RbBi from first-principles*

We employ first-principles calculations to investigate the topological phase and thermoelectric properties of hypothetical bialkali bismuthide compounds (Na, K)₂RbBi. The topological phase transitions of these compounds under hydrostatic pressure within GGA-PBE and TB-mBJ approaches are investigated. The topological surface states and Z₂ topological index are also calculated. The electronic properties and transport coefficients are obtained using the PBE-GGA and TB-mBJ approaches combined with the Boltzmann transport equation. The relaxation times are calculated using the deformation potential theory to obtain the electronic thermal and electrical conductivity. We find that the compound has significantly large Grüneisen parameters, indicating the strong anharmonic scattering of acoustic phonons leading to very low lattice thermal conductivity. These materials also have a desirable power factor leading to a relatively flat p-type zT over a wide temperature range. We calculate the elastic tensors and phonon dispersions, respectively, and prove their mechanical and dynamical stability, making them good candidates for thermoelectric applications over a broad range of temperatures.