[gmx-users] fudgeLJ?

nicolas Dinter dinter at rc.m-kagaku.co.jp
Mon Aug 30 11:19:55 CEST 2004

Dear Berk,

I use my own force field, so in my itp file I generated a pair list, but
normaly using genpair=yes (i.e gromacs takes the 1-4 pairs in the list) and
fudgeLJ must change the 1-4LJ energy; unfortunatly not.
Do you know why?

Nicolas Dinter

-----Original Message-----
From: gmx-users-bounces at gromacs.org
[mailto:gmx-users-bounces at gromacs.org]On Behalf Of Berk Hess
Sent: lundi 30 août 2004 18:11
To: gmx-users at gromacs.org
Subject: RE: [gmx-users] fudgeLJ?

>From: "nicolas Dinter" <dinter at rc.m-kagaku.co.jp>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: <gmx-users at gromacs.org>
>Subject: [gmx-users] fudgeLJ?
>Date: Mon, 30 Aug 2004 15:33:34 +0900
>Dear Gromacs users,
>I tried to use the fudgeLJ and fudgeQQ command,
>I had to my itp file:
>;nonbondtype	combrule	genpair	fudgeLJ	fudgeQQ
>1			1		yes		0.5		1
>but the LJ energies are the same than without adding this comand, when I
>change fudgeQQ the Coul14 energy is multiplied by the given coefficiant in
>the itp file.
>Is sobebody can explain me why with fudgeLJ=1 fudgeQQ=0.5 I have changes
>with fudgeLJ0.5 fudgeQQ=1 not.

I have already updated the manual for the next release on this point,
since it is not completely clear.
fudgeQQ always works, also when gen-pairs=no
fudgeLJ only has an effect on the generated pair parameters.
You did not tell which forcefield you are using, but I would guess
that it has all pairs listed explicitly in the pairtypes section in
Then no pairs need to be generated, even if gen-pairs=yes.


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