One advantage of the dynamic calculations is that any effects of temperature can be explicitly included in the calculation. Figure compares the absorption spectra of Form I calculated at 88 and 300 K using super-cell SCI8. The Figure shows that in the low frequency regime the high temperature absorption peaks are shifted to lower frequency because of the larger cell size. This effect is noticeable up to about 1700 cm -1 . Apart from this systematic effect, the spectra up to 1700 cm -1 are very similar but with a broadening of the high temperature absorption peaks.