Abstarct:
The electronic band structure of UPdAs2 is calculated using full potential linearized augmented plane wave implemented in the WIEN2k code. Calculations were started with the exchange-correlation potential in the form proposed by Perdew, Burke and Ernzerhof (PBE). We additionally studied PBE+U approach with the Coulomb repulsion energies U applied to the uranium 5f orbital and varying from 0 to 4 eV. PBE+OP with orbital polarization term was one more tested approach. To reproduce magnetic sequence + + −− a doubled in c axis supercell is built. Initial magnetic moments on inequivalent uranium atoms are assumed to be opposite. The antiferromagnetic ground state is con rmed by comparison of total energies calculated for various magnetic con gurations. Results of PBE+U(1.0 eV)+J(0.5 eV) and PBE+OP approaches are in the best agreement with the neutron scattering measurements of magnetic moments. The calculated total magnetic moment on uranium atoms is predicted to be equal to 1.47 µB.
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The crystallographic and magnetic data of UPdAs2 compound were reported by Murasik et al. [1]. Preliminary magnetic measurements have shown that compound orders antiferromagnetically below 240 K. A subject of the neutron di raction studies was a polycrystalline sample. It has been shown that magnetic moments are oriented along the c axis and localized on uranium atoms.
Details of calculations
To construct crystal structure we used experimental lattice parameters (a = 3.973(1) Å, c = 9.480(3) Å) and Wycko positions [1]. To reproduce the sequence of magnetic moments orientation + + −− a supercell doubled along c axis was built and the uranium atoms positions were split into two nonequivalent types U1 and U2 (see Fig. 1 and Table I). A space group of the supercell has not changed and remained P4/nmm. The antiferromagnetic solution was not assumed in advance. Seven inequivalent atoms forming the supercell were treated as separate types. The magnetic sequence + + −− were initiated by setting opposite signs of an initial spin splitting on uranium atoms. It allowed the system to reach an antiferromagnetically ordered ground state.
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