Limiting Factors and Computer Time Considerations

The simulation was based on the 5-state RIS model mainly because it is, at the moment, the best statistical description of atactic poly(propylene). It should be borne in mind, however, that the ab initio simulation technique is not restricted to RIS models. Any model with sufficient predictive power may be used as a basis for the simulation The conformational (or more generally geometric) statistics may be replaced by the results of a molecular dynamics or Monte Carlo study, or any other method. Within computer time limitations, the relevant geometries may be fed into Eq. 3.15 and used as a basis for the quantum chemistry calculations. 

The practical applicability of the method is limited both by physico-chemical 

The latter naturally depend to a large degree on the available computing 

The essential physical condition for a meaningful test of the simulation is an experimental spectrum that meets the assumptions of the simulation. The NMR lineshape should result from the inhomogeneous distribution of geometries and should not be distorted by experimental effects (motional broadening, insufficient proton decoupling, transversal relaxation, CP efficiency). Complete motional averaging (i.e. liquid-like behavior), however, can easily be taken into account. 

The direct electronic packing effects should be small. In polar systems or samples with hydrogen bonding, problems might occur. 

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