<html>
Thanks for your earlier answer Eric :-)<br><br>
Another question about the force fields .....<br><br>
From Scott et al. (1999), equation 52 is for dihedrals in the GROMOS
format. As constants it has the force constant, phase shift and
multiplicity, with the variable being the dihedral angle.<br><br>
In the dihedrals defined within ffG43a2xbon.itp for the GROMOS-96 force
fields the dihedrals types are defined something like this:<br>
<x-tab> </x-tab># first
gd_number to define the G96 proper dihedral type<br>
<x-tab> </x-tab># an angle
in degrees, which I assume is theta max<br>
<x-tab> </x-tab># some
value, which I suspect is the force constant<br>
<x-tab> </x-tab># and the
multiplicity all on the same line<br>
<x-tab> </x-tab># next
line is a comment on which dihedrals it is appropriate for<br>
<x-tab> </x-tab># then
another number, this I suspect is the phase shift.<br><br>
Am I correct in my interpretation of the lay out of the
ffG43a2xbon.itp?<br><br>
It doesn't make a lot of sense though (well the first three values do ;-)
), since from table 5.3 and 5.4 in the GROMACS 3.1.1 manual, proper
dihedrals are define in terms of theta max, force constant and
multiplicity (also shown by equation 4.52). There is no place for
the phase shift?!?! Isn't that implemented or used with
GROMACS?<br><br>
Another proper dihedral issue .... I get the feeling this has been
brought up previously, but I can't happen to find it in the archives at
the moment. If you have more than one multiplicity and force
constant for a proper dihedral, can you simply define two for the same
proper dihedral? For example multiplicity of 1 and 2 with different force
constants for each multiplicity.<br><br>
Catch ya,<br>
<x-sigsep><p></x-sigsep>
<b>Dr. Dallas Warren<br>
</b><i>Research Fellow<br>
</i>Department of Pharmaceutical Biology and Pharmacology<br>
Victorian College of Pharmacy<br>
Monash University<br>
381 Royal Parade<br>
Parkville VIC 3010<br>
<font color="#0000FF"><u>dallas.warren@vcp.monash.edu.au<br>
</u></font>+61 3 9903 9083</html>