Yunzhou Lv

Cubic C96: a novel carbon allotrope with a porous nanocube network

A novel cubic porous carbon allotrope C96 carbon with intriguing physical properties was predicted. It has 96 atoms in the conventional cell, possessing a Pmm space group. The basic building block of C96 carbon is a planar six-membered carbon ring. The structural stability, mechanical properties, and dynamical properties of C96 carbon were extensively studied. It is a semiconductor (1.85 eV) with a lower density (2.7 g cm−3) and a larger bulk modulus (279 GPa) and is stable under ambient conditions. The hardness of C96 carbon (25 GPa) is larger than that of T carbon (5.6 GPa). Due to the structural porous feature and lower density, C96 carbon can also be expected to be a good hydrogen storage material.

High-temperature superconductivity in compressed solid silane.

Crystal structures of silane have been extensively investigated using ab initio evolutionary simulation methods at high pressures. Two metallic structures with P21/c and C2/m symmetries are found stable above 383 GPa. The superconductivities of metallic phases are fully explored under BCS theory, including the reported C2/c one. Perturbative linear-response calculations for C2/m silane at 610 GPa reveal a high superconducting critical temperature that beyond the order of 102 K.

Ab initio structure determination of n-diamond

A systematic computational study on the crystal structure of n-diamond has been performed using first-principle methods. A novel carbon allotrope with hexagonal symmetry R32 space group has been predicted. We name it as HR-carbon. HR-carbon composed of lonsdaleite layers and unique C3 isosceles triangle rings, is stable over graphite phase above 14.2 GPa. The simulated x-ray diffraction pattern, Raman, and energy-loss near-edge spectrum can match the experimental results very well, indicating that HR-carbon is a likely candidate structure for n-diamond. HR-carbon has an incompressible atomic arrangement because of unique C3 isosceles triangle rings. The hardness and bulk modulus of HR-carbon are calculated to be 80 GPa and 427 GPa, respectively, which are comparable to those of diamond. C3 isosceles triangle rings are very important for the stability and hardness of HR-carbon.

Structural, mechanical, and electronic properties of Rh2B and RhB2: first-principles calculations.

The crystal structures of Rh2B and RhB2 at ambient pressure were explored by using the evolutionary methodology. A monoclinic P21/m structure of Rh2B was predicted and donated as Rh2B-I, which is energetically much superior to the previously experimentally proposed Pnma structure. At the pressure of about 39 GPa, the P21/m phase of Rh2B transforms to the C2/m phases. For RhB2, a new monoclinic P21/m phase was predicted, named as RhB2-II, it has the same structure type with Rh2B. Rh2B-I and RhB2-II are both mechanically and dynamically stable. They are potential low compressible materials. The analysis of electronic density of states and chemical bonding indicates that the formation of strong and directional covalent B-B and Rh-B bonds in these compounds contribute greatly to their stabilities and high incompressibility.

A novel stable hydrogen-rich SnH8 under high pressure

A first-principles calculation is applied to perform a comprehensive study of the Sn–H system. Besides the common tetravalent hydride, a novel SnH8 crystal with the space group Im2 is reported with the most dominant enthalpy from structure searching techniques. All the H atoms of SnH8 are in the form of H2 or H3 units with electrons localized around them, showing covalent bond character. The rich and multiple Fermi surface distribution displays a metallic feature. Further electron–phonon coupling calculations reveal the high Tc of 63–72 K at 250 GPa.

Investigation of stable germane structures under high-pressure

The evolutionary structure-searching method discovers that the energetically preferred compounds of germane can be synthesized at a pressure of 190 GPa. New structures with the space groups Ama2 and C2/c proposed here contain semimolecular H2 and V-type H3 units, respectively. Electronic structure analysis shows the metallic character and charge transfer from Ge to H. The conductivity of the two structures originates from the electrons around the hydrogen atoms. Further electron-phonon coupling calculations predict that the two phases are superconductors with a high Tc of 47-57 K for Ama2 at 250 GPa and 70-84 K for C2/c at 500 GPa from quasi-harmonic approximation calculations, which may be higher than under actual conditions.

Pressure-induced phase transition of SnH4: a new layered structure

The lattice structure, electronic properties, and superconductivity of SnH4 under high pressure were determined by first-principle calculations. A new layered structure C2/m with charge transfer from the Sn to H atoms was predicted to be the most stable high-pressure form. In the layered structure, each Sn atom combines with four H atoms and two H2 units, forming six Sn–H bonds of very similar lengths. The rich and multiple Fermi surface distribution in the Brillouin zone shows metallic features with the conductivity deriving from the electrons around the hydrogen atoms. The estimated high Tc of ca. 64–74 K at 500 GPa is attributed to the strong electron–phonon coupling from the vibration phonon modes of the H atoms.

Crystal structures and properties of nitrogen oxides under high pressure

First-principles calculations were performed to investigate the structural, electronic, and elastic properties of N2O4 and N2O5. Two new phases, namely, P42212 N2O4 and P21/m N2O5, are determined under high pressure through an ab initio evolutionary algorithm. For N2O4, the Im3 phase transforms to the P42212 structure at 35 GPa. The pressure–volume curves of N2O4 and N2O5 show that this transition has a first-order nature. The calculated phonon dispersion and elastic constants of Im3 N2O4, P42212 N2O4, and P21/m N2O5 demonstrate that the dynamic and mechanical stable pressure ranges are 2–35, 35–80, and 29–120 GPa, respectively. The electronic properties and projected density of states imply that these three structures are insulators. Furthermore, the N–N and N–O bond length of nitrogen oxides under high pressure are discussed.