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[lammps-users] Problem with Ackland Analysis
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[lammps-users] Problem with Ackland Analysis

From: Olivier Politano <olivier.politano@...1102...>
Date: Fri, 4 May 2018 11:40:30 +0200

Dear Lammps users,

We are still working with Lammps 12Apr13. When we perform an ackland analysis with this version of LAMMPS, we obtain the following image for some atomic configuration. BCC atoms are represented in blue and FCC atoms are green.

If we perform the same calculation with a version of LAMMPS 7Dec15 or 11Aug17, the result is drastically different. Many BCC atoms of the structure are erroneously tagged as FCC. 

I also computed the atomic environment with the CNA adaptative algorithm available in OVITO. The result obtain with OVITO is coherent with the oldest version of LAMMPS (12 Apr 13). BCC atoms are represented in blue and FCC atoms are green and white atoms are unknown.

With the cross-checking of the results with the CNA adaptative procedure of OVITO, I suspect the Ackland analysis to be erroneous in the newer version of LAMMPS.

I went through the file « compute_ackland_atom.cpp » in the USER-MISC directory and I found some modifications between the versions 12Apr13 and 7Dec15 (or later). However, I did not find mentions of these changes in the webpage "Latest Features and Bug Fixes in LAMMPS » or in the source file.

So, I’m wondering if someone also noticed this drastic difference of result for the Ackland analysis and if there is a bug or a problem with the newer implementation of Ackland.