Re: Re: [gmx-users] gain the force field parameter by quantum mechanics calculation

[zjim]

Many thanks, David
I did the frequency calculation, and i got the bending force constant(0.2331) and the stretch force constant(0.8402). but I can't associate them to the force constant in the opls FF. and as a test,i also calculate the stretch force constant of H-C(2.4214) and C-C (6.1634), the value is not proportional to the value in opls ff (C-C:224412.5 C-H:284702.4). can you give some more advice, thank you again.

the frequency calculation output as follow
 
C-C
                   ?A        
Frequencies --  1063.9177
Red. masses --     3.6307
Frc consts  --     2.4214
IR Inten    --     0.0000
Raman Activ --    16.1188
Depolar     --     0.2891

C-H
Frequencies --  3182.0979
Red. masses --     1.0331
Frc consts  --     6.1634
IR Inten    --    72.1900
Raman Activ --     0.0000
Depolar     --     0.0302

I-I-I(bending)
                        1     
                    PIU    
 Frequencies --    55.8400 
 Red. masses --   126.9004 
 Frc consts  --     0.2331 
 IR Inten    --     0.0874 

I-I-I(stretch )
    3    
  Frequencies --    106.0065
 Red. masses --   126.9004
 Frc consts  --     0.8402 
IR Inten    --     0.0000

 



> On Sat, 2005-04-16 at 11:11 +0800, zjim wrote:

> > hi every one

> > when there is no parameter for some atom types of a molecule, such as

> > triiodide ion . Quantum mechanics calculation method (DFT MP2) seems

> > to a reasonable solution. the partial charge is easy to calculate by

> > add the key words "ChelpG", but how to calculate the force constant

> > (fc) of the bond , angle ,together with dihedral. If there is someone

> > know, please give some advice. 

> > thank you very much!

> In principle you can deduce it from a frequency calculation.

> 

> > 

> > Zhou Jin ming

> > Shanghai Institute of Organic Chemistry

> > Computational Chemistry Lab

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> >   什么邮箱可以设置 图片签名档，发送电子名片？ 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> > 

> >   什么邮箱可以设置 图片签名档，发送电子名片？ 

> > 

> > _______________________________________________

> > gmx-users mailing list

> > gmx-users at gromacs.org

> > http://www.gromacs.org/mailman/listinfo/gmx-users

> > Please don't post (un)subscribe requests to the list. Use the 

> > www interface or send it to gmx-users-request at gromacs.org.

> -- 

> David.

> ________________________________________________________________________

> David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,

> Dept. of Cell and Molecular Biology, Uppsala University.

> Husargatan 3, Box 596,          75124 Uppsala, Sweden

> phone:  46 18 471 4205          fax: 46 18 511 755

> spoel at xray.bmc.uu.se    spoel at gromacs.org   http://xray.bmc.uu.se/~spoel

> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

> 

> _______________________________________________

> gmx-users mailing list

> gmx-users at gromacs.org

> http://www.gromacs.org/mailman/listinfo/gmx-users

> Please don't post (un)subscribe requests to the list. Use the 

> www interface or send it to gmx-users-request at gromacs.org.

> 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20050418/4a2be406/attachment.html>