[gmx-users] unit conversion

[Justin Lemkul]

On 6/30/13 12:11 PM, Hyunjin Kim wrote:
> Hi,
>
> When I convert FF parameters from OPLS (in Gromacs) to Charmm, I divide
> bond and angle force constants, i.e., Kb and Ktheta, by 836.8 and 8.368.
> However, parameters for tip3p water do not convert properly in this ways.
>
> For example, Kb = 502416.0 kJ/mol/nm^2 for OW-HW in Gromacs and 450.0
> kcal/mol/A^2 in Charmm.
> 502416.0/836.8 = 600.4 instead of 450.0.
>
> I wonder what I did is incorrect.
>

CHARMM has its own special variation of TIP3P that corresponds to the values you 
are trying to produce.  In tip3.itp, it's the #ifdef CHARMM_TIP3P block.  The 
other parameters are for standard TIP3P.

-Justin

-- 
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Justin A. Lemkul, Ph.D.
Postdoctoral Associate

Department of Pharmaceutical Sciences
School of Pharmacy
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jalemkul at outerbanks.umaryland.edu | (410) 706-7441

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