Significant roles of hydrophobic interactions in diverse areas including chemical, biological, and geological processes motivated us to investigate the adsorption of [BMIM][PF6] on a substrate. Optimal adsorption position and orientation of ion-pair on graphene surface was determined and adsorption energies were calculated. Molecular doping, i.e. charge transfer between ionic liquid and surface, was discussed based on density of states and molecular orbitals of adsorbate. Accordingly, carbon atoms of graphene adsorb cation for appropriate interactions. Interesting properties of adsorbed IL such as structure, orientation, charge distribution, surface adhesive energy, and charge transfer with distinctive properties such as frontier molecular orbitals, natural bond orbital, and density of states of IL/graphene system were also investigated. Ab initio molecular dynamics simulation clarifies that both imidazolium ring of the cation and anion interact remarkably with the solid surface. This observation is in good agreement with experimental and computational results. Cohesive energy equal to -168 meV indicates strong interaction between IL and solid surface. Cohesive energy density is a considerable value for a surface with 13.49 Å diameter. Molecular dynamics explains the properties of condensed phase of ionic liquid over graphene and regenerates orientation of ring with respect to the surface as first principles computations.

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