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The results of a systematic moleculardynamics study of the interfacialstructure between the gold (100) surface and two room-temperatureionic liquids, namely, 1-butyl-3-methylimidazolium hexafluorophosphate([BMIm][PF6]) and 1-butyl-3-methylimadazolium bis(trifluoromethylsulfonyl)imide([BMIm][NTf2]), are herein reported. It is found that nearan uncharged surface the IL structure differs from its bulk, havingan enhanced density extended until the two first layers. Interfaciallayering is clearly observed at the gold surface, with a higher effectfor the [BMIm][NTf2] IL but a higher packing for [BMIm][PF6]. In both ILs the alkyl side chains are oriented parallelto the interface while the imidazolium rings tend to be parallel tothe interface in about 60% of the cases. The presence of the interfacehas a higher impact on the orientation of the cations than on thechemical properties of the counterion. The surface potential dropacross the interface is more pronounced toward a negative value for([BMIm][PF6]) than for ([BMIm][NTf2]), due torelatively larger local density of the anions for ([BMIm][PF6]) near the gold surface. [ABSTRACT FROM AUTHOR]