Simulationoflowindexrutilesurfaceswitha transferablevariable-chargeTi–Ointeratomicpotential andcomparisonwithabinitioresults VargheseSwamy a, * ,JosephMuscat a ,JulianD.Gale b ,NicholasM.Harrison b,c a CSIRO Minerals, Box 312, Clayton South, Victoria 3169, Australia b Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, SW7 2AY, UK c CCLRC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, UK Received16May2001;acceptedforpublication15November2001 Abstract The ability of a recently derived transferable variable-charge Ti–O interatomic potential to simulate low-coordi- nationenvironmentshasbeentestedbyapplicationtothe(110)and(001)rutilesurfaces.Hartree–Fockanddensity functional theory calculations of the (110) rutile surface were also performed. Comparison of the variable-charge results with data from first principles and two other standard forcefield calculations, along with experimental data, revealsthatthevariable-chargemodelappearstobeinadequateforsurfacesimulations.Theatomicrelaxationspre- dictedbyalltheforcefieldsarenotonlymutuallyinconsistentbutarealsoindisagreementwithabinitioandexper- imentaldata.Thequantummechanicaltreatments,ontheotherhand,yieldrelaxationdatainagreementwitheach other,butdifferenttoexperimentaldataonthe(110)surface.Thesurfaceformationenergiesobtainedfortherelaxed (110),(100),and(001)surfacesarealsonotintherightorderwhencomputedwiththevariable-chargemodel.The lowionicchargespredictedbythemodelappeartobeamajorreasonforthisfailure.Inclusionofsurfacedatainthe parameterisation of the model is likely to improve the transferability to low-coordination environments. Ó 2002 ElsevierScienceB.V.Allrightsreserved. Keywords: Titanium oxide; Surface relaxation and reconstruction; Surface energy; Ab initio quantum chemical methods and calculations;Densityfunctionalcalculations 1. Introduction Because of the importance of TiO 2 as an in- dustrial material and a model transition metal oxide,therehavebeenmanypreviousattemptsto generate interatomic potentials that are capable of accurately describing the properties of tita- nium oxides. However, the range of applicability of many potential models is limited to a small number of polymorphs or one oxidation state of SurfaceScience504(2002)115–124 www.elsevier.com/locate/susc * Corresponding author. Address: Center for Research in Computational Thermochemistry, Ecole Polytechnique de Montreal, C.P. 6079, Succursale Centre-Ville, Montreal, Que- bec,Canada,H3C3A7.Fax:+1-514-340-5840. E-mailaddresses: varghese.swamy@polymtl.ca,vswamy2000@ hotmail.com(V.Swamy). 0039-6028/02/$-seefrontmatter Ó 2002ElsevierScienceB.V.Allrightsreserved. PII:S0039-6028(01)01925-2