Tight binding modeling of halid perovskites

Soline Boyer-Richard (1) , Reinhard Scholz (2) , Jean-Marc Jancu (1) , Claudine Katan (3) , Jacky Even (1)

1 FOTON - Fonctions Optiques pour les Technologies de l'informatiON
2 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]
3 ISCR - Institut des Sciences Chimiques de Rennes

The free-electron model is built upon the assumption that electrons propagate almost freely and that their wave functions can be approximated by plane waves. As an " opposite " starting point, one can use localized atomic orbitals as a basis set to perform band-structure calculations; this is the tight binding (TB) or linear combination of atomic orbitals (LCAO) approach. This method has been introduced for periodic crystals by Slater and Koster 1 and was extensively used in the past to rationalize the physical properties of a wide range of compounds, from transition metals to semiconductor crystals 2. In this paper we use this approach to investigate the properties of HOP, considering the reference cubic structures of the 3D ABX 3 family. Our tight-binding model is based on a 16 functions basis without SOC or a 32 functions basis with SOC. For cubic ABX 3 halide perovskites, we consider one " s " and three " p " orbitals for the B atom, and the same for each of the three X atoms in the simple cubic unit cell, as already presented for a qualitative analysis of the band structure 3. No basis function is taken into account for the A organic molecule, which's position is not fixed because it has rotational degrees of freedom/disorder in the cubic phase. We only consider first neighbor interactions, only between B and X atoms. We have chosen the minimal sp 3 basis as developed by Slater and Koster and we have tried to reproduce the already known experimental data like energy band-gap and effective masses around the bandgap with our semi-empirical TB model. Nine parameters are considered without SOC: four different diagonal matrix elements related to the atomic energies of the chemical constituents B and X: E sB , E pB , E sX and E pX. Five transfer matrix elements refer to the overlap integral of atomic functions: V ss , V sBpX , V sXpB , V ppσ , V ppπ. SOC only appears for p orbitals with two SOC values Δ soB and Δ soX.

Domaines: Optique / photonique

Soline Boyer-Richard, Reinhard Scholz, Jean-Marc Jancu, Claudine Katan, Jacky Even. Tight binding modeling of halid perovskites. 2èmes Journées Pérovskites Hybrides (JPH 2016), May 2016, Rennes, France. ⟨hal-01341705v1⟩