PPT Slide
If we want to move beyond using these spectra as a
fingerprint and really interpret the bands in terms of
molecular structure then we need to be able to assign
all of the vibrations. Using density functional theory (DFT)
calculations we can obtain a good estimate of the
vibrations. However, it turns out the a major discrepancy
arises due to the failure of the harmonic approximation.
In the following, we illustrate the math behind the
harmonic approximation and we show pictures of DFT
calculations on adenine that illustrate the failure of the
harmonic approxmation for certain of the vibrational