[Wien] (no subject)

[Israel Pérez]

Hi Prof. P. Blaha

I need some help with supercell calculations. I'd like to investigate the effect of replacing Se with Te in the system FeSe. Structure file is as shown below.  


FeSe                                                                           
P   LATTICE,NONEQUIV.ATOMS:  2129_P4/nmm                                       
MODE OF CALC=RELA unit=ang                                                     
  7.119735  7.119735 10.364585 90.000000 90.000000 90.000000                   
ATOM  -1: X=0.25000000 Y=0.75000000 Z=0.00000000
          MULT= 2          ISPLIT=-2
      -1: X=0.75000000 Y=0.25000000 Z=0.00000000
Fe         NPT=  781  R0=0.00005000 RMT=    2.1900   Z: 26.0                   
LOCAL ROT MATRIX:    0.7071068-0.7071068 0.0000000
                     0.7071068 0.7071068 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -2: X=0.25000000 Y=0.25000000 Z=0.23720000
          MULT= 2          ISPLIT=-2
      -2: X=0.75000000 Y=0.75000000 Z=0.76280000
Se         NPT=  781  R0=0.00005000 RMT=    1.9400   Z: 34.0                   
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
  16      NUMBER OF SYMMETRY OPERATIONS
-1 0 0 0.00000000
 0-1 0 0.00000000
 0 0-1 0.00000000
       1
 0-1 0 0.00000000
-1 0 0 0.00000000
 0 0-1 0.00000000
       2
 0 1 0 0.00000000
 1 0 0 0.00000000
 0 0 1 0.00000000
       3
 1 0 0 0.00000000
 0 1 0 0.00000000
 0 0 1 0.00000000
       4
-1 0 0 0.50000000
 0 1 0 0.00000000
 0 0 1 0.00000000
       5
-1 0 0 0.50000000
 0-1 0 0.50000000
 0 0 1 0.00000000
       6
 0-1 0 0.50000000
-1 0 0 0.50000000
 0 0 1 0.00000000
       7
 0 1 0 0.50000000
-1 0 0 0.00000000
 0 0-1 0.00000000
       8
 0 1 0 0.00000000
-1 0 0 0.50000000
 0 0 1 0.00000000
       9
 0-1 0 0.00000000
 1 0 0 0.50000000
 0 0-1 0.00000000
      10
 0-1 0 0.50000000
 1 0 0 0.00000000
 0 0 1 0.00000000
      11
 0 1 0 0.50000000
 1 0 0 0.50000000
 0 0-1 0.00000000
      12
-1 0 0 0.00000000
 0 1 0 0.50000000
 0 0-1 0.00000000
      13
 1 0 0 0.50000000
 0-1 0 0.00000000
 0 0-1 0.00000000
      14
 1 0 0 0.00000000
 0-1 0 0.50000000
 0 0 1 0.00000000
      15
 1 0 0 0.50000000
 0 1 0 0.50000000
 0 0-1 0.00000000
      16

Then I copy it to a new session and create a supercell 2X2X1 with lattice F. The program recognizes 8 inequivalent atoms, each with two positions (total of 16 atoms). Then I replace the last atom of Se by Te so that I have a doping of 25% and set its RMT to 2 and the atomic number to 52. RMT_Fe=2.1 and RMT_Se=1.96. Here I have a couple of questions. First, I wonder if we have to label all inequivalent atoms (for instance, Fe1, Fe2, Se1, Se2, etc.) because when I compute xnn, I got a warning like this
WARNING: Mult not equal. PLEASE CHECK outputnn-file WARNING: ityp not equal. PLEASE CHECK outputnn-file WARNING: ityp not equal. PLEASE CHECK outputnn-file NN created a new SFeSeTe.struct_nn file
NN created a new CASE.STRUCT_NN FILE
0.016u 0.000s 0:00.01 100.0%	0+0k 0+160io 0pf+0w
If I continue to x group I got another warning such as this:

warning: !!! Number of inequivalent atoms has changed. !!! Old value= 8 New value= 6 warning: !!! Bravais lattice has changed.
sgroup found: 12 (C 2/m) [unique axis c] cell choice 2


Why? And then the program suggests to change the sgroup. If I don't accept and continue I get an error in editinst step: 

error: SFeSeTe.inst not consistent with Zedit SFeSeTe.inst and rerun lstart afterwards or change Z in StructGen!

On the other hand, if I labeled the atoms, the warnings after xnn is executed don't appear anymore. However, when I run  sgroup, I got a warning:
warning: !!! Struct file is not consistent with space group found. 

sgroup found: !!! Struct file is not consistent with space group found. Number and name of space group: 2 (P -1)

which causes errors in forthcoming steps. Should I labeled them and why? What is the correct procedure to avoid these warnings and perform supercell calculations successfully. I'm a beginner with supercell calculations.

I have already read the manual but the information is not enough to solve this problem. I also checked the wien list of problems. There are some similar to mine but the warnings and errors are different. I'd appreciate any assistance you may have. 

Regards

Thanks

Israel  Perez
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