[gmx-users] oplsaa vs. charmm

Mark Abraham Mark.Abraham at anu.edu.au
Sat May 28 01:51:33 CEST 2011

On 28/05/2011 2:05 AM, Peter C. Lai wrote:
> On 2011-05-27 10:50:14AM -0500, simon sham wrote:
>> Hi,
>> I have recently done two simulations on a protein at high temperature near its melting temperature. At the beginning I used CHARMM forcefield, and then OPLSAA to double check the results. There are some differences in the structures between the forcefield used.  I know different forcefields can give different results. All parameters in the simulations were the same except the forcefield. Is there anyway I can tell which forcefield gives more reliable results?
> Also you never stated what RMSD/RMSFs between the two and if they are
> significant to what you care to see (i.e. if you expect, say, alpha
> helix to random coil transition, what changes in the unfolding do you see
> that make you suspect one forcefield is better than the other?). Also if this
> is in a solvated system, the rest of the forcefield has been parameterized
> with the implicit assumption that TIPS3P (Charmm-specific) water will be used
> so make sure you have switched your water type when using CHARMM.

Not necessarily required. See http://dx.doi.org/10.1021/ct700053u and 


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