We describe a method for performing density-functional calculations for topologically disordered condensed matter. This method combines the recursion and the linear-muffin-tin-orbital (LMTO) methods, and uses the tight-binding representation. In the present version, the LMTO matrix elements are evaluated in the atomic-sphere approximation (ASA). Various levels of approximation for the ASA Hamiltonian, such as the two-center tight-binding one, are systematically derived and tested. The method is applied to crystalline bcc Fe and to amorphous ${\mathrm{Fe}}_{80}$${\mathrm{B}}_{20}$. Charge self-consistency is only treated for the average Fe and the average B atoms. The Fe-B bonding is found to be covalent. A Stoner theory is derived and used to describe the ferromagnetism. The structures of our density of states for ferromagnetic ${\mathrm{Fe}}_{80}$${\mathrm{B}}_{20}$ agree in detail with reliable photoemission data.

Electronic-structure calculations for amorphous solids using the recursion method and linear muffin-tin orbitals: Application to Fe80B20.

Electronic and magnetic structures of \ensuremath{\gamma}-phase disordered ${\mathrm{Mn}}_{100\ensuremath{-}x}{\mathrm{Ir}}_{x}$ alloys including ${L1}_{2}$-type ordered ${\mathrm{Mn}}_{3}\mathrm{Ir}$ alloy have been investigated by the first-principles approach using the tight-binding (TB) linear muffin tin orbital (LMTO) method. For the ${L1}_{2}$-type ordered ${\mathrm{Mn}}_{3}\mathrm{Ir}$ alloy, a triangular $(T1)$ magnetic structure is considered to be stable, reflecting in a dip structure around the Fermi level in the density of states. For the \ensuremath{\gamma}-phase disordered ${\mathrm{Mn}}_{3}\mathrm{Ir}$ alloy, on the other hand, the most stable structure is suggested to be the $3Q$ structure among the multiple-Q spin density wave (MSDW) structures. The N\'eel temperature is estimated to be about 735 K from the effective exchange constant ${J}_{0},$ in good agreement with the experimental value of about 730 K. With decreasing Ir concentration in the \ensuremath{\gamma}-phase disordered ${\mathrm{Mn}}_{100\ensuremath{-}x}{\mathrm{Ir}}_{x}$ alloys, the transition from the $3Q$ to the $2Q$ structure takes place in the vicinity of $x=13$ under the constant lattice parameters with the axial ratio of $c/a=1.$ This critical concentration x is close to the observed concentration at which the axial ratio changes from $c/a=1$ to $c/ag1.$ However, it should be stressed that these two critical concentrations do not necessarily coincide with each other, that is, the critical concentration of the magnetic structure transition is lower than that of the lattice distortion. This theoretical expectation has been verified by the experimental structural and magnetic data.

First-principles study of the magnetic structures of ordered and disordered Mn-Ir alloys

1.Nucleation and growth of bimetallic nanoparticles.- 2.Bimetallic nanoparticles, grown under UHV on insulators, studied by scanning probe microscopy.- 3.Probing nanoalloy structure and morphology by X-ray scattering methods.- 4.Transmission electron microscopy: a multifunctional tool for the atomic-scale characterization of nanoalloys.- 5.Electronic structure of nanoalloys: a guide of useful concepts and tools.- 6.Chemical order and disorder in alloys.- 7.Segregation and phase transitions in reduced dimension: from bulk to clusters via surfaces.- 8.Computational methods for predicting the structures of nanoalloys.- 9.Magnetism of low-dimension alloys.- 10.Optical, structural and magneto-optical properties of metal clusters and nanoparticles.- 11.Surface studies of catalysis by metals: nanosize and alloying effects.

Nanoalloys : synthesis, structure and properties

We present here an application of the augmented-space recursion technique for binary disordered alloys The method allows us to incorporate effects like clustering, short-ranged order and off-diagonal disorder arising out of size mismatch and consequent lattice distortions We base our calculations on the TB-LMTO Hamiltonian of Andersen and co-workers We study three alloy systems: AgPd, CuZn and FeTi, and compare our results with earlier work

Electronic structure of random binary alloys

The thermal and mechanical properties of Cu, Au pure metals and their ordered intermetallic alloys of Cu3Au(L12), CuAu(L10) and CuAu3(L12) are studied by using the molecular dynamics simulation. The effects of temperature and concentration on the physical properties of CuxAu1−x are analysed. Sutton–Chen (SC) and quantum Sutton–Chen (Q-SC) many-body potentials are used. The simulation results such as cohesive energy, density, elastic constants, bulk modulus, heat capacity, thermal expansion, melting points and phonon dispersion curves are in good agreement with the available experimental data at the various temperatures. Q-SC potential parameter results are usually closer to experimental values than the ones predicted from SC potential parameters.

https://iopscience.iop.org/article/10.1088/0965-0393/13/5/002/pdf

Thermal and mechanical properties of Cu–Au intermetallic alloys

We present a theoretical study of the electronic structure of ordered, partially ordered, and disordered phases of the ${\mathrm{Cu}}_{3}$Au alloy using the scalar-relativistic linear muffin-tin orbitals (LMTO) method in conjunction with the coherent-potential approximation. We study the change in the electronic structure caused by the gradual increase of disorder in the alloy by varying the long-range-order parameter S continuously from its maximum (S=1) to the minimum (S=0) possible value. Calculations for the disordered phase (S=0) are performed with and without relaxation of the lattice. The relaxed-lattice calculation takes into account, in an approximate way, the possible deviations from the ideal lattice structure due to the difference in the sizes of the constituent atoms. As a side issue, we address the problem of transferability of the LMTO parameters of the individual alloy components in the pure crystalline phase to the alloy calculation.

Comparative study of the electronic structure of ordered, partially ordered, and disordered phases of the Cu3Au alloy.

We present the electronic density of states (DOS) in ordered and disordered ${\mathrm{Cu}}_{50}$${\mathrm{Pd}}_{50}$ and ${\mathrm{Cu}}_{75}$${\mathrm{Pd}}_{25}$ alloys calculated by using the linear-muffin-tin-orbitals (LMTO) method. For ordered alloys the results are obtained via a self-consistent standard LMTO method. We then show how the LMTO potential parameters for pure Cu and pure Pd (in the fcc phases) can be appropriately transferred to the ordered-alloy calculation to produce results that are in excellent agreement with the self-consistent calculation. For disordered alloys we present the electronic DOS calculated via LMTO-recursion and LMTO-CPA (coherent-potential-approximation) methods, and study the effect of the relaxation of the lattice, i.e., the deviation from the ideal lattice structure, due to different sizes of the Cu and the Pd atoms, on the electronic structure of these alloys. We also discuss how the above scheme of transferring parameters from the pure components to the alloy can be used in the calculation for the disordered phase to obtain nearly-self-consistent results.

J Kudrnovsk

Papers

Comparative study of the electronic structure of ordered, partially ordered, and disordered phases of the Cu3Au alloy.

Electronic structure of ordered and disordered CuxPd1-x alloys via the linear-muffin-tin-orbitals method.