Why is the polarization value of AlN different from the experimental value?

[wntjr1024]

I optimized AlN with a hybrid GGA using an LCAO calculator with a maximum force of 0.03 eV, and then obtained the polarization and piezo electric tensor, but they are very different from the experimental values. I would like to know the cause of this.

my AlN polarization data

my AlN piezoelectric tensor data


and reference data

[Anders Blom]

That is a actually quite a large value to converge forces, I would use 0.001 or lower. But quantities like the piezoelectric tensor are also very sensitive to the numerical details, so you need to ensure convergence in primarily k-points.