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1

Ab Initio Lattice Dynamics of MgB_2

100%

Parlinski K.

Acta Physica Polonica A

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2001

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vol. 100

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issue 5

767-772

EN

Using the density functional theory, the phonon dispersion relations, the phonon density of states, mean square displacements, and thermodynamic functions of superconducting MgB_2 crystals have been calculated. The modes of graphite-like boron network belong to optic phonon branches, which are rather independent of the Mg vibrations.

2

Ab initio Calculation of Quasi-Equilibrium Microcracks in Cubic Boron Nitride

63%

Góra D., Parlinski K.

Acta Physica Polonica A

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2002

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vol. 102

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issue 3

437-442

EN

A crack in cubic boron nitride crystal was simulated within the ab initio density-functional theory. The lattice constant, critical stress intensity factor K_c, which describes crack creation stress, and fracture surface energy Γ were calculated from the elongated 2×6×1 supercell and these quantities agree quite well with the experimental data. We conclude that density-functional theory can be used to estimate crack's material constants.

3

Comparative Study of the Electronic Structures of Fe_3O_4 and Fe_2SiO_4

51%

Piekarz P., Oleś A., Parlinski K.

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issue 2

307-312

EN

The electronic properties of two spinels Fe_3O_4 and Fe_2SiO_4 are studied by the density functional theory. The local Coulomb repulsion U and the Hund exchange J between the 3d electrons on iron are included. For U = 0, both spinels are half-metals, with the minority t_{2g} states at the Fermi level. Magnetite remains a metal in a cubic phase even at large values of U. The metal-insulator transition is induced by the X_3 phonon, which lowers the total energy and stabilizes the charge-orbital ordering. Fe_2SiO_4 transforms to a Mott insulating state for U > 2 eV with a gap Δ_g ~ U. The antiferromagnetic interactions induce the tetragonal distortion, which releases the geometrical frustration and stabilizes the long-range order. The differences of electronic structures in the high-symmetry cubic phases and the distorted low-symmetry phases of both spinels are discussed.

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3 Acta Physica Polonica A

1 2010

1 2002

1 2001

3 Parlinski K.

1 Góra D.

1 Oleś A.

1 Piekarz P.

Ab Initio Lattice Dynamics of MgB_2

Ab initio Calculation of Quasi-Equilibrium Microcracks in Cubic Boron Nitride

Comparative Study of the Electronic Structures of Fe_3O_4 and Fe_2SiO_4