[QE-users] How does pw.x make the cell choice for space group No.12 with unique axis b ?

[Michal Husak]

You should describe your structure by the space group setting.
IBRAW and Wickoff position will be handled automatically
+ you can copy the coordinates directly form the CIF ....


>Dear QE experts,
>
>
>I find it confusing in the description Wyckoff position 
>specifications in the card ATOMIC_POSITIONS.
>
>https://www.quantum-espresso.org/Doc/INPUT_PW.html
>
>
>For space group No.12 under the convention unique axis b, there are 
>three cell choices. The Wyckoff position 4i has different forms for 
>the three choices, namely (according to ITA)
>
>UNIQUE AXIS b, CELL CHOICE 1
>
>4i  x,0,z  ;  x+1/2,1/2,z  ;  xb,0,zb  ;  xb+1/2,1/2,zb
>
>UNIQUE AXIS b, CELL CHOICE 2
>
>4i  x,0,z  ;  x,1/2,z+1/2  ;  xb,0,zb  ;  xb,1/2,zb+1/2
>
>UNIQUE AXIS b, CELL CHOICE 3
>
>4i  x,0,z  ;  x+1/2,1/2,z+1/2  ;  xb,0,zb  ;  xb+1/2,1/2,zb+1/2
>
>(xb means x-bar)
>
>
>If I am to write the ATOMIC_POSITIONS card, how should I specify the 
>parameters x and z? How do I know that pw.x takes CELL CHOICE 1/2/3 ?
>
>
>Thank you for your help.
>
>
>Best regards,
>
>Yunlong Lian