The input file is shown below:

&GLOBAL
  PROJECT Si_bulk8
  RUN_TYPE ENERGY_FORCE
  PRINT_LEVEL LOW
&END GLOBAL
&FORCE_EVAL
  METHOD Quickstep
  &SUBSYS
    &KIND Si
      ELEMENT   Si
      BASIS_SET DZVP-GTH-PADE
      POTENTIAL GTH-PADE-q4
    &END KIND
    &CELL
      A     5.430697500    0.000000000    0.000000000
      B     0.000000000    5.430697500    0.000000000
      C     0.000000000    0.000000000    5.430697500
    &END CELL
    &COORD
      Si    0.000000000    0.000000000    0.000000000
      Si    0.000000000    2.715348700    2.715348700
      Si    2.715348700    2.715348700    0.000000000
      Si    2.715348700    0.000000000    2.715348700
      Si    4.073023100    1.357674400    4.073023100
      Si    1.357674400    1.357674400    1.357674400
      Si    1.357674400    4.073023100    4.073023100
      Si    4.073023100    4.073023100    1.357674400
    &END COORD
  &END SUBSYS
  &DFT
    BASIS_SET_FILE_NAME  BASIS_SET
    POTENTIAL_FILE_NAME  GTH_POTENTIALS
    &QS
      EPS_DEFAULT 1.0E-10
    &END QS
    &MGRID
      NGRIDS 4
      CUTOFF 300
      REL_CUTOFF 60
    &END MGRID
    &XC
      &XC_FUNCTIONAL PADE
      &END XC_FUNCTIONAL
    &END XC
    &SCF
      SCF_GUESS ATOMIC
      EPS_SCF 1.0E-7
      MAX_SCF 300
      &DIAGONALIZATION  ON
        ALGORITHM STANDARD
      &END DIAGONALIZATION
      &MIXING  T
        METHOD BROYDEN_MIXING
        ALPHA 0.4
        NBROYDEN 8
      &END MIXING
    &END SCF
  &END DFT
  &PRINT
    &FORCES ON
    &END FORCES
  &END PRINT
&END FORCE_EVAL

The main sections in the input file are:

• ''GLOBAL'': contains general options for the CP2K run, such as the name of the job, the type of run etc.
• ''FORCE_EVAL'': contains all parameters associated with the evaluation of forces on atoms, this includes the initial atomic coordinates.

We look at each section in detail. The GLOBAL section in Si_bulk8.inp is presented below:

&GLOBAL
  PROJECT Si_bulk8
  RUN_TYPE ENERGY_FORCE
  PRINT_LEVEL LOW
&END GLOBAL

We will be doing a static energy and force calculation, in this case, we must set ''RUNTYPE'' to ENERGY_FORCE. Keyword ''PROJECT'' is an alias for PROJECT_NAME, which sets the root-name of the calculation, in this case Si_bulk8. Any output files automatically generated by CP2K will have the name prefixed by Si_bulk8. ''PRINT_LEVEL'' controls the default verbosity of the main output of CP2K, in this example, it is set to “low”. The verbosity of the output can be fine-tuned by overriding this setting in each individual subsection of the input.

We now explain the section FORCE_EVAL line-by-line.

METHOD Quickstep

The keyword ''METHOD'' chooses the method for evaluating the forces on atoms to QUICKSTEP, i.e. Density Functional Theory using the Gaussian and Planewaves (GPW) method.

&FORCE_EVAL                           ! This section defines method for calculating energy and forces
 
   METHOD Quickstep                   ! Electronic structure method (DFT,...)
   &DFT
      &POISSON                        ! Solver requested for non periodic calculations
         PERIODIC NONE
         PSOLVER  WAVELET             ! Type of solver
      &END POISSON
      &QS                             ! Parameters needed to set up the Quickstep framework
         METHOD GAPW                  ! Method: gaussian and augmented plane waves
      &END QS
 
      &XC                             ! Parametes needed to compute the electronic exchange potential
         &XC_FUNCTIONAL NONE          ! No xc functional
         &END XC_FUNCTIONAL
         &HF                          ! Hartree Fock exchange. In this case is 100% (no fraction specified).
            &SCREENING                ! Screening of the electronic repulsion up to the given threshold.
               EPS_SCHWARZ 1.0E-10    ! Threshold specification
            &END SCREENING
         &END HF
      &END XC
   &END DFT
 
 
   &SUBSYS                            ! This section defines the system
      &CELL                           ! Unit cell set up
         PERIODIC NONE                ! Non periodic calculation
         ABC 10 10 10                 ! Lengths of the cell vectors A, B, and C
      &END CELL
      &COORD                          ! This section specify all the atoms and their coordinates
          H                   2.468   3.488   4.000
          C                   3.534   3.516   4.000
          C                   4.715   3.514   4.000
          H                   5.782   3.482   4.000
      &END COORD
      &TOPOLOGY
          &CENTER_COORDINATES
          &END
      &END TOPOLOGY
 
      &KIND H                                      ! potential and basis for H
         &BASIS
           3
     1  0  0  3  1
            12.25200000          0.02282200
             1.86870000          0.15564000
             0.41821000          0.48898000
     1  0  0  1  1
             0.10610000          1.00000000
     1  1  1  1  1
             1.00000000          1.00000000
         &END
         POTENTIAL ALL
         &POTENTIAL
          1    0    0
          0.20000000    0
         &END
      &END KIND
      &KIND C                         ! potential and basis for C
         &BASIS
            5
     1  0  0  6  2
          1252.60000000          0.00557360          0.00000000
           188.57000000          0.04149600         -0.00027440
            42.83900000          0.18263000         -0.00255830
            11.81800000          0.46129000         -0.03337500
             3.55670000          0.44931000         -0.08730500
             0.54258000          0.00000000          0.53415000
     1  0  0  1  1
             0.16058000          1.00000000
     1  1  1  3  1
             9.14260000          0.04449900
             1.92980000          0.23108000
             0.52522000          0.51227000
     1  1  1  1  1
             0.13608000          1.00000000
     1  2  2  1  1
             0.80000000          1.00000000
         &END
         POTENTIAL ALL
         &POTENTIAL
            4    2    0
            0.34883045    0
         &END
      &END KIND
   &END SUBSYS
&END FORCE_EVAL                     ! This section defines method for calculating energy and forces
 
&GLOBAL                             ! Section with general information regarding which kind of simulation to perform an parameters for the whole PROGRAM
   PRINT_LEVEL LOW                  ! Global print level
   PROJECT c2h4                     ! Name of the project. This word will appear as part of a name of all ouput files (except main ouput file, specified with -o option)
   RUN_TYPE GEO_OPT                 ! Geometry optimization
&END GLOBAL