| 1. |
- Maier, Stefan, et al.
(författare)
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Sb-5s lone pair dynamics and collinear magnetic ordering in Ba2FeSbSe5
- 2021
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 103:5
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Tidskriftsartikel (refereegranskat)abstract
- Neutron diffraction and x-ray pair distribution function experiments were performed to investigate the magnetic and local crystal structures of Ba2FeSbSe5 and to compare them with the average (i.e., long range) structural model previously obtained by single-crystal x-ray diffraction. Changes in the local crystal structure (i.e., in the second coordination sphere) are observed upon cooling from 295 to 95 K, resulting in deviations from the average (i.e., long range) crystal structure. In this paper, we demonstrate that these observations cannot be explained by local or long-range magnetoelastic effects involving Fe-Fe correlations. Instead, we found that the observed differences between local and average crystal structure can be explained by Sb-5s lone pair dynamics. We also find that, below the Ned temperature (T-N = 58 K), the two distinct magnetic Fe3+ sites order collinearly, such that a combination of antiparallel and parallel spin arrangements along the b axis results. The nearest-neighbor arrangement (J(1) = 6 angstrom) is fully antiferromagnetic, while next-nearest-neighbor interactions are ferromagnetic in nature.
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| 2. |
- Mondal, Arobendo, et al.
(författare)
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Large-Scale Computation of Nuclear Magnetic Resonance Shifts for Paramagnetic Solids Using CP2K
- 2018
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 14:1, s. 377-394
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale computations of nuclear magnetic resonance (NMR) shifts for extended paramagnetic solids (pNMR) are reported using the highly efficient Gaussian-augmented plane-wave implementation of the CP2K code. Combining hyperfine couplings obtained with hybrid functionals with g-tensors and orbital shieldings computed using gradient-corrected functionals, contact, pseudocontact, and orbital-shift contributions to pNMR shifts are accessible. Due to the efficient and highly parallel performance of CP2K, a wide variety of materials with large unit cells can be studied with extended Gaussian basis sets. Validation of various approaches for the different contributions to pNMR shifts is done first for molecules in a large supercell in comparison with typical quantum-chemical codes. This is then extended to a detailed study of g-tensors for extended solid transition-metal fluorides and for a series of complex lithium vanadium phosphates. Finally, lithium pNMR shifts are computed for Li3V2(PO4)(3), for which detailed experimental data are available. This has allowed an in-depth study of different approaches (e.g., full periodic versus incremental cluster computations of g-tensors and different functionals and basis sets for hyperfine computations) as well as a thorough analysis of the different contributions to the pNMR shifts. This study paves the way for a more-widespread computational treatment of NMR shifts for paramagnetic materials.
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