In this exercise, we are going to learn the basics of using CP2K by calculating the total energy, optimizing the geometry, and printing the projected density of states (PDOS) of a single H$_2$O molecule. We will also investigate how different parameters such as the DFT functional and basis sets affect the accuracy and duration of our calculations.

In the first part of the exercise, we will go through the input and steps needed to perform a single-point calculation of a water molecule. The first thing we need is to create an input file describing our system and choosing the methods we want to use. Below is a simple example input that we need.

water.inp

&GLOBAL
  PROJECT   h2o
  RUN_TYPE  ENERGY
  IOLEVEL   LOW
&END GLOBAL
&FORCE_EVAL
  METHOD QS
  &DFT
    BASIS_SET_FILE_NAME GTH_BASIS_SETS
    POTENTIAL_FILE_NAME GTH_POTENTIALS
    LSD 0
    &QS      
      EPS_DEFAULT 1.0E-10
    &END QS
    &SCF
      MAX_SCF    300
      EPS_SCF    1.0E-06
      SCF_GUESS  ATOMIC
      &MIXING
        METHOD  DIRECT_P_MIXING
        ALPHA   0.6
      &END MIXING
      &DIAGONALIZATION
	    ALGORITHM STANDARD
      &END DIAGONALIZATION       
    &END SCF
    &MGRID
      NGRIDS        4
      CUTOFF        300
      REL_CUTOFF    60
    &END
    &XC
      &XC_FUNCTIONAL BLYP
      &END XC_FUNCTIONAL
    &END XC
  &END DFT
  &SUBSYS
    &CELL
      ABC    15.0  15.0  15.0
      ANGLES 90.00 90.00 90.00
    &END CELL
    &COORD
      O  0 0 0
      H  0.7 0.7 0
      H -0.7 0.7 0
    &END COORD
    &KIND H                 
      BASIS_SET DZVP-GTH
      POTENTIAL GTH-BLYP-q1
    &END KIND
    &KIND O
      BASIS_SET DZVP-GTH
      POTENTIAL GTH-BLYP-q6
    &END KIND
    &PRINT
      &ATOMIC_COORDINATES
      &END
    &END PRINT 
  &END SUBSYS
&END FORCE_EVAL