Author Topic: Different results for the same data file  (Read 69 times)

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Different results for the same data file
« on: November 29, 2018, 10:07:00 AM »
Hello Alex,

I have two versions install on my Mac machine, I tried to use the Polyhedral template matching, I got the different results in Ovito 3.0.0 and earlier 2.9 versions. I attached the snapshot below. Correct one is OVITO 2.9.

Can you tell me why this discrepancy?

Thanks,
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Alexander Stukowski

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Re: Different results for the same data file
« Reply #1 on: November 29, 2018, 04:13:44 PM »
Hi,

I compared Ovito 2.9.0 and Ovito 3.0.0-dev307 and they give identical PTM results for my test datasets. Are you sure you used the same settings for the PTM modifier in both cases? If yes, please send your dataset so I can reproduce your results.

-Alex

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Re: Different results for the same data file
« Reply #2 on: November 30, 2018, 05:48:24 PM »
Hello Alex,

I attached the file which I used for. I still get the different results. I just want to look individual type for particular structure type say FCC. Do you have any other way than Polyhedral template matching (CNA also behaving similar as Polyhedra template matching).

Thanks,

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Alexander Stukowski

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Re: Different results for the same data file
« Reply #3 on: November 30, 2018, 05:59:32 PM »
Dear ad,

Please check again the value of the "RMSD cutoff" parameter of the PTM modifier. My suspicion is that you have been using different cutoff values (0 in Ovito 2.9.0 but a non-zero cutoff in Ovito 3.0.0).

It is always a good idea to use a non-zero RMSD threshold value (e.g. 0.1, which is the default value in Ovito 3.0.0) when performing the PTM. Without a cutoff, the PTM will try to assign a crystalline structure to any atom, even if the atomic structure is very far off from the ideal lattice structure. The tolerance is basically infinite in this case and that is why you see many crystalline atoms even though your system is amorphous.

With a cutoff value of 0.1, as in Ovito 3.0.0, you get more reasonable results. You will also see that other structure identification algorithms such as Common Neighbor Analysis (CNA) will agree with the PTM in this case. All atoms are classified as "Other", which is typical for amorphous or liquid structures.   

-Alex