Optical absorption yy and zz component

[ams_nanolab]

In the script

http://quantumwise.com/documents/tutorials/latest/SiliconOptical/index.html/chap.Si.Band.html
It is given....
-------------------------------------
# get the real and imaginary part of the e_xx component of the dielectric tensor
d_r = spectrum.evaluateDielectricConstant()[0,0,:]
d_i = spectrum.evaluateImaginaryDielectricConstant()[0,0,:]
----------------------

what do I do to select the e_zz component of the tensor? I cant understand the index in [0,0,:] as it is unlike [x,y,z]

[Umberto Martinez]

If you want to select e_zz use
d_r = spectrum.evaluateDielectricConstant()[2,2,:]

evaluateDielectricConstant and same for iImaginary will indeed give you the dielectric tensor for each energy point.

You can print the tensor for the point zero, for example with:
spectrum.evaluateDielectricConstant()[:,:,0]

with he first two indices you select the component you wish, e.g e_xx, e_zz, e_xy, ...

[ams_nanolab]

Thanks 

[ams_nanolab]

Another thing... It is sometimes important (for nanostructures) to evaluate the optical spectra not just in individual directions like xx, yy and zz but take a sum or trace of the dielectric tensor like e=e_xx+e_yy+e_zz  and do the calculations for optical absorption.
How to modify the script for that 

would

d_r = spectrum.evaluateDielectricConstant()[0,0,:]+spectrum.evaluateDielectricConstant()[1,1,:]+spectrum.evaluateDielectricConstant()[2,2,:]

do the trick? or something else is needed 

[ams_nanolab]

Please reply... this is a bit urgent.. 

[Umberto Martinez]

The trick is correct. You can are summing the diagonal components.
You may also want to consider taking the average in a similar way for the calculation of optical absorption.
But this is up to you.

The dielectric tensor for a nanostructure has the same meaning as the one for a bulk system.
You are free to do whatever you wish with it