# Example: Raman: NH3¶

Download Freq_NH3_RAMAN.run

Summary:

• Analytical frequencies with subsequent calculation of Raman intensities in a range
• Numerical frequencies including all Raman intensities

Raman Intensities for Selected Frequencies

The RamanRange keyword can be used to calculate Raman intensities for a range of frequencies only. Using this option is a fast alternative for the existing method of calculating Raman intensities, which is described in the second part of this example.

Two values defining an interval of frequencies to calculate the Raman intensities for. The Raman intensities are calculated by numerical differentiation of the polarizability tensor. Only frequencies frequencies withing the interval that are known to be Raman-active will be included.

$ADFBIN/adf <<eor title NH3 frequencies and calculation of Raman intensities in the range 0-2000 cm-1 atoms N 0.0000 0.0000 0.0000 H 0.4729 0.8190 0.3821 H -0.9457 0.0000 0.3821 H 0.4729 -0.8190 0.3821 end Basis Type TZP Core Small End AnalyticalFreq end thermo T=300,400 BeckeGrid Quality good End end input eor mv TAPE21 NH3_freqs.t21$ADFBIN/adf <<eor
title NH3 Raman intensities in the range 0-2000 cm-1
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
Restart NH3_freqs.t21
Fragments
H t21.H
N t21.N
End
RamanRange 0.0 2000.0
thermo  T=300,400
BeckeGrid
Quality good
End
end input
eor


Raman Intensities for All Frequencies

Raman scattering intensities and depolarization ratios for all molecular vibrations at a certain laser frequency can be calculated in a single run. The run type must be Frequencies and the RESPONSE key is used to specify that Raman intensities are computed.

In this example the static Raman scattering is calculated (ω = 0). This type of calculation is very similar to an IR intensity calculation. In fact, all IR output is automatically generated as well. At all distorted geometries the dipole polarizability tensor is calculated. This is very time-consuming and is only feasible for small molecules.

\$ADFBIN/adf <<eor
title NH3 frequencies with Raman intensities
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
H t21.H
N t21.N
End
geometry
frequencies
end
response
raman
end
thermo  T=300,400
BeckeGrid
Quality good
End
end input
eor