Search

Using first-principles calculations based on density functional perturbation theory, we demonstrate hydrogenation-induced superconductivity in monolayer TiB2H. Hydrogen adatoms destroy the Dirac state of monolayer TiB2 and monolayer TiB2H has a high vibration frequency. Monolayer TiB2H is a phonon-mediated superconductor. Monolayer TiB2H has a predicted T c of 8 K, which further increases under external tensile strain. Thus, this study extends our understanding of superconductivity in two-dimensional (2D) materials and its potential applications. [ABSTRACT FROM AUTHOR]

Metallization of methane (CH4) has always been an interesting issue. Here, we report a study on the structure, metallization and superconductivity in K-doped CH4 under pressure, based on the particle swarm optimization, density functional theory, and density functional perturbation theory. Summarizing the thermodynamical and dynamical stabilities, the electronic band structures, and the electron–phonon interaction calculations, we predicted that K-doped CH4 in P 2 1 ∕ m space-group is a metal and a possible superconductor in the pressure range of 7 0 − 9 0 GPa. The superconducting critical temperature is about 12.7 K at 80 GPa. It was found that the charge transfer from K to CH4 drives the metallization and mainly contributes to the electron–phonon interaction. The result confirms that CH4 can become a metal and superconductor under the electron doping and the relative low pressure. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons doped by metal have exhibited the potential of high temperature superconductivity. Understanding the basic properties of materials is the key to reveal the superconductivity. Here, a systemically theoretical study has been done to explore crystal structures and electronic properties of pristine and potassium-doped 1,2;8,9-dibenzopentacene, compared with [7]phenacenes case. We determined that vdW-DF2 functional is more suitable to describe the non-local interaction in a molecular crystal. Based on this functional, we predicted the crystal structures and investigated in detail the K atomic positions in a system. It was found that the intralayer doping leads to lower total energy. From the calculated formation energy, for each 1,2;8,9-dibenzopentacene molecule, the doping of two electrons is more stable under the relatively K-poor condition while the doping of four electrons is more stable under the K-rich condition. Between these two phases, the three-electron doping phase stabilises in a narrow region of K chemical potential. Combining with the electronic states at Fermi level, we analysed the reasons of superconductivity enhancement in doped 1,2;8,9-dibenzopentacene. This work further deepens the understanding of 1,2;8,9-dibenzopentacene superconductor. [ABSTRACT FROM PUBLISHER]

Based on the density functional theory, a theoretical determination method is applied to investigate structural and electronic properties of anthracene up to 27 GPa. The lattice parametersa, b, c, decrease by 1.53(−18.2%), 0.76(−12.8%), and 0.93(−8.4%), respectively, while the monoclinic angle β increased by 4.65° in this pressure region. At the highest pressure of 27 GPa the unit cell volume is decreased by 58.9%. These findings are shown to be in agreement with experimental results and hint towards the evolution of intermolecular interaction with pressure. The calculated electronic band splitting and the band gap reduce smoothly to some extent with the pressure increasing. Moreover, a pressure-induced decrease of the band gap is observed. [ABSTRACT FROM PUBLISHER]

Abstract: The structural, elastic and electronic properties of BiI3 are investigated using the first-principles pseudopotential calculations within the framework of density functional theory. The calculated equilibrium structural parameters agree well with the experimental values. The results show that rhombohedral R-3 structure is low enthalpy structure at zero pressure. R-3 structure will transform into SbI3-type structure (space group P21/c) at about 7.0GPa. At zero pressure, BiI3 with R-3 symmetry meets the mechanical stability criteria, but BiI3 with P-31m symmetry is an unstable one mechanically. For R-3 structure, the obtained bulk, shear, and Young’s moduli are 25.6, 15.3 and 38.3GPa, respectively. BiI3 presents large elastic anisotropy. Debye temperature of R-3 structure calculated is 181K. The metallization pressure of R-3 structure is about 133GPa and that of predicted high pressure phase P21/c structure is about 61GPa, indicating BiI3’s potential application as a nuclear radiation detector under high pressure environment. [Copyright &y& Elsevier]

Using first-principles calculations based on density functional perturbation theory, we demonstrate hydrogenation-induced superconductivity in monolayer TiB2H. Hydrogen adatoms destroy the Dirac state of monolayer TiB2 and monolayer TiB2H has a high vibration frequency. Monolayer TiB2H is a phonon-mediated superconductor. Monolayer TiB2H has a predicted T c of 8 K, which further increases under external tensile strain. Thus, this study extends our understanding of superconductivity in two-dimensional (2D) materials and its potential applications. [ABSTRACT FROM AUTHOR]

The mechanical and thermodynamic properties of actinium and lanthanum dihydride have been investigated by first-principles calculations based on the density functional theory with generalized gradient approximation. The equilibrium geometries, elastic constants, Poisson’s ratio, various moduli, elastic wave velocities, and Debye temperature were systematically studied. All elastic constants of actinium dihydride were found to be smaller than those of lanthanum dihydride. Phonon band structures and partial density of states were also investigated. The two compounds have similar phonon band structures. The volume expansions, the heat capacities, and the isothermal bulk moduli at finite temperature were also obtained under the quasiharmonic approximation. [ABSTRACT FROM AUTHOR]

The crystal structures of actinium dihydride (AcH 2 ) in a wide pressure range of 0–200 GPa have been investigated by using an unbiased structure searching method coupling with first-principles density functional calculations. A series of pressure-induced phase transitions are predicted for AcH 2 , as Fm -3 m → P 4 2 / mmc → Imma → P 6/ mmm , and the calculated pressures of the phase transitions are 12, 27, and 68 GPa. Under pressure, the coordination number of H atom increases and the nature of chemical bonds changes. The electronic band structures show that all of the competitive phases are metallic. The pressure-induced charge transfer drives the phase transition. Phonon calculations show the competitive phases are thermodynamically stable within their favored pressure range. Our results elucidate the phase transition mechanisms of AcH 2 under pressure, and have major implications for the high-pressure behaviors of actinide and rare-earth metal dihydrides. [ABSTRACT FROM AUTHOR]