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Re: [lammps-users] soft potential
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Re: [lammps-users] soft potential

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Mon, 10 Jul 2017 15:34:39 -0400

On Mon, Jul 10, 2017 at 2:42 PM, Monir Hosseini Anvari
<monir1@...1290...> wrote:
> Hi everyone,
> In order to calculate the excess chemical potential of an adsorbed molecule
> onto the surface, I need to estimate the free energy by gradually decoupling
> it. To do so, I used the hybrid pair style to assign lj/cut/coul/long
> potential to the surface atoms and lj/cut/soft to the atoms in the molecule,

why lj/cut/soft and not lj/cut/coul/long/soft?

> and specified the required coefficients of each pair in the input file. To
> equilibrate the system within an NPT ensemble, I started with a lambda vaue
> of 1. However, I receive the error "Illegal pair style command". Could you
> please help me find out what the problem is?

does your lammps executable contain the lj/cut/soft pair style? (run
the executable with the -h flag to find out).
if not, then the pair style and its arguments will be added as
arguments to the previous pair style command in the hybrid pair_style
definition and thus trigger the illegal pair style command.
if yes, then check the arguments for the pair style definition carefully.


> When using only the lj/cut/coul/long potential, there is no such issue. So
> as an alternative approach, is it ok if I change the epsilon value of the
> test atoms manually in several runs (by factors of 0.0 to 1.0), and then do
> the subsequent calculations to obtain the free energy?
> I'd truly appreciate your response.
> Thanks in advance.
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Dr. Axel Kohlmeyer  akohlmey@...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.