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Dear VASP users:
I want to built a rhombohedral structrue A2B3, following the manual I think the POSCAR file of structure can be written as follows:
first POSCAR
A2B3
1
2.132 -1.231 10.1527
0.000 2.462 10.1527
-2.132 -1.231 10.1527
3 2
Cartesian
0.000 0.000 0.000
0.000 0.000 6.48
0.000 0.000 -6.48
0.000 0.000 12.14665
0.000 0.000 -12.14665

second POSCAR:
Sb2Te3
1.00
2.132 -1.231 10.1527
0.000 2.462 10.1527
-2.132 -1.231 10.1527
3 2
Direct
0.0 0.0 0.0
0.21275 0.21275 0.21275
0.78725 0.78725 0.78725
0.39880 0.39880 0.39880
0.60120 0.60120 0.60120

I use the software VESTA to get a 3-dimentional picture with the above two POSCAR, although they have the same number of atoms in the unit cell and the volume of the unit cell is the same, the distribution of atoms in the unit cell seem to quite different.Do the POSCAR files mean the same structure?
Any suggestions will be welcomed, thanks for your attention.

Let A = [0.0 0.0 0.0
0.21275 0.21275 0.21275
0.78725 0.78725 0.78725
0.39880 0.39880 0.39880
0.60120 0.60120 0.60120 ];

B = [2.132 -1.231 10.1527
0.000 2.462 10.1527
-2.132 -1.231 10.1527 ];

The matrix product C = A*B then gives you the carteesian coordinates:

C = [ 0.00000 0.00000 0.00000
0.00000 0.00000 6.47996
0.00000 0.00000 23.97814
0.00000 0.00000 12.14669
0.00000 0.00000 18.31141];

Subtracting 3*10.1527 from element C(3,3) and C(5,3) gives you the coordinates in the first POSCAR file, so the coordinates are the same. Your VESTA software probably doesn't understand the meaning of either the direct entries or the carteesian coordinate entries.

Best regards,
/Dan

[quote author= [0.0 0.0 0.0
0.21275 0.21275 0.21275
0.78725 0.78725 0.78725
0.39880 0.39880 0.39880
0.60120 0.60120 0.60120 ];

B = [2.132 -1.231 10.1527
0.000 2.462 10.1527
-2.132 -1.231 10.1527 ];

The matrix product C = A*B then gives you the carteesian coordinates:

C = [ 0.00000 0.00000 0.00000
0.00000 0.00000 6.47996
0.00000 0.00000 23.97814
0.00000 0.00000 12.14669
0.00000 0.00000 18.31141];

Subtracting 3*10.1527 from element C(3,3) and C(5,3) gives you the coordinates in the first POSCAR file, so the coordinates are the same. Your VESTA software probably doesn't understand the meaning of either the direct entries or the carteesian coordinate entries.

Best regards,
/Dan[/quote]

Dear forsdan,
Thank you so much for your reply. I got what you mean.

Best wishes,
Chris

VESTA assumes the positions are fractional, i.e. it ignores the Cartesian flag in POSCAR!