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1

Ab initio Calculations of Phonon Dispersion Relations in Aluminium

100%

Scharoch P., Parliński K., Kiejna A.

Acta Physica Polonica A

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2000

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vol. 97

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issue 2

349-354

EN

A direct method and ab initio force constants were used to calculate phonon dispersion curves and phonon density in Al. The force constants were determined from the Hellmann-Feynman forces induced by the displacement of an atom in the 2×2×2 fcc crystallographic supercell. This size of the supercell gives exact phonon frequencies at Γ, X, L, W points of the Brillouin zone. The calculated phonon dispersion curves are in good agreement with the experimental data.

2

The Novel Spin-Charge Patterns in Correlated Electron Systems Described by Extended Hubbard Hamiltonian

80%

Rościszewski K., Oleś A.

Acta Physica Polonica A

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2004

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vol. 105

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issue 5

495-500

EN

Inhomogeneous spin and charge orderings in doped two-dimensional correlated electron systems described by the extended Hubbard Hamiltonian were investigated. At the crossover from stripe phases to charge order phases, the novel types of ordering connected with highly symmetric superlattice-type spin and charge patterns were identified. In particular, the emergence of local hexagonal-like symmetry is of interest as such patterns are generic in complex, nonlinear dynamic systems.

3

A New Approach to Deriving Interatomic Many-Body Interactions in Metals

80%

Gurskii Z., Krawczyk J.

Acta Physica Polonica A

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1998

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vol. 94

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issue 4

671-682

EN

An original method of treating the kinetic and exchange-correlation energies functionals in terms of many particle interactions was developed. It is based on utilizing the local density approximation. The total electron density, extracted from the ab initio band structure calculations, is expressed as a linear superposition of contributions from the individual pseudoions embedded in the uniform background. The explicit expressions for the pair and triplet potentials are presented. The general form for the part of the pair interatomic interactions caused by the kinetic and the exchange-correlation effects is obtained. Relationship between the developing approach and the perturbation theory in pseudopotential is analysed. Unlike the perturbation theory the advanced approach allows one to calculate accurately the so-called reducible contributions to the pair potential arising from the n -particle (n>2) interactions. It corresponds to summing certain series in pseudopotential. Contribution of the electron-nonlocal pseudopotential interactions to the pair interatomic ones is considered within the concept of the fully separable pseudopotentials.

4

Interplay of Crystal Structure Preference and Magnetic Ordering in High Entropy CrCoFeNiAl Alloys

80%

Jasiewicz K., Kaprzyk S., Tobola J.

Acta Physica Polonica A

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2018

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vol. 133

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issue 3

511-513

EN

In this work, some relations between crystal structure and magnetic ordering in CrCoFeNiAl HEAs are discussed in view of the KKR-CPA calculations. Remarkably, it is noticed that the transition between fcc and bcc phases in the analysed CrCoFeNi_{x}Al and CrCoFeNiAl_{x} alloys is closely related to change in ordering of the local magnetic moments, namely the magnetic moment on Cr is either parallel (ferromagnetic) or antiparallel (ferrimagnetic) to the magnetic moments of other atoms (Co, Fe and Ni). On the whole, the theoretical diagram showing the fcc-bcc phase preference and their coexistence vs. alloy composition well corroborates with available experimental data.

5

The Electronic Structure of the RMn_{2}Ge_{2} (R = Ca, Y, La, Ba) Antiferromagnets

70%

Toboła J., Malaman B., Venturini G.

Acta Physica Polonica A

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2000

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vol. 97

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issue 5

761-765

EN

The electronic structure of the tetragonal RMn_{2}Ge_{2} (R = Ca, Y, La, Ba) antiferromagnets is presented using the self-consistent Korringa-Kohn-Rostoker method. According to the neutron refinements, two types of collinear antiferromagnetic structure are taken into account: AF_{1} for YMn_{2}Ge_{2} and AF_{2} for the other compounds. The calculated magnetic moments on Mn: 2.17μ_{B} (YMn_{2}Ge_{2}), 2.84 μ_{B} (CaMn_{2}Ge_{2}), 2.95 μ_{B} (LaMn_{2}Ge_{2}), and 3.47 μ_{B} (BaMn_{2}Ge_{2}) remain in good agreement with the neutron data (in μ_{B}) 2.20, 2.67, 3.05, and 3.66, respectively. As seen on antiferromagnetic density of states, all systems are metallic, however BaMn_{2}Ge_{2} is found near semimetallic limit. The total energy Korringa-Kohn-Rostoker computations on CaMn_{2}Ge_{2}, performed in both antiferromagnetic phases, result in preferring of the AF _{2} structure.

6

Hyperfine Interactions of ^{57}Fe in Pt_3Fe - Ab Initio and Mössbauer Effect Studies

61%

Deniszczyk J., Satuła D., Waliszewski J., Rećko K., Olszewski W., Parzych G., Szymański K.

Acta Physica Polonica A

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2009

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vol. 115

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issue 1

197-199

EN

The Mössbauer effect and ab initio investigations of an electric field gradient at ^{57}Fe nuclei in Pt_3Fe compound are presented. It is shown that nonzero ^{57}Fe electric field gradient exists in the cubic Pt_3Fe. Ab initio study of Pt_3Fe in antiferromagnetic state confirms the presence of electric field gradient at ^{57}Fe nuclei. Lattice, local valence electron (3d, 4p) and weakly bound 3p core electron contributions to electric field gradient are separated out and discussed in the context of the electronic structure changes upon the antiferromagnetic phase transition.

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Ab initio Calculations of Phonon Dispersion Relations in Aluminium

The Novel Spin-Charge Patterns in Correlated Electron Systems Described by Extended Hubbard Hamiltonian

A New Approach to Deriving Interatomic Many-Body Interactions in Metals

Interplay of Crystal Structure Preference and Magnetic Ordering in High Entropy CrCoFeNiAl Alloys

The Electronic Structure of the RMn_{2}Ge_{2} (R = Ca, Y, La, Ba) Antiferromagnets

Hyperfine Interactions of ^{57}Fe in Pt_3Fe - Ab Initio and Mössbauer Effect Studies