[QE-users] Different crystal structure between pw.x and ph.in output files for non-centrosymmetric compund

[Arena Konta]

Hello,
 
I try to do calculations for noncentrosymmetric superconductor CaIrSi3 ( tetragonal BaNiSn3-type crystal
structure, with space group I4mm (no. 107)) using QE 6.3: 
 
************************************************************************
&SYSTEM
       ibrav = 0
celldm(1)=7.90529
nat=5
ntyp=3
 
/
 
 
 
 CELL_PARAMETERS alat
 1.000000000000000   0.000000000000000   0.000000000000000
  0.000000000000000   1.000000000000000   0.000000000000000
  0.500000000000000   0.500000000000000   1.180025338847321
 
 
 
  
ATOMIC_POSITIONS (crystal)
Ir   0.763090000000000   0.763090000000000   0.473820000000000
Ca   0.409750000000000   0.409750000000000   0.180500000000000
Si   0.650890000000000   0.150890000000000   0.698220000000000
Si   0.150890000000000   0.650890000000000   0.698220000000000
Si   0.000000000000000   0.000000000000000   0.000000000000000
 
******************************************************************************
 
scf goes fine and I get at the beginning of the output:
         
   bravais-lattice index     =            0
     lattice parameter (alat)  =       7.9053  a.u.
     unit-cell volume          =     582.9680 (a.u.)^3
     number of atoms/cell      =            5
     number of atomic types    =            3
     
 
     celldm(1)=   7.905290  celldm(2)=   0.000000  celldm(3)=   0.000000
     celldm(4)=   0.000000  celldm(5)=   0.000000  celldm(6)=   0.000000
 
     crystal axes: (cart. coord. in units of alat)
               a(1) = (   1.000000   0.000000   0.000000 )
               a(2) = (   0.000000   1.000000   0.000000 )
               a(3) = (   0.500000   0.500000   1.180025 )
 
     reciprocal axes: (cart. coord. in units 2 pi/alat)
               b(1) = (  1.000000  0.000000 -0.423720 )
               b(2) = (  0.000000  1.000000 -0.423720 )
               b(3) = (  0.000000  0.000000  0.847439 )
 
 
     
But when I start ph.x calculation (in the same folder using exactly the same values) I get:
     
     
     bravais-lattice index     =            0
     lattice parameter (alat)  =       7.9053  a.u.
     unit-cell volume          =     582.9680 (a.u.)^3
     number of atoms/cell      =            5
     number of atomic types    =            3
     
 
 
     celldm(1)=   15.81058  celldm(2)=   Infinity  celldm(3)=    0.68783
     celldm(4)=    0.00000  celldm(5)=    0.36346  celldm(6)=    0.00000
 
     crystal axes: (cart. coord. in units of alat)
               a(1) = (  1.0000  0.0000  0.0000 )
               a(2) = (  0.0000  1.0000  0.0000 )
               a(3) = (  0.5000  0.5000  1.1800 )
 
     reciprocal axes: (cart. coord. in units 2 pi/alat)
               b(1) = (  1.0000  0.0000 -0.4237 )
               b(2) = (  0.0000  1.0000 -0.4237 )
               b(3) = (  0.0000  0.0000  0.8474 )
 
 
Why there are such differences in celldm? 
 
-- 
with regards
 
Arena Konta
The Institute of Thermophysics in Novosibirsk Scientific Center
     

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