! rutile_kpoints.inp - rutile TiO2, 6-atom primitive cell, energy + forces WITH k-points
! Improved companion of input_file.inp (same structure, basis, pseudopotentials, PBE).
! Tutorial: CP2K chapter 2, section 11.  Works with CP2K 2023.x - 2026.2.
!
! The 6-atom cell is only 4.593 x 4.593 x 2.959 A: Gamma-only sampling (as in
! input_file.inp) is far from converged. Here a Monkhorst-Pack mesh is used.
! Because OT does not support k-points in CP2K <= 2026.2, standard
! diagonalization with Broyden density mixing is used instead.
!
!   rm -f rutile_k446.out; cp2k.psmp -i rutile_kpoints.inp -o rutile_k446.out
!   cp2k.psmp -E KX=3 -E KY=3 -E KZ=3 -i rutile_kpoints.inp -o rutile_k333.out
!
! Requires rutile.xyz (6 lines "El x y z", Angstrom, no header) in the same directory.

&GLOBAL
  PROJECT rutile_k${KX-4}${KY-4}${KZ-6}
  RUN_TYPE ENERGY_FORCE
  PRINT_LEVEL MEDIUM
&END GLOBAL

&FORCE_EVAL
  METHOD QS
  &PRINT
    &FORCES ON
    &END FORCES
  &END PRINT
  &DFT
    BASIS_SET_FILE_NAME BASIS_MOLOPT
    POTENTIAL_FILE_NAME GTH_POTENTIALS
    &MGRID
      CUTOFF 400
      REL_CUTOFF 60
    &END MGRID
    &QS
      EPS_DEFAULT 1.0E-12
    &END QS
    &KPOINTS
      ! reciprocal lengths: 1/a = 0.218 1/A, 1/c = 0.338 1/A -> use more points along c
      SCHEME MONKHORST-PACK ${KX-4} ${KY-4} ${KZ-6}
    &END KPOINTS
    &SCF
      SCF_GUESS ATOMIC
      EPS_SCF 1.0E-7
      MAX_SCF 100
      &DIAGONALIZATION
        ALGORITHM STANDARD
      &END DIAGONALIZATION
      &MIXING
        METHOD BROYDEN_MIXING
        ALPHA 0.3
        NBUFFER 8
      &END MIXING
    &END SCF
    &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
    &END XC
  &END DFT
  &SUBSYS
    &CELL
      ! room-temperature experiment: a = 4.594 A, c = 2.959 A, u = 0.305 (approx.)
      ABC [angstrom] 4.593 4.593 2.959
      PERIODIC XYZ
    &END CELL
    &COORD
@INCLUDE rutile.xyz
    &END COORD
    &KIND O
      BASIS_SET DZVP-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q6
    &END KIND
    &KIND Ti
      BASIS_SET DZVP-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q12   ! semicore: 3s2 3p6 3d2 4s2 = 12 electrons
    &END KIND
  &END SUBSYS
&END FORCE_EVAL