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1
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DFT Study of Octanuclear Molecular Chromium-Based Ring Using New Pseudopotential Parameters

100%
Brzostowski B., Ślusarski T., Kamieniarz G.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1115-1117
EN
We present a comprehensive study of magnetic properties of Cr_8F_8(Piv)_{16} molecular ring (in short Cr8) using the package SIESTA with several choices of chromium pseudopotential parameters. We use generalized gradient approximation to investigate properties of Cr8 ring approximated by replacing the pivallic group by H atoms (hydrogen saturation). For different choice of chromium pseudopotential we examine the electronic and magnetic properties of Cr8 molecule. We compare highest occupied molecular orbital and the lowest unoccupied molecular orbital gaps for both spin channels, magnetic moments, and exchange interaction parameter J. The influence of pseudopotential parameters on obtained results is discussed. Finally our results are compared with other theoretical approaches and experimental data.
2
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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.
3
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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.
4
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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.
5
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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.
6
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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.
7
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Application of the Package SIESTA to Linear Models of a Molecular Chromium-Based Ring

100%
Ślusarski T., Brzostowski B., Tomecka D., Kamieniarz G.
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issue 5
967-968
EN
We investigate for the first time the electronic and magnetic properties of the linear models of Cr_8F_8(Piv)_{16} molecular ring using the SIESTA package. In the first step the proper values of the SIESTA parameters and the optimal basis set needed for the convergence of the total energy are established. Next the estimates of the magnetic coupling J confirming the previous density functional theory calculations are presented.
8
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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.
9
Content available remote

Anisotropy, Geometric Structure and Frustration Effects in Molecule-Based Nanomagnets

52%
Kamieniarz G., Kozłowski P., Antkowiak M., Sobczak P., Ślusarski T., Tomecka D., Barasiński A., Brzostowski B., Drzewiński A., Bieńko A., Mroziński J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
992-998
EN
In this paper we review our results of comprehensive study of molecular nanomagnets recently synthesized in the form of the chromium-based molecules and bimetallic copper-containing chains as well as we present some new findings. We focus on effects of anisotropy, geometry and frustration appearing in various thermodynamic properties of the nanoscale magnets which are described by Heisenberg-like spin models and simulated by accurate numerical methods. We show that bond-dependent exchange anisotropy is needed to model magnetic torque in the Cd-doped chromium ring. We argue that only in the limit of infinite rings (n → ∞) frustration can be considered as the opposite to bipartiteness in the odd numbered (3 ≤ n ≤ 9) s = 3/2 quantum spin rings. We analyse the influence of exchange interactions and anisotropy on magnetic susceptibility of bimetallic (S = 3/2, s = 1/2) chains composed of Cu ions linked to different 3d ions by fitting experimental data. We reach the remarkable consistency of the density functional theory estimates of the magnetic couplings in Cr_8 molecule and provide strong support to the spin models exploited in the literature.
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