Is it possible to study/converge magnetic surfaces? repost..

Valerio Bellini valerio... at unimore.it
Mon Oct 24 17:37:30 CEST 2011


Dear all,
I am trying to simulate with CP2K-Quickstep a magnetic surface, in 
particular
a slab of 4 layers of Ni(111).
I have not manage to converge the system. Here are my considerations:

-) the two dimensional cell is not large (5x5), and I tried hexagonal 
and rectangular
two-dimensiional cells. Since no k-points are considered in CP2K, I know 
that
this cell is rather small, and in order to have converged properties one 
should
use a larger one.
-) I used the mixing/diagonalization options suggested for metallic 
surfaces
(recent message from Marcella Iannuzzi on the 4th October).
-) I tried to vary the ALPHA,BETA,NBROYDEN parameters. I also tried to use
direct mixing+DIIS scheme. Things did not change much.
-) I managed to converge the system only with OT scheme, but although I 
converge
the system up to 10-7, the results does not seem to me converged to the 
ground state,
since the magnetic moments of different atoms in the same layer are not 
the same,
while they should be due to symmetric reasons.

I made a step back and converged an isolated Ni(111) monolayer, and in that
case managed to converge with OT but also with standard 
diagonalization+broyden
mixing, and with the latter scheme I was able to reach always a 
converged system
in terms of equal magnetic moments for all the atoms.

I both case (ML and 4 layers slab) I set a multiplicity which is reasonable
considering the total moment in the cell that the system should acquire
(in case of the ML, I varied also the multiplicity and found the one 
giving the
ground state, while for the 4 layers slab I set it to a reasonable value,
could easily be it is not the ground state one).

My questions are:

1) Are there chances that increasing the two-dimensional cell dimensions,
convergence will be reached also for the slab?
Before trying I would like to have an opinion on that; in other words, 
could the dimension
of the two-dimensional cell be the responsible of the missing 
convergence with
diagonalization+broyden techniques?

2) Have anybody ever managed to converged a magnetic surface with this 
code?

Here is a typical input file I used:

&GLOBAL
   PROJECT  ./working
   RUN_TYPE ENERGY_FORCE
   PRINT_LEVEL MEDIUM
&END GLOBAL
&FORCE_EVAL
   METHOD Quickstep
&DFT
     BASIS_SET_FILE_NAME  ./BASIS_MOLOPT
     POTENTIAL_FILE_NAME  ./GTH_POTENTIALS
     RESTART_FILE_NAME ./working-RESTART.wfn
     LSD T
     MULTIPLICITY 71
&MGRID
       CUTOFF 500
       NGRIDS 5
&END MGRID
&QS
       EXTRAPOLATION PS
       EXTRAPOLATION_ORDER 3
&END QS
&SCF
       SCF_GUESS restart
       EPS_SCF 1.0E-7
       MAX_SCF 500
&OUTER_SCF ON
         MAX_SCF 20
         EPS_SCF  1.0E-7
&END OUTER_SCF
       ADDED_MOS 1000
&SMEAR ON
         METHOD FERMI_DIRAC
         ELECTRONIC_TEMPERATURE [K] 300
&END SMEAR
&DIAGONALIZATION ON
         ALGORITHM STANDARD
&END DIAGONALIZATION
&MIXING ON
         METHOD BROYDEN_MIXING
         ALPHA   0.05
         BETA    1.5
         NBROYDEN  8
&END MIXING
&END SCF
&XC
&VDW_POTENTIAL
         POTENTIAL_TYPE PAIR_POTENTIAL
&PAIR_POTENTIAL
           REFERENCE_FUNCTIONAL PBE
           TYPE DFTD3
           PARAMETER_FILE_NAME ./dftd3.dat
&END PAIR_POTENTIAL
&END VDW_POTENTIAL
&XC_FUNCTIONAL
&PBE
&END PBE
&END XC_FUNCTIONAL
&XC_GRID
&END XC_GRID
&END XC
&END DFT
&SUBSYS
&CELL
       PERIODIC XY
       ABC 12.45416482 12.45416482 40
       ANGLES 90 90 120
&END CELL
&COORD
Ni     0.000000     0.000000     7.797460
Ni    -1.245416     2.157125     7.797460
Ni    -2.490833     4.314249     7.797460
Ni     2.490833    -4.314249     7.797460
Ni     1.245416    -2.157125     7.797460
Ni     2.490833     0.000000     7.797460
Ni     1.245416     2.157125     7.797460
Ni     0.000000     4.314249     7.797460
Ni     4.981666    -4.314249     7.797460
Ni     3.736249    -2.157125     7.797460
Ni     4.981666     0.000000     7.797460
Ni     3.736249     2.157125     7.797460
Ni     2.490833     4.314249     7.797460
Ni     7.472499    -4.314249     7.797460
Ni     6.227082    -2.157125     7.797460
Ni    -4.981666     0.000000     7.797460
Ni    -6.227082     2.157125     7.797460
Ni    -7.472499     4.314249     7.797460
Ni    -2.490833    -4.314249     7.797460
Ni    -3.736249    -2.157125     7.797460
Ni    -2.490833     0.000000     7.797460
Ni    -3.736249     2.157125     7.797460
Ni    -4.981666     4.314249     7.797460
Ni     0.000000    -4.314249     7.797460
Ni    -1.245416    -2.157125     7.797460
Ni     0.000000     1.438083     9.831216
Ni    -1.245416     3.595208     9.831216
Ni     3.736250    -5.033291     9.831216
Ni     2.490833    -2.876166     9.831216
Ni     1.245417    -0.719042     9.831216
Ni     2.490833     1.438083     9.831216
Ni     1.245417     3.595208     9.831216
Ni     6.227082    -5.033291     9.831216
Ni     4.981666    -2.876166     9.831216
Ni     3.736250    -0.719042     9.831216
Ni     4.981666     1.438083     9.831216
Ni     3.736250     3.595208     9.831216
Ni     8.717915    -5.033291     9.831216
Ni     7.472499    -2.876166     9.831216
Ni     6.227082    -0.719042     9.831216
Ni    -4.981666     1.438083     9.831216
Ni    -6.227082     3.595208     9.831216
Ni    -1.245416    -5.033291     9.831216
Ni    -2.490833    -2.876166     9.831216
Ni    -3.736249    -0.719042     9.831216
Ni    -2.490833     1.438083     9.831216
Ni    -3.736249     3.595208     9.831216
Ni     1.245417    -5.033291     9.831216
Ni     0.000000    -2.876166     9.831216
Ni    -1.245416    -0.719042     9.831216
Ni     1.245416     0.719042    11.864973
Ni    -0.000000     2.876166    11.864973
Ni    -1.245417     5.033291    11.864973
Ni     3.736249    -3.595208    11.864973
Ni     2.490833    -1.438083    11.864973
Ni     3.736249     0.719042    11.864973
Ni     2.490833     2.876166    11.864973
Ni     1.245416     5.033291    11.864973
Ni     6.227082    -3.595208    11.864973
Ni     4.981666    -1.438083    11.864973
Ni    -6.227082     0.719042    11.864973
Ni    -7.472499     2.876166    11.864973
Ni    -8.717915     5.033291    11.864973
Ni    -3.736250    -3.595208    11.864973
Ni    -4.981666    -1.438083    11.864973
Ni    -3.736250     0.719042    11.864973
Ni    -4.981666     2.876166    11.864973
Ni    -6.227082     5.033291    11.864973
Ni    -1.245417    -3.595208    11.864973
Ni    -2.490833    -1.438083    11.864973
Ni    -1.245417     0.719042    11.864973
Ni    -2.490833     2.876166    11.864973
Ni    -3.736250     5.033291    11.864973
Ni     1.245416    -3.595208    11.864973
Ni    -0.000000    -1.438083    11.864973
Ni     0.000000     0.000000    13.898730
Ni    -1.245416     2.157125    13.898730
Ni    -2.490833     4.314249    13.898730
Ni     2.490833    -4.314249    13.898730
Ni     1.245416    -2.157125    13.898730
Ni     2.490833     0.000000    13.898730
Ni     1.245416     2.157125    13.898730
Ni     0.000000     4.314249    13.898730
Ni     4.981666    -4.314249    13.898730
Ni     3.736249    -2.157125    13.898730
Ni     4.981666     0.000000    13.898730
Ni     3.736249     2.157125    13.898730
Ni     2.490833     4.314249    13.898730
Ni     7.472499    -4.314249    13.898730
Ni     6.227082    -2.157125    13.898730
Ni    -4.981666     0.000000    13.898730
Ni    -6.227082     2.157125    13.898730
Ni    -7.472499     4.314249    13.898730
Ni    -2.490833    -4.314249    13.898730
Ni    -3.736249    -2.157125    13.898730
Ni    -2.490833     0.000000    13.898730
Ni    -3.736249     2.157125    13.898730
Ni    -4.981666     4.314249    13.898730
Ni     0.000000    -4.314249    13.898730
Ni    -1.245416    -2.157125    13.898730
&END COORD
&KIND Ni
       POTENTIAL GTH-PBE-q18
       BASIS_SET DZVP-MOLOPT-SR-GTH
&END KIND
&END SUBSYS
&END FORCE_EVAL






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