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Nano-engineering: Electronic structure of thermoelectric materials

First principles DFT methods were applied to model thermoelectric materials, TMs. Use of local basis sets (gaussians) required special calibration, but it also allowed for an atomistic description of the electronic structure and of its change upon TMs’ structural changes. The effects of chemical doping/substitution was highlighted by projecting the density of states onto the set of atoms which are most responsible of such effects. Application of Bader’s theory allowed for chemical understanding of doping effects.

TMs electronic structures were linked to their electronic transport properties (ETPs) using the semi-classical Boltzmann’s transport theory and the approximation of constant relaxation time. Two different approaches were adopted to model the ETPs of chemically-doped TMs.

In the first, the frozen bands of the undoped materials are used but with a number of electrons increased by an amount equal to actual doping and Fermi energy levels accordingly recomputed. In the second approach, the band structures of the fully chemical-doped systems are used to account directly for the modifications of bands due to dopants. To find the optimum doping level within either of the two considered approaches, we introduced the electronic figure of merit, Z(e)T=( S(2)[sigma]/[kappa](e) )T, where [kappa](e) is the electronic contribution to the thermal conductivity.

More information on the NANOTHERMEL project can be found at:

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Italian National Research Council
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