IR and Raman Spectroscopy
In ORCA you can perform the IR & Raman spectrums straight ahead, alongside with the
geometry optimization. ORCA will perform the Numerical Derivatives with the final geometry
of your optimization.
The Frequency Analysis also confirms that our geometry is a minimum. If all frequencies are
positive, then no matter which new geometry step the algorithm takes, the energy will increase.
If you are a begginer you can check
this tutorial that drives you step by step to perform this calculation.
Lets perform a Frequency & Raman analysis for the isoprene molecule.
Instructions
- Build the molecule in wxmacmolplt.
- Perform the Numerical frequency analysis or the analytical frequencies,
with the NumFreq or AnFreq keyword.
- Add the Raman analysis keywords (%elprop).
%elprop
The electric properties module was implemented to calculate the first order
(electric dipole and quadruple moments) and second order (polarizabilities).
Polar 1 Analytic calculation.
2 Numeric diff of dipole moments.
3 Fully numeric second derivatives.
Numerical differentiation requires a tight or verytight converged SCF.
[emma@pople]$ vi isoprene.inp
#IR & Raman Calculation
#Isoprene molecule
! RKS PBE TZVP
! PMODEL #Initial density guess
! XYZfile #Type of coordinates
! TightSCF #SCF convergence criteria
! PAL8 #Number of core processors
! Opt #Geometry optimization
! NumFreq #Numerical Derivatives
! NumFreq #Infra Red Spectrum.
%elprop #Electric Properties
Polar 1 #Raman Spectrum.
end
%method
Grid 2 #110 grid points for the SCF
FinalGrid 4 #302 grid points
end
#Type Charge Multiplicity
* xyz 0 1
C -0.26 -0.11 -0.00
C -1.36 -0.87 -0.00
C -2.69 -0.26 -0.00
C -3.84 -0.94 -0.00
C -1.28 -2.35 -0.00
H -0.30 0.98 -0.00
H 0.74 -0.54 -0.00
H -2.70 0.83 -0.00
H -3.89 -2.03 -0.00
H -4.81 -0.42 -0.00
H -0.22 -2.70 -0.00
H -1.79 -2.76 0.90
H -1.79 -2.76 -0.90
*
[emma@pople]$/path/to/orca isoprene.inp
Alternative for torque users
[emma@pople]$qsub orca_4.2.1.pbs