How to calculate the dielectric constants ??

Dear All,

Please, I need your help in how to calculate the dielectric constants using CASTEP. I can obtain the electronic dielectric contribution part from the optical properties calculations, but still remaining the lattice vibration contribution part; that is need to be added to the electronic contribution to obtain the total dielectric tensor, which is what I'm asking about.

I will really appreciate any help & thank you in advace.

king regards,

Ahmd