The energetic ground state of gold clusters with up to 318 atoms consists of complex geometries that have only a limited resemblance to the perfect icosahedra, decahedra, and octahedra that are encountered for some magic numbers. The structure changes in most cases completely by the addition of a single atom. Other low-energy structures are so close in energy that their Boltzmann weight is not negligible at room temperature.

The stable polymeric nitrogen and polynitrogen compounds have potential applications in high-energy-density materials. For beryllium nitrides, there is one known crystalline form, Be 3 N 2 , at ambient conditions. In the present study, the structural evolutionary behaviors of beryllium polynitrdes have been studied up to 100 GPa using first-principles calculations and unbiased structure searching method combined with density functional calculations. One stable structural stoichiometry of beyrllium polynitride has been theoretically predicted at high pressures. It may be experimentally synthesizable at high pressures less than 40 GPa. It is therefore possible to synthesize BeN 4 by compressing solid Be 3 N 2 and N 2 gas under high pressure and BeN 4 may be quenching recoverable to ambient conditions. The predicted high-pressure P2 1 /c-BeN 4 compound contains a novel variety of polynitrogen, extended polymeric 3D puckered N 10 rings network. To the best of our knowledge, this is the first time that stable N 10 rings network are predicted in alkaline-earth metal polynitrides. The decomposition of P2 1 /c-BeN 4 is expected to be highly exothermic, releasing an energy of approximately 6.35 kJ•g −1 . The present results open a new avenue to synthesize polynitrogen compound and provide a key perspective toward the understanding of novel chemical bonding in nitrogen-rich compounds. Results of the present study suggest that it is possible to obtain energetic polynitrogens in main-group nitrides under high pressure.

Based on an ab initio evolutionary algorithm, a novel carbon polymorph with an orthorhombic Cmcm symmetry is predicted, named as C carbon, which has the lowest enthalpy among the previously proposed cold-compressed graphite phases.

In this paper, we suggest a novel potential superhard material, a new carbon nitride phase consisted of sp(3) hybridized bonds, possessing a cubic P2(1)3 symmetry (8 atoms/cell, labeled by cg-CN) which is similar to cubic gauche nitrogen (cg-N) by first-principles calculations. It is a metallic compound, while most of other superhard materials are insulators or semiconductors. The Vickers hardness of cg-CN is 82.56 GPa, and if we considered the negative effect of metallic component on hardness, it is 54.7 GPa, which is much harder than any other metallic materials. It is found that a three-dimensional C-N network is mainly responsible for the high hardness. Both elastic constant and phonon-dispersion calculations show that this structure remains mechanically and dynamically stable in the pressure ranges from 0 to 100 GPa. Furthermore, we compared our results with many other proposed structures of carbon nitride with 1:1 stoichiometry and found that only cg-CN is the most favorable stable crystal structure. Formation enthalpies calculations demonstrate that this material can be synthesizable at high pressure (12.7-36.4 GPa).

The structures and properties of rhenium nitrides are studied with density function based first principle method. New candidate ground states or high-pressure phases at Re:N ratios of 3:2, 1:3, and 1:4 are identified via a series of evolutionary structure searches. We find that the 3D polyhedral stacking with strong covalent N-N and Re-N bonding could stabilize Re nitrides to form nitrogen rich phases, meanwhile, remarkably improve the mechanical performance than that of sub-nitrides, as Re3N, Re2N, and Re3N2. By evaluating the trends of the crystal configuration, electronic structure, elastic properties, and hardness as a function of the N concentration, we proves that the N content is the key factor affecting the metallicity and hardness of Re nitrides.

The structural and dynamical properties of solid ammonia borane were investigated by means of extensive density functional theory calculation up to 60 GPa. Molecular dynamics simulations suggest that the Cmc2(1) phase found by recent room-temperature x-ray diffraction experiments can be obtained from the Pmn2(1) structure at high pressure and low temperature. Two new high-pressure phases were found on further compression at room temperature. We also found that all three high-pressure phases have proton-ordered structures, and the separation of the NH(3) and BH(3) rotation observed in the simulations can be explained by their distinct rotational energy barriers. The role of dihydrogen bonds in the high-pressure phases is discussed.

We synthesized orthorhombic FeB-type MnB (space group: Pnma) with high pressure and high temperature method. MnB is a promising soft magnetic material, which is ferromagnetic with Curie temperature as high as 546.3 K, and high magnetization value up to 155.5 emu/g, and comparatively low coercive field. The strong room temperature ferromagnetic properties stem from the positive exchange-correlation between manganese atoms and the large number of unpaired Mn 3d electrons. The asymptotic Vickers hardness (AVH) is 15.7 GPa which is far higher than that of traditional ferromagnetic materials. The high hardness is ascribed to the zigzag boron chains running through manganese lattice, as unraveled by X-ray photoelectron spectroscopy result and first principle calculations. This exploration opens a new class of materials with the integration of superior mechanical properties, lower cost, electrical conductivity, and fantastic soft magnetic properties which will be significant for scientific research and industrial application as advanced structural and functional materials.

We show by means of first-principles calculations that in boron nanostructures a large variety of two-dimensional structures can be obtained, all with similar energetic properties. Some of these new structures are more stable than both the B 80 fullerenes initially proposed by Szwacki et al. [Phys. Rev. Lett. 98, 166804 (2007)] and boron nanotubes. At variance from other systems like carbon, disordered configurations are energetically comparable with ordered ones. Cage-like structures that are not ordered are thus comparable in energy to the more ordered original B 80 fullerene. A comparison with other more disordered structures like bulk-like boron clusters is also presented. We found that in the presence of other seed structures (like Sc 3 or Sc 3 N), some endohedral cage-like structures are energetically preferred over bulk-like clusters. This result opens a new pathway for the synthesis of the B 80 fullerene as an endohedral fullerene as was done in the case of the C 80 fullerene.