#! /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