Hello Yash Ghoda

With my previous experience, Crystallography and Computational Chemistry sometimes don't deal with crystal in the same manner. For example in VESTA, you must define a crystal symmetry before doing anything, and VESTA don't draw individual atoms. Which means that when i t generates a CIF file, it may show the minimum atoms, with the associated space group. Quantum ESPRESSO and XCrysden allow you do draw the atoms as you wish, but they will determine the symmetry ACCORDING to atomic positions. Do a simple SCF calculation with this structure, and check what is the symmetry Quantum ESPRESSO are understanding about your structure.

In output file, before the energies vales, you will see a section like this:

atomic species valence mass pseudopotential

Cs 9.00 132.90545 Cs( 1.00)

Pb 14.00 207.21000 Pb( 1.00)

I 7.00 126.90447 I ( 1.00)

16 Sym. Ops., with inversion, found

I Don't remember now how many symmetries tetragonal must have, but you can also execute the calculation with the command:

verbosity='high'

Put this in the &CONTROL card, preferably after the other commands. This will allow the code to generate a detailed explanation of the symmetry of your crystal. Also, I can see that XCrysden is not setting your crystal as tetragonal, it's very different from the structure that is shown in VESTA. You could try to remove the symmetry from the crystal and export a list of atoms with all of them. Please, let me know if you need more help.

Best regards,

Ricardo Tadeu

@RicardoTadeuMaia. Thank you so much for your kind help.

After going through cordinates in vesta, i was able to construct "VESTA" Looking structure in xcrysden. But upon,running scf i am getting 16 symmetric operations with inversion for my Bct structure.

Only problem now is that, upom running vc relax one of the atom, (Si in case) goes missing from the periodic boundary, which ultimately again makes crystal far from what i was expecting.

If i let ibrav to be 0 no such issu

e in relaxation or xcrysden is arising.

16 symmetry operations with inversion is correspondent to BCT? I can't remember right now.

Vc-relax has another tricky problem. Did you put in your code the command:

cell_dofree= 'ibrav'

In &CELL card? This command forces QE to preserve the ibrav of the structure. But if you put a structure that QE don't understand as tetragonal, it will not be tetragonal in the last step. But there is another tricky bug in the last step of vc-relax, something about the atomic coordinates "crystal" or "alat". Please, send a private message, and we can deal with it.