The Density Functional Theory Research Of Ag Atoms Adsorbed In TiO₂（110） Surface

Using metal deposite on the surface of TiO₂（110） surface is an effective way toimprove its catalytic activity in modification. Researchs on the modified surface and whoseelectronic structure property can reveal the catalytic reaction mechanism, also can guide thedesign of experiments, which have scientific significance.The deposition of precious metals on TiO₂surface, can change the charge distributionof the system, influence the properties of surface, and improve the photoelectricperformance. Through the precious metal decorate, on one hand it can promote theseparation of the hole and the light electronic, on the other hand it can change band structureof TiO₂, which have more advantageous to absorb the low energy photons, and make a gooduse of the sun. Rutile TiO₂（110） face is the most stable surface on thermodynamics, wehope this caculation can have a useful meaning in theory on the preparation of materials andits application.Surface load of Au, Ag and Cu nanoparticles often show different physical andchemical properties.Recent experiments has shown that, compared the Au, Cu and Ag in thecatalytic process of water-catalysis, we can found that they have very strong catalyticactivity in this process, therefore it is necessary to study the mechanic of precious metalsdepsoiting on the metal oxide.In the first chapter we mainly introduces the knowledge of Surface science,then thecurrent particle of small molecules and Au, Ag and Cu adsorpted on TiO₂（110） surface. Inthe second chapter we briefly introduce its theoretical basis, the density functional theory（DFT）, and two exchange correlation functional, then we introduce the potential and theplane wave group, and finally we briefly introduce the scientific computingpackage---VASP.In the third chapter, we optimize the stucture of Ag atoms on stoichmetric TiO₂（110）surface, we use the periodic supercell model, GGA plane wave potential group, PW91exchange correlation functional, three O-Ti-O layers, the vacuum layer of10angstrom, andthe energy cut is400eV, Helman-Feymann force for the convergence standard is0.05 eV/angstrom.We find that （1） comparing the adsorption enerny, the Ag atoms are preferadsorpted on bridge site that is between the oxygen atoms, while in high coverages, the Agatoms tend to adsorpted on the top of the oxygen atoms.（2） From the figure of density ofstates we can see that after absorption the Ag atoms and its adjacent O atoms has formedchemical bonds; from difference charge density diagram analysis we can draw theconclusion that the Ag atoms and its adjacent atoms on the surface has transfered the charge,and search the characteristic of antibacterial.（3） from bader charge analysis, we calculatedthe charge of Ag atoms and adjacent atoms, which are consistent with the conclusion of thedensity of states and difference analysis before. At the same time, from bader chargedistribution and work function analysis, we can conclude that Ag atoms and TiO₂surfacehad transferd charges, which make electron enrichment near Ag atoms, and reduce thecomposite chance of TiO₂photoelectron and photohole.The fourth chapter we calculated the behavior of Ag atoms adsorbed on reducedsurface. Through the calculation we can see the Ag atoms prefered to adsorb on defectswhich is the activation center for defects,and providing charges to Ag atoms, through thedensity states of charge and charge density difference analysis, we can conclude that the Agatoms and Ti atoms has formed chemical bonds, which also occured charge transfer. Due tothe introduction of oxygen defects, which transfer charge to Ag atoms, making the numberof charge on Ag atoms more than its valence electrons, that reduces the photocatalyticactivity of TiO₂.