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i've been doing a simulation using LJ model, but i'm having a troublesome time on figuring out, what's happening with the energy :uhh:

This is the LJ potencial:

[tex]E = 4\epsilon\left[\left(\frac{\sigma}{R}\right)^{12} - \left(\frac{\sigma}{R}\right)^6\right][/tex]

but i've been using this simplified form given on Fosdick's book:

[tex]E = \left[\left(\frac{1}{R}\right)^{12} - \left(\frac{2}{R}\right)^6\right][/tex]

And for time integration i'm using the velocity Verlet method.

I am using noble gases only, and in this example, i have 3 atoms forming an equilaterum triangle. The system starts with KE = 0, and PE < 0.

What happens is that while the atoms approach eachother, the KE increases (as one would expect), and the PE decreases (it is always a negative value, so it increases in absolute value).

When they are too close, they repel themselfs and the opposite happens.

So i have a kind-of "harmonic" motion, where the [tex]E[/tex] increases and decreases. :yuck:

To give you an idea of the values i have, i initially have an [tex]E[/tex] = -0.00051 and can go up to [tex]E[/tex] = -0.3619

My suspection of why this doesn't work migth be because of the values i'm using in the simulation. (and yes... i really don't know what is the magnitude of the SI units i am using here... much less the ones i should be using :shy: )

time step = 0.01

particle mass = 1

radius = 0.6

distance between each particle = 5

I've read that using the conservation of energy, one can do some corrections on the values obtained.... but uhh, i think what i have here i something completely different.

Thanks in advance for any help.

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# Lennard-Jones model and Energy Conservation

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