[gmx-users] ambar to opls force field

[Nilesh Dhumal]

Thanks Justin.

I am using flexibale water model for my system. I am refering a paper J.
Chem. Phys. 124, 024503 (2006). Author have used Amber type force field.

i.e. 1/2 Kbond (r-req)**2 + 1/2 Kangle(theta-thetaeq)**2.

Kbond = 443153.3808 kJ/mol nm**2

Kangle= 317.5656 kJ/mol rad**2.

I am using olss-aa force field parameters in Gromacs  VERSION 4.0.7.

I checked some papers in which author have used opls aa force field. 1/2
factor is not in opls force field IF I compare opls and amber.

My question is in .itp file should I use Kbond and Kangle as it is or
should I consider the 1/2 factor then I use them.

Thanks

Nilesh

On Fri, May 6, 2011 6:36 pm, Justin A. Lemkul wrote:
>

>
> Nilesh Dhumal wrote:
>
>> Hello,
>>
>>
>> How can I convert ambar force field to opls force field.
>>
>>
>> Should I half the force constant of bond (Ka)  and angle (Kb)?
>>
>>
>
> Why would you do that?  Most of the bonded parameters in OPLS were taken
> from AMBER directly, IIRC.  If you need to parameterize some new bonded
> parameters, you'd be better served deriving them in a way that is
> compatible with the modern OPLS-AA force field (probably QM/geometry
> optimization), rather than trying to hack something together.
>
> -Justin
>
>
> --
> ========================================
>
>
> Justin A. Lemkul
> Ph.D. Candidate
> ICTAS Doctoral Scholar
> MILES-IGERT Trainee
> Department of Biochemistry
> Virginia Tech
> Blacksburg, VA
> jalemkul[at]vt.edu | (540) 231-9080
> http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
>
>
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