Insight into the structures, melting points, and mechanical properties of NbSi2 from first-principles calculations

Studies are carried out on the equilibrium structural, mechanical properties, and melting points of NbSi2 with four ground-state crystal structures (C40, C11(b), C54, and C49) using first-principles approach. By means of the calculated formation enthalpies and phonon dispersion, it is found that these NbSi2 phases are thermodynamically and dynamically stable. C54-NbSi2 is uncovered to possess the lowest energy and formation enthalpy, implying that it is expected to be the most favorite structure for NbSi2. The results of the calculated elastic constants reveal that four NbSi2 phases are mechanically stable. We further find that the mechanical properties of C54-NbSi2 are superior to those of the other NbSi2 phases. The melting points of these NbSi2 phases are calculated to examine their thermal stability. The elastic anisotropy is calculated and discussed using three patterns. The results prove that C54- and C40-NbSi2 have good elastic isotropy, as confirmed by the given three-dimensional plots of elastic moduli. Analyzing the difference charge density and Mulliken overlap population provides the explanation about the relationship between bonding characteristics and mechanical properties.