[gmx-users] Implemetation of the CHARMM27 ff into gromacs : managment of dihedral terms

[Nicolas SAPAY]

Hello everybody,

I am quite interested by the implementation of the CHARMM27 force field
into Gromacs. I have read few messages  on the Gromacs mailing list and
have downloaded the CHARMM conversion on this web page:

http://www.gromacs.org/old/topologies/force_fields.php

So, I have some questions about this translation.
- The dihedral terms (proper angles) initially treated by a periodic
function have been converted to Ryckeart-Bellemans potential. Why this
choice? And how the conversion has been done?

-  In a same time, improper angles initially treated by harmonic terms
have been converted to periodic terms. Why? I'm not sure to understand
this choice.

Additionally, I have seen that the Urey-Bradley constants were ewritten in
the ffcharmmbon.itp file. I guess they are parsed but not really used by
Gromacs or the implemtation of the potential has been achieved?

Thanks for your answers!

Nicolas

-- 
[ Nicolas Sapay Ph.D. ]
University of Calgary, Dept. of Biological Sciences
2500 University Dr. NW, Calgary AB, T2N 1N4, Canada
Tel: (403) 220-6869
Fax: (403) 289-9311