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. The input keyword is as follows:

RAMANRANGE low high

low, high

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 within the interval that are known to be Raman-active will be included. This means that 2*N single-point TDDFT calculations will be performed, where N is the number of Raman-active frequencies within the range. Imaginary frequencies are specified using negative values, which is consistent with the notation adopted within ADF.

Main advantages of the method:

• Full symmetry at each displaced geometry is used, which does not only speeds the calculation up but
  also makes it more accurate.
• Only Raman-active modes are included in the calculation, which may save a lot of time for molecules
  with symmetry.
• There is no need to recalculate frequencies if you already have a t21 file with them as it can be used
  as a restart file.