#! /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