# Dresden 2017 – wissenschaftliches Programm

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# MM: Fachverband Metall- und Materialphysik

## MM 35: Electronic Structure Theory: New Concepts and Developments in Density Functional Theory and Beyond

### MM 35.9: Poster

### Dienstag, 21. März 2017, 18:30–20:30, P2-OG4

**Groundstates of the ternary clathrate ***Ba*_{8}** ***Ni*_{x}** ***Ge*_{46−x−y}** **_{y}** obtained with an iterative cluster expansion approach** — •Martin Kuban, Santiago Rigamonti, Maria Troppenz, and Claudia Draxl — Humboldt-Universität zu Berlin

Intermetallic clathrates are promising candidates for the construction of thermoelectric (TE) devices. These rely on a junction between *n*- and *p*-type semiconductors. The clathrate compound *Ba*_{8} *Ni*_{x} *Ge*_{46−x−y} _{y} is of special interest, as it presents a crossover from *p*-type to *n*-type conductivity around *x*=4.0 [1]. Thus, a junction on the same base material could be tailored. In this work, we perform an *ab-initio* study of the structural stability and electronic properties of this compound in the composition range 0 ≤ *x* ≤ 6 and 0 ≤ *y* ≤ 4. Both the substitutional species (Ni) and vacancies () are treated on the same footing, through a cluster expansion (CE) in the quasi-ternary Ge/Ni/ sublattice. The large size of this sublattice (46 sites) leads to a combinatorial explosion of the number of configurations, i.e. the possible arrangements of the substitutional atoms and vacancies in the lattice. As this prevents the use of standard CE methodology, we make use of an iterative CE technique (iCE) as implemented in the code `CELL` [2]. The iCE is based on efficient samplings of the configurational space. The structural properties (lattice constants, bond distances, etc.) as well as the electronic bandstructure of the stable structures are analyzed.

[1] U. Aydemir *et al.*; Dalton Trans **44**, 7524 (2015).

[2] S. Rigamonti *et al.*, in preparation.