Can I use fix momentum for this purpose?

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Dear Ray, Thanks very much!

I do not quite understand your reply. Do you mean I should let one surface of my system to be fixed?

But in my case, projectile’s velocity parallels y axis, and I need to let surfaces at +x, -x, +y, -y axis to be free boundaries. Along z axis periodic boundary condition is applied.

So I think maybe fix one surface is not applicable.

Best Regards

Liu

2015-08-31

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Dear Ray, Thanks very much!

I do not quite understand your reply. Do you mean I should let one surface
of my system to be fixed?

Yes, in this case the -y axis (or to be more exact the xz plane) should be
immobilized.

But in my case, projectile's velocity parallels y axis, and I need to let
surfaces at +x, -x, +y, -y axis to be free boundaries. Along z axis
periodic boundary condition is applied.

I don't see why you have to have free boundaries in cascade simulations.

Ray

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Dear Ray:

I need to use free boundaries because I want to simulate cascade in nanostructure rather than in bulk. The system’s size is relatively small. If the boundary is fixed, I am afraid it cannot represent a real system.

Best Regards

Liu

2015-08-31

5

Dear Ray:

I need to use free boundaries because I want to simulate cascade in
nanostructure rather than in bulk. The system's size is relatively small.
If the boundary is fixed, I am afraid it cannot represent a real system.

​if the system is a free nano-particle, then whatever momentum is
transferred *will* cause translation or rotation. in that case, you must
not use a thermostat, either (what would the particle couple to?).

axel.