Why do I obtain non-zero values in the stiffness and piezoelectric tensors for R3c geometry with VASP ?

I calculated the stiffness and piezoelectric tensors for LiNbO3 (R3c) and, instead of obtaining something similar to this reference [https://materialsproject.org/materials/mp-3731/#piezo-props],...

03 August 2020 7,978 2 View