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<blockquote type=cite class=cite cite> And the function 4.52 is the
most simplest function for dihedral angles.I think it's not the Gromos
43a2's dihedral angles function,it's Gromacs'. Now, I hope to know the
difference of dihedral function between Gromacs and
Gromos.</blockquote><br>
From what I can gather, there is no difference between the GROMACS and
GROMOS dihedrals. Both use an angle maximum, force constant and
multiplicity to define the potential. They also have a phase shift
which you can implement in the equation, but no mention of this is made
in the topology discussions or the manner in which you can use it if
needed.<br><br>
So if you use the GROMOS forcefields, then you define a dihedral
type/number, something like gd_#. If you look at table 5.3 the
parameters that can be set for a proper dihedral is the angle maximum,
force constant and then multiplicity. Each gd_# has a defined angle
maximum, force constant and multiplicity.<br><br>
<blockquote type=cite class=cite cite> Second, if I want to use
dihedral angle type 3,there are more than one force constant in dihedral
function. In ffG43a2bond.itp, there is only one force
constant.Where can I put or find the other force
constant?</blockquote><br>
By dihedral type 3, do you mean Ryckaert-Bellemans potentials? If
so, then there is only one that comes with the force fields, and this is
for the CH2-CH2 dihedral optimised for alkanes. The values for this
is shown on page 89-90 of the manual.<br><br>
If you want to use a R-B for other dihedrals, then you either have to
generate them yourself, or I noticed that a couple of days ago someone
mentioned that OPLS has more defined in it so you may be able to transfer
some over from there.<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>