My Community

Hello,

I'm tying to preform a simple [111] surface energy calculation for BCC iron. I'm noticing that the ion positions in the OUTCAR don't agree with what written in the POSCAR. Needless to say my calculations are not converging in the desired fashion. Here is my POSCAR file:

BCC Fe 9-layer 111 Slab
1.00
3.52 -2.03 0.00
3.52 2.03 0.00
0.00 0.00 23.12
9
Selective dynamics
Cartesian
0.00 0.00 0.00 T T T
1.17 -2.03 1.64 T T T
2.34 0.00 3.28 T T T
0.00 0.00 4.92 T T T
1.17 -2.03 6.56 T T T
2.34 0.00 8.20 T T T
0.00 0.00 9.84 T T T
1.17 -2.03 11.48 T T T
2.34 0.00 13.12 T T T

The initial positions in my OUTCAR are given by:

position of ions in cartesian coordinates (Angst):
0.00000000 0.00000000 0.00000000
4.69000000 0.00000000 1.64000000
2.34000000 0.00000000 3.28000000
0.00000000 0.00000000 4.92000000
4.69000000 0.00000000 6.56000000
2.34000000 0.00000000 8.20000000
0.00000000 0.00000000 9.84000000
4.69000000 0.00000000 11.48000000
2.34000000 0.00000000 13.12000000

As you can see the Z-direction positions agree, but the X- and Y-directions do not agree. Why would I be getting this problem? Thanks.

Regards

Modey3

the positions of atoms 2, 5 and 8 are outside the range of the 2D unit cell. Vasp translates them back into the range of the 2D cell given by the Bravais matrix by adding a unit vector of a2.