From: Walter Roberson <>
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Subject: Re: Crater function plot.
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Date: Thu, 29 Jan 2009 13:23:02 -0600
Xref: comp.soft-sys.matlab:514794

Kallol Das wrote:

> Actually I am modeling a molecular dynamics simulation. I need some sample crater functions as
> the input files. The momentum, velocity and other stuffs are included in my MD code. I just
> need some crater functions as a input to the code.

> The crater functions that I am looking for is something like a predicted shape of surface if
> it is hit by an atom. I just need the surface shape. And some variables namely theta,
> maximum height of the ripple, and a decaying factor by which I can change the shape of the surface.

> The surface will look very similar to the craters made on the earth surface by the meteors?

Hmmm, something doesn't sound right.

If you are doing this for molecular dynamics then you need to take into account the
electrostatic repulsion or attraction between the atom and the molecular surface.
And your molecular surface will, on the scale of an atom, be quite bumpy, and on
that scale it is *not* going to move like earth does. For one thing, with meteors
(or the like) hitting the earth, the meteor embeds itself in the earth (unless
the shockwave of compressed air is enough to push most of it back out of
the hole), but an atom hitting a molecular surface has a non-negligible chance
of bouncing out again, possibly after having knocked an atom or a chain out of
the molecule. And the reaction of the molecule to having an atom or chain knocked
out is going to depend upon the chemistry of the molecule. "Atom hitting a molecule
or surface leading to a molecular change" is a fair description of normal chemical
reactions involving gases or (simple) liquids around the target molecule.

When you are working at the level of single atom interaction with something, you
need to ask whether there will be quantum effects or relativistic effects or
wave-particle duality effects. 

Are you trying to model something like "sputtering"?