How to calculate vibrational spectra of organic molecules? I watched a ted talk (Luca Turin: The science of scent) and was wondering if anyone had any examples of how to calculate vibrational spectra of molecules (used as fragrances)?  Would love to figure out how he computed these charts.
The usual approach is:


Find the equilibrium geometry (within the Born-Oppenheimer app.).
Expand the energy in Taylor series till second order term. The first order will be 0 because of the minimum energy condition.
Include this expression in the Hamiltonian.
Generate a coordinate transformation to get normal coordinates.
Relate second order derivative of the potential energy with the force constant of Hook law (Using second order term we can identify it with a harmonic oscillator). Then get the harmonic frequencies.
The software employed should give also the intensity for each frequency.
Plot intensity vs. frequency/energy/wave length. You'll get only "points". To transform them to a continuous function you can use a Lorentzian like function.


Details can be found in most computational quantum chemistry books.