Determination of the hyperfine magnetic field in magnetic carbon-based materials: DFT calculations and NMR experiments

Freitas, Jair C. C.; Scopel, Wanderlã L.; Paz, Wendel S.; Bernardes, Leandro V.; Cunha-Filho, Francisco E.; Speglich, C.; Araújo‐Moreira, F. M.; Pelc, Damjan; Cvitanić, Tonči; Požek, Miroslav

doi:10.1038/srep14761

Cited by 23 publications

(18 citation statements)

References 52 publications

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“…Indeed, such calculations have been helpful in the identification of point defects in different semiconductors by comparing the experimental and calculated hyperfine constants [27][28][29][30][31]. However, the nature of many ground or excited states relevant to defects and their applications are such that DFT methods deliver results of widely varying accuracy [32], meaning that great care must always be taken when this method is applied.…”

Section: Introductionmentioning

confidence: 99%

Defect states in hexagonal boron nitride: Assignments of observed properties and prediction of properties relevant to quantum computation

2018

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Section: Introductionmentioning

confidence: 99%

Defect states in hexagonal boron nitride: Assignments of observed properties and prediction of properties relevant to quantum computation

2018

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“…Ideal graphene sheet is nonmagnetic, then to use graphene for spintronic applications the major challenge is to make graphene magnetic. In this sense, the experimental observation of magnetic properties in graphene and related materials [4][5][6][7][8] has drawn huge interest, especially considering the applications of these materials in spintronics, quantum information processing and others.…”

Section: Introductionmentioning

confidence: 99%

Interaction between single vacancies in graphene sheet: An ab initio calculation

Scopel¹,

Paz²,

Freitas³

2016

Solid State Communications

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In order to investigate the interaction between single vacancies in a graphene sheet, we have used spin-polarized density functional theory (DFT). Two distinct configurations were considered, either with the two vacancies located in the same sublattice or in different sublattices, and the effect of changing the separation between the vacancies was also studied. Our results show that the ground state of the system is indeed magnetic, but the presence of the vacancies in the same sublattice or in different sublattices and the possible topological configurations can lead to different contributions from the π and σ orbitals to magnetism. On the other hand, our findings reveal that the net magnetic moment of the system with the two vacancies in the same sublattice move towards the value of the magnetic moment per isolated vacancy with the increase of the distance between the vacancies, which is ascribed to the different contributions due to π electrons. Moreover, it is also found that the local magnetic moments for vacancies in the same sublattice are in parallel configuration, while they have different orientations when the vacancies are created in different sublattices. So, our findings have clearly evidenced how difficult it would be to observe experimentally the emergence of magnetic order in graphene-based systems containing randomly created atomic vacancies, since the energy difference between cases of antiferromagnetic and ferromagnetic order decreases quickly with the increase in the distance separating each vacancy pair.

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“…[18][19][20][21][22][23][24] However, methods for performing accurate calculations of this type are still being developed. Small molecules containing the types of functionalities found in diamond and h-BN defects may be described to chemical accuracy using standard ab initio computational methods such as quantum Monte Carlo (QMC), 25 coupledcluster singles and doubles (CCSD) 26 theory with perturbation corrections for triples excitations (CCSD(T)), 27 related timedependent approaches such as equations of motion coupled cluster (EOMCCSD), [28][29] singles and doubles multi-reference configuration interaction (MRCI), 30 as well as its approximation, complete-active-space self-consistent field (CASSCF) 31 theory with perturbative corrections for singles and doubles excitations (CASPT2).…”

Section: Introductionmentioning

confidence: 99%

Understanding and Calibrating Density-Functional-Theory Calculations Describing the Energy and Spectroscopy of Defect Sites in Hexagonal Boron Nitride

Reimers

Ali

Kobayashi

et al. 2018

J. Chem. Theory Comput.

145

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Defect states in 2D materials present many possible uses but both experimental and computational characterization of their spectroscopic properties is difficult. We provide and compare results from 13 DFT and ab initio computational methods for up to 25 excited states of a paradigm system, the V N C B defect in hexagonal boron nitride (h-BN). Studied include include: (i) potentially catastrophic effects for computational methods arising from the multi-reference nature of the closed-shell and open-shell states of the defect, which intrinsically involves broken chemical bonds, (ii) differing results from DFT and time-dependent DFT (TDDFT) calculations, (iii) comparison of cluster models to periodic-slab models of the defect, (iv) the starkly differing effects of nuclear relaxation on the various electronic states as broken bonds try to heal that control the widths of photoabsorption and photoemission spectra, (v) the effect of zero-point energy and entropy on free-energy differences, (vi) defect-localized and conduction/valence band transition natures, and (vii) strategies needed to ensure that the lowest-energy state of a defect can be computationally identified. Averaged state-energy differences of 0.3 eV are found between CCSD(T) and MRCI energies, with thermal effects on free energies sometimes also being of this order. However, DFT-based methods can perform very poorly. Simple generalized-gradient functionals like PBE fail at the most basic level and should never be applied to defect states. Hybrid functionals like HSE06 work very well for excitations within the triplet manifold of the defect, with an accuracy equivalent to or perhaps exceeding the accuracy of the ab initio methods used. However, HSE06 underestimates triplet state energies by on average 0.7 eV compared to closed-shell singlet states, while open-shell singlet states are predicted to be too low in energy by 1.0 eV. This leads to miss-assignment of the ground state of the V N C B defect. Long-range corrected functionals like CAM-B3LYP are shown to work much better and to represent the current entry level for DFT calculations on defects. As significant differences between cluster and periodic-slab models are also found, the widespread implementation of such functionals in periodic codes is in urgent need.

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Determination of the hyperfine magnetic field in magnetic carbon-based materials: DFT calculations and NMR experiments

Cited by 23 publications

References 52 publications

Defect states in hexagonal boron nitride: Assignments of observed properties and prediction of properties relevant to quantum computation

Defect states in hexagonal boron nitride: Assignments of observed properties and prediction of properties relevant to quantum computation

Interaction between single vacancies in graphene sheet: An ab initio calculation

Understanding and Calibrating Density-Functional-Theory Calculations Describing the Energy and Spectroscopy of Defect Sites in Hexagonal Boron Nitride

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