eps(charmm)*4.184=epsilon(Gromacs)<br>0.15*4.184=0.6276<br><br>Rmin/2(Charmm)*2/(2^1/6)=sigma(Gromacs)<br>2.27*2/(2^(1/6))=0.404468(nm)<br><br>Cheers,<br>Jianhui<br><br>Date: Fri, 24 Sep 2010 15:55:44 +0200<br>
From: "ABEL Stephane 175950" <<a href="mailto:Stephane.ABEL@cea.fr">Stephane.ABEL@cea.fr</a>><br>
Subject: [gmx-users] CHARMM -> gromacs epsilon and sigma conversiion<br>
factors<br>
To: <<a href="mailto:gmx-users@gromacs.org">gmx-users@gromacs.org</a>><br>
Message-ID:<br>
<<a href="mailto:F654B3EE96986E4B8DC6EF0919C88DA301038BAD@LODERI.intra.cea.fr">F654B3EE96986E4B8DC6EF0919C88DA301038BAD@LODERI.intra.cea.fr</a>><br>
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<br>
Hi all,<br>
<br>
I would like to add new atom types in the charmm27.ff for futures
simulations of glyolipids in water with gmx 4.5.1. I have finished to
convert the bonded in GROMACS format. However, I am little puzzled with
the vdW paramaters. I would like to know how to convert them (i.e. what
are the conversion factors used to convert the CHARMM sigma and epsilon
parameters to gromacs sigma and epsilon values ?).<br>
<br>
For example for the chloride atom CLA<br>
<br>
CHARMM 27<br>
<br>
; atom ignored epsilon Rmin/2 ignored eps,1-4 Rmin/2,1-4<br>
CLA 0.0 -0.150 2.27 ! chloride<br>
<br>
GROMACS ffcharmmnb.itp<br>
<br>
;name at.num mass charge ptype sigma epsilon<br>
CLA 17 35.450000 -1.00 A 0.404468018036 0.6276<br>
<br>
Thanks in advance for your help<br>
<br>
Stefane<br>