[Wien] How do calculate αopt by εxx≈εyy ≠ εzz?

[Marzieh Gh]

Dear Prof.Blaha & Tran

I have calculated static dielectic functions  by YS-PBE0 approximation
according your paper( J. Phys.: Condens. Matter 25 (2013) 435503 (8pp)) ,
But  static dielectic functions in my case (KTiOPO4) have different values
in 3 directions(εxx≈εyy ≠ εzz).

 How do calculate α(opt)? which ε insert in formula(αopt= 0.147+ 0.634/ε*)?

Please help me
Best Regards,

-- 
Marzieh Ghoohestani
PhD Student of Computational Nano Physics
Nano Research Center, Department of Physics
University of Technology, Isfahan, Iran
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