First-principles investigation of thermoelectric transport in Nb₃X₄ (X = S, Se)

Recent transport measurements reveal that the quasi-one-dimensional metals Nb₃X₄ (X = S, Se) exhibit ultrahigh thermoelectric power factors in the temperature range 30 K ≤ T ≤ 75 K -among the largest reported for any known material. Motivated by these findings, we perform first-principles density functional theory (DFT) calculations using Quantum ESPRESSO and transport analyses with BoltzTraP2, comparing our results with experimental data. Convergence tests were conducted to ensure numerical reliability. Thermoelectric properties were evaluated using a relaxation time that is constant or inversely proportional to the density of states, the latter modeling interband scattering.