[gmx-developers] TIP3P and TIP4P parameters

[Michael Shirts]

So, looking over the original TIP3P and TIP4P paper (Jorgensen, Chandrasekhar,
and Madura, JCP, v. 79 n. 2, July 15 1983, p. 926), and looking over the
parameters there, and comparing them to ffoplsaanb.itp it seems as though the
LJ parameters for the waters should be:

TIP3P
 opls_111   OW     15.99940    -0.834       A    3.15061e-01  6.36272e-01
TIP4P
 opls_113   OW     15.99940     0.000       A    3.15358e-01  6.48694e-01

instead of:

TIP3P
 opls_111   OW     15.99940    -0.834       A    3.15061e-01  6.36812e-01
TIP4P
 opls_113   OW     15.99940     0.000       A    3.15365e-01  6.48954e-01

Yes, it is in the last digit of accuracy as pubished in the paper, but
original model parameters should be treated as exact when a unit conversion (1
kcal/mol = 4.184 kJ/mol) is applied.  I know they aren't big differences, but
some weird non-linear effects can sometime occur in the density, etc.

Cheers,
Michael Shirts
Pande Group
Stanford University