Dear GROMACS users 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.
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. I would appreciate any help. Thank you in advance Zuzana.
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