CNA error for high temperature and track

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1

Dear all.

I have a question for CNA/atom to check vacancy.

I deleted one atom in simulation box to make vacancy.

Duringmigration (using NVE), I was tring to find vacancy and track it.

For this, I used CNA or coordination number to find vacancy in simulation box, and chunk to track it.

for bcc alpha iron, cut off of 3.5 is used in the input file.

With low temperatures (350K, 400K …), I can find only one vacancy in the simulation box with OVITO.

However, when I use high temperatures (800K, 1000K),
the CNA gives many wrong atoms, but it is not real vacancy, because of thermal fluctuations.

How can I get the right vacancy? What do I have to concern more?

Do I need to have more longer time for stablization of temp?

Does the box size or boundary atoms affect to the CNA?

To track, vacancy, can I use chunk or are there any other good methods?

2

For a high-temperature, disordered material, there

is no simple definition of “vacancy”. Any method

in LAMMPS (CNA, coord/atom, centro/atom, etc)

will have increasing troubles as you raise the temp.

Ditto for similar methods in OVITO.

Steve