Detailed ab initio electronic 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.