Question about hexagonal crystal axes alignment

[hakonanes]

Hi @marcdegraef (and others),

are hexagonal master patterns in EMsoft simulated with the a axis east and the c* axis out of plane?

I'm asking because I'm toying with kinematical simulations in kikuchipy (docs), where we align e1 || a and e3 || c*, which I believe is used throughout EMsoft for stereographic projections. However, I end up with the strongest reflections being rotated 30 degrees compared to EMsoft, i.e., it looks like e1 || a*:

Band simulation in kikuchipy (a = red, b = green, c = blue):

Dynamical simulations in EMsoft with the same phase:

Is the assumption that the alignments are the same wrong? If not, the difference might come from a wrong reflector list in kikuchipy (and/or the non-realistic kinematical intensities).

[marcdegraef]

Hi Håkon,

EMsoft uses the following convention for all crystal systems:  e_1 || a and pointing east, and e_3 || c* (i.e., normal to the a-b plane).  If you do note a rotation of 30°, it is possible that there is an issue with the orientation of the point group elements... Can you post the space group number for this case so I can check?

Thanks, Marc.

On 6/15/22 12:15 PM, Håkon Wiik Ånes wrote:

Hi @marcdegraef https://github.com/marcdegraef (and others),

are hexagonal master patterns in EMsoft simulated with the a axis east and the c* axis out of plane?

I'm asking because I'm toying with kinematical simulations in kikuchipy (docs https://kikuchipy--537.org.readthedocs.build/en/537/user_guide/kikuchi_pattern_simulations.html#Silicon-carbide-6H), where employ the crystal axes alignment |e1 || a| and |e3 || c*|, which I believe EMsoft throughout for stereographic projections. However, I end up with the strongest reflectors being rotated 30 degrees compared to EMsoft (a = red, b = green, c = blue)

bilde https://user-images.githubusercontent.com/12139781/173874376-dc20eb91-a9f3-4dcf-84e5-7dd2d8f0a240.png

Dynamical simulations in EMsoft with the same phase

hex_emsoft https://user-images.githubusercontent.com/12139781/173875371-ca097f52-b5bf-46c9-bb45-bd675d93572b.png

Is the assumption that the alignments are the same wrong? If not, the difference might come from a wrong reflector list in kikuchipy (and/or the non-realistic kinematical intensities).

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[hakonanes]

Thank you for the quick reply. OK, that is as expected (since you wrote it in your 2013 paper with Callahan).

The space group is 186. For completeness, here's the relevant information in the crystal file:

AtomData
[[0.    0.333 0.667 0.    0.333 0.667]
 [0.    0.667 0.333 0.    0.667 0.333]
 [0.    0.167 0.667 0.125 0.292 0.833]
 [1.    1.    1.    1.    1.    1.   ]
 [0.005 0.005 0.005 0.005 0.005 0.005]]
Atomtypes
[14 14 14  6  6  6]
CreationDate
[b'Jun 17 2020']
CrystalSystem
[4]
LatticeParameters
[  0.3073   0.3073   1.5079  90.      90.     120.    ]
Natomtypes
[6]
ProgramName
[b'EMmkxtal.f90']
SpaceGroupNumber
[186]
SpaceGroupSetting
[1]

[hakonanes]

This discrepancy has been resolved by a fix in the latest release of orix 0.12.0 (see the changelog https://orix.readthedocs.io/en/stable/changelog.html#id1). New kinematical simulations (using only about 400 reflections and not 900 as in the other simulation above):