Time-varying calculations, spectral function

All of these direct NOE penalty functions have several features in common. First, they are all, in principle, more correct than refinement against calculated distances. Unfortunately, they vary from moderately to extremely costly in terms of CPU time. Each implementation also raises the question of the nature of the spectral density function used to model the molecule s motions. In each case, except that of Baleja et al.,66 isotropic motion was assumed, although all the methods could be readily adapted to use more elaborate spectral density functions. As experience with these methods accumulates, it should become clear when the extra computational time is worth investing and what the effects of different motional models are. 

Fig. 10.10 Absorption spectral lineshapes calculated as the Fourier transform of the Kubo relaxation function <)> (). (A) (indicated in arbitrary time units) is varied, while a is fixed at 1 reciprocal time unit (B) is fixed at 1 time unit and a is varied as indicated. To use the full Fourier transform (Eq. 10.70), < (r) is treated as an even function of time (Fig. 10.1 lA)...

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