[Pw_forum] Space Group Issue

[Amar Singh]

Dear Paolo Giannozzi ​, Thanks for your valuable suggestion, it helped up to some extent. I really appreciate your help.I tried your suggestion, with approximate values of lattice parameters for rhombohedral setting (as I have lattice parameters for only hexagonal settings). Following is the part of script (celldm(1) = a=b=c = 4.1 A and celldm(4) = alpha = beta = gamma = Cos (89.8))   celldm(1) = 7.589, celldm(4) = 0.00317,    nat =  3,    ntyp = 3,    ecutwfc = 40 space_group = 161 rhombohedral=.false.....ATOMIC_POSITIONS crystal_sgBa 0.0139  0.0139 0.0139 1 1 1Ti 0.5000  0.5000  0.5000 0 0 0O 0.5213  0.5213  0.0328 1 1 1​But I am still getting 6 Ba, 6 Ti and 6 O.Now, when I changed rhombohedral = .true., I am getting the 2 atoms of each kind, as you predicted. My first question is that if the unit cell given by me has a volume ~ 64 A3 which fits one BaTiO3 unit, how can space group generate two units of BaTiO3 for same volume ??​My other problem is that the CIF file which I have (true data reported from X-ray diffraction) has lattice parameters for hexagonal setting​ a = b = 5.5 A, c = 13 A and alpha = beta = 90, gama = 120. ​Now for this unit cell, R3c should be able to generate 6 units of BaTiO3. ​How can I write my input script to give me this unit cell optimized with 30 atoms (6 + 6 + 18). rhombohedral = false works fine for Ba and Ti, but not for O somehow ?​thanks
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