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Using the first-principles calculations, we have investigated the effects of the charge doping and biaxial strain on the charge density wave (CDW) of monolayer octahedral titanium disulfide (1T-TiS2). Our results show that proper electron doping can suppress the (2 × 2) CDW instability and the larger electron doping promotes a (7 × 3) CDW phase involving a spontaneous breaking of the hexagonal crystal symmetry. Strain can affect the stability of doped monolayer 1T-TiS2, but neither compressive strain nor tensile strain alone can stabilize the pristine one. When TiS2 layers are decorated by metal atoms, such as Li, Na, K, Ca, and Al, the transferred charge can also suppress the (2 × 2) CDW instability. The stable doped 1T-TiS2 is predicted to exhibit good phonon-mediated superconductivity, which can be further enhanced by strain. Our results reveal a unique CDW phenomenon in the electron-doped monolayer 1T-TiS2 and that doping combined strain is efficient to modulate phonon softening, electron-phonon coupling, and superconductivity. [ABSTRACT FROM AUTHOR]

Combining the extended cluster expansion method and the first-principles calculations, we have systematically investigated the structural stabilities of nitrogen doped C 60 fullerene. With the structural recognition, we have calculated all possible isomers of C 60-n N n (n = 1–4) to obtain their ground state structures using the first-principles method. For C 60-n N n (n = 5–9) heterofullerenes, we have estimated the energy by the extended cluster expansion method to screen the candidates efficiently, followed by first-principles confirmation for the low-lying structures. For C 60-n N n with more than 9 nitrogen atoms, we developed a classification method to select the candidates and successfully obtained the low-lying isomers. The most stable structures for C 60-n N n (n = 3–11) we obtained have lower energies compared to the structures in previous studies. Notably, we have found 26 low-lying structures of C 48 N 12 azafullerenes, from their 11.6 billion isomers. We propose an energy prediction method to deal with the numerous nonequivalent structures, highly improving the structural screening efficiency. Firstly, we obtain the ground states of C 60-n N n for n = 2–4 and the interactive energies used for fitting in the ExCE method. Then the ExCE method is used to obtain the low-lying isomers of C 60-n N n for n = 5–9. On the basis of the investigations at 2-body substructures in the calculated azafullerenes, we propose a classification method to filter out the majority of the isomers with low stability, therefore we adopt ExCE method to predict the stability of the rested isomers and obtain the most stable isomers of C 60-n N n for n = 10–12. Apart from C 58 N 2 and C 48 N 12 , all the most stable isomers we obtained have higher stabilities than those of the ones reported in literatures so far. It is found that azafullerenes will not be stable if there is any pentagonal ring with more than one heteroatom, or two nitrogen atoms are in ortho positions of hexagonal rings. For C 48 N 12 heterofullerenes, we have obtained many structures with similar stabilities. Besides the ones predicted by Hultman and Manaa we have found other 24 low-lying isomers whose stabilities are between these two structures. Image 1 [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal dichalcogenides (TMDs) exhibit many novel properties due to dimension, lattice distortion, electron-electron interaction etc. Here, we determine that 1T-VTe 2 with space group P 3 ‾ m 1 is an antiferromagnetic metal by first-principles calculations, and three metastable structures are predicted, i.e., the P 21 / m and C 2 / m antiferromagnetic semiconductor phases and P 3 m 1 ferrimagnetic half-metal phase. Besides, the C 2 / m phase can be transfered to the P 3 m 1 phase by electron doping, while hole doping can induce a transition from C 2 / m phase to P 3 ‾ m 1 phase. These transitions could be ascribed to a strong coupling of charge, lattice, and spin degrees of freedom in VTe 2. The diverse electronic and magnetic properties of VTe2 provide a good platform for researchers to understand the interactions between spin, charge and lattice. • 1-VTe 2 is clarified to be antiferromagnetic metal ground state. • Three VTe 2 phases with different magnetic states and electronic structures are predicted. • Carrier doping can induce transitions between different phases. • Strong spin-lattice-charge interaction is found in VTe 2. [ABSTRACT FROM AUTHOR]

Hydrogen storage with Ti decorated nano-materials is attributed to the d levels of Ti with unsaturated bonding, whose configuration significantly affects the system's stability and activity. Using first-principles calculations, we have investigated hydrogen adsorption and desorption on the Ti decorated defective graphene under various strains (from 0% to 15%), in which Ti atoms' dispersing are energetically stable. According to the phase diagram, we showed that hydrogen uptake can be modulated as a function of chemical potential and strain, since the strain modifies the configuration of d levels, and consequently affects the binding between H 2 and Ti atom. Remarkably, Ti decorated defective graphene under 15% strain could be considered as an ideal media of hydrogen storage, in which the desorption temperature of H 2 is expected to be ∼300 K at 0.5 atm. The control of strain is found to be dominant to the H 2 uptake, besides the temperature and pressure. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploring new materials has attracted more and more attention, due to the improvement of technology and industry. Theoretically, the first-principles calculations combined with global optimization have been applied to predicting the properties of materials accurately and accelerate the discovery of new materials. For certain multi-component materials, the atoms are nearly at the lattice sites and the material exploration can be enhanced with biased screening. Based on the space symmetry, the calculations of duplicate structures can be avoided, and the specified constraints are applied to filter the energetically unstable candidates out. To provide the reasonable candidates for the first-principles calculations, we have released a program of Structures of Alloy Generation And Recognition (SAGAR), which can be conveniently used through the website. Herein, we will present several examples to show that the biased screening is practical and efficient, determining structures with high stabilities and novel properties. We have studied the distribution of up to 50% Cl vacancy concentration in NaCl and revealed semiconductor–metal transition in the boron/nitrogen co-doped diamond. The ground state anti-ferrormagnetic configuration of VCl 2 is determined, as well as the low-lying hydrogenated-C6 0 structures with high symmetry. Our results indicate that the biased screening with proper constraint will effectively enhance the material exploration. [ABSTRACT FROM AUTHOR]

Combining the congruence check and the first-principles calculations, we have systematically investigated the structural stabilities and gap distributions of possible diamondoids (CnHm) with the carbon numbers (n) from 10 to 41. A simple method for the nomenclature is proposed, which can be used to distinguish and screen the candidates with high efficiency. Different from previous theoretical studies, the possible diamondoids can be enumerated according to our nomenclature, without any predetermination from experiments. The structural stabilities and electronic properties have been studied by density functional based tight binding and first-principles methods, where a nearly linear correlation is found between the energy gaps obtained by these two methods. According to the formation energy of structures, we have determined the stable configurations as a function of chemical potential. The maximum and minimum energy gaps are found to be dominated by the shape of diamondoids for clusters with a given number of carbon atoms, while the gap decreases in general as the size increases due to the quantum confinement. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

The dispersion of transition metals (TM) has been an ongoing challenge for quasi-molecular H 2 storage. Here we have investigated the adsorption of TM (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) on benzoquinone (BQ), by using the first-principles methods. It is found that Sc or Ti (Sc/Ti) atom is energetically favored to bind with ortho-BQ (OBQ) to form OBQ–Sc/Ti complex when compared to their bulk structures. Notably, the coordination number of Sc/Ti is only two, thereby providing enough empty d orbitals for H 2 storage without geometrical blocking. Four H 2 molecules can be accommodated by each OBQ–Sc complex via Kubas-like interaction, with the adsorption energy of 0.20 eV/H 2 and the H 2 storage capacity of ∼5.0 wt%. For practical application, two types of structures have been proposed for H 2 storage using BQ molecule as building block, which would guarantee the dispersing of Sc atom and avoid clustering of OBQ–Sc complexes. In particular, for Sc-decorated oxygen-terminated zigzag graphene nanoribbons, the capacity of H 2 storage reaches up to 6.0 wt%. [ABSTRACT FROM AUTHOR]

Using density-functional theory calculations, we investigated the adsorption of transition-metal (TM) atoms (TM = Se, Ti, V, Cr, Mn, Fe, Co, and Ni) on carbon doped hexagonal boron nitride (BN) sheet and the corresponding cage (Bi2Ni2). With carbon substitution of nitrogen, Sc, V, Cr, and Mn atoms were energetically favorable to be dispersed on the BN nanostructures without clustering or the formation of TM dimers, due to the strong binding between TM atoms and substrate, which contains the half-filled levels above the valence bands maximum. The carbon doped BN nanostructures with dispersed Sc could store up to five and six H2, respectively, with the average binding energy of 0.3 ∼ 0.4 eV, indicating the possibility of fabricating hydrogen storage media with high capacity. We also demonstrated that the geometrical effect is important for the hydrogen storage, leading to a modulation of the charge distributions of d levels, which dominates the binding between H2 and TM atoms. [ABSTRACT FROM AUTHOR]

The antiferromagnetic-semiconductor extreme tensile strain (8%) states of La 0.7 Ca 0.3 MnO 3 membranes was achieved by Hong et al. (2020) [23]. To understand such tunable magnetic and electronic properties in these La 2 3 M 1 3 MnO 3 (M=Ca, Sr) systems, we have investigated the magnetic and electronic behaviors of La 2 3 M 1 3 MnO 3 (M=Ca, Sr) under strain and charge doping using first-principles calculations. A ferromagnetic-semiconductor phase is predicted for La 2 3 Sr 1 3 MnO 3 beyond 4% biaxial tensile strain. Meanwhile, its energy gap and magnetic anisotropic energy increase as the strain increases. We also discover that the change of magnetic exchange energy in La 2 3 Ca 1 3 MnO 3 under charge doping is in analogy to the scenario directly changing the Ca concentrations. Based on the magnetic competition analysis, it is expected that the carrier concentration and strains dominate the magnetic ground state while the La/Ca distributions have little impact. The highly tunable magnetic-electronic properties offer opportunities for the future magnetic-electronic materials design and applications. • DFT SCAN calculations give excellent structure and magnetic moments of the studied systems. • A ferromagnetic semiconductor is predicted for La 2/3 Sr 1/3 MnO 3 under biaxial tensile strain. • Carrier concentration combined with strains dominate the magnetic coupling. • Magnetic anisotropic energy is enhanced by 30 μeV by strains for La 2/3 Sr 1/3 MnO 3. [ABSTRACT FROM AUTHOR]