[gmx-users] All atom FF to united atom FF

Dallas Warren dallas.warren at vcp.monash.edu.au
Tue Apr 1 05:25:01 CEST 2003

I have found some parameters for ethylene oxide groups which were derived 
for an all atom force field.  However, with the simulations I am performing 
with various other components I am using an united atom force field 
(ffG43a2x with some of my own modifications).  I would like to continue 
calculations by ignoring the hydrogens attached to the carbon atoms because 
it significantly reduces the number of atoms in the systems, and therefore 
increases the calculation speed.

I have a feeling that it is non-trivial to move to an united atom force 
field and would require re-derivation/determination of the carbon 
non-bonding parameters to fit the experimental/quantum data so that the 
hydrogen ion interactions are grouped in with the carbons.  Is this the 
case?  Or can you simple drop out the hydrogen atoms?

Wouldn't be too hard to try out the all and united in that case and see 
what sort of difference it would make .... will certainly try that if 
someone else knows better.


Catch ya,

Dr. Dallas Warren
Research Fellow
Department of Pharmaceutical Biology and Pharmacology
Victorian College of Pharmacy
Monash University
381 Royal Parade
Parkville VIC 3010
dallas.warren at vcp.monash.edu.au
+61 3 9903 9083
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