Research on thermoelectric materials has nowadays attracted much attention due to their potential in converting wasted heat into electricity. An important factor determining the efficiency of such materials is the dimensionless figure of merit ZT, which is inversely proportional to the thermal conductivity. Optimal thermoelectrics are shown to be doped semiconductors, in which the major contribution to the thermal conductivity is mainly due to phonons. In this paper, we describe our modeling of the lattice thermal conductivity from first-principles density-functional theory (FP-DFT) calculations. The theory is based on the well-known relaxation time approximation solution to the Boltzmann equation: k = ∑from (nl) v_(nk)~2 C_v(nk) τ_(nk)/3 Phonon dispersions and their lifetimes τ_(nk) are calculated using a lattice dynamics model, the parameters of which, the force constants, are calculated from FP-DFT. The details of our modeling can be found in [1,2]. This is a real space approach to force constants. Other groups have adopted a reciprocal space approach and have applied it to Si, Ge[3]- and C-diamond[4] thermal conductivity studies.
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