[gmx-users] Fwd: charm to gromacs

[francesco oteri]

Actually I solved the problem,
I did a mistake in the bond conversion. Actually I found the right formula:

k_gromacs = k_charmm**418.4**2

rising form the conversion from angstrom to nanometer....




---------- Messaggio inoltrato ----------
Da: francesco oteri <francesco.oteri at gmail.com>
Date: 08 marzo 2012 10:49
Oggetto: charm to gromacs
A: Discussion list for GROMACS users <gmx-users at gromacs.org>


Dear gromacs users,
I am trying to convert a charmm style parameter file into gromacs. So I al
trying to understand how converting the force constants from CHARMM to
gromacs.
Using the CHARMM27 force field as a reference, I've noticed that to convert
the bond constant the following formula is supposed to be used:

k_gromacs = k_charmm**4184**2
In fact if I try to convert the following line from
par_all27_prot_lipid.prm charmm file:
CEL1  CEL1  440.000     1.340   ! butene, yin,adm jr., 12/95

I obtain the right result ( 440.000*4184*2. = 368192.0)
charmm27/ffbonded.itp    CEL1    CEL1    1       0.134   368192.0


But to convert the angle constants I've to use the following formula:

k_gromacs = k_charmm**4.184**2.

how demostrated by the conversion of the following line:

par_all27_prot_lipid.prm  CEL1    CEL1    CTL2   48.00     123.50   ! from
2-butene, yin,adm jr., 12/95

into

charmm27/ffbonded.itp   CEL1    CEL1    CTL2    5       123.50  401.664 0.0
    0.0



My question is:

Why in the former case I need the constant 4184 while in the latter the
constant 4.184 is supposed to be used? Am I miss something?




-- 
Cordiali saluti, Dr.Oteri Francesco
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20120308/568b30e9/attachment.html>