASIS_SET TZV2P-MOLOPT-SR-GTH
      POTENTIAL GTH-PADE
    &END KIND
  &END SUBSYS
  &DFT
    BASIS_SET_FILE_NAME BASIS_MOLOPT_UCL
    BASIS_SET_FILE_NAME GTH_BASIS_SETS
    POTENTIAL_FILE_NAME GTH_POTENTIALS
    &SCF
      SCF_GUESS RESTART
      MAX_SCF 500
      &OT .TRUE.
      &END OT
    &END SCF
    &XC
      &XC_FUNCTIONAL PADE
      &END XC_FUNCTIONAL
    &END XC
  &END DFT
  &PRINT
    &FORCES ON
    &END FORCES
 &END PRINT
&END FORCE_EVAL

MY_BASIS_SETS is generated by

$ cat GTH_BASIS_SETS BASIS_MOLOPT_UCL > MY_BASIS_SET

As2S3.xyz:
20
As2S3 (A,B,C)=(11.475 A, 9.577 A, 4.256 A) 
(alpha,beta,gamma)=(90.0°,90.68°,90.0°)
As     -2.87968     3.78519    -1.78703
As     -6.29671     8.38345     4.62715
As     -7.89374     4.70768     1.81738
As     -1.28266     7.46095     1.02274
As     -4.79404     4.29440     1.17991
As     -4.38236     7.87423     1.66021
As    -10.88155     5.01715    -0.01930
As      1.70516     7.15148     2.85942
S      -4.38840     2.75627    -0.40167
S      -4.78799     9.41236     3.24179
S      -9.07372     4.85434     3.77704
S      -0.10268     7.31429    -0.93692
S      -2.91319     3.98145     2.45383
S      -6.26321     8.18718     0.38629
S      -9.35548     3.43549     0.63482
S       0.17909     8.73314     2.20530
S      -0.92786     3.77410    -0.59081
S      -8.24854     8.39453     3.43094
S      -6.41721     2.99693     2.18326
S      -2.75919     9.17170     0.65686

the output (minus the SFC run and the timing informations) (look at atoms 
1-2 and 13-14!):
 DBCSR| Multiplication driver                                               
XSMM
 DBCSR| Multrec recursion 
limit                                              512
 DBCSR| Multiplication stack size                                           
1000
 DBCSR| Maximum elements for images                                    
UNLIMITED
 DBCSR| Multiplicative factor virtual 
images                                   1
 DBCSR| Randmat seed                                                    
12341313
 DBCSR| Multiplication size 
stacks                                             3
 DBCSR| Number of 3D layers                                               
SINGLE
 DBCSR| Use MPI memory 
allocation                                              T
 DBCSR| Use RMA 
algorithm                                                      F
 DBCSR| Use Communication 
thread                                               T
 DBCSR| Communication thread 
load                                             87


  **** **** ******  **  PROGRAM STARTED AT               2016-11-13 
18:55:20.125
 ***** ** ***  *** **   PROGRAM STARTED ON                pinco.pallino
 **    ****   ******    PROGRAM STARTED BY                              
fontanar
 ***** **    ** ** **   PROGRAM PROCESS ID                                 
92218
  **** **  *******  **  PROGRAM STARTED IN /home/fontanar/

 CP2K| version string:                    CP2K version 5.0 (Development 
Version)
 CP2K| source code revision 
number:                                             
 CP2K| cp2kflags: libint fftw3 libxc parallel mpi3 scalapack libxsmm 
libgrid lib
 CP2K|            deriv_max_am1=6 libint_max_am=8
 CP2K| is freely available from                            
https://www.cp2k.org/
 CP2K| Program compiled at                        sam. nov.  5 22:37:09 CET 
2016
 CP2K| Program compiled on                                pinco.pallino
 CP2K| Program compiled for                                            impi
 CP2K| Data directory path                              
/home/fontanar/cp2k/data
 CP2K| Input file name                                          
As2S3_forces.inp
...
...
...
  Electronic density on regular grids:       -111.9999999385        
0.0000000615
  Core density on regular grids:              111.9999999829       
-0.0000000171
  Total charge density on r-space grids:        0.0000000444
  Total charge density g-space grids:           0.0000000444

  Overlap energy of the core charge distribution:              
92.65065405538122
  Self energy of the core charge distribution:               
-398.65263980352455
  Core Hamiltonian energy:                                    
105.34301297451202
  Hartree energy:                                             
196.75976380751200
  Exchange-correlation energy:                                
-41.98461449052979

  Total energy:                                               
-45.88382345664910

 ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):              
-45.883823518851351


 ATOMIC FORCES in [a.u.]

 # Atom   Kind   Element          X              Y              Z
      1      1      As        -18.30244796  -211.32223506    15.97738109
      2      1      As         18.30955215   211.29826724   -15.97476790
      3      1      As          0.03033974    -0.01535037    -0.02243601
      4      1      As         -0.03033573     0.01527827     0.02246948
      5      1      As         -0.06302510    -0.01399788    -0.06420679
      6      1      As          0.06288169     0.01397371     0.06420477
      7      1      As         -0.14318658     0.03752386     0.05230394
      8      1      As          0.14341018    -0.03742549    -0.05230464
      9      2      S          -0.04378316    -0.00438881     0.05507047
     10      2      S           0.04393888     0.00437103    -0.05527078
     11      2      S           0.15237734     0.06345576    -0.07781696
     12      2      S          -0.15250573    -0.06340104     0.07801514
     13      2      S          18.35579677   211.32485524   -15.99099261
     14      2      S         -18.36294583  -211.30098802    15.98856882
     15      2      S          -0.00508091    -0.11845479     0.09971522
     16      2      S           0.00502481     0.11846616    -0.09985495
     17      2      S           0.00456838    -0.00974499     0.01222899
     18      2      S          -0.00470629     0.00972000    -0.01233881
     19      2      S           0.00523795     0.02733833    -0.00734223
     20      2      S          -0.00512153    -0.02726010     0.00737305
 SUM OF ATOMIC FORCES          -0.00001092     0.00000307    
-0.00000070     0.00001136
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