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From: | Florian Weik |
Subject: | Re: [ESPResSo-users] ESPResSo Lennard-Jones cut-off question |
Date: | Mon, 14 Jul 2014 14:18:32 +0200 |
Dear all,I was playing around with the "analyze energy" command when I found that it gave me zero energy for systems which I assumed was supposed to give non-zero energies. I tested a small script as follows:setmd box_l 10 10 10
inter 0 0 lennard-jones 1.0 1.0 3.0
part 0 pos 0 0 0 type 0
part 1 pos 0 0 2.1 type 0
puts [analyze energy]I was expecting a non-zero energy but it returns the following:{ energy 0.0 } { kinetic 0.0 } { 0 0 nonbonded 0.0 }If I change the lennard-jones cut-off to 3.1, however, I get a non-zero energy; I get the following output{ energy -0.041592730503778354 } { kinetic 0.0 } { 0 0 nonbonded -0.041592730503778354 }I dug up an old thread from 24 Aug 2007 and it saysFor the future you can test your question more easily yourself with:
setmd box_l 10 10 10
part 0 pos 1 1 1 type 0
part 1 pos 1.5 1 1 type 1
inter 0 1 lennard-jones 2 2 1 1 0
analyze energy
If this doesn't give you a nonzero energy, please bug me again!This does not, in fact, give me a nonzero energy; it gives me a zero energy. I played around with the feature some more and I think that the Lennard-Jones cuts off at 1 less than the cut-off value specified (or r_cut - 1). Is this really the way the potential works or did I do something wrong? I tried this on different machines and they gave me the same results. I am using ESPresSo 3.2.0.--
Kue, Karl Thomas Y.
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