Structural, mechanical and electronic properties and hardness of ionic vanadium dihydrides under pressure from first-principles computations

Abstract

Based on a combination of the CALYPSO method for crystal structure prediction and first-principles calculations, we explore the crystal structures of VH2 under the pressure range of 0−300 GPa. The cubic Fm-3m phase with regular VH8 cubes is predicted to transform into orthorhombic Pnma structure with fascinating distorted VH9 tetrakaidecahedrons at 47.36 GPa. Both the Fm-3m phase at 0 GPa and the Pnma phase at 100 GPa are mechanically and dynamically stable, as verified with the calculations of elastic constants and phonon dispersions, respectively. Moreover, the calculated electronic band structure and density of states indicate both stable phases are metallic. Remarkably, the analyses of the Poisson’s ratio, electron localization function (ELF) and Bader charge substantiate that both stable phases are ionic crystals on account of effective charges transferring from V atom to H. On the basis of the microscopic hardness model, the Fm-3m and Pnma crystals of VH2 are potentially incompressible and hard materials with the hardness values of 17.83 and 17.68 GPa, respectively.

A ten-fold coordinated high-pressure structure in hafnium dihydrogen with increasing superconducting transition temperature induced by enhancive pressure

“…S1 and Table S1 of supplementary information. A series of the earlier known HfH 2 structures (e.g., Fm-3m, Cmma, P4/nmm, and I4/mmm) [47][48][49][50][51] is successfully replicated within a specific pressure range, which demonstrates the effectiveness of the CALYPSO method adopted in structure search of HfH 2 . To further clarify the high-pressure structural phase transition of HfH 2 , we plot the enthalpypressure curve (relative to the reference phase I4/mmm) in Fig.…”

Work of Adhesion Analysis for Metal-Substituted W4C4 Carbides in a Cobalt Matrix

“…Figure also displays a mixture of covalent, ionic, and metallic bonds. Generally, covalent bonds and lone pair or inner shell electrons have values larger than 0.5 in ELF analysis while ionic or metallic bonds have ELF values of less than 0.5 . As an example, in Figure (a) one may see that the electrons are concentrated around the carbon atom (indicated by a color range of 0.5 to 0.75), representing covalent bonding.…”

“…Generally, covalent bonds and lone pair or inner shell electrons have values larger than 0.5 in ELF analysis while ionic or metallic bonds have ELF values of less than 0.5. 58 As an example, in Figure 3(a) one may see that the electrons are concentrated around the carbon atom (indicated by a color range of 0.5 to 0.75), representing covalent bonding. Additionally, some electrons are located between the carbon and cobalt atoms, indicating ionic bonding.…”

Systematic Data-Driven Modeling of Bimetallic Catalyst Performance for the Hydrogenation of 5-Ethoxymethylfurfural with Variable Selection and Regularization

“…On the other hand, the correlation with materials hardness is not directly obvious. However, hardness has been correlated through first principles with the microstructure and chemical bonding in the materials such as in refs − . Both microstructure and bonding determine the ability of catalytic active sites to interact effectively with reactant molecules depending on the possibility to establish effective bonds between the metal sites and the reactants based on geometry and strength of intermolecular forces leading to effective activation of those in the course of the reaction.…”