[gmx-users] Tables with forcefield

[Sai Pooja]

Thanks M!

I am using the standard 6-12 tables available with the gromacs package. For
-table and -tablep options to start with.

I want to understand 1 thing. The forcefield files and the topology file
specifies sigma and epsilon parameters. If I change the combination rule to
1 in the forcefield.itp file, and use tables, how does gromacs convert the
sigma, epsilon values in the topology file to C6 and C12?

Pooja

On Fri, Sep 24, 2010 at 7:07 PM, ms <devicerandom at gmail.com> wrote:

> Hi,
>
> Clarification: I may not be able to help you directly but I can suggest you
> which information you should perhaps give us to enable people more
> knowledgeable than me to help.
>
>
> On 24/09/10 17:33, Sai Pooja wrote:
>
>> I use combination rule 1; but I also define all tabulated interactions for
>>> all possible *pairs* under the [ nonbond_params ] section, so the
>>> combination rule actually doesn't matter much.
>>>
>>
>>
>> Are you suggesting that I can change the combination rule in the
>> forcefield.itp file but I must also supply a table for pairs using -tablep
>> option for this to work?
>>
>
> I am not "suggesting": I am only saying what I am doing :)
>
>
>  Does this mean that one cannot use tables with forcefield parameters?
>>>
>>>>
>>>>
>>>
>> Clarification: I want to use forcefield parameters with user defined
>> tables
>> i.e. I want to use sigma and epsilon values generated by pdb2gmx along
>> with a user-defined modified potential energy function using tables.
>>
>
> This is absolutely doable -I do it everyday, in fact. So, don't despair. :)
>
> Now, it seems that you talked about a problem with convergence of the
> SETTLE algorithm. I know little about it, but, couldn't it simply be that
> your tables are "wrong" (that is, they don't play well with algorithms?)
> What is their shape, actually, and on which atomtypes/groups are you
> applying your table? What is the forcefield you are using along with the
> table?
>
> M.
>
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-- 
Quaerendo Invenietis-Seek and you shall discover.
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