Detailedab initioelectronic structure study of two approximants to Al-Mn based icosahedral quasicrystals

The electronic structure of three available models of {α}-AlMnSi and of three models of a hypothetical approximant in the Al-Pd-Mn system are studied by means of the linear muffin-tin orbital method in the atomic sphere approximation. The effect of the atomic sphere approximation is investigated. The energy resolution of our best calculation is estimated to be 50--100 meV. By comparing the available models the importance of accurate atomic positions for the electronic structure is demonstrated. In the density of states of {α}-AlMnSi and the AlPdMn approximant a wide pseudogap ({~}1 eV) is found near the Fermi energy. Total energies for various possible positions of the Si atoms in {α}-AlMnSi are compared. It is found to be favorable for the Si atoms to partially occupy three of the classes of inequivalent Al atoms. The full charge density of {α}-AlMnSi is calculated and compared with available experimental results. In contrast to the experimental results the strongest bonding is found to be between Si and Mn atoms.