Showing papers by "Levente Vitos published in 2002"
TL;DR: Ab initio alloy theories are employed to map the elastic properties of austenitic stainless steels as a function of chemical composition and can be used in the search for new steel grades.
Abstract: The most recent advances in theory and methodology are directed towards obtaining a quantitative description of the electronic structure and physical properties of alloy steels. Specifically, we employ ab initio alloy theories to map the elastic properties of austenitic stainless steels as a function of chemical composition. The so generated data can be used in the search for new steel grades, and, as an example, we predict two basic compositions with outstanding properties among the austenitic stainless steels.
112 citations
TL;DR: In this article, the stability of cubic perovskite with respect to octahedral rotations is investigated by ab initio total-energy calculations, and the proposed theoretical ground-state crystal structure has the orthorhombic Pbnm symmetry.
Abstract: The stability of cubic ${\mathrm{CaSiO}}_{3}$ perovskite with respect to octahedral rotations is investigated by ab initio total-energy calculations. The proposed theoretical ground-state crystal structure has the orthorhombic Pbnm symmetry. Pressure gradually reduces the average tilting of the ${\mathrm{SiO}}_{6}$ octahedra relative to the cubic axis, from 7\ifmmode^\circ\else\textdegree\fi{} at zero pressure to 4\ifmmode^\circ\else\textdegree\fi{} at about 150 GPa. The energy difference between the orthorhombic and cubic phases at 0 GPa is 63 meV per f.u. and shows weak pressure dependence. A possible stabilization of the cubic phase at finite temperatures by entropy effects is discussed.
72 citations
TL;DR: In this paper, total energy calculations based on the exact muffin-tin orbitals theory are used to determine elastic properties of random alloys in the face-centered and body-centered cubic crystallographic phases.
Abstract: Ab initio total energy calculations, based on the exact muffin-tin orbitals theory, are used to determine elastic properties of ${\mathrm{Ag}}_{1\ensuremath{-}c}{\mathrm{Zn}}_{c}$ random alloys in the face-centered and body-centered cubic crystallographic phases. The compositional disorder is treated within the framework of the coherent potential approximation. The cubic elastic constants B, ${C}^{\ensuremath{'}},$ and ${C}_{44}$ and the Debye temperatures are calculated for the whole range of concentrations, $0l~cl~1.$ Experimental data are in very good agreement with the present results. Rapid variations of ${C}^{\ensuremath{'}}$ and ${C}_{44}$ are observed at high Zn concentrations, which contradicts the common empirical observation that alloying has only minor effects on elastic properties.
45 citations
TL;DR: The full charge density exact muffin-tin orbitals method has been used to study the stability of lithium manganese oxides exhibiting different crystallographic forms as discussed by the authors, and the effect of doping of the Mn sites by Co was considered with the primary aim to predict the stabilization of the layered structure.
26 citations
TL;DR: The adopted crystal structure of perovskites is determined by the balance between the interaction of the semicore states of the A and B atoms and oxygen ions as discussed by the authors, and the structural setup always stabilizes the cubic phase at large pressures, while small or negative pressures favor nonvanishing octahedral tiltings.
Abstract: The adopted crystal structure of the $\mathrm{AB}{\mathrm{O}}_{3}$ perovskites is determined by the balance between the interaction of the semicore states of the A and B atoms and oxygen ions. Topological considerations show that the structural setup always stabilizes the cubic phase at large pressures, while small or negative pressures favor nonvanishing octahedral tiltings. As an example, we show that the structural distortion in ${\mathrm{CaSiO}}_{3}$ perovskite is slightly depressed with hydrostatic pressure, but it increases significantly with increasing volume.
24 citations
TL;DR: In this paper, total energy calculations performed for ScAlO 3 perovskite, using the global parametrization method (GPM) in conjunction with the exact muffin-tin orbitals theory, show that the orthorhombic Pbnm structure remains stable relative to the cubic structure for pressures up to 150 GPa.
Abstract: Total energy calculations performed for ScAlO 3 perovskite, using the global parametrization method (GPM) in conjunction with the exact muffin-tin orbitals theory, show that the orthorhombic Pbnm structure remains stable relative to the cubic structure for pressures up to 150 GPa. The slightly larger compressibility of AlO 6 octahedra relative to the ScO 12 polyhedra is reflected in increasing polyhedral volume ratio, V Sc /V Al and in a moderate reduction of the orthorhombic distortion with hydrostatic pressure. This observation indicates limitations in the structural analogy between ScAlO 3 and the geophysically important MgSiO 3 perovskite.
16 citations
TL;DR: In this paper, the authors extended the revised global parametrization method (revGPM) of orthorhombic perovskites with Pbnm symmetry to describe the changes in the lattice parameters and internal atomic coordinates within a broad range of structural distortions, including the vicinity of the ortho-hor-cubic phase transition.
15 citations
12 citations
TL;DR: In this paper, the use of computational quantum mechanics for the theoretical modeling of material properties of steel was described, which depend on the microstructure formed during the manufacturing process of steel.
9 citations
01 Jan 2002
TL;DR: In this article, a first-principles calculation based on density-functional theory and the exact muffin-tin orbitals method was performed for surfaces of different orientations, vicinal surfaces, and interfaces of several metals throughout the periodic table.
Abstract: First-principles calculations, based on density-functional theory and the exact muffin-tin orbitals method, have been performed for surfaces of different orientations, vicinal surfaces, and interfaces of several metals throughout the periodic table. Apart from investigating the energetics of different surface configurations (steps, kinks, islands), these calculations allow us to examine the stability of small particles, and to compare the total energies of Wulff-constructed single-crystal clusters to those of multiply- twinned (MT) structures with icosahedral coordination. We have shown that the MT geometry is stable for several late-transition-metal clusters below a certain particle size. For Pd clusters, our calculation supports the appearance of ferromagnetic order for icosahedral symmetry with a small magnetic moment per atom, which explains the recent experimental observation that small Pd clusters exhibit spontaneous ferromagnetic order.
2 citations
TL;DR: In this article, an equilibrium crystal structure of orthorhombic Pbnm symmetry was proposed to investigate the stability of cubic CaSiO3 against octahedral rotations.
Abstract: Ab initio total energy calculations, combined with the global parametrization method of perovskite structures, are used to investigate the stability of cubic CaSiO3 against octahedral rotations. We propose an equilibrium crystal structure of orthorhombic Pbnm symmetry. The larger compressibility of the SiO6 octahedra relative to the CaO12 polyhedra is reflected in gradual reduction of the orthorhombic distortion with hydrostatic pressure.