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Re: [lammps-users] Reading Energy in Custom Pair Function
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Re: [lammps-users] Reading Energy in Custom Pair Function

From: S M <smatrix_2012@...8...>
Date: Sun, 18 Jun 2017 18:16:56 +0000

Ok, here is the full scenario:

I have a group of atoms at low temperature that interact with each other only via a LJ potential. At every timestep, I want to read the potential energy (from the LJ interaction) of every atom. Then, I want to identify the atom with the maximum potential energy, and weaken the forces acting on it, so that it is able to rapidly escape from the vicinity of the rest of the atoms.

- When writing my previous email, I was thinking of applying a repulsive pair potential to the atom having the maximum potential energy, that would effectively weaken the original LJ interaction. That is why I thought about writing a custom pair potential that applies only to that specific atom in the group.

- Now, I am thinking that the same can be achieved by applying an additional force on that same atom (and subsequent reaction forces on the other atoms), similar to the 'fix addforce' function. In this case, I would have to write a custom fix.

In either of the above, I have to identify the atom with the maximum potential energy at every timestep.

Can anybody provide some advice about how to proceed?


From: jewett.aij@...24... <jewett.aij@...24...> on behalf of Andrew Jewett <jewett@...1937...>
Sent: Saturday, June 17, 2017 1:55 AM
To: S M
Cc: lammps
Subject: Re: [lammps-users] Reading Energy in Custom Pair Function

On Jun 16, 2017 5:45 PM, "S M" <smatrix_2012@...8...> wrote:

I am writing a custom pair potential, where I first need to read the energy of every particle

Can you clarify what you mean here?
Is the pair style you are writing not already calculating the (pair contribution to) the energy per particle?  (... that is...excluding many-body forces or long range electrostatics.... Are you using these?) 
What contributions to the energy do you mean?
Contributions to the energy from bonds, angles, dihedrals... containing that atom?  (What about fixes like "fix spring" or "fix wall"?)

the custom pair potential is applied, and then apply the custom pair potential to certain particles based on their energy readings.

I am guessing that I need to use the "pair->vdW" command.

This is not an input script command (and this string does not appear anywhere in the source code)

Can anybody suggest a definite strategy in terms of writing necessary codes?

My guess would be what you are trying to do is not easy to do in a general way.  But perhaps if you clarify what you want, someone can suggest something.




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