The analyzed space group by pymatgen does not match the space group the heusler or perovskite should have (225/221)

[MilesZhao]

Hi there,

Thanks for your help! Now I can generate the materials of heusler and perovskite, which is great!

I generated 1000 samples and tried to understand them. Below are two examples of heusler and perovskie materials, respectively.

ex mat1:
# generated using pymatgen data_MgAgO3 _symmetry_space_group_name_H-M 'P 1' _cell_length_a 4.24242926 _cell_length_b 3.87654877 _cell_length_c 3.97564435 _cell_angle_alpha 90.00000000 _cell_angle_beta 90.00000000 _cell_angle_gamma 90.00000000 _symmetry_Int_Tables_number 1 _chemical_formula_structural MgAgO3 _chemical_formula_sum 'Mg1 Ag1 O3' _cell_volume 65.38338299 _cell_formula_units_Z 1 loop_ _symmetry_equiv_pos_site_id _symmetry_equiv_pos_as_xyz 1 'x, y, z' loop_ _atom_site_type_symbol _atom_site_label _atom_site_symmetry_multiplicity _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z _atom_site_occupancy Ag Ag0 1 0.00018641 0.00516879 0.01218479 1 O O1 1 -0.00928536 0.47925205 0.51363987 1 O O2 1 0.43859372 0.00218750 0.53234377 1 O O3 1 0.50947471 0.50731383 -0.00132978 1 Mg Mg4 1 0.46758641 0.45861037 0.47057847 1

ex mat2:
# generated using pymatgen data_GdCrO2 _symmetry_space_group_name_H-M 'P 1' _cell_length_a 3.51839519 _cell_length_b 3.70698476 _cell_length_c 3.81973004 _cell_angle_alpha 90.00000000 _cell_angle_beta 90.00000000 _cell_angle_gamma 90.00000000 _symmetry_Int_Tables_number 1 _chemical_formula_structural GdCrO2 _chemical_formula_sum 'Gd1 Cr1 O2' _cell_volume 49.81935364 _cell_formula_units_Z 1 loop_ _symmetry_equiv_pos_site_id _symmetry_equiv_pos_as_xyz 1 'x, y, z' loop_ _atom_site_type_symbol _atom_site_label _atom_site_symmetry_multiplicity _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z _atom_site_occupancy Gd Gd0 1 0.00339958 0.00629250 0.01095058 1 O O1 1 0.49762579 -0.00460633 0.49799109 1 Cr Cr2 1 0.49284538 0.50370067 0.49876646 1 O O3 1 0.50543748 0.41581251 0.10943751 1

ex mat1 is perovskite and ex mat2 is heulser.

I am not an expert in material science. When I used pymatgen to analyze their space groups, it gave me 'Pm' for ex mat2 and 'P1' for ex mat1. Does this mean the generated two materials are potential materials for heulser and perovskite? After DFT optimization, potentially they will be heulser and perovskite?

Thank you!
Yong

[cjcourt]

@MilesZhao Thanks for your question.

The space groups in the output files from generate.py are estimated using the pymatgen SpaceGroupAnalyzer.

I am not 100% familiar with how it works but generally I would not use it as an estimate of material quality, since a space group is just a measure of symmetry, and the space group is not a defining feature of a crystal structure.

For example, Heusler compounds appear in 3 different space groups. The foremost is the regular Heusler, X2YZ, Cu2MnAl-type compound (space group Fm3̅m). The second type is the inverse Heusler compound, Hg2CuTi type (F43m), and, finally, the XYZ MgCuSb-type half-Heusler. All three of these types of crystal structures can be encoded using a single tetrahedral unit cell in space group F43̅m. So as you can see, the space group is not fixed for a given material class.

You can see how this changes if you edit the lattice angles (parameters alpha, beta and gamma), in generate.py. For instance, if you set all three to 60 degrees, as would be common for a Heusler compound in the Tetrahedral Fm3̅m space group, you will get different results.

As for your point about if these material candidates would be feasible. It is impossible to say without further analysis, there are many many factors that should be explored for this to be determined.

Hope this helps.
CC

[MilesZhao]

thanks.