Example: Rescan frequencies: NH3

Download Freq_NH3_Scan.run

#! /bin/sh

# Sometimes spurious imaginary frequencies are calculated where one would expect
# a very low (nearly zero) frequency. Most frequently this happens when there is
# a barrier-free rotation of, for example, methyl groups. The SCANFREQ keyword
# allows one to rescan calculated frequencies in order to find out if they were
# calculated accurately.

# In this example analytical frequencies are calculated. Next recalculation of
# certain NH3 frequencies are performed by scanning along normal modes from a
# restart file. In this calculation the frequencies are calculated numerically
# with finite displacements using symmetry.

$ADFBIN/adf <<eor
  title NH3 analytic frequencies 
  atoms
    N               0.0000    0.0000    0.0000
    H               0.4729    0.8190    0.3821
    H              -0.9457    0.0000    0.3821
    H               0.4729   -0.8190    0.3821
  end
  Basis
    Type TZP
    Core Small
  End
  AnalyticalFreq
  End
  BeckeGrid
    Quality verygood
  End
eor

mv TAPE21 NH3_anl.t21

$ADFBIN/adf <<eor
  title Re-calculate NH3 frequencies by scanning along normal modes from a restart file
  atoms
    N               0.0000    0.0000    0.0000
    H               0.4729    0.8190    0.3821
    H              -0.9457    0.0000    0.3821
    H               0.4729   -0.8190    0.3821
  end
  Fragments
    N t21.N
    H t21.H
  End
  ScanFreq 0 4000
  Restart 
    File NH3_anl.t21
  End
  BeckeGrid
    Quality verygood
  End
eor

mv TAPE21 NH3_symm2.t21