Different mechanism of stereochemical activity and birefringence in post-transition metal halides: A first-principles investigation.

The post-transition metal cations are widely used in rechargeable batteries, solar-cells, and birefringent compounds. In this paper, the electronic structures and birefringence of ternary CsSnX 3 (X ​= ​Cl, I), CsPbX 3 (X ​= ​Cl, Br, I), and binary MX 2 (M ​= ​Sn, Pb; X ​= ​Cl, Br) compounds are investigated using the first-principles methods. The results show that these metal halides own different mechanism in stereochemical activity and birefringence, i.e., the stereochemical activity of lone-pair electrons are determined by energy difference between cation s states and halogen p states, and the stereochemical activity decreases from Cl to I. While the cation p states play an important role in determining the birefringence, and the birefringence increased from Cl to I. [Display omitted] • Electronic structures and optical properties of post-transition metal halides are investigated. • Stereochemical activity of lone-pair electrons are determined by energy difference of cation-s and halogen-p states. • Cation p states play an important role in determining the birefringence. [ABSTRACT FROM AUTHOR]