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Re: [lammps-users] Different potential energy calculation results
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Re: [lammps-users] Different potential energy calculation results

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Tue, 19 Dec 2017 09:45:30 -0500

On Tue, Dec 19, 2017 at 3:33 AM, Xiao Jia <xiaoj@...1508...> wrote:
Dear LAMMPS users,

I am referring the function single () defined in pair.cpp to calculate the pairwise force coefficient fpair and the potential energy.
eng=pair->single (i, j, itype, jtype, rsq, factor_coul, factor_lj, fpair);
The current potential I am using is EAM potential.

The weird observation I have is that my summation of the potential energy (eng value of each pair) from all the pairs does not match with the output from log file. The value I get is -21936114 and the value from log file is -63005273, the difference is close to 3 times. 

The calculation of pressure based on fpair seems to be consistent with the value from log file, but the difference in potential energy is hard to understand. 

​your e-mail is missing two important pieces of information.

1) which LAMMPS version you are using exactly. what you are reporting sounds a lot like a bug that was fixed not so long ago.
2) an example input deck that allows to quickly reproduce your issue (in case this is a real bug and still exists with the latest patch release).



I will appreciate it so much if anyone can give me any idea about this issue.

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Dr. Axel Kohlmeyer  akohlmey@...12...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.