[CP2K-user] BS setting for spin polarized calculation

[Jiapeng Liu]

Dear CP2K users,

I am performing a spin-polarized calculation of perovskite SrFeO3, which 
has been optimized using VASP in material project. According to the results 
shown here https://materialsproject.org/materials/mp-510624/, the material 
shows a magnetic moment of 4.17 \muB. I would like to reproduce the results 
using CP2K and the following are my input files for the calculation. For 
the BS section, I would like to simulate the Sr2+, Fe4+(3d4,4s0) high spin 
state, O2-. And the multiplicity is set as 2*total spin+1=65 as the 
simulation supercell is 2x2x2.

However, I noticed that in the output file, the total electrons in spin 1 
is 208 and 144 in spin 2 after Re-scaling. 
 Spin 1
 Re-scaling the density matrix to get the right number of electrons for 
spin 1
                  # Electrons              Trace(P)               Scaling 
factor
                          208               192.000                        
1.083
 Spin 2
 Re-scaling the density matrix to get the right number of electrons for 
spin 2
                  # Electrons              Trace(P)               Scaling 
factor
                          144               160.000                        
0.900

I am wondering why it is not 192 in spin 1 and 160 in spin 2. Am I correct 
in setting the multiplicity state? I am quite confused about this part. And 
my other question is how to accelerate the scf convergence, the results 
shown in the output seem to oscillate near the final energy for quite many 
steps. Can you help me with this, thank you for your help.


&GLOBAL
   PROJECT SrFeO3_bulk
   RUN_TYPE ENERGY
   PRINT_LEVEL MEDIUM
&END GLOBAL

&FORCE_EVAL
   METHOD Quickstep
   &DFT
      UKS    .TRUE.
      CHARGE  0
      MULTIPLICITY  65
!      RELAX_MULTIPLICITY  1
      BASIS_SET_FILE_NAME  BASIS_MOLOPT
      POTENTIAL_FILE_NAME  GTH_POTENTIALS
      &POISSON
         PERIODIC XYZ
      &END POISSON
      &QS
         EXTRAPOLATION USE_GUESS ! required for K-Point sampling
         METHOD GPW
      &END QS
      &MGRID
         NGRIDS 4
         CUTOFF 500
         REL_CUTOFF 60
      &END MGRID
      &SCF
         SCF_GUESS ATOMIC
         EPS_SCF 1.0E-6
         MAX_SCF 200
         ADDED_MOS 40
         &DIAGONALIZATION
            ALGORITHM STANDARD
            EPS_ADAPT 0.01
         &END DIAGONALIZATION
         &OUTER_SCF
            EPS_SCF 1.0E-5
            MAX_SCF 3
         &END OUTER_SCF
         &SMEAR  ON
            METHOD FERMI_DIRAC
            ELECTRONIC_TEMPERATURE [K] 500
         &END SMEAR
         &MIXING
            METHOD BROYDEN_MIXING
            ALPHA 0.4
            BETA  1.5
            NBROYDEN 8
         &END MIXING
      &END SCF
      &XC
         &XC_FUNCTIONAL PBE
         &END XC_FUNCTIONAL
      &END XC
      &KPOINTS
         SCHEME MONKHORST-PACK 4 4 4
!         WAVEFUNCTIONS REAL
         SYMMETRY .TRUE.
         FULL_GRID .FALSE.
         PARALLEL_GROUP_SIZE -1
      &END KPOINTS
   &END DFT
   &SUBSYS
      &CELL
         ABC [angstrom] 3.91181515 3.91181515 3.91181515
         PERIODIC XYZ
         MULTIPLE_UNIT_CELL 2 2 2
      &END CELL
      &TOPOLOGY
!         COORD_FILE_NAME  sfo_mp-510624.cif
!         COORD_FILE_FORMAT  CIF
         MULTIPLE_UNIT_CELL 2 2 2
      &END TOPOLOGY
      &COORD
         SCALED
         Sr  0.5  0.5  0.5
         Fe  0.0  0.0  0.0
         O   0.5  0.0  0.0
         O   0.0  0.5  0.0
         O   0.0  0.0  0.5
      &END
      &KIND Sr
         ELEMENT Sr
         BASIS_SET DZVP-MOLOPT-SR-GTH
         POTENTIAL GTH-PBE-q10
         &BS
           &ALPHA
             NEL -2
             L    0
             N    5
           &END ALPHA
           &BETA
             NEL -2
             L    0
             N    5
           &END BETA
         &END BS
      &END KIND
      &KIND Fe
         ELEMENT Fe
         BASIS_SET DZVP-MOLOPT-SR-GTH
         POTENTIAL GTH-PBE-q16
!         MAGNETIZATION 4
         &BS
           &ALPHA
             NEL -2   2
             L    0   2
             N    4   3
           &END ALPHA
           &BETA
             NEL -2  -6
             L    0   2
             N    4   3
           &END BETA
         &END BS
      &END KIND
      &KIND O
         ELEMENT O
         BASIS_SET DZVP-MOLOPT-SR-GTH
         POTENTIAL GTH-PBE-q6
         &BS
           &ALPHA
             NEL  2
             L    1
             N    2
           &END ALPHA
           &BETA
             NEL  2
             L    1
             N    2
           &END BETA
         &END BS
      &END KIND
   &END SUBSYS
&END FORCE_EVAL
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