
Studies of structural and magnetic properties of iron nanowires from first principles
Zelený, Martin ; Šob, Mojmír ; Hafner, J.
In this work we study the structure and stability of iron ultrathin freestanding nanowires by firstprinciples density functional approach. For total energy calculations, we use the Vienna ab initio Simulation Package (VASP) in the projector augmentedwave (PAW) representation. The evolution of electronic structure and magnetism of iron chains as a function of compression and stretch is investigated. The forming of different types of structures is analyzed: simple linear chain, dimerized chain, ideal twodimensional (2D) zigzag structure relaxed in x and y directions, fully relaxed 2D structure, and threedimensional (3D) structure with tetrahedral arrangements. It turns out that the structure of iron nanowires and types of interatomic bonds are strongly dependent on their stretch or compression.


Studium tantalu pomocí potenciálů typu bondorder
Čák, Miroslav ; Mrověc, M. ; Vitek, V. ; Šob, Mojmír
We present a bondorder potential (BOP) study for the bcc transition metal tantalum. The BOPs are a realspace semiempirical scheme for the description of interatomic interactions based on the tightbinding approximation. The potentials are applied to the calculation of total energy profile along the tetragonal deformation path and gammasurface of {110} plane. Our results are in a good agreement with the ab initio calculated values which indicates that BOPs are capable to describe properly the bonding in bcc transition metals.

 
 

Elektronová struktura slitin india a cínu
Všianská, Monika ; Legut, Dominik ; Šob, Mojmír
The InSn system is interesting due to the existence of the simple hexagonal (sh) structure for compositions from 75 to 87 at% Sn at 25 ºC and from 73 to 85 at% Sn at 150 ºC. These alloys are usually referred to as gammaSn. Here we study the electronic structure and total energy of gammaSn with the help of virtual crystal approximation and demonstrate that sh structure has the lowest energy in the interval of existence of gammatin.


Studium magnetismu hranic zrn z prvních principů
Čák, Miroslav ; Šob, Mojmír ; Hafner, J.
Grain boundaries (GBs) represent an important class of twodimensional extended defects in materials. Segregation of impurity atoms is responsible for a degradation of mechanical properties. Recently, it was found that application of magnetic annealing leads to decreasing concentration of impurities at GBs in Fe0.8%Sn alloy and improves its ductility To understand the mechanism of this process it is necessary to study magnetism of clean GBs as well as of GBs with segregants at the microscopic (ab initio) level. In the present work, we investigate the Sigma5(310) GB in iron.


Electronic structure InSn alloys
Všianská, Monika ; Legut, Dominik ; Šob, Mojmír
The InSn system is interesting by the existence of a simple hexagonal phase for compositions from 72 to 87 at% Sn at 25 °C and from 73 to 85 at% Sn at 150 °C. These alloys are usually referred to as gamma–Sn. The InSn alloys are disordered in the whole concentration interval. In this contribution, energetics and electronic structure of InSn system is studied from first principles. A simplified version of virtual crystal approximation is employed to describe disorder. It turns out that the present approach is capable of describing phase composition of InSn system in the whole concentration interval. In particular, we are able to reproduce the existence of simple hexagonal phase around 80 at% Sn.

 

Ab initio studie magnetismu Ni a Co podél trigonální deformační dráhy
Zelený, Martin ; Šob, Mojmír
We have calculated the total energies of nickel and cobalt as a function of volume and trigonal deformation for various magnetic phases and found the phase boundaries between the FM and NM modifications. The calculated contour plots can be used for the understanding and prediction of lattice parameters and magnetic states of Ni and Co thin films on various fcc (111) metallic substrates.


Energetika strukturních změn MoSi2
Káňa, Tomáš ; Legut, Dominik ; Šob, Mojmír
We employed ab initio calculations to investigate total energy profiles along the transformation paths connecting the C11b, C40 and C54 structures in MoSi2. The transformations were realized by change of the stacking sequence of the atomic planes. We found that the total energy profiles of the proposed paths have high energy barriers between endpoint structures: 1.4 eV/f.u (f.u is the formula unit) for the C40C54 path, 1.8 eV/f.u for the C11bC40 path and finally 2.5 eV/f.u. for the C11bC54 path.
