In this exercise, you will perform geometry optimization using DFT.

In the previous exercises we initially specified all parameters – pseudopotential and basis set coefficients as well as atom coordinates – in the input file. Later we used the pseudpotentials and basis sets from a file provided by CP2K.

Now we go further and also factor out the atomic structure to make it easier to automate different calculations for the same structure or the same calculation for different structures. The format used for this is the same you will get for trajectories for example.

First create two files with (different) coordinates for Ethane C2H8 (do not confuse with Ethene C2H6 from before):

ethane1.xyz

       8

C     0.750           0.000           0.000
C    -0.750           0.000           0.000
H    -1.050           0.000          -0.850
H    -1.050           0.736           0.425
H    -1.050          -0.736           0.425
H     1.050           0.000          -0.850
H     1.050           0.736           0.425
H     1.050          -0.736           0.425

ethane2.xyz

       8

C     0.750           0.000           0.000
C    -0.750           0.000           0.000
H    -1.050           0.000           0.850
H    -1.050           0.736          -0.425
H    -1.050          -0.736          -0.425
H     1.050           0.000          -0.850
H     1.050           0.736           0.425
H     1.050          -0.736           0.425

The input file looks almost the same as the one for the previous calculations:

ethane.inp

&GLOBAL
  PROJECT ethane
  RUN_TYPE ENERGY
  PRINT_LEVEL MEDIUM
&END GLOBAL

&FORCE_EVAL
  METHOD Quickstep              ! Electronic structure method (DFT,...)
  &DFT
    BASIS_SET_FILE_NAME  BASIS_MOLOPT
    POTENTIAL_FILE_NAME  POTENTIAL

    &POISSON                    ! Solver requested for non periodic calculations
      PERIODIC NONE
      PSOLVER  WAVELET          ! Type of solver
    &END POISSON
    &SCF                        ! Parameters controlling the convergence of the scf. This section should not be changed. 
      SCF_GUESS ATOMIC
      EPS_SCF 1.0E-6
      MAX_SCF 300
    &END SCF
    &XC                        ! Parametes needed to compute the electronic exchange potential 
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
    &END XC
  &END DFT

  &SUBSYS
    &CELL
      ABC 10 10 10
      PERIODIC NONE              ! Non periodic calculations. That's why the POISSON section is needed 
    &END CELL
    &TOPOLOGY                    ! Section used to center the atomic coordinates in the given box. Useful for big molecules
      &CENTER_COORDINATES
      &END
      COORD_FILE_FORMAT xyz
      COORD_FILE_NAME  ./ethane1.xyz
    &END
    &KIND H
      ELEMENT H
      BASIS_SET DZVP-MOLOPT-GTH
      POTENTIAL GTH-PBE-q1
    &END KIND
    &KIND C
      ELEMENT C
      BASIS_SET DZVP-MOLOPT-GTH
      POTENTIAL GTH-PBE-q4
    &END KIND
  &END SUBSYS
&END FORCE_EVAL

and should give the following energy once you run it:

ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):              -14.746153797151329