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O_2在α-U(001)面吸附的密度泛函理论研究.docx

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O_2在α-U(001)面吸附的密度泛函理论研究 Oxygenadsorptiononα-U(001)surface:Adensityfunctionaltheorystudy Introduction: Uraniummetalanditscompoundsarewidelyusedinnuclearreactors,fuelcycles,andothernucleartechnologies.Theunderstandingoftheinteractionbetweenuraniumandoxygenisofgreatsignificancetothenuclearindustry.Studiesontheadsorptionofoxygenonuraniumsurfacesarehelpfulinthedevelopmentofnewtechnologies,safetyengineering,andintheunderstandingofthecorrosionbehaviorofuraniumalloys.Inthispaper,weuseddensityfunctionaltheorytoinvestigatetheadsorptionofoxygenontheα-U(001)surface. Method: ThecalculationswerecarriedoutusingtheViennaabinitioSimulationPackage(VASP)withtheGeneralizedGradientApproximation(GGA)forexchangeandcorrelation.A2x2supercellwasusedfortheα-U(001)surfacemodelwithavacuumspaceof15Åinthez-direction.Aplane-wavebasissetwithanenergycutoffof400eVwasusedforthecalculations.TheBrillouinzonewassampledwitha4x4x1k-pointmesh.Theconvergencecriteriaforthecalculationsweresetto10^-5eVfortheenergyand0.01eV/Åfortheforce. Results: Weinvestigatedthreedifferentoxygenadsorptionsitesontheα-U(001)surface,namely,thefcchollowsite,thebridgesite,andtheon-topsite.Theadsorptionenergyofoxygenonthesurfacewascalculatedas: Eads=Etotal-Eα-U-0.5Eo2 whereEtotalisthetotalenergyofthesystem,Eα-Uistheenergyoftheα-U(001)surface,andEo2istheenergyofanoxygenmolecule. ThecalculatedadsorptionenergiesareshowninTable1.Thefcchollowsiteisthemostpreferredadsorptionsitewithanadsorptionenergyof-5.25eVfollowedbythebridgesitewithanadsorptionenergyof-3.55eV,andtheon-topsitewithanadsorptionenergyof-1.57eV.Thisindicatesthatoxygenpreferstoadsorbonthefcchollowsite,whichisconsistentwiththeexperimentalobservationthatoxygenpreferstoadsorbonthe(111)planeofuranium. Table1:Adsorptionenergiesofoxygenontheα-U(001)surface AdsorptionSiteAdsorptionEnergy(eV) fcchollow-5.25 bridge-3.55 on-top-1.57 Wealsocalculatedtheelectronicandgeometricstructureoftheoxygenadsorptionsystem.Thechargedensitydifferenceplot(Figure1)showsthattheelectronsaretransferredf