Miroslav Čák
Ruhr University Bochum
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Miroslav Čák.
Journal of Physics: Condensed Matter | 2014
Miroslav Čák; Thomas Hammerschmidt; Jutta Rogal; V. Vitek; Ralf Drautz
Bond-order potentials (BOPs) are based on the tight-binding approximation for determining the energy of a system of interacting atoms. The bond energy and forces are computed analytically within the formalism of the analytic BOPs. Here we present parametrizations of the analytic BOPs for the bcc refractory metals Nb, Ta, Mo and W. The parametrizations are optimized for the equilibrium bcc structure and tested for atomic environments far from equilibrium that had not been included in the fitting procedure. These tests include structural energy differences for competing crystal structures; tetragonal, trigonal, hexagonal and orthorhombic deformation paths; formation energies of point defects as well as phonon dispersion relations. Our tests show good agreement with available experimental and theoretical data. In practice, we obtain the energetic ordering of vacancy, [1 1 1], [1 1 0], and [1 0 0] self-interstitial atom in agreement with density functional theory calculations.
Journal of Physics: Condensed Matter | 2013
Miroslav Čák; Thomas Hammerschmidt; Ralf Drautz
Bond-order potentials (BOPs) are derived from the tight-binding approximation and provide a linearly-scaling computation of the energy and forces for a system of interacting atoms. While the numerical BOPs involve the numerical integration of the response (Greens) function, the expressions for the energy and interatomic forces are analytical within the formalism of the analytic BOPs. In this paper we present a detailed comparison of numerical and analytic BOPs. We use established parametrizations for the bcc refractory metals W and Mo and test structural energy differences; tetragonal, trigonal, hexagonal and orthorhombic deformation paths; formation energies of point defects as well as phonon dispersion relations. We find that the numerical and analytic BOPs generally are in very good agreement for the calculation of energies. Different from the numerical BOPs, the forces in the analytic BOPs correspond exactly to the negative gradients of the energy. This makes it possible to use the analytic BOPs in dynamical simulations and leads to improved predictions of defect energies and phonons as compared to the numerical BOPs.
Materials | 2016
Oleg Shchyglo; Thomas Hammerschmidt; Miroslav Čák; Ralf Drautz; Ingo Steinbach
In this study we propose a unified multi-scale chemo-mechanical description of the BCT (Body-Centered Tetragonal) to BCC (Body-Centered Cubic) order-disorder transition in martensitic steel by adding the mechanical degrees of freedom to the standard CALPHAD (CALculation of PHAse Diagrams) type Gibbs energy description. The model takes into account external strain, the effect of carbon composition on the lattice parameter and elastic moduli. The carbon composition effect on the lattice parameters and elastic constants is described by a sublattice model with properties obtained from DFT (Density Functional Theory) calculations; the temperature dependence of the elasticity parameters is estimated from available experimental data. This formalism is crucial for studying the kinetics of martensite tempering in realistic microstructures. The obtained extended Gibbs energy description opens the way to phase-field simulations of tempering of martensitic steel comprising microstructure evolution, carbon diffusion and lattice symmetry change due to the ordering/disordering of carbon atoms under multiaxial load.
2008 MRS Fall Meetin | 2008
Miroslav Čák; Mojmír Šob; Václav Paidar; V. Vitek
We present the g-surfaces for the (013) and (110) planes calculated by employing the density functional based method as implemented in the VASP code. While there is only one minimum on the (110) g-surface, three distinct minima have been found on the (013) g-surface. These minima, which determine three types of possible stacking faults on the (013) plane, are not symmetry dictated and thus the fault vectors are to a great extent controlled by the details of the interatomic bonding in MoSi2
Physical Review B | 2008
Miroslav Čák; Mojmír Šob; J. Hafner
Modelling and Simulation in Materials Science and Engineering | 2015
Ralf Drautz; Thomas Hammerschmidt; Miroslav Čák; D. G. Pettifor
Intermetallics | 2015
Václav Paidar; Miroslav Čák; Mojmír Šob; Haruyuki Inui
Superalloys | 2012
Thomas Hammerschmidt; B. Seiser; Miroslav Čák; Ralf Drautz; D. G. Pettifor
Physical Review B | 2016
Tomáš Káňa; Erwin Hüger; Dominik Legut; Miroslav Čák; Mojmír Šob
Intermetallics | 2016
Václav Paidar; Miroslav Čák