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Hi Felix<br>
<br>
Take a look to 4.2.1 section in the manual. Gromos force constants
(k^b) has this extra nm-2 factor because they are defined as: <br>
2 k^b bij^2 = k^{b,harm} (equation 4.39 in the manual version
4.5.4)<br>
<br>
So you have to divide your derived harmonic force constants (in
KJ/(mol*nm^2) by 2 and bij^2 (equilibrium distance or ideal bond
length as stated in gromos files) to get the gromos one (k^b). It
could also be useful for you to visit the new GROMOS website as
there is some free downloadable FF documentation.<br>
<br>
Javier<br>
<br>
El 06/07/11 08:48, Rausch, Felix escribió:
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<div><font face="Arial" color="#000000" size="2">Dear
Gromacs-users,</font></div>
<div> </div>
<div><font face="Arial" size="2">I would like to add a new bond
type to the ffbonded.itp of the Gromos53a6 force field. For
that, I tried to obtain the force constant for my new bond by
performing vibrational frequency calculations with Gaussian.
With that, I obtained the force constant in mDyne/A.</font></div>
<div><font face="Arial" size="2">My problem is now: How can I
convert this value to kJ/(mol*nm(4)) as required for the force
field? I already tried, but I only end up at
kJ/(mol*nm(2)). Also arround the web I could only find a
factor for conversion of mDyne/A to kJ/(mol*nm(2)). Is there
any trick or hint you can give me about that?</font></div>
<div> </div>
<div><font face="Arial" size="2">Thanks for your help,</font></div>
<div><font face="Arial" size="2">Felix</font></div>
<div><font face="Arial" size="2"> </font></div>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Javier CEREZO BASTIDA
PhD Student
Physical Chemistry
Universidad de Mua
Murcia (Spain)
Tlf.(+34)868887434</pre>
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