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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 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]

Combining the congruence check and the first-principles calculations, we have systematically investigated the structural stabilities and gap distributions of possible diamondoids (C n H m ) 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 pre-determination 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.

The unique electronic property induced diversified structure of boron (B) cluster has attracted much interest from experimentalists and theorists. B30-40 were reported to be planar fragments of triangular lattice with proper concentrations of vacancies recently. Here, we have performed high-throughput screening for possible B clusters through the first-principles calculations, including various shapes and distributions of vacancies. As a result, we have determined the structures of Bn clusters with n = 30-51 and found a stable planar cluster of B49 with a double-hexagon vacancy. Considering the 8-electron rule and the electron delocalization, a concise model for the distribution of the 2c-2e and 3c-2e bonds has been proposed to explain the stability of B planar clusters, as well as the reported B cages.