Force fields

From the discussion above it should be obvious that the accuracy of any molecular mechanics method is entirely dependent on the quality of the parameterization used. In theory one could parameterize specifically for each simulation that is to be run but this would be extremely time-consuming and would also make the parameters non-transferable. Instead, in order to preserve the transferability of the force field one attempts to minimize the number of parameters by reducing the system to a set of building blocks. For example, in proteins this is typically the set of individual amino acid residues.

There are a large number of different force fields that have been developed over the years and all have their advantages and disadvantages. For example, the CHARMM force fields include charmm19 (15), charmm22 (27), charmm27 (28), and AMBER force fields include FF94 (6), FF96 (29), FF99 (30), FF99SB (31), FF03 (32, 33). A comprehensive review of the various force fields is beyond the scope of this chapter. For further information the reader is encouraged to read the various papers referring to each force field. In line with the topic of this book, which is the study of cellulose, we will concentrate our discussion on the force fields available for carbohydrates.