[gmx-users] bond stretching force constant from QM data
v.gogonea at csuohio.edu
Mon Jan 27 16:19:44 CET 2003
Sure, unfortunately I did not get anything up to now :-(
I will summarize if I will get something.
On Monday, January 27, 2003, at 10:15 AM, Alexandre Suman de Araujo
> Valentin Gogonea wrote:
>> Dear CCLers and GMX users,
>> I am trying to estimate the force constant for Fe-S bond stretching
>> from QM calculations and use it with Gromos87 force field (gromacs).
>> I carried out UB3LYP/6-31+G** calculations for Fe-SCH3
>> (charge=+1,multip=5) and Fe-Imidazole (+2,5) with G98 and I got the
>> following force constants (I used a conversion factor from mDyne/A to
>> KJ/(mol nm2) of 60230):
>> mDyne/A kJ/(mol nm2) Gromos87
>> Fe-S 1.839 110763
>> Fe-N 0.757 45594 418400
>> 1) Is it acceptable to scale properly (using the QM and Gromos Fe-N
>> force constants) the Fe-S force constant to be in the same range as
>> the Fe-N force constant in the Gromos87 force field. Did anybody use
>> this kind of approach or there is a better way to estimate and adjust
>> the QM determined force constant to a force field force constant?
>> 2) For an angle bending the force constant required in the forcefield
>> has units of kJ/(mol rad2), while the one obtained from QM
>> calculations has units of kJ/(mol nm2). I believe that the former can
>> be obtained from the latter if one assumes that the oscillator length
>> for this particular normal mode is the distance between the endpoints
>> of the angle. This should be valid for a torsion angle too. Is this
>> I would appreciate any insight that I can get from the list and I
>> thank you for your help.
>> Valentin Gogonea
>> Department of Chemistry
>> Cleveland State University
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> Hi Valentin
> I have the same problem that you and I'm very interested in the
> answers that you can get. If you receive anyone in private, can you
> send it to me???
> Alexandre Suman de Araujo
> asaraujo at if.sc.usp.br
> UIN: 6194055
> IFSC - USP - Sa~o Carlos - Brasil
> gmx-users mailing list
> gmx-users at gromacs.org
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