Theoretical Study Of Planar Molecule Self Assembled Monolayers On Metal(111) Surface

The first-principle technique has been employed to determine the structure of the NO dimer?NO?2 molecular chains and monolayers on virtual Rh?111?,?NO?2monolayer and multilayer on Rh?111?.First many?NO?2 monomers are assembled into two stable molecular chains in the virtual Rh?111?,the bind energies of them are0.309 eV and 0.266 eV,respectively,in which the?NO?2 monomers parallel to each other and arrange in order,the O atoms and N atoms are shown?100?and?111?structures,respectively.It is a self-assembly system.Then based on these molecular chains,two molecular chains are assembled into two stable monolayers?labeled as M1 and M2?in the virtual Rh?111?-?1×?3?,the coverage is 1.00 ML,respectively.In the M1,the angle between the N-N bond of?NO?2 monomer and substrate is 70o-90o,and in the M2,the N-N bond is parallel to the substrate.In M2/Rh?111?,?NO?₂ molecules are adsorbed on the top,hcp hollow and fcc hollow sites.When?NO?₂ on the top site,the electron structure is Rh^+0.14—N⁰=O^-0.14,while when?NO?₂ on two hollow sites,the electron structure is Rh^+0.34—N^-0.18=O^-0.16,so two hollow sites are better than the top site.When?NO?₂ multilayer on Rh?111?,?NO?₂ molecules are adsorbed vertically on two hollow sites,the N-N bond is parallel to the substrate in the first monolayer,the angle between the N-N bond and substrate is 70o-90oin the multilayer.The interaction between the neighbor monolayres is about 0.01 eV,and the height of the vacuum is 0.31±0.02 nm.As the halogen bond has better directionality and compatibility than hydrogen bond,it is important to study the adsorption of the molecular self-assemble monolayer with halogen bond on the metal surface.The 2,7-Br₂Py monolayer on the Au?111?surface has studied by Pham^[44]in 2014,the interaction between the monolayer is the Br-H bond.The adsorption system of 2,7-Br₂Py/Au?111?is coarse in the literature^[44],and the monolayer in the literature is not symmetrical enough.And the self-assembly monolayer is usually symmetrical.So the atomic structures of the adsorption system,the adsorption height and the charge transfer need to be discussed in detail.The first-principle technique has been employed to determine the structure of the2,7-Br₂Py molecular chains and monolayer on virtual Au?111?,2,7-Br₂Py monolayer on the Au?111?.Firstly,according to the structural parameter of the Au?111?,six possible 2,7-Br₂Py molecular chains have been built on virtual Au?111?.After the geometry optimization,there are two stable molecular chains with the distances between the neighbor molecules are 1.031 nm and 1.073 nm,respectively.The interaction between the neighbor molecules in the molecular chain is about 0.09 eV.Secondly,based on the stable molecular chain,five possible 2,7-Br₂Py monolayers have been built on virtual Au?111?.After the geometry optimization,there are only one stable monolayer with the lattice parameters in two directions are 1.031 nm and1.073 nm,respectively.The interaction between the neighbor molecules in the monolayer is 0.127 eV.So the interaction between the neighbor molecular chains in the monolayer is about 0.03 eV.That is,the monolayer is compond of two molecular chains.According to the bind energy and the electron density,the monolayer is more stable than that in the literature[8],and it is a self-assembly system.The interaction between the monolayer is the Br-H bond.The lattice parameters in two direction of the monolayer is corresponding to the Au?111?-?2?3×?13?R14 surface.Finally the stable monolayer is horizontal adsorbed on the Au?111?-?2?3×?13?R14 surface,the adsorption height is taken as 0.40±0.01 nm after geometry optimization,and the charge transfer from the Au surface to the 2,7-Br₂Py monolayer is 0.34 e.Based on the adsorption height and the charge transfer,it is the physics adsorption.