I am using Vasp.6.2.1 to compute O K-edge XAS of a Pt/O surface system.

According to the tutorials in XANES_in_Diamond, XAS_theory and F. Karsai et al., Phys. Rev. B 98, 235205 (2018)., I know the absorption spectrum is directly proportional to the imaginary part of the dielectric function, which is calculated by vasp.

At the same time, for the dielectric tensor, from D. Franta, J. Appl. Phys. 127, 223101 (2020). and C. Ambrosch-Draxl and J. O. Sofo, Comput. Phys. Commun. 175, 1 (2006)., I learn about that

In my computation, I use a orthogonal supercell, but there are non-diagonal components:For orthorhombic or higher symmetry only diagonal components exist.

#------------------------------------------------[POSCAR]

Code: Select all

```
11.2210973099999993 0.0000000000000000 0.0000000000000000
0.0000000000000000 9.7177553299999992 0.0000000000000000
0.0000000000000000 0.0000000000000000 25.1999999999999993
```

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```
frequency dependent IMAGINARY DIELECTRIC FUNCTION (independent particle, no local field effects) density-density
E(ev) X Y Z XY YZ ZX
...
523.041135689617 0.000009617600 0.000009741858 0.000005636892 0.000000000000 0.000000106472
0.000000000000
523.073657478992 0.000009747511 0.000009727933 0.000005659724 0.000000000000 0.000000084890
0.000000000000
...
```