[gmx-users] C6 attractive term off OPLSAA

Justin A. Lemkul jalemkul at vt.edu
Mon Nov 29 19:47:03 CET 2010

nishap.patel at utoronto.ca wrote:
> Hello,
>    I have a concern regarding C6 attractive term in LJ potential. I am 
> using OPLS-AA force field, and I wish to turn off attractive term C6 by 
> setting the parameters to zero. One of the suggestion was to add a 
> [nonbond_params] in my ffoplsaanb.itp file and set the C6 to zero 
> between the non-bonded pair. In my system for example, which consists of 
> one methanol in water, I wish to set C6 term to zero between my solute 
> and solvent. Since OPLSAA is all atom force field it treats each atom 
> individually and has sigma and epsilon for each atom, so I am not sure 
> how I would actually set my nonbond_params in my nb.itp file. I realize 
> I need to convert each sigma and epsilon to C6 and C12, so say for 
> example for methanol in water my [nonbond_params] would look something 
> like this?
> [ nonbond_params ]
> ; i    j func          c6           c12
>       CT        OW  1   0.00      calculated value for C12 here?
>       CT        HW1  1  0.00
>       CT        HW2  1  0.00
> CT is the carbon in Methanol. OW, HW1 an HW2 correspond to atoms in 
> TIP3P water model
> Is that correct? Would I have to do that for each atom in methanol?

Sounds about right to me.


> Any suggestions would be appreciated.
> Thanks.
> Nisha P


Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


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