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Mapping of the DFT Spin Configuration Energies of Cr8Cd Molecular Ring onto the Energy Structure of Falicov-Kimball Model

100%
Wojciechowski M., Brzostowski B., Lemański R., Kamieniarz G.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
410-412
EN
A comprehensive study of electronic and magnetic properties of a recently synthesized nonametalic chromium-based heteronuclear molecule Cr₈CdF₉(O₂C-C(CH₃)₃)₁₈ is presented, using DFT and Falicov-Kimball (FK) model approach. The magnetic moments are calculated and the spin charge density map is discussed. The exchange coupling parameters between transition metals ions are extracted, taking into account all the nonequivalent spin configurations. It is demonstrated that the energies of the spin configurations can be reproduced by the FK model with a set of parameters consistent with that for the parent Cr8 molecule. For molecular ring considered, the ground state corresponds to the antiferromagnetic configuration and the ferromagnetic configuration yields the highest energy.
2
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DFT Estimation of Exchange Coupling Constant of Cr₈ Molecular Ring using the Hybrid Functional B3LYP

100%
Wojciechowski M., Brzostowski B., Kamieniarz G.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
407-409
EN
A study of electronic and magnetic properties of an octametallic chromium-based homonuclear molecule Cr₈F₈(CO₂-C(CH₃)₃)₁₆ is presented, using density functional theory (DFT) approach and linearized augmented plane wave (LAPW) method with Perdew, Burke and Ernzerhof (PBE) and Becke 3-term correlation (B3LYP) functionals. The exchange coupling parameters between transition metals ions are extracted, taking into account two different (ferro- and antiferromagnetic) spin configurations. The value J=3.1 meV found for the hybrid B3LYP functional improves significantly the one obtained for the PBE functional and gives an evidence for the superiority of the former in simulation of molecular nanomgnets. Moreover, the hybrid functional yields excellent spin density localisation, an enhancement of the HOMO-LUMO gaps and the value 2.81 μ_B of magnetic moment at the chromium centre in good agreement with experiment.
3
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The Study of Magnetic Molecules Containing Cr₉ Chromium-Based Rings within Density Functional Theory

100%
Brzostowski B., Wojciechowski M., Kamieniarz G.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
961-963
EN
We examine the electronic and magnetic properties of three frustrated Cr₉ molecules with a single bond defect using density functional theory method. Five non-equivalent broken-symmetry spin configurations with S=±3/2 for Cr are considered, the corresponding differences between the total energies are calculated and the exchange interaction parameters J extracted using different scenarios. We find that the couplings for all molecules are antiferrimagnetic. We also estimate the fundamental gaps and in addition, the high occupied molecular orbitals and low occupied molecular orbitals are plotted and discussed.
4
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Advantages of the DFT Augmented Symmetry Approach to Simulations of the Chromium-Based Ring Cr₈ within B3LYP Functional

100%
Brzostowski B., Wojciechowski M., Kamieniarz G.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
591-593
EN
The DFT estimates of magnetic couplings in molecular nanomagnets are computationally demanding and their values have not achieved the satisfactory accuracy in spite of a lot of effort. We concentrate here on comprehensive tests for predictions of the recently proposed augmented symmetry approach aiming at reducing the computational complexity of the DFT calculations which is particularly important for the Wien2k code. Using the B3LYP functional, we demonstrate the numerical stability of magnetic couplings, magnetic moments and the HOMO-LUMO gaps, changing the fraction of exact exchange α. We reach the significant gain in the computing time without a loss in the accuracy of the final results with respect to those obtained by the standard PBE approach. We conclude that the value α=0.25 leads to best estimation of magnetic couplings for hybrid functionals within Wien2k.
5
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Fundamental Gaps in Cr_{8}, Cr_{7}Ni and Cr_{7}Cd Molecules

100%
Brzostowski B., Wojciechowski M., Kamieniarz G.
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vol. 126
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issue 1
234-235
EN
In this paper we investigate fundamental gaps of three octametallic Cr-based molecular rings Cr_{8}F_{8}(Piv)_{16}, Cr_{7}NiF_{8}(Piv)_{16} and Cr_{7}CdF_{8}(Piv)_{16} using the SIESTA package. We find that for the ground-state antiferromagnetic configurations, the gap of the homometallic ring is significantly higher than those of the heterometallic rings. In addition, the HOMO and LUMO orbitals are plotted and discussed.
6
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ESR Studies of Paramagnetic Centers in Pharmaceutical Materials - Cefaclor and Clarithromycin as an Example

88%
Skowronska A., Wojciechowski M., Ramos P., Pilawa B., Kruk D.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
514-517
EN
Electron spin resonance (ESR) studies of two antibiotics, Cefaclor and Clarithromycin, have been performed in order to investigate concentration and dynamics of free radicals generated in these compounds due to thermal sterilization. For Cefaclor three combinations of temperature and heating time have been applied: 160°C, 170°C, 180°C for 120 min, 60 min, and 30 min, respectively, according to the pharmaceutical sterilization norm. Clarithromycin has been heated at 160°C for 120 min. The ESR lineshape has been investigated versus microwave power ranging from 2.2 mW to 70 mW. Electron spin-spin relaxation time has been estimated from the ESR lineshape analysis. Concentrations of radicals generated due to different sterilization procedures have been compared with the purpose to select the best sterilization scheme.
7
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DFT and Falicov-Kimball Model Approach to Cr_{9} Molecular Ring

76%
Brzostowski B., Wojciechowski M., Lemański R., Kamieniarz G., Timco G., Tuna F., Winpenny R.
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vol. 126
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issue 1
270-271
EN
Based on density functional theory (DFT) calculations, we present electronic and magnetic properties of nanometallic homo-nuclear chromium-based molecular rings Cr_{9}F_{9}Cl_{2}(O_{2}C-C(CH_{3})_{3})_{17} recently synthesized. The magnetic moments are calculated, the spin density maps are discussed and the exchange interaction parameter is extracted. The complementary studies are carried out using the Falicov-Kimball model which reproduces very well the energy levels determined by different magnetic broken symmetry configurations obtained by DFT.
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