[gmx-users] symmetrical LJ binary mixture simulation

[Mark Abraham]

Hi,

There's no way to implement that. I suggest you consider alternative ways
of inducing phase separation that is achieved with parameters that follow
geometric combination rules.

Mark

On Wed, May 17, 2017 at 11:40 AM Hyuntae Jung <hjung52 at wisc.edu> wrote:

> 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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