Motion of Methane Molecules inside a Carbon Nanotube

Two methane molecules inside a carbon nanotube

Two methane molecules inside an "armchair" carbon nanotube (7,7) of radius 4.75 A and length of 24.535 A. for more detalis click here
I used two kinds of potential in the molecular dynamics simulation:
1). Brenner potential for short-range interactios on the carbon atoms of the nanotube wall and between the hydrogen atoms and the carbon atom of the methane molecule.
2). Lennard-Jones potential for long-range interactions between the methane and the carbon atoms of the tube wall.
Next, Newton's equations of motion are integrated using predictor-corrector algorithm. From the algorithm, we can get new positions, velocities, and accelerations of the particles(atoms) after one time step of 0.5 fsec. I repeat these calculations during a wanted period.
The animation was made using Aviz program**. The total time of each simulation is 35 psec, in temperature of 77K.

Click for animation avg(r^2)=4.679 A^2
Click for animation avg(r^2)=1.302 A^2
Click for animation avg(r^2)=1.772 A^2
Click for diffusion animation