# Compute the force

Hi,

In my system under run(in 2d), I have a single particle. And it has
been defined in a group. The particle is not subjected to any external
forces. Only it is interacting with other particles via L-J(lj/cut)
interaction and the whole system has been placed in an NVT ensemble.

Now if I want to compute the force( in each timestep) on the single
particle, which command will suffice the purpose .

Advanced happy new year to everyone .

best,

Hi,

In my system under run(in 2d), I have a single particle. And it has
been defined in a group. The particle is not subjected to any external
forces. Only it is interacting with other particles via L-J(lj/cut)
interaction and the whole system has been placed in an NVT ensemble.

Now if I want to compute the force( in each timestep) on the single
particle, which command will suffice the purpose .

huh? why should you need a special command for that?

axel.

Hi,

In my system under run(in 2d), I have a single particle. And it has
been defined in a group. The particle is not subjected to any external
forces. Only it is interacting with other particles via L-J(lj/cut)
interaction and the whole system has been placed in an NVT ensemble.

Now if I want to compute the force( in each timestep) on the single
particle, which command will suffice the purpose .

huh? why should you need a special command for that?

I need to know the profile of the force acting on the particle throughout
the run

Saikat

huh? why should you need a special command for that?

I need to know the profile of the force acting on the particle throughout
the run

you are missing the point:

if you do an MD run, you *have* the force already.
that is how MD works: you compute the force on
each particle and then you integrate the equations of motion.

those forces can be accessed right away, no need
to specifically compute them. this computation is
the whole point of writing an MD code in the first place.

axel.

The forces are stored in variables fx fy fz

Use dump custom command to output them throughout the trajectory

Regards

And you can do that for a single atom if you
wish, by assigning that atom to a group.

Steve

And you can do that for a single atom if you
wish, by assigning that atom to a group.

Exactly Steve,I have already assigned the atom(which is single,for
this particular type)in a group and it is subjected to some
forces, defined by the interaction.

As Axel mentioned "if you do an MD run, you *have* the force already.
that is how MD works: you compute the force on
each particle and then you integrate the equations of motion.", I
just want to know the values of the force in each timestep.

I just require the command which will provide me the values.

Saikat

And you can do that for a single atom if you
wish, by assigning that atom to a group.

Exactly Steve,I have already assigned the atom(which is single,for
this particular type)in a group and it is subjected to some
forces, defined by the interaction.

As Axel mentioned "if you do an MD run, you *have* the force already.
that is how MD works: you compute the force on
each particle and then you integrate the equations of motion.", I
just want to know the values of the force in each timestep.

I just require the command which will provide me the values.

how about a little RTFM? you can start here:

axel

you can simply dump the force components via the dump custom command.

Steve