# How can I find primitive axis for any bulk or 2D (monolayer) material

I am doing DFPT calculations using VASP+Phonopy. To plot phonon band structure, I need a band.conf file in which we need to provide primitive axis. There is an option to use --pa=auto but in my case, it is not working, or maybe for DFPT, we need to supply a proper primitive axis.

Is there any way or code using which we can know the primitive axis of any system?

POSCAR for my system is mentioned below:

System
1.00000000000000
5.2830000000000004    0.0000000000000000    0.0000000000000000
0.0000000000000000    5.2830000000000004    0.0000000000000000
0.0000000000000000    0.0000000000000000   20.0000000000000000
Ta   N
2     4
Direct
0.0000000038778781 -0.0000000040248837  0.4999999999997483
0.5000000098083184  0.4999999954548999  0.4999999998722517
0.1428654795841584  0.6428651637231821  0.5338481609868386
0.8571345120369003  0.3571348472078131  0.5338481661924134
0.6428651606314468  0.8571345203839439  0.4661518370931707
0.3571348450612953  0.1428654882550420  0.4661518358555774

• The documentation says that the primitive axis is the transformation matrix from the primitive cell to the supercell and that it is optional. Are you wanting help defining this matrix using software or help with getting the automatic primitive cell detection in phonopy to work? If it’s the latter, maybe a description of the error message or a minimal example that demonstrates the issue would help get an answer. Aug 27 at 4:13
• Yes, I want to define pimitive_axis to get the phonon band structure. Please let me know if I need to supply some information from my side. Aug 27 at 4:25
• Are you sure that your cell is not already a primitive cell? Aug 29 at 7:54
• Yes, it is already a primitive cell. This is just an example. I am focusing to get a permanent solution to get the primitive axis to get the phonon band structure of any structure. Aug 29 at 13:05
• @astha just to be clear: you are looking for a code that, given a general cell, will output the corresponding primitive cell? Aug 29 at 19:43