<< error generating Special Quasi Random Structures >>

[I. Camps]

Hello USPEXers,

I am trying to generate Special Quasi Random Structures - SQRS (from example T18_order_without_relaxation, USPEX 9.2.7)

The system I am trying to simulate is TixCo(1-x)O2. In this case I need a SQRS of 96 atoms with 16 atoms of Ti, 16 atoms of Co (equivalent to x=0.5) and 64 atoms of O.

The error was:
"Could not generate a structure after 30000 tries or 15 minutes. Please check the input files. The calculation has to stop."

Any ideas?

Best regards,

Camps

[huy pham]

Hi,

In your INPUT file, the valence of O should be 2 instead of -2 I think,

Cheers,
Huy

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Pham Cong Huy
PhD student, Condensed Matter Section
SISSA International School for Advanced Studies
Via Bonomea 265, I- 34136, Trieste, Italy
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cp...@sissa.it

[huy pham]

IonDistances should not be
1.5 1.5 1.5
1.5 1.5 1.5
1.5 1.5 1.5
Use
1.5 1.5 1.5
0.0 1.5 1.5
0.0 0.0 1.5

[Artem Oganov]

Right - valence is always positive, so "2" (not "-2" which would be charge).

Also, in Camps's INPUT.txt there is a line

% 1090

that needs to be removed.

 

Most importantly - for generating SQS, you need an initial (ordered or somewhat disordered) supercell in Seeds/POSCARS.

 

Cordially yours,

Artem
******************
Prof. Artem R. Oganov
Department of Geosciences and Department of Physics and Astronomy, State University of New York, Stony Brook, NY 11794-2100

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NEWS: Evolutionary metadynamics: a novel method to predict crystal structures. Cryst. Eng. Comm. 14, 3596-3601. (2012).
******************
NEWS: Evolutionary crystal structure prediction enabled for molecular crystals: Acta Cryst. B68, 215-226 (2012). [Feature Article]
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NEWS: Structure of "superhard graphite" established: Scientific Reports 2, 471 (2012).
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NEWS: Structure of magnesium borohydride established: Phys. Rev. Lett. 109, 245504 (2012).
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NEWS: Stable xenon oxides predicted: Nature Chemistry 5, 61-65 (2013).
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IUCr Commission on Crystallography of Materials: http://www.iucr.org/iucr/commissions/crystallography-of-material

[I. Camps]

Hello,

First of all: thank you very much for the suggestions (Prof. Artem and Huy). Finally, I got the SQS!

But I have some questions. For my system (16 Ti atoms, 16 Co atoms and 64 O atoms):

-) I had to decrease the ion distance to almost zero to generate the SQS

0.05 0.05 0.05
0.0 0.05 0.05
0.0 0.0 0.05

Is this normal? I tried with 1.5, 1.0, 0.5, 0.25, but always get the complains

-) From the results I had two files: POSCAR and POSCAR_order. In the POSCAR_order, what is the meaning of the fourth number that appear at the end of each line containing the coordinates? Ex:

POSCAR: 0.25 0.75 0.25

POSCAR_order: 0.25 0.75 0.25 2.6479

-) Is there any tool (or hack) that "convert" the POSCAR output to a file format containing the atoms and the crystal structure information?

Best regards,

Camps