Electronic structure of ordered and disordered Cu 3 Au and Cu 3 Pd

摘要: In ordered L${1}_{2}$-type ${\mathit{A}}_{3}$B compounds, each A atom is coordinated by 8A+4B atoms, while B 12A atoms. By symmetry, all A-A, A-B, and B-B bond lengths are equal. When this structure disorders to form the substitutionally random ${\mathit{A}}_{0.75}$${\mathit{B}}_{0.25}$ alloy, acquires a distribution of different types coordination shells. Concomitantly with reduction in site symmetries, (i) topologically atoms (and separately, atoms) can have unequal charges, (ii) various bonds need not be equal average 〈R〉 (i.e., 〈${\mathit{R}}_{\mathit{A}\mathrm{\ensuremath{-}}\mathit{A}}$〉\ensuremath{\ne}〈${\mathit{R}}_{\mathit{A}\mathrm{\ensuremath{-}}\mathit{B}}$〉\ensuremath{\ne} 〈${\mathit{R}}_{\mathit{B}\mathrm{\ensuremath{-}}\mathit{B}}$〉). Furthermore, (iii) there bond-length values around 〈${\mathit{R}}_{\mathit{i}\mathit{j}}$〉 for three chemical types. work we study effects such charge fluctuations relaxational [(ii) (iii)] on electronic ${\mathrm{Cu}}_{3}$Au ${\mathrm{Cu}}_{3}$Pd. The alloys modeled special quasirandom (SQS), whereby sites periodic supercell occupied so that first few radial correlation functions closely reproduce an infinite substitutional network. Instead requiring ``see'' identical, medium, as case homogeneous site-coherent-potential approximation (SCPA), thus create distinct local environments whose corresponds alloy.Application first-principles local-density method (linearized augmented-plane-wave method) SQS then provides energy-minimizing equilibrium relaxations, density, density states, formation enthalpy. We find neglected SCPA lead significant stabilization alloy (\ensuremath{\sim}30% lowering mixing enthalpy) substantial (\ensuremath{\sim}1 eV) nonrigid shifts energy levels.