Approaches to Seebeck coefficient by ab initio calculation using molecular orbital method

The β-phase FeSi₂ semiconductor has a high Seebeck coefficient and high oxidation resistance at high temperature, low cost and ecological adaptability as well. We analyzed the characteristics of β-FeSi₂ thermoelectric material from the electronic structure with the DV-Xα method. We put the Fe and Si atoms of the β-FeSi₂ at the actual positions and also simulated p-type and n-type semiconductors. We found the donor or acceptor level in the energy gap by substituting a metal for the Fe atom. The impurity atom creates the donor or acceptor level. We made a hypothesis that the Seebeck coefficient depends on the energy gap and the orbital structures. The purpose of our study is to discuss and elucidate the electron transferring HOMO (Highest Occupied Molecular Orbital) to donor level or LUMO (Lowest Unoccupied Molecular Orbital) to accepter level in the energy gap. And also we found the Seebeck coefficients are 133 μ V/K and 200μ V/K on Mn-added and Co-added FeSi₂ from the energy gap respectively