polarisation direction in LOPTICS

[call_me_Al]

Hi everyone,

In the framework of the linear optical response, using LOPTICS, VASP outputs the complex dielectric function for several directions, xx, yy, zz and xy, yz ,zx.

I suppose that these correspond to the various directions of the incident beam, or electric field, but I am not sure.

My question is: how is the polarisation of the light defined in VASP (LOPTICS), if it is linear, which direction is the orientation relative to the unit cell?

What do the off axis dielectric function number mean (xy, yz, zx)?

I would like to get a kind of 'average' dielectric function for all directions, so I am rotating the unit cell and averaging many values of the dielectric function. Does this make sense?

thanks!