! si_bulk8_energy.inp - single point of bulk Si, 8-atom conventional cubic cell
! Tutorial: CP2K chapter 2, section 10.  Works with CP2K 2023.x - 2026.2.
!
! Gamma point only (default):
!   rm -f si8_k0.out; cp2k.ssmp -i si_bulk8_energy.inp -o si8_k0.out
! Monkhorst-Pack NK x NK x NK mesh, selected from the command line:
!   rm -f si8_k4.out; cp2k.ssmp -E NK=4 -i si_bulk8_energy.inp -o si8_k4.out
!
! Diagonalization + smearing is used (and not OT) because OT does not support
! k-points in CP2K <= 2026.2.

&GLOBAL
  PROJECT si8_k${NK-0}
  RUN_TYPE ENERGY
  PRINT_LEVEL MEDIUM
&END GLOBAL

&FORCE_EVAL
  METHOD QS
  &DFT
    BASIS_SET_FILE_NAME BASIS_MOLOPT
    POTENTIAL_FILE_NAME GTH_POTENTIALS
    &MGRID
      CUTOFF 300
      REL_CUTOFF 50
    &END MGRID
    &QS
      EPS_DEFAULT 1.0E-10
    &END QS
    ! The KPOINTS section is only read when NK is set to a non-zero value.
    @IF ${NK-0} /= 0
    &KPOINTS
      SCHEME MONKHORST-PACK ${NK-0} ${NK-0} ${NK-0}
    &END KPOINTS
    @ENDIF
    &SCF
      SCF_GUESS ATOMIC
      EPS_SCF 1.0E-7
      MAX_SCF 100
      ADDED_MOS 20            ! empty bands needed by the smearing
      &DIAGONALIZATION
        ALGORITHM STANDARD
      &END DIAGONALIZATION
      &MIXING
        METHOD BROYDEN_MIXING
        ALPHA 0.4
        NBUFFER 8
      &END MIXING
      &SMEAR ON
        METHOD FERMI_DIRAC
        ELECTRONIC_TEMPERATURE [K] 300
      &END SMEAR
    &END SCF
    &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
    &END XC
  &END DFT
  &SUBSYS
    &CELL
      ! experimental lattice constant of Si at room temperature: 5.431 A
      ABC [angstrom] 5.431 5.431 5.431
      PERIODIC XYZ            ! default
    &END CELL
    &COORD
      SCALED T                ! fractional coordinates
      Si  0.00  0.00  0.00
      Si  0.00  0.50  0.50
      Si  0.50  0.00  0.50
      Si  0.50  0.50  0.00
      Si  0.25  0.25  0.25
      Si  0.25  0.75  0.75
      Si  0.75  0.25  0.75
      Si  0.75  0.75  0.25
    &END COORD
    &KIND Si
      BASIS_SET DZVP-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q4
    &END KIND
  &END SUBSYS
&END FORCE_EVAL