The ability of a force field to maintain the unit cell aspect ratios gives an early indication of whether the model is behaving correctly. As shown in the panels above, the unit cell volume is closely maintained near the experimental value throughout all simulations, but the individual unit cell dimensions drift away from their experimental values, particularly in simulations with the CHARMM22 and OPLS force fields. While the protein force field has the most influence over the evolution of the unit cell dimensions during each simulation, the water model also can have an effect; the three-point water models all give similar results, though some slight differences are apparent, when applied with the FF99SB or FF03 force fields. In contrast, the four-point TIP4P-2005 water model tends to give the poorest results when paired with the FF99SB or FF03 force fields, and no generalizations can be made about pairings of water models with the CHARMM22 or OPLS force fields. The inset legend in the upper right panel applies to all panels.