Hartree potential that may serve as an input for the PPM can be produced by various DFT codes. A slab calculations are necessary for a creation of the Hartree potential. The calculated system should be in the lower part of the unit cell, but z coordinates of the top-most layer has to be above zero! At least 10 Ǎ of vacuum above a slab geometry has to be used. 15-20 Ă of Vacuum are recommended. Here we show examples how to produce a hartree potential, for couple of DFT codes:

== Fireball ==

A __fireball.in__ for creation of an __fftpot.xsf__ file with Hartree potential with using a McWEDA functional should look like:

  &OPTION
  basisfile =     'answer.bas'
  lvsfile =       'input.lvs'
  kptpreference = 'input.kpts'
  nstepf     = 1
  icluster   = 0
  itdse      = 0
  iqout      = 1
  ifixcharge = 1     ! 0 if you don't have pre-calculated atomic charges in CHARGES
  iquench    = -1
  &END
  
  &OUTPUT
  iwrtxsf = 1   ! print the important file
  iwrtden = 1   ! print the important file
  &END
  
  &MESH
  ifixg0 = 1            ! 
  g0     = 0.0,0.0,0.0  ! do not shift the position of atoms in fftpot.xsf with respect to the answer.bas
  Ecut = 300.0d0        ! not really necessary, but gives grid sampling approximately 100 pm.
  &END

A __fireball.in__ file for calculations with XC on a grid computations:

  &OPTION
  basisfile     = 'answer.bas'
  lvsfile       = 'input.lvs'
  kptpreference = 'samplek.kpts'
  nstepf     = 1
  icluster   = 0
  itdse      = 0
  iqout      = 1
  ifixcharge = 0
  dt         = 0.5
  iquench    = -1
  iks        = 1
  imcweda    = 0
  idogs      = 0
  bmix       = 0.05
  &END
  
  &OUTPUT
  iwrtxsf = 1   ! print the important file
  iwrtden = 1   ! print the important file
  &END
  
  &MESH
  ifixg0 = 1            ! 
  g0     = 0.0,0.0,0.0  ! do not shift the position of atoms in fftpot.xsf with respect to the answer.bas
  Ecut = 300.0d0        ! not really necessary, but gives grid sampling approximately 100 pm.
  &END

== VASP  ==

[[http://www.vasp.at/]]

A __LOCPOT__ file containing the Hartree potential is produced during standart //VASP// run. One just have to care about a dipole correction (if necessary). The __LOCPOT__ file has to be convert into an *.xsf file, eg. via [[http://theory.chm.tu-dresden.de/~jk/software.html]]

== FHI-AIMS ==


[[http://aimsclub.fhi-berlin.mpg.de/]]

Add following sequention into your __control.in__ file:

  output cube hartree_potential
    cube origin lx ly lz

where lx, ly & lz are shifting the output cube file so the written grid would be at the beginning of the Cartesian system. PPM can now read geometry from a cube file created by //FHI-AIMS// and shift it according to the shift of the cube cell; however for good run of the PPM calculation at least lz has to be properly specified. l = length of lattice vector / 2 - 0.05; But proper shift is used only, when the lattice vector follows some Cartesian direction.