On Tue, 20 Feb 2007, Oleksandr Voznyy wrote:
First, the net force on a neutral system must be zero?
yes.
But from the
output, I don't see this. I even tried to run one atom in a big periodic
cell. To my surprise, the force on this single atom is not zero?
How far is it from zero?
You need also a good grid, i.e. high EnergyCutoff to get it closer to zero.
siesta: Atomic forces (eV/Ang):
siesta: 1 0.081809 0.078704 -0.082804
siesta: ----------------------------------------
siesta: Tot 0.081809 0.078704 -0.082804
This might be the problem since I used the default Cut-off of 100 Ry. I
remember people told me that I need at least 300 Ry. I didn't realize that
this affects the total force.
I'll have to make balance between accuracy and the computation time.
Thanks again.
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Physics explains everything!
-- You Lin
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You Lin
Department of Physics
University of South Florida
4202 East Fowler Avenue
Tampa, FL 33620
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Tel: (813) 974-8233 [Office]
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Homepage: http://shell.cas.usf.edu/~ylin
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