First Principles Investigations Of The Adsorption And Mechanics Properties Of Precious Metal And Their Alloys

In this paper, the adsorption of small molecules on metal and alloy surfaces, and the structural, elastic, electronic and thermodynamic properties have been investigated using the pseudo-potential plane wave method by the first principles.Firstly, the chemisorption of NO on pure(Pt(111) and Pt(100)) and bimetallic(Au/Pt(111) and Au/Pt(100)) surfaces have been investigated using the pseudo-potential plane wave method within the generalized-gradient approximation density functional theory(GGA+DFT). The different compositions and facets can produce varied catalytic effects. NO tends to be adsorbed on site coordinated with more Pt atoms, and the substitution number of the top-layer Pt by Au atoms affect the d-band center and adsorption energy. With the increasing atomic number of surface Au, the d-band center moves away from the Fermi level, and the adsorption energies decrease. And when the top-layer concentrations of Au are equal, Au/Pt(100) exhibits better catalytic toward NO adsorption than Au/Pt(111). The further electronic states analysis reveals that the interaction between NO and metal surfaces is mainly via the hybridization of NO 5σ/2π* orbitals and metal d-bands.Secondly, the hydrogen sulfide adsorption and dissociation on pure(Pd(111)and Au(111)) and alloy(Pd/Au(111) and Au/Pd(111)) surfaces have been investigated by the first principles. H2 S tends to be adsorbed on top site, HS prefers to locate on bridge site, and the S and H locate on fcc site on various surfaces. Compared the adsorption of sulfur-containing species and hydrogen on pure and alloy metal surfaces, a similar trend of adsorption energies on the metal surfaces(Pd/Au(111) >Pd(111) > Au(111) > Au/Pd(111)) is found. The dissociation process of H2 S on the Pd(111) and Pd/Au(111) surfaces is predicted to be exothermic. However, on Au(111) and Au/Pd(111), the dissociation process is endothermic. H2 S dissociation is more likely to happen on Pd/Au(111) surface. The d-band center moves away from the Fermi level, and the adsorption energy decreases. According to the local density of states analysis, the inner Au atoms of Pd/Au(111) can enhance the top-layer d-band intensity, whereas the inner Pd atoms of Au/Pd(111) cause the opposite effect.The further electronic states analysis reveals the interaction between H2 S and metal surfaces.Thirdly, the effects of pressure on the structural, elastic and electronic properties of Ir3 Zr are investigated by means of the first-principles calculations. The calculatedlattice parameters and volume decrease with increasing pressures. With the rising of pressure up to 45 GPa, the values of elastic constants Cij, bulk modulus B, shear modulus G, Young modulus E, Poisson’s ratio ?, anisotropy index A and Debye temperature(TD) present the linearly increasing. Additionally, the B/G values exhibit an upward trend with increasing pressure, which means that higher pressure can improve its ductility. Zr Ir3 exhibits a brittle characteristic at zero pressure. When the pressure reaches 10 GPa, the Cauchy pressure and B/G value show ductile feature.The pressure-dependence behavior of density of states, Mülliken charge and bond length are analyzed.Lastly, the structural and elastic properties of the L12 structure Ir3 Nb and Ir3 V under pressure have been investigated by means of the first principles calculations.The calculated lattice parameters and elastic modulus are in good agreement with available experimental and theoretical results. The elastic constants(C11, C12, C44) of Ir3 Nb and Ir3 V show that they are mechanical stable structures under pressure. The Cauchy pressures and B/G value show Ir3 Nb and Ir3 V are brittle in nature. When the pressure reaches 45 GPa, Ir3 Nb and Ir3 V change from brittle to ductile. Through quasi-harmonic Debye model, the temperature and pressure dependences of variation of the volume, bulk modulus, thermal expansion coefficient, heat capacities and Debye temperature are predicted in a wide pressure(0-50 GPa) and temperature(0-1200 K) ranges.