First-principles Full-potential Calculations Research Articles

Ab initio calculation of band edges modified by (001) biaxial strain in group IIIA–VA and group IIB–VIA semiconductors: Application to quasiparticle energy levels of strained InAs/InP quantum dot

Results of first-principles full potential calculations of absolute position of valence and conduction energy bands as a function of (001) biaxial strain are reported for group IIIA–VA (InAs, GaAs, InP) and group IIB–VIA (CdTe, ZnTe) semiconductors. Our computational procedure is based on the Kohn–Sham form of density functional theory (KS DFT), local spin density approximation (LSDA), variational treatment of spin-orbital coupling, and augmented plane wave plus local orbitals method (APW+lo). The band energies are evaluated at lattice constants obtained from KS DFT total energy as well as from elastic free energy. The conduction band energies are corrected with a rigid shift to account for the LSDA band gap error. The dependence of band energies on strain is fitted to polynomial of third degree and results are available for parameterization of biaxial strain coupling in empirical tight-binding models of IIIA–VA and IIB–VIA self-assembled quantum dots (SAQDs). The strain effects on the quasiparticle energy levels of InAs/InP SAQD are illustrated with empirical atomistic tight-binding calculations.

Structural stability of carbon in the face-centered-cubic (Fm [formula omitted]m) phase

The structural stability of carbon in the face-centered-cubic (Fm 3 ̄ m) phase has been investigated by means of first-principles full-potential calculations. We have calculated the total energy as a function of the isotropic, tetragonal, and trigonal deformations for bulk fcc carbon. We find that the total energy shows a minimum for the isotropic deformation at the lattice parameter a=3.08 Å, but exhibits maxima for the tetragonal and trigonal deformations. This means that the fcc structure is not a true metastable phase of carbon. Possible mechanisms contributing to the stabilization of fcc carbon thin films on diamond are discussed.

Elastic stability and electronic structure of fcc Ti, Zr, and Hf: A first-principles study

The structural stability and electronic structure of face-centered-cubic Ti, Zr, and Hf were studied by means of first-principles full-potential calculations. The total-energy calculations demonstrate that Ti, Zr, and Hf have a locally stable fcc structure, i.e., the elastic stability criteria for a cubic crystal are fulfilled by the calculated elastic constants. The electronic densities of states for the fcc phase are significantly different from those for the corresponding hcp phases, for the three metals involved in this study. In particular, we found that the values of the electronic densities of states at the Fermi level for the fcc phase are approximately $100%$ higher with respect to the hcp phase.

Origin of thec/avariation in hexagonal close-packed divalent metals

The origin of the $c/a$ variation in hcp divalent metals (Be, Mg, Zn, and Cd), which ranges from 1.568 to 1.886, has been investigated by first-principles full-potential calculations in the framework of the density functional theory. We find that the ideal hcp structure $(c/a=1.633)$ is electronically unstable to $c/a$ distortions for all elements, however the distortion driving band energy is countered by the electrostatic part of the total energy, which favors the ideal close packing. In particular, Zn and Cd with $c/a$ ratios $g$ ideal follow the bonding principle of optimum hybridization between s and p valence bands, a situation similar to the metallic elements in the neighboring group-IIIa in the Periodic Table. For Mg the electronic instability is not effective because the electrostatic part of the total energy dominates over the band energy. However, under expansion a distortion to $c/a$ ratios $g$ ideal occurs. Finally, Be represents a special case. Typically of second-row elements, s and p valence bands mix intimately which creates an electronic structure quite distinguished from the other divalent metals. A $c/a$ distortion cannot improve $s\ensuremath{-}p$ band hybridization but $p\ensuremath{-}p$ bonding is increased for $c/al$ ideal.

Large magnetocrystalline anisotropy in bilayer transition metal phases from first-principles full-potential calculations

The computational framework of this study is based on the local-spin-density approximation with first-principles full-potential linear muffin-tin orbital calculations including orbital polarization (OP) correction. We have studied the magnetic anisotropy for a series of bilayer CuAu(I)-type materials such as $\mathrm{Fe}X,$ $\mathrm{Mn}X(X=\mathrm{N}\mathrm{i},\mathrm{P}\mathrm{d},\mathrm{P}\mathrm{t}),$ CoPt, NiPt, MnHg, and MnRh in a ferromagnetic state using experimental structural parameters to understand the microscopic origin of magnetic-anisotropy energy (MAE) in magnetic multilayers. Except for MnRh and MnHg, all these phases show perpendicular magnetization. We have analyzed our results in terms of angular momentum-, spin- and site-projected density of states, magnetic-angular-momentum-projected density of states, orbital-moment density of states, and total density of states. The orbital-moment number of states and the orbital-moment anisotropy for $\mathrm{Fe}X$ $(X=\mathrm{N}\mathrm{i},\mathrm{P}\mathrm{d},\mathrm{P}\mathrm{t})$ are calculated as a function of band filling to study its effect on MAE. The total and site-projected spin and orbital moments for all these systems are calculated with and without OP when the magnetization is along or perpendicular to the plane. The results are compared with available experimental as well as theoretical results. Our calculations show that OP always enhances the orbital moment in these phases and brings them closer to experimental values. The changes in MAE are analyzed in terms of exchange splitting, spin-orbit splitting, and tetragonal distortion/crystal-field splitting. The calculated MAE is found to be in good agreement with experimental values when the OP correction is included. Some of the materials considered here show large magnetic anisotropy of the order of meV. In particular we found that MnPt will have a very large MAE if it could be stabilized in a ferromagnetic configuration. Our analysis indicates that apart from large spin-orbit interaction and exchange interaction from at least one of the constituents, a large crystal-field splitting originating from the tetragonal distortion is also a necessary condition for having large magnetic anisotropy in these materials. Our calculation predicts large orbital moment in the hard axis in the case of FePt, MnRh, and MnHg against expectation.