absorption spectrum

[samaneh]

Hi
As I know the imaginary part of dielectric function has 3 components
for E||X E||Y E||Z (e.g. in the QE code out put file of epsilon.x)
Would you please explain why there is just one component for E||X and E||Y (E||ab plane)
in yambo code?
Thanks
Best regards
S. Ataei, University of Tehran, Iran

[Daniele Varsano]

Dear Samaneh,
I'm not sure I have well understood your question.
The dielectric function is a tensor \eps_ij. The absorption then is given by the trace of the tensor in case of isotropic average (e.g. gas phase molecules or in solution),
(eps_xx+eps_yy+eps_zz)/3.
In Yambo the direction of the field is given by (BLongDir or LongDrXd depending of the used approximation), in output you have the diagonal part of the tensor
corresponding then to the absorption along the chosen direction, if you are interested in different direction of the electric field you need to run different calculations corresponding to different LongDir. This is the same that epsilon.x does (according to the manual, as I'm not an expert of that utility), which gives in output the diagonal part of the dielectric matrix (unless off-diagonal component are requested in input), and I imagine it repeats three calculations for three cartesian direction, in independent particle approximation.
Hope it helps,
Best,
Daniele

[samaneh]

Thanks
would you please tell me for longDir 1 0 0 in yambo code
the imaginary part of dielectric function is the same for X and Y direction
is that because of the longDir 1 0 0 or because of the symmetry of the compound??
what is the meaning of the direction of longDir 1 0 0?
does it mean the X direction?
best

[Daniele Varsano]

Dear Samaneh,
yes (100) means the x-direction. If it happens that (100) gives the same absorption than y-direction (010), it should be because of symmetries.
Best,
Daniele

[samaneh]

Hi,
Would you please tell me what is the difference between
BLongDir and LongDrXs?
thanks

[Daniele Varsano]

The first is the direction for the absorption in the bse solution. The latter for the RPA calculation of the static screening.
Best
Daniele