[CP2K-user] [CP2K:18906] Incorrect optimized geometry using CELL_OPT

[Diego López]

Dear CP2K users,

I am kind of new using cp2k but I have been using the software fo a couple 
of months. I am trying to optimize both geometry and cell parameters of 
different semiconductor material but the obtained geometries are distorted 
compared with experimental data or relaxed geometries obtained using 
Quantum Espresso or VASP. 

My optimized geometries have a lack of symmetry compared with experimental 
data, i.e. the atoms that should be aligned in an especific axis tend to 
alternate the positions in the crystal, so my results are no compatible 
with the expected ones.

Which parameters should I change in my calculations? I tried lowering the 
EPS_SCF to increase accuracy, increasing the supercell and using larger 
basis sets but the result does not change. I attatch an example of input 
that I used for these calculations.

&GLOBAL
  PROJECT
  RUN_TYPE CELL_OPT
  PRINT_LEVEL MEDIUM
&END GLOBAL

&FORCE_EVAL
  METHOD Quickstep              ! Electronic structure method (DFT,...)
  STRESS_TENSOR ANALYTICAL
  &DFT
    BASIS_SET_FILE_NAME  BASIS_MOLOPT
    POTENTIAL_FILE_NAME  GTH_POTENTIALS
    MULTIPLICITY 301
    UKS
    &POISSON                    ! Solver requested for non periodic 
calculations
      PERIODIC XYZ
    &END POISSON
     &XC
      &XC_FUNCTIONAL PBE
       &PBE
        PARAMETRIZATION PBESOL
       &END
      &END XC_FUNCTIONAL
     &END XC
    &SCF
      SCF_GUESS ATOMIC
      MAX_SCF 40
      EPS_SCF 3E-06
      &OT
      PRECONDITIONER FULL_KINETIC
      MINIMIZER CG
      &END OT
      &OUTER_SCF
       MAX_SCF 320
       EPS_SCF 3E-06
      &END
    &END SCF
    &MGRID
      NGRIDS 4
      CUTOFF 550
      REL_CUTOFF 90
    &END MGRID
    &QS
      METHOD GPW
      EXTRAPOLATION ASPC
      EPS_DEFAULT 1E-014
    &END
  &END DFT
  &SUBSYS
    &CELL
      ABC 3.601367151 4.818258107 25.0
      ALPHA_BETA_GAMMA 90 90 90
      PERIODIC XYZ
      SYMMETRY ORTHORHOMBIC
      MULTIPLE_UNIT_CELL 5 5 1
    &END CELL
    &TOPOLOGY                    ! Section used to center the atomic 
coordinates in the given box. Useful for big molecules
      COORD_FILE_FORMAT xyz
      COORD_FILE_NAME  ./crsbr.xyz
      MULTIPLE_UNIT_CELL 5 5 1
    &END
    &KIND Cr
      ELEMENT Cr
      BASIS_SET SZV-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q14
      MAGNETIZATION 3.0
    &END KIND
    &KIND S
      ELEMENT S
      BASIS_SET SZV-MOLOPT-GTH
      POTENTIAL GTH-PBE-q6
    &END KIND
    &KIND Br
      ELEMENT Br
      BASIS_SET SZV-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q7
    &END KIND
  &END SUBSYS
&END FORCE_EVAL
&MOTION
  &CELL_OPT
    TYPE DIRECT_CELL_OPT
    MAX_ITER 200
    OPTIMIZER LBFGS
    KEEP_SYMMETRY
  &END CELL_OPT
&END MOTION

Thanks in advanced

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