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[MD] Lennard Jones 
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#1
Dec2413, 09:34 AM

P: 39

Hi
For a simulation regarding Lennard Jones fluids I'm getting divergences. I have particles in a fixed volume. I calculate distances between these particles to find the force. However in the first iteration I already get divergences (NaN values in matlab). I use [tex]F_x^{ij} = 24\varepsilon \left( 2r_{ij}^{14}r_{ij}^{8}\right)\cdot \Delta x_{ij}[/tex] Where the i,j have to do with the particles I'm viewing. For each direction I get such a force. But some of the particles get so close that this force and hence the acceleration effectively become infinity. My simulation obviously breaks down at this point. I tried changing the timestep, this doesn't do anything. It worked at some point but I don't recall changing anything after that. Except adding the thermostat code which I can turn off. The divergence remains. You can find my (messy) code in this pastebin http://pastebin.com/62v1yTCY I've been looking at it for hours already yet I can't find any solution. JorisL Edit; I had divergences before. Those were caused by an error in applying the periodic boundary conditions. I forgot using the nearest image convention at that time. 


#2
Dec2513, 06:50 PM

P: 39

I found the mistake.
In my initialization of the cubic lattice, I had a break off variable g. I initialized this one as g = 1. Which caused the last point to to coincide with my first point and so I got immediate divergences. At least 4 hours to waste :S J 


#3
Dec2513, 06:53 PM

P: 2,804

You may have wasted 4 hours on this, but it took you 20+ years to get to this point...



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