XML file with OPLS-AA forcefield parameters is outdated

[iGulitch]

Hello!

I noticed that the xml file, which is [AFAIK] ported from Gromacs , is significantly outdated as long as the Gromacs file itself also. I noticed significant differences between the numerical parameters in the xml file and in the supplement of the most recent OPLS paper .

For instance, epsilon values for the atom types opls_900, 901, and 902 in Foyer and Gromacs :

<Atom type="opls_900" charge="-0.9" sigma="0.33" epsilon="0.71128"/>
<Atom type="opls_901" charge="-0.78" sigma="0.33" epsilon="0.71128"/>
<Atom type="opls_902" charge="-0.63" sigma="0.33" epsilon="0.71128"/>

differ from those in the paper :

900 07 NT   -0.900     3.300     0.170 N primary amines                                 
901 07 NT   -0.780     3.300     0.170 N secondary amines                                 
902 07 NT   -0.630     3.300     0.170 N tertiary amines          

i.e. 0.71128 vs. 0.170, respectively.

Are you planning to update the xml file eventually according to the new quantitative data of the OPLS FF authors?

Perhaps, I also noticed a typo in your xml file :

<Type name="opls_903" class="CT" element="C" mass="12.011" def="[C;X4](H)(H)(H)([N;%opls_900])" desc="CH3(N) primary aliphatic amines" overrides="opls_906" doi="10.1021/ja984106u"/>
<Type name="opls_904" class="CT" element="C" mass="12.011" def="[C;X4](H)(H)(H)([N;%opls_901])" desc="CH3(N) secondary aliphatic amines" overrides="opls_906" doi="10.1021/ja984106u"/>
<Type name="opls_905" class="CT" element="C" mass="12.011"/>
<Type name="opls_906" class="CT" element="C" mass="12.011" def="[C;X4]([N;%opls_900])(H)(H)" desc="CH2(N) primary aliphatic amines" overrides="opls_136" doi="10.1021/ja984106u"/>

says that the atom types opls_903 and opls_904 override the atom type opls_906 that in turn overrides opls_136. The latter statement looks reasonable, since both opls_906 and opls_136 carbon atoms are CH2 :

<Type name="opls_136" class="CT" element="C" mass="12.01100" def="[C;X4](C)(C)(H)H" desc="alkane CH2" doi="10.1021/ja9621760"/>

At the same time, the former statement sounds strange, since it claims that the carbon atom data CH3 overrides the carbon atom data CH2. Perhaps, instead of opls_906 you meant opls_135 :

<Type name="opls_135" class="CT" element="C" mass="12.01100" def="[C;X4](C)(H)(H)H" desc="alkane CH3" doi="10.1021/ja9621760"/>

that is CH3 carbon atom also? In this case, it makes perfect sense. Would you clarify, please?

Thanks!