# Example: Rescan frequencies: NH3¶

#! /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
End