  Water is perhaps the most simulated liquid. Recently three water models have
been developed following the adaptive force matching (AFM) method that provides
excellent predictions of water properties with only electronic structure
information as a reference. Compared to many other electronic structure based
force fields that rely on fairly sophisticated energy expressions, the AFM
water models use point-charge based energy expressions that are supported by
most popular molecular dynamics packages. An outstanding question regarding
simple force fields is whether such force fields provide reasonable
transferability outside of their conditions of parameterization. A survey of
three AFM water models, B3LYPD-4F, BLYPSP-4F, and WAIL are provided for
simulations under conditions ranging from the melting point up to the critical
point. By including ice-Ih configurations in the training set, the WAIL
potential predicts the melting temperate, TM, of ice-Ih correctly. Without
training for ice, BLYPSP-4F underestimates TM by about 15 K. Interestingly, the
B3LYPD-4F model gives a TM 14 K too high. The overestimation of TM by B3LYPD-4F
mostly likely reflects a deficiency of the B3LYP reference. The BLYPSP-4F model
gives the best estimate of the boiling temperature TB and is arguably the best
potential for simulating water in the temperature range from TM to TB. None of
the three AFM potentials provides a good description of the critical point.
Although the B3LYPD-4F model gives the correct critical temperature TC and
critical density, there are good reasons to believe the agreement is reached
fortuitously. Links to Gromacs input files for the three water models are
provided at the end of the paper.
