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Theory Study and Present CT Trend of Organic Charge Transfer Complexes
Published in Atsushi Nagai, Koji Takagi, Conjugated Objects, 2017
Atsushi Nagai, Daniel J. Siegwart
Approaches to charge transfer (CT) complexes lend themselves to many interesting tests. Novel CT compounds based on organic molecules with π‐conjugated ring objects attract high attention because they offer the possibility to tailor the electronic structure of organic electronic devices.1 The wave functions of electronic π‐systems of the donor and acceptor constituents can be sensitively tuned via a change of the change density by adding specific ligand groups at the periphery of the molecule. Characteristic of such compounds is a highly correlated electronic ground state that can show superconductivityt spin density wavest or charge density waves.2Thust this class of compounds is highly interesting not only because of potential applications but also for fundamental research. Growing crystals in a solventthoweverJ is prohibitive for the standard techniques of electronic structure investigations because of the unavolidable surface contaminations.
Reduced magnetic disorder at low temperature in Ca3Co2O6 via zinc substitution
Published in Philosophical Magazine, 2020
B. D. White, A. B. C. Mantilla, J. Jesenovec
Early studies on Ca3Co2O6 reported numerous plateaus in isothermal magnetisation measurements (M vs. H) at low temperature [2,3,5,14], indicating field-induced transitions between several nearly degenerate magnetic structures. Specialised probes including resonant x-ray scattering [15–17], neutron diffraction [2,4,10,12,18–21], muon spin-relaxation [22], and 59Co NMR [7,13,23,24] have been used to study the interchain and intrachain magnetic interactions as well as identify the magnetic ground states of Ca3Co2O6 in zero and applied fields. Long-range magnetic order emerges in zero-field near TN ∼ 24 K as is seen in bulk thermodynamic measurements [25–27]. The corresponding magnetic state, which is not actually the ground state of Ca3Co2O6, is a longitudinal, amplitude-modulated spin-density wave (SDW) order [10,15]. This unstable SDW state coexists below roughly 10 K with a metastable, long-range commensurate antiferromagnetic order [12] as well as a short-range magnetic order [10,12,19–21]. The short-range order likely emerges as a result of the competition between the two nearly degenerate long-range magnetic orders [12]. Polarised neutron diffraction measurements near 1.8 K have established that the SDW phase fraction is 40%, while that of the short-range magnetic order and the commensurate antiferromagnetic order are 40% and 20%, respectively [20].
The time-dependent density matrix renormalisation group method
Published in Molecular Physics, 2018
Herein, we take an example of triplet exciton dissociation as shown in Figure 4. In the computations, the model parameters are those generally chosen for polyacetylene: t0 = 2.5 eV, α = 4.1 eV/Å, K = 21 eV/Å2, M = 1349.14 eVfs2/Å2, a = 1.22 Å. In order to consider the intermolecular hopping, we assume hoppings exist between the donor and acceptor molecules and the hopping integral in the centre of the chain is set as 0.5 eV. It is shown that upon photoexcitation the spin density wave is formed in the central part of the conjugated polymer. Due to the strong electron–phonon couplings within conjugated systems, there is strong connection between electronic structure and geometric structure. Therefore, the π-conjugated system tends to relax down to the bottom of the potential energy surface of the lowest triplet excited state. As could be found in Figure 4 that two spin density peaks emerge and depart from each other gradually before they become close to the electron donor/acceptor part. This is a soliton–antisoliton picture for the lowest triplet excited state which has been revealed by previous theoretical studies [82]. We also notice that such soliton–antisoliton pair picture dissapears after the triplet exciton is diffused to the donor–acceptor interface and the spin density waves are then transferred to the electron donor and acceptor parts through electron hoppings. We do not find polaron-pair states during the charge separation process.
The correlation between structure, multifunctional properties and application of PVD MAX phase coatings. Part I. Texture and room temperature properties
Published in Surface Engineering, 2020
In the review of Ingason et al. [253], it is suggested that the magnetisation of the MAX phases was complex, for which Mn2GaC is a clear example. Moreover, they highlighted the various explanations proposed: itinerant magnetism, Pauli paramagnetism, spin density wave states to non-collinear spin ordering, antiferromagnetism and ferromagnetism. On this basis, they hinted that the present large discrepancy between the measured and computed magnetic moments, where the measured moments are often significantly lower than calculated ones, may not only be due to different sample quality and routes, but also to an incomplete understanding of the magnetic interaction within the sample.