[gmx-users] symmetrical LJ binary mixture simulation

[Hyuntae Jung]

Dear Mark Abraham,


Sorry for frustrating this,


I was supposed to explain the Lennard Jones (6-12) potential form for Van der Waals interaction.

In other words, I consider the binary system with two spheres (A and B) which interact only Van der Waals interaction with 6-12 potential form, U=4*epsilon*[(sigma/r)^12 - (sigma/r)^6] :

(1)  sigma_AA = sigma_BB = sigma_AB = 1

(2) epsilon_AA = epsilon_BB = 1 and epsilon_AB = 0.5

where is not standard combination rule.


If my explanation is not enough, you may see this article:

Liquid-liquid interfacial properties of a symmetrical Lennard-Jones binary mixture

F. J. Martínez-Ruiz, A. I. Moreno-Ventas Bravo, and F. J. Blas

The Journal of Chemical Physics 143, 104706 (2015); doi: 10.1063/1.4930276

To study liquid-liquid phase separation with simple model, I wanted to find a way to do MD simulations using the symmetrical LJ binary mixture model. But in my mind, if LJ-PME method in Gromacs had supported even custom combination rule, it would be great.

Thank you,
Hyuntae Jung

________________________________
From: gromacs.org_gmx-users-bounces at maillist.sys.kth.se <gromacs.org_gmx-users-bounces at maillist.sys.kth.se> on behalf of Mark Abraham <mark.j.abraham at gmail.com>
Sent: Wednesday, May 17, 2017 3:29 AM
To: gmx-users at gromacs.org
Subject: Re: [gmx-users] symmetrical LJ binary mixture simulation

Hi,

On Wed, May 17, 2017 at 5:29 AM Hyuntae Jung <hjung52 at wisc.edu> wrote:

> Hello, gromacs users.
>
>
> I wonder if it is possible to simulate a symmetrical LJ binary mixture
> implementing LJ-PME methods.
>
>
> The mixture is composed of A and B-type LJ particles and their sizes
> (sigma) are unity (=1). The interaction energy (epsilon) of A-A and B-B is
> unity, but heterogeneous interaction (A-B) is 0.5. While I try to apply
> LJ-PME method, the parameter, "lj-pme-comb-rule" is not supported for this
> case (Either geometric or LB combination rule is allowed).
>

I'm unfamiliar with the description of epsilon as the "interaction energy,"
and unsure what you've actually tried to get that error message. I suggest
you take a look at the functional forms that we've documented, and express
your intent in similar ways, and see what you learn.

Is there any possible way to work such an user-defined combination rule
> using LJ-PME method in Gromacs?


No, the choice of combination rules, and management of that choice is
crucial to the implementation and its performance. It's not at all clear to
me that you need a custom combination rule, however.

Mark

If not possible in Gromacs, any simulation packages which supports those
> system with LJ-PME?
>
>
> Sincerely,
>
> Hyuntae Jung
>
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