| 1. |
- Kuklin, Artem V., et al.
(författare)
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Electronic and optical properties of C16S8 and C16S4Se4 molecules and crystals
- 2022
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Ingår i: New Journal of Chemistry. - Cambridge, United Kingdom : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 46:28, s. 13513-13518
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Tidskriftsartikel (refereegranskat)abstract
- Hetero[8]circulenes have been proposed as promising fluorescent emitters for organic light-emitting diodes and as emerging materials in the construction of organic solar cells. Among them, octathio[8]circulene (C16S8) and its derivative tetrathiotetraseleno[8]circulene (C16S4Se4) crystals have been highlighted as efficient charge transport materials in field-effect devices. Using density functional theory, we investigate in this paper the electronic and optical properties of the C16S8 and C16S4Se4 molecules and crystals in order to revise previously reported controversial experimental data and report highly reproducible new results. We find that formation of the crystals results in a significant band gap decrease (similar to 0.6-0.7 eV) caused by relatively strong intermolecular interactions. A partial replacement of S atoms with Se atoms also leads to a small band gap reduction. The C16S8 crystal demonstrates a band gap of 3.32 eV, while a band gap of 3.20 eV is found for C16S4Se4. Both C16S8 and C16S4Se4 compounds are optically transparent in the visible region, confirming the absence of red coloration reported previously in one of experimental papers. The C16S8 and C16S4Se4 crystals demonstrate anisotropic electronic, mechanical and optical properties. These findings might initiate future experimental studies of the red color origin for C16S8 and provide insight for the design and engineering of C16S8 and C16S4Se4 based charge transport and optical devices.
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| 2. |
- Begunovich, Lyudmila V., et al.
(författare)
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Single-layer polymeric tetraoxa[8]circulene modified by s-block metals : toward stable spin qubits and novel superconductors
- 2021
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 13:9, s. 4799-4811
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Tidskriftsartikel (refereegranskat)abstract
- Tunable electronic properties of low-dimensional materials have been the object of extensive research, as such properties are highly desirable in order to provide flexibility in the design and optimization of functional devices. In this study, we account for the fact that such properties can be tuned by embedding diverse metal atoms and theoretically study a series of new organometallic porous sheets based on two-dimensional tetraoxa[8]circulene (TOC) polymers doped with alkali or alkaline-earth metals. The results reveal that the metal-decorated sheets change their electronic structure from semiconducting to metallic behaviour due to n-doping. Complete active space self-consistent field (CASSCF) calculations reveal a unique open-shell singlet ground state in the TOC-Ca complex, which is formed by two closed-shell species. Moreover, Ca becomes a doublet state, which is promising for magnetic quantum bit applications due to the long spin coherence time. Ca-doped TOC also demonstrates a high density of states in the vicinity of the Fermi level and induced superconductivity. Using the ab initio Eliashberg formalism, we find that the TOC-Ca polymers are phonon-mediated superconductors with a critical temperature T-C = 14.5 K, which is within the range of typical carbon based superconducting materials. Therefore, combining the proved superconductivity and the long spin lifetime in doublet Ca, such materials could be an ideal platform for the realization of quantum bits.
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| 3. |
- Begunovich, Lyudmila, V, et al.
(författare)
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Triple VTe2/graphene/VTe2 heterostructures as perspective magnetic tunnel junctions
- 2020
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Ingår i: Applied Surface Science. - : ELSEVIER. - 0169-4332 .- 1873-5584. ; 510
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Tidskriftsartikel (refereegranskat)abstract
- New perspective 1.4 nm thick spin-polarized triple heterostructures based on graphene sandwiched between two vanadium ditelluride monolayers (VTe2/graphene/VTe2) were studied using ab initio DFT technique. Both possible trigonal prismatic (H-VTe2) and octahedral (T-VTe2) VTe2 phases were considered to design and study graphene-based heterostructures. It was shown that the interaction with graphene changes the electronic structure of 2D T-VTe2 from metallic to half-metallic, making T phase perspective to be used for magnetic tunnel junctions. The electronic subsystem of graphene fragment is slightly hole doped. Calculated tunnel magne-toresistance ratio for the favorable heterostructure configuration estimated within the Julliere model is 220%, which opens a way to use VTe2/graphene/VTe2 as prospective magnetic tunnel junction in novel spintronic nanodevices based on tunnel magnetic resistance and spin transfer torque effects.
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| 4. |
- Karaush-Karmazin, Nataliya N., et al.
(författare)
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Structure, stability and electronic properties of one-dimensional tetrathia- and tetraselena[8]circulene-based materials : a comparative DFT study
- 2020
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Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 44:17, s. 6872-6882
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Tidskriftsartikel (refereegranskat)abstract
- Conjugated polymers gain much attention due to the promising applications in organic electronic device technology. In this work, we theoretically study the structures and electronic properties of a novel class of nanostructures, namely one-dimensional tetrathia[8]circulenes (TTC) and tetraselena[8]circulenes (TSC) predicted to be promising semiconducting soft materials. It is found that all nanoribbons are thermodynamically stable and that their electronic properties depend significantly on the type of fusing between the monomers. In particular, the band gap tends to decrease while moving from the directly fused TTC/TSC ribbons to the structures coupled via a benzene-core linker and then to the ribbons fused through a four-membered ring. Therefore, both coupling type and length of oligomers allow one to manipulate the electronic and optical properties of the studied ribbons. The band structure calculations of infinite nanoribbons reveal direct band gaps that decrease from 2.28 to 2.14 eV for the TTC ribbons of the first and second fusion types. The TSC structures demonstrate the same trend exhibiting band gap narrowing from 2.41 (type I) up to 2.11 eV (type II). The type III ribbons possess a lack of periodicity due to the close-lying energy minima for the possible twisting configurations of TTC and TSC moieties relative to the linking four-membered ring.
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| 5. |
- Anithaa, V. S., et al.
(författare)
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Adsorption of volatile organic compounds on pristine and defected nanographene
- 2022
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Ingår i: Computational and Theoretical Chemistry. - : Elsevier. - 2210-271X .- 2210-2728. ; 1211
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of volatile organic compounds (VOCs) which are a class of air pollutants affecting the environment and human health is considered as the favourable technology for enrichment, separation and utilization of VOCs. In the present work, the adsorption properties of air polluting carbocyclic and heterocyclic VOCs such as toluene, p-xylene and indole onto pristine/defected nanographene (with and without dopants) are investigated using density functional theory (DFT). Adsorption of indole is higher (-0.544 to -1.786 eV) in pristine/defected nanographene (with and without dopant) than p-xylene and toluene. The reactivity of defect on adsorption of VOCs is found high for indole with defected nanographene (DG) and toluene with DG-N indicating the influence of sheet type for adsorption rely on the type of the VOCs adsorbate. The charge transfer and type of interaction between the sheet and VOCs are interpreted using Hirshfeld charge analysis, QTAIM and RDG analysis. The influence of VOCs adsorption is high on the electronegativity and electrophilicity index of the pristine/defected nanographene whereas energy gap and hardness show less influence. The noticeable changes in the TDOS and energy gap on adsorption of VOCs with respect to the type of sheet infers that the doped defected sheet have high affinity than the pristine sheet moreover, the suitable sheet for adsorption of VOCs depends on the type of VOCs adsorbate.
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| 6. |
- Avramov, Pavel, V, et al.
(författare)
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Topological and quantum stability of low-dimensional crystalline lattices with multiple nonequivalent sublattices
- 2022
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Ingår i: New Journal of Physics. - : Institute of Physics (IOP). - 1367-2630. ; 24:10
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Tidskriftsartikel (refereegranskat)abstract
- The terms of topological and quantum stabilities of low-dimensional crystalline carbon lattices with multiple non-equivalent sublattices are coined using theoretical analysis, multilevel simulations, and available experimental structural data. It is demonstrated that complex low-dimensional lattices are prone to periodicity breakdown caused by structural deformations generated by linear periodic boundary conditions (PBC). To impose PBC mandatory limitations for complex low-dimensional lattices, the topology conservation theorem (TCT) is introduced, formulated and proved. It is shown that the lack of perfect filling of planar 2D crystalline space by structural units may cause the formation of (i) structure waves of either variable or constant wavelength; (ii) nanotubes or rolls; (iii) saddle structures; (iv) aperiodic ensembles of irregular asymmetric atomic clusters. In some cases the lattice can be stabilized by aromatic resonance, correlation effects, or van-der-Waals interactions. The effect of quantum instability and periodicity breakdown of infinite structural waves is studied using quasiparticle approach. It is found that both perfect finite-sized, or stabilized structural waves can exist and can be synthesized. It is shown that for low-dimensional lattices prone to breakdown of translation invariance (TI), complete active space of normal coordinates cannot be reduced to a subspace of TI normal coordinates. As a result, constrained TI subspace structural minimization may artificially return a regular point at the potential energy surface as either a global/local minimum/maximum. It is proved that for such lattices, phonon dispersion cannot be used as solid and final proof of either stability or metastability. It is shown that ab initio molecular dynamics (MD) PBC Nose-Hoover thermostat algorithm constrains the linear dimensions of the periodic slabs in MD box preventing their thermostated equilibration. Based on rigorous TCT analysis, a flowchart algorithm for structural analysis of low-dimensional crystals is proposed and proved to be a powerful tool for theoretical design of advanced complex nanomaterials.
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| 7. |
- Baryshnikov, Gleb V., et al.
(författare)
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Cyclo[18]carbon : Insight into Electronic Structure, Aromaticity, and Surface Coupling
- 2019
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Ingår i: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 10:21, s. 6701-6705
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Tidskriftsartikel (refereegranskat)abstract
- Cyclo[18]carbon (C-18) is studied computationally at the density functional theory (DFT) and ab initio levels to obtain insight into its electronic structure, aromaticity, and adsorption properties on a NaCl surface. DFT functionals with a small amount of Hartree-Fock exchange fail to determine the experimentally observed polyyne molecular structure, revealing a cumulene-type geometry. Exchange-correlation functionals with a large amount of Hartree-Fock exchange as well as ab initio CASSCF calculations yield the polyyne structure as the ground state and the cumulene structure as a transition state between the two inverted polyyne structures through a Kekule distortion. The polyyne and the cumulene structures are found to be doubly Huckel aromatic. The calculated adsorption energy of cyclo[18]carbon on the NaCl surface is small (37 meV/C) and almost the same for both structures, implying that the surface does not stabilize a particular geometry.
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| 8. |
- Gusev, Alexey, et al.
(författare)
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Structure and tuneable luminescence in polymeric zinc compounds based on 3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole
- 2020
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Ingår i: Polyhedron. - : Elsevier BV. - 0277-5387 .- 1873-3719. ; 191
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic-organic hybrid polymers based on 3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole (3,4-Hbpt) ligand were synthesized and subsequently characterized by single-crystal X-ray diffraction, FT-IR spectra, elemental analyses, thermogravimetric (TG) analyses and PXRD. The X-ray diffraction analyses revealed that the complexes [Zn(3,4-Hbpt)Cl-2] and [Zn(3,4-Hbpt)Br-2] possess a 1-D helical chain structure constructed of the 3,4-Hbpt ligands connecting the zinc cations. The [Zn(3,4-bpt)(OAc)] complex demonstrates a 2D sheet structure bridged by tridentate 3,4-bpt-anions. All compounds exhibit substantial thermal stability and show photo-fluorescent properties that result from the ligand pi-pi* transition. Ultraviolet-to-visible tunable emission for two of the complexes is observed.
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| 9. |
- Karaush-Karmazin, Nataliya N., et al.
(författare)
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Impact of molecular and packing structure on the charge-transport properties of hetero[8]circulenes
- 2021
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 9:4, s. 1451-1466
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Tidskriftsartikel (refereegranskat)abstract
- In organic photovoltaic cells, absorption of light leads to the formation of excitons, which then diffuse to the donor/acceptor interface to generate photocurrent. The distance from which excitons can reach the interface is constrained by the exciton diffusion length, which has been difficult to quantitatively model or predict due to structural and energetic disorder. Modern non-fullerene acceptors have been shown to possess exceptionally large diffusion lengths, along with well-defined molecular and packing structures, suggesting that a predictive framework for materials design and computational screening may be possible. In this work, we demonstrate that the large diffusion coefficient recently observed in an archetypical non-fullerene acceptor, IDIC, can be accurately quantified using density functional theory, and that the low energetic disorder means that the crystal structure provides a meaningful starting point to understand exciton motion in thin films. Accounting for the short- and long-range excitonic interactions, as well as spatiotemporal disorder, we demonstrate that both Monte-Carlo techniques and a simple sum-over-rates method can accurately predict experimental values for exciton diffusivity and diffusion length. The simplicity and accuracy of this approach are directly linked to the structural order of these materials, and an electronic coupling profile that is unusually resilient to thermal distortions - highlighting the potential of the sum-over-rates method for computational materials screening. Moreover, we show that these factors, combined with the low reorganisation energy and significant long-range electronic coupling, lead to diffusion rates that approach the upper limit of incoherent energy transfer and long diffusion lengths that relieve constraints on organic solar cell device architectures.
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| 10. |
- Kuklin, Artem, V, et al.
(författare)
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CrI3 magnetic nanotubes : A comparative DFT and DFT plus U study, and strain effect
- 2020
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 123
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, structural and electronic properties of CrI3 magnetic nanotubes (NTs) are studied using density functional theory. Both armchair and zigzag CrI3 nanotubes demonstrate a high correlation in strain energy between each other independently on accounting the Hubbard correction. The strain energies decrease with expansion of the tube diameter making the tubes' synthesis with a diameter larger than 45 angstrom to be energetically possible. The nanotubes of both zigzag and armchair chirality are ferromagnetic semiconductors with band gaps close to that of the CrI3 monolayer. The band gaps are suppressed by reducing the tube diameters due to the structural stress leading to deformation of the Cr-I crystal field and changes in the bond lengths. The external strain can be utilized to flexibly tune the electronic properties of CrI3 nanotubes with the desired spin-up/spindown band gap ratio. Strong distortion of the octahedral Cr-I crystal field under compression results in nontrivial behavior in the spin-up band gap of (4, 4) tube. Stretching of tubes leads to the enhancement of the exchange energy that should result in higher Curie temperature, therefore providing a good platform for potential applications in spintronic nanodevices.
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