[gmx-users] kappa in Generalized reaction field

[Berk Hess]

>From: Tomoshi Kameda <kameda-tomoshi at aist.go.jp>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: gmx-users at gromacs.org
>Subject: [gmx-users] kappa in Generalized reaction field
>Date: Mon, 15 May 2006 17:28:27 +0900
>
>Hi all
>
>I'm going to ask about the definition of kappa in Generalized
>Reaction-field.
>
>
>In manual-3.3.pdf and manual-3.2.pdf (eq 4.17),
>kappa**2 = ...SUM (c_i * z_i)
>
>But, in Ref.51 (eq 5),
>kappa**2 = ...SUM (c_i * (z_i)**2)
>
>
>Is eq.4.17 correct?

I would say the reference is correct.
David van der Spoel removed the square from the code in 1999,
I don't know why.
Also in the code there is an additional factor of 2.

But with charged groups in solution I would stongly advise
against using a (generalized) reaction field, as this can produce
strong artifacts.
Use PME instead.

Berk.