How to read space group diagrams

[@frankjohnson123]

Tremendously helpful, thank you very much

[@shivamkansara1968]

Dear Dong Zhou, In Pm-3m, P for primitive, m for mirror, -3 for three fold symmentry followed by inversion and m for mirror. So what is meaning of mirror here ? 2 for what and last one for what ?

[@mentalflow]

Are you asking about (x, -y, -z)? You can say it's a 2-fold rotation along x axis, or consecutive mirror operations with respect to the xz plane (y->-y) and xy plane (z->-z), or some other composite interpretation as long as their action makes (x, y, z) to (x, -y, -z)

[@shivamkansara1968]

@@mentalflow Than you for reply. As I understood that in Pm-3m, P stands for primitive lattice. m is mirror plane along principle axis (111) and -3 is three fold rotation wrt xy, yz and xz axis plane as well as inversion in ??? points. and there is again mirror plane along ???? plane. First of all, had I right explained ? If yes so ??? is my question. I mean in which planes and which points?

[@mentalflow]

For cubic lattices, the Bravais group is m-3m where m001=(x,y,-z), -3=(-z, -x, -y) is along 111, m110=(-y, -x, z)

[@mentalflow]

Actually Pm-3m is only a short notation for P 4/m -3 2/m. You cannot generate all symmetries from the 3 symmetries (m, -3, m) I mentioned in the previous comment. They are only generators for cubic lattice point group, not the space group. img.chem.ucl.ac.uk/sgp/large/221az1.htm

[@shivamkansara1968]

@@mentalflow Thank you @Dong Zhou for clearing my confusions.

[@shivamkansara1968]

Dear Dong Zhou, FAPbI3 (HC(NH2)2PbI3) perovskite structure has Imm2 space group. here I stands for the body centered lattice but in this structure, Can you please help me to find body centered lattice ? Thank you

[@mentalflow]

I don’t understand your question. Do you want me to find that crystal structure? I don’t know what is an efficient way to find that. There are a few open data sets, you can try your luck there

[@shivamkansara1968]

@@mentalflow No actually I want to understand the body center atom in FAPBI3 structure. It has Imm2 space group and 'I' stands for body center. Hope now It would be clear. shorturl.at/cBDQY

[@mentalflow]

@@shivamkansara1968 I don't have access to that paper. It's better to look at the real crystal structure say in Mercury to see all the symmetries. Or img.chem.ucl.ac.uk/sgp/large/044az1.htm for a simple representation. Each circle represents an atom in the ASU

[@yassineab8476]

Thank you for the video and your effort Why do we have screw operation in C121?

[@mentalflow]

compare (-x, y, -z) and (x+1/2, y+1/2, z)

[@KULDEEPSINGH-hl6oe]

Hello sir, can you provide me atmic position of Al2Mn2O7 compound which belongs to monoclinic phase and P2/m space group?

[@mentalflow]

I don’t know where to find that structure. I work on molecular crystals exclusively

[@mentalflow]

You can try your luck on these inorganic crystal data sets www.crystallography.net/cod/ rruff.geo.arizona.edu/AMS/amcsd.php database.iem.ac.ru/mincryst/search.php? webmineral.com/MySQL/xray.php icsd.products.fiz-karlsruhe.de/en