NH₃: Raman

Sample directory: adf/Freq_NH3_RAMAN/

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 (available since ADF2007.01) 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 polatizability tensor. Only frequencies frequencies withing the interval that are known to be Raman-active will be included.

$ADFBIN/adf <<eor
title NH3 frequencies with subsequent 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
integration  5.0
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
integration  5.0
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 
integration  5.0
end input
eor