[Pw_forum] Space Group Issue

[Amar Singh]

Dear Friends,​Its my first appearance on forum and hope I can reach you via pw_forum at pwscf.org. I am trying to optimize the structure of BaTiO3 in R3C space group (No. 161). I am using the lattice parameters as suggested on QE website, Celldm (1) = a (bohr) and Celldm (3) = c/a. While b = a and angles are 90, 90 and 120 (hexagonal setting) are fixed for the space group. Space group should be able to generate 30 atoms (6 BaTiO3 units) in the unit cell. Following is the part of script I am using.&system    ibrav =  4,    celldm(1) = 10.578, celldm(3) = 2.475,    nat =  3,    ntyp = 3,    ecutwfc = 40 space_group = 161ATOMIC_POSITIONS crystal_sgBa 0.00000 0.00000 0.26640 1 1 1Ti 0.00000 0.00000 0.01568 1 1 1O 0.1338 0.3363 0.08333 1 1 1As I start the run, I am encountered with the error message "ibrav not compatible with the space group number". If I look for other ibrav options (http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#CELL_PARAMETERS), I do not find any other having a and c/a as inputs (as they are the only independent lattice parameters for hexagonal setting of R3C space group !). Please suggest me what should I try, and if I am doing anything wrong !!thanksAS
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