[Pw_forum] non-cubic dielectric tensor in a cubic crystal.
myoussef at mit.edu
Mon Jan 11 23:37:19 CET 2016
I also get a non-cubic dielectric tensor for cubic semiconductors when I allow the computation of the nonanalytic terms by specifying a q-vector and q is not equal 0. But I do not fully understand what is going on here. I think (but not very sure) if you do not specify q then you actually calculate the nonanalytic terms for q->0 and then you recover the correct cubic tensor with zone center phonons contribution.
On the other hand calculating epsilon_0 by applying electric field and relaxing the ions yields a reasonable cubic dielectric tensor.
I hope somebody can help in clarifying this.
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