#! /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 VibrationalAnalysis
# task (using ModeRefinement) 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.
AMS_JOBNAME=NH3 $AMSBIN/ams <<eor
System
Symmetrize Yes
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
end
Task SinglePoint
Properties
NormalModes Yes
End
Engine ADF
title NH3 analytic frequencies
beckegrid quality=Good
basis
type TZP
core Small
end
EndEngine
eor
AMS_JOBNAME=ScanFreq $AMSBIN/ams <<eor
LoadSystem
File NH3.results/adf.rkf
End
LoadEngine NH3.results/adf.rkf
Task VibrationalAnalysis
VibrationalAnalysis
Type ModeRefinement
NormalModes
ModeFile NH3.results/adf.rkf
ModeSelect
FreqRange 0 4000
End
End
End
eor