Extreme structure and spontaneous lift of spin degeneracy in doped perforated bilayer graphenes

Extreme structure and spin states of doped and undoped perforated bigraphenes was studied using DFT simulations. It was found that folded nanopores possess extremely high curvature of 0.34 Å−1. Dramatic structural deformation causes severe changes of the chemical properties of carbon atoms localized at the nanopores converting the folded edges to local oxidative fragments. It was found that asymmetrical coordination of either Li, Ca, or Al to the nanopores is coupled with electron transfer from metal to edge carbon atoms and breakdown of local inversion symmetry. Li-, Ca-, and Al-doped perforated AA bigraphene revealed ferromagnetic spin ordering with magnetic moments of 0.38, 0.14, and 0.32μB/unit cell, respectively, and spin polarization energy gain of 0.037eV for Ca-doped superlattice. It was shown that ferromagnetic spin ordering of bigraphene nanopores contradicts to the Nagaoka's theorem, which excludes strong electron correlations as a reason of spin polarization. Spontaneous lift of spin degeneracy was interpreted in terms of perturbing intense local electrostatic fields from extra electron charges localized at the nanopore edges, coupled with breakdown of space inversion and local translation invariances. It was shown that spin energy splitting is proportional to the matrix elements calculated on Bloch states with opposite wavevectors and perturbing electrostatic fields

Localized d-electron effect on spin polarization of vertical heterostructures of nanoporous bilayer graphene

The paper presents a novel composite material based on nanoporous AB-stacked bilayer graphene. The influence of the dopant atom on the electronic properties of the heterostructure and its position in the pore is investigated herein. The proposed effect is considered on composite materials doped with calcium and manganese atoms in order to correctly evaluate the influence of the valence shell filling type without the local field effect caused by the structural properties of an AB-stacked bilayer graphene

Towards advanced complex quantum materials for spin-related applications and photo-induced heterogeneous catalysis: The case of (Fen) @g-CN1 (n = 2,3) and (Mn)@(g-CN1)2

Perspective heterostructures based on Fe and Mn adatoms on 2D g-C3N4 films of different morphology were designed and investigated by means of DFT GGA/PBE and GGA/HSE levels of theory. Spontaneous spin polarization of g-C3N4 and a variety of electronic properties were theoretically investigated. It was found that GGA HSE DFT potential is suitable to describe the main properties of g-C3N4-based heterostructures with transition metal adatoms. It was revealed that (Mn)@(g-CN1)2 heterostructure is a half-metal with 0.5 eV band gap in α-channel. (Fen)@g-CN1, n = 2,3) demonstrate different semiconducting properties which are determined by structure and number of Fe adatoms in the unit cells. The presence of several independent centers of Fe forming polyatomic clusters was stated as one of the interests in catalysis. It was found that all considered heterostructures may serve as perspective quantum materials in different spin-related application

Structure and properties of exotic nano- and mesodiamonds with pentagonal symmetry

A comprehensive critical survey of structures of exotic nano-, meso- and microdiamonds with dodecahedral and icosahedral symmetry (N/MDPS) is presented. Due to their high dodecahedral or icosahedral symmetry, the unique complex atomic and electronic structure of N/MDPS leads to transport and mechanical properties very promising for photonic, quantum, and nanomechanical applications. To explain the nature of diamonds, theoretical models have been proposed based on the formation of twinned structures consisting of either 5 or 20 symmetrically equivalent tetrahedral and prismatic fragments of the face-centered cubic lattice with the formation of star-shaped or icosahedral clusters, respectively. It has been shown that these twinned nano- and mesodiamonds have limited dimensions due to accumulation of uncompensated structural stresses arising from the deviation of the angles between diamond facets from perfect 72 degrees in tetrahedral fragments of the face-centered cubic lattice to 70.5 degrees between five symmetrically equivalent twinned fragments

Potential energy surfaces of adsorption and migration of transition metal atoms on nanoporus materials: The case of nanoporus bigraphene and G-C3N4

Abstract First-row transition metal (TM) atoms adsorption and migration on nanoporus 2D materials like bigraphene with double vacancies and g-C3N4 as the active sites for TM nanocluster’s growth was studied within the framework of density functional theory. Both thermodynamic and kinetic aspects of composite synthesis were discussed. It was found that potential barriers of adatom’s migration from bigraphene’s outer surface to the interlayer space through the double vacancy are rather low values. High potential barriers of TM migration along the carbon plane prevents TM clusterization due to enhanced chemical activity of double vacancies which gives a possibility to capture the surface adatoms. As was shown for the monolayer graphene, the decrease of vacancies concentration reduces the barrier of adatom migration along the surface while the second graphene sheet in bigraphene stabilizes the structure. The behavior of TM-atom regarding g-CN2 and g-CN1 nanosheets was investigated. Potential energy surfaces were obtained and discussed. The migration barriers were found surmountable that means high probability of migration of TM adatoms to global minima and formation of TM vacancies. Comparison of barriers values with Boltzmann factor demonstrated that just standalone temperature fluctuations cannot initiate structural transitions. The properties of designed structures can be of interest of catalysts and biosensors for biomedical applications

Unique Nanomechanical Properties of Diamond−Lonsdaleite Biphases: Combined Experimental and Theoretical Consideration of Popigai Impact Diamonds

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