QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: wntjr1024 on April 9, 2025, 08:58

Title: Why is the polarization value of AlN different from the experimental value?
Post by: wntjr1024 on April 9, 2025, 08:58

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
(https://i.postimg.cc/v4Cbt7Sp/Al-N-polarization-by-q-ATK.png) (https://postimg.cc/v4Cbt7Sp)
my AlN piezoelectric tensor data
(https://i.postimg.cc/BjjJF7NT/Al-N-piezoelectrictensor-by-q-ATK.png) (https://postimg.cc/BjjJF7NT)

and reference data
(https://i.postimg.cc/d0gYXB4f/Reference-Al-N-polarization-and-piezoelectrictensor.png) (https://postimages.org/)

Title: Re: Why is the polarization value of AlN different from the experimental value?
Post by: Anders Blom on April 29, 2025, 01:02

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.