I meant the same as Francois, mixing two force fields is dangerous.
Better to stick with one. The problem is the interaction between both
force fields, think nobody investigated how they should interact. So if
you find a way for doing this and want to publish your results you must
convince the reviewer of the journal that your way has absolute no flaws.
If you accomplish this, and can convince many people, than i think you
can hope for many citations (because it is now accepted that one can mix
both force fields). But this would need very much work.
So the easier way is to use one force field and stick with it, since you
want to investigate your system. And not how to mix two force fields
(much more work then only to investigate your system).
Am 21.02.2012 17:55, schrieb Guoxiong Su:
> Dear Francois,
>
> Thank you for your reply. I will do as suggested to find a RESP charge for OPLS.
> Then how can I get the LJ parameters between those 'GAFF-particles' and 'OPLS-particles' since they are using two kinds of combine rules?
>
> Sincerely,
> Guoxiong
>
> On Feb 21, 2012, at 10:27 AM, FyD wrote:
>
>> Dear Guoxiong Su,
>>
>> Mixing two force fields is always dangerous.
>>
>> I would compute a highly consistent set of charges for all the
>> molecules to be studied. If you want to use OPLS you can find a RESP
>> approach for OPLS.
>> See R. H. Henchman and J. W. Essex, J. Comput. Chem., 1999, 20, 483?498.
>> This approach should be easy to implement in the R.E.D. program.
>>
>> A new box for benzonitrile can be created for Amber.... Then, whatever
>> you decide to use (may be try first SCNB = 2.0& SCEE = 1.2) your
>> benzonitrile box has to be tested/studied...
>>
>> regards, Francois
>>
>>
>>> I am trying to solvate a molecular triad in a benzonitrile box. For
>>> this molecular triad, I used Antechamber to generate the topology
>>> file with GAFF. The charge is calculated using AM1-BCC. I have done
>>> some literature search and I found OPLS force filed has the
>>> parameters for benzonitrile. Is it reasonable to mix GAFF with OPLS
>>> force field in AMBER?
>>>
>>> I have read though the mailing list and I found some people was
>>> mixing AMBER force field with the Glycam force field (e.g.
>>> http://archive.ambermd.org/200906/0240.html). I knew that for GAFF,
>>> SCNB = 2.0 and SCEE = 1.2. What values are they in OPLS? Is it 1.0
>>> since OPLS doesn't have any scaling? The combine rules of GAFF and
>>> OPLS for the Lennard-Jones potentials are different as well. GAFF
>>> follows the AMBER rules and OPLS uses geometric mean for sigma and
>>> epsilon. Is it possible to use two kinds of combine rules in AMBER?
>>
>>
>>
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>
>
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Received on Tue Feb 21 2012 - 09:30:03 PST
