Tight-Binding Molecular Dynamics with Fermi Operator Expansion:Application to Vacancy Defects in Silicon

By using tight-binding molecular dynamics with Fermi operator expansion, we study vacancy defects in Silicon. The code has been developed for checking silicon crystal, point defect formation energies, etc. The crystal configuration for checking varies among the systems of 64, 216, 512, and 1000 atoms. We have also checked the expansion condition of Fermi operator; the smearing width (∆ε), the maximum order of expansion polynomials. The testing shows the good results, compared with the ab initio results. The dynamical behaviors of defects both in the liquid state and the non-self-diffusion state, are still being investigated. In order to support the data analysis, a visualization of multi-vacancy is also constructed

Effects of topological band structure on thermoelectric transport of bismuthene

Two-dimensional bismuth (Bi) layer, known as bismuthene, exhibits Z2 topological bulk states due to large spin-orbit coupling that inverts the bands. Using the tight-binding method, we calculate the band structure of buckled bismuthene to understand its topological and trivial phases. We determine the thermoelectric properties for some considered phases, incorporating the edge states contribution, by using the linearized Boltzmann transport equation with a constant relaxation time approximation. It is shown that the thermoelectric figure of merit, ZT, actually drops in undoped topological bismuthene due to the edge effects. Surprisingly, the topological edge states enhance ZT at large doping with the Fermi energy near the bottom of bulk bands when bismuthene is nearly metallic