Doping dependence of thermoelectric performance in Mo$_3$Sb$_7$: first principles calculations*

Experimental studies have indicated the substantial thermoelectric promise of doped Mo$_3$Sb$_7$, with a figure-of-merit ZT of 0.9 (H. Xu {\it et al}, J. Appl. Phys. {\bf 105}, 053703 (2009)) already achieved at high temperature. However, optimal doping levels have not yet been achieved. We study doping of Mo$_3$Sb$_7$ with transition metals (Ni,Fe,Co,Ru) via first principles calculations, including electronic structure, lattice dynamics and Boltzmann transport. We discuss the selection of dopant and the potential thermoelectric performance of optimally doped Mo$_{3}$Sb$_{7}$.