First-principles Simulation And Calculation Of Mechanical Properties Of TiN&NbN, And Structure Stability Of CO Adsorbed On TiN Surface

Recently, the first-principles calculation based on density functional theory(DFT) makes remarkable progress. Large amount of calculation programs are applied to many fields, such as condensed matter physics, materials science, computer science, geophysics, and so on, which makes the first-principles an significant method in scientific field.Transition metal nitrides are widely used in many industry fields because they have many excellent properties, such as high hardness, high intensity, abrasion resistance, and so on. TiN and NbN are such two important materials. Many first-principles studies about electronic structure and mechanical properties of3d transition metals included TiN have been done abroad, but for NbN is so scarce.Through the first-principles calculation, we’ve studied lattice constants, elastic constants, bulk modulus, shear modulus, poisson’s ratio and density of state of transition metal compounds TiN and NbN. The results show that both of these two nitrides are stable, and their lattice constants are consistent with the experimental values. The elastic constants of TiN C44(187) are higher than NbN C44(113), which is just the reason for TiN’s high shear modulus. At the same time, higher G/B ratio of TiN than NbN makes TiN own stronger covalent bond, which helps to increase the resistance to deformation ability of TiN, consistent with TiN’s high shear modulus(216GPa). The results above show that both TiN and NbN have high hardness and TiN is much higher. At last, we calculate the band structures and density of states of TiN and NbN, whose results confirmed that these two compounds present metal properties, and pseudopotential gaps around femi level suggest that these materials have high stability. Partial density of states suggest that the main contribution on metal properties of TiN is Ti-3d and N-2p orbits, NbN is Nb-4d and B-2p orbits, and TiN with higher conductivity than NbN.In addition, based on the first-principles calculations, we also studied the adsorption of CO on TiN(111) surface different positions with DFT-GGA method and slab model. The main contents contain adsorption energy, adsorption position, change of CO molecular bond length, DOS and PDOS of CO molecular before and after adsorption. Reaults are summarized as follow:the structure CO adsorbed on the top is the most stable structure; CO molecular bond length varies most in the hollow structure, which suggest CO molecular’s activation performance is the strongest on the hollow; DOS analysis indicates that after absorption, CO molecular’s electronic orbits interact with atomic’s d orbits on substrate surface, HUMO5σ and LUMO2π*orbits contribute most, which is consistant with Blyholder model. What’s more, according to the HOMO LUMO gap, we predict that top and bridge structures are more stable than hollow, which is consistent with adsorption energies.