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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Dear GROMACS users<br>
I want to run simulations of polyethyleneoxide melt. In literature I have
found united atoms force fields that performed well for this kind of
simulation. For dihedral potential I need to extend the Ryckaert-Bellemans
potential up to the order of six. I have looked at the mailing list and found
some information which give advice to change the code for this kind of
potential. But I could not figure out where to do this changes and how to do
them. I would need some detail to do it. I do not have experience with
something like this. <br>
<br>
My second question also concerns PEO. I tried to use GROMOS force field as well
for simulations. I used the parameters from ffG53a5 files. In ffG53a5bon.itp I
am not sure which code of dihedrals sould be used for C-C-O-C and O-C-C-O and
which one for the bond angles. In the case of bond angle I found type ga_8 as
suitable, but it seems me from the description that it sould be the same for
all three bonds in PEO. This seems to be not OK, since the bending of C-O-C
angle is characterized by larger bending constant. <br>
<br>
I would appreciate any help. Thank you in advance<br>
<br>
Zuzana.<o:p></o:p></span></font></p>
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