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The elastic anisotropy and thermodynamic properties of the recently synthesized Pnnm-CN have been investigated using first-principles calculations under high temperature and high pressure. The calculated equilibrium crystal parameters and normalized volume dependence of the resulting pressure agree with available experimental and theoretical results. Within the considered pressure range of 0–90 GPa, the dependences of the bulk modulus, Young’s modulus, and shear modulus on the crystal orientation for Pnnm-CN have been systematically studied. The results show that the Pnnm-CN exhibits a well-pronounced elastic anisotropy. The incompressibility is largest along the c-axis. For tension or compression loading, the Pnnm-CN is stiffest along [001] and the most obedient along [100] direction. On the basis of the quasi-harmonic Debye model, we have explored the Debye temperature, heat capacity, thermal expansion coefficient, and Grüneisen parameters within the pressure range of 0–90 GPa and temperature range of 0–1600K.

Silicon-based clusters have attracted particular attention because they are regard as building blocks for developing silicon-based nanomaterials. However, pure silicon clusters have low chemical stability owing to their dangling bonds. Doping with lanthanide atoms is a good way to form closed-shell of M@Sin clusters and alter their electronic and magnetic properties. Here, we systematically study the lanthanide element Pr doped neutral and anionic silicon clusters by using density functional theory. Extensive searches for ground-state structures of Sin+1λ and PrSinλ (n = 1–9, λ = 0, − 1) clusters were carried out based on the comparison between experimental photoelectron spectroscopy and simulated spectra. Furthermore, the calculated AEA values of our obtained structures show good agreement with the experimental values. Based on averaged binding energies, fragmentation energies and HOMO–LUMO gaps, their relative stabilities were analyzed. Furthermore, the patterns of HOMOs for the most stable isomers were investigated to gain insight into the nature of bonding. The results show that some σ-type and few π-type bonds are formed among Si and Pr atoms. To achieve a insight into localization of charge and charge-transfer information, the Mulliken population are analyzed and discussed. [ABSTRACT FROM AUTHOR]

In order to explore new magnetic superhalogens, we have systematically investigated the structures, electrophilic properties, stabilities, magnetic properties, and fragmentation channels of neutral and anionic FemFn (m = 1, 2; n = 1-7) clusters using density functional theory. Our results show that a maximum of six F atoms can be bound atomically to one Fe atom, and the Fe-Fe bonding is not preferred in Fe2Fn0/- clusters. The computed electron affinities (EAs) indicate that FeFn with n ≥ 3 are superhalogens, while Fe2Fn can be classified as superhalogens for n ≥ 5. To further understand their superhalogen characteristic, the natural population analysis charge distribution and the HOMOs of anionic clusters were also analyzed. When the extra negative charge and the content of HOMO are mainly located on F atoms, the clusters could be classified as superhalogens with EAs substantially surpass that of Cl. By calculating the binding energies per atom and the HOMO-LUMO gaps, FeF3, FeF4-, Fe2F4, Fe2F5-, and Fe2F7- clusters were found to have higher stabilities, corresponding to the Fe atoms that are attained at their favorite +2 and +3 oxidation states. Furthermore, we also predicted the most preferred fragmentation channel and product for all the ground state clusters. Even more striking is the fact that both neutral and anionic FemFn (m = 1, 2; n = 1-7) clusters carry large magnetic moments which mainly come from 3d orbital of iron atom. [ABSTRACT FROM AUTHOR]

First-principles calculations combined with particle swarm optimisation technique are employed to provide an in-depth understanding of the structures, stabilities, electronic properties, and hardnesses for hafnium triboride. Three novel structures of HfB3 with C2/m, Cmmm, and Pmma phases are predicted under the ambient pressure. The new phases are energetically much superior to the previously proposed m-AlB2-, and TMB3-type (TM = W, Mo) structures. The mechanical and thermodynamic stabilities of the new structures are confirmed by the elastic constants and formation enthalpies. The phonon dispersion curves reveal that they are dynamic stable. The large bulk, shear modulus, and small Poisson's ratio of the C2/m and Pmma phases, make them the promising high incompressible materials. It is worth mentioning that the considerable hardness of 40.8 GPa testifies the most stable C2/m-HfB3 to be considered as a potential superhard material. On the basis of the electronic density of states and chemical bonding analysis, one can find that the strong B-B and Hf-B covalent bonds are present in HfB3 compounds. Particularly, higher incompressible and hardness of the C2/m-HfB3 may also relate to its stacking of 'sandwiches' structure. [ABSTRACT FROM AUTHOR]