[gmx-users] bond stretching constants in ffgmxbon.itp

David van der Spoel spoel at xray.bmc.uu.se
Mon Sep 6 11:50:06 CEST 2004

On 6 Sep 2004, B. Nick wrote:

>Dear all,
>I want to implement NERD united atom force
>field constants in the ffgmx force field.
>The values I calculated from literature are
>all close to the CH2 parameter of the ffgmx
>force field. BUT the bond strechting constant
>is about a factor 1000 off. (From Kb=96500K/A^2 given
>in the paper I calculate 802,35 kJ/mol A^2, by multiplication
>with kB. This is ok for the other constants. But the
>ffgmx entry for CH2 CH2 is 334720.)

>Aren't the units in the force field table for Kb, kJ/mol A^2 ?

nm iso Angstrom
The functional form has the half in it. Not all others do that. Have you 
also looked at kJ versus kcal?
>Do I still have to divide the force constant given in the table
>by two to get the energy as given by the formular 4.33
>in the manual?
>Thanks for any help,
>Birgitta Nick
>DWI an der RWTH Aachen, Germany
>gmx-users mailing list
>gmx-users at gromacs.org
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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

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