Example: Asymptotically correct XC potentials: CO¶

#!/bin/sh


# For property calculations, XC potentials with asymptotically correct (-1/r)
# behavior outside the molecule, the results tend to be superior to regular LDA
# or GGA calculations. This is especially true for small molecules and for
# properties that depend heavily on the proper description of the outer region
# of the molecule. In the example, all-electron basis sets are used. This is
# mandatory for the SAOP potential.

# In the first example, excitation energies are calculated with the GRACLB
# potential. This potential requires one number as argument: the experimental
# ionization potential in atomic units. This number can be either based on an
# experimental value, or on previous GGA total energy calculations.


AMS_JOBNAME=GRACLB $AMSBIN/ams <<eor
System
  symmetrize
  atoms
     O  0             0   0
     C  1.128205364   0   0
  end
end

Task SinglePoint

Engine ADF
  title CO excitations grac potential
  beckegrid
    quality good
  end
  excitations
    lowest 10
    onlysing
  end
  basis
    core None
    type TZ2P
  end
  xc
    model GRACLB 0.515
  end
EndEngine

eor


# The same calculation with the SAOP XC potential would differ in the XC block
# only:


AMS_JOBNAME=SAOP $AMSBIN/ams <<eor
System
  symmetrize
  atoms
     O  0             0   0
     C  1.128205364   0   0
  end
end

Task SinglePoint

Engine ADF
  title CO excitations SAOP
  beckegrid
    quality good
  end
  excitations
    lowest 10
    onlysing
  end
  basis
    core None
    type TZ2P
  end
  xc
    model SAOP
  end
EndEngine

eor


# SAOP depends on the orbitals which makes it more expensive to evaluate than
# GRAC for large molecules, but is much easier to use, since it does not require
# an ionization potential parameter as input.