In this theoretical study, within the nearest neighbor tight-binding model, the density of states (DOS), Pauli magnetic susceptibility (PMS), and electronic heat capacity (EHC) of graphyne-like systems, i.e. α-, β-, γ-,
-graphyne, and graphdiyne are calculated and the results are compared with that of a graphene monolayer. It is observed that α-, β- and
-graphyne are semimetals with a zero bandgap similar to a graphene monolayer, while γ-graphyne and graphdiyne have no states around the Fermi level. In addition, the intra-bandgaps are seen in the DOS of graphyne structures and the van-Hove singularities in the DOS of all systems. These lead to the crossovers occurred in the PMS curves and the Schottky anomaly peaks in the EHC curves, which are divided into two low and high temperature regions. Also, it is found that close to the temperature of zero, the PMS and EHC of all semimetal systems are slightly higher than semiconducting systems. From the theoretical stand point, this phenomenon stems from the proportional relation of the PMS and EHC with DOS.
This work investigates the ground state’s stability of the bulk and three Heuslerene Co2CrAl compounds, named as α, β, and γ phases, by density functional theory (DFT) with the generalized gradient approximation (GGA), GGA+U, and GGA+U+mBJ approximations. The results demonstrate the ground state stability of all mentioned cases since they pass the thermodynamic, elastic, and phonon stability tests. All three structures are more stable in the ferromagnetic phase than the antiferromagnetic phase. In the β phase, Young’s and Shear’s moduli were 73.97 GPa and 24.83 GPa, respectively. The thermodynamic diagram has shown existence of the accessible region, which indicates the possibility of making this structure. For all three structures, the phonon branches in the symmetry paths are positive, which represent the complete dynamic stability of these compositions in the presence of mechanical stresses and thermal vibrations. According to the electronic calculations, the bulk phase of Co2CrAl is a half-metal with 3μB magnetic moment and 100% spin polarization at the Fermi level. Furthermore, all imposed approximations approve that α and γ Heuslerenes are metal for both spin directions, while the GGA+U+mBJ approximation indicates that β phase is a ferromagnetic half-metal of 1μB magnetic moment. Based on the electron density diagrams, the highest (lowest) amount of electron density is created on the α (β) phase surface.
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