Structural, Magnetic,Electronic,and Catalysts Properties Of FePt Nanoclusters:a First-Principles Study

1. We have systematically studied the structural, electronic and magnetic properties of FenPt13-n (n=0-13) nanoclusters in the framework of first principles density functional theory. It is demonstrated that Fe atom prefers to occupy central position. For Pt-rich and Fe-rich nanoclusters FenPt13-n (n=1,2,9-12), the energetically favorable nanoclusters are characterized with Fe atom occupying the center site. A set of isomers FenPt13-n (n=3-8) are deformed completely to exhibit maximum Fe-Pt bonds. The binding energy curve as a function of Fe atoms displays like a parabolic shape, and the most stable nanocluster is found for n=5. In addition, all the nanoclusters show the ferromagnetic coupling, and the sequential substitution of Fe atoms with Pt atoms yields the overall increasing magnetic moments. The local Fe magnetic moments are remarkably enhanced as the result of Pt gradually doping. Charge difference density and Bader charge analyses show that electrons are transferred from Fe atoms to Pt atoms. Moreover, Fe atoms of Pt-rich nanoclusters loose more electrons than that of the Fe-rich nanoclusters, which yields large number of Fe d holes. This is corresponding to the variance of local Fe moments.2. First principles density functional calculations have been performed to investigate the adsorption and the first dehydrogenation step of NH3on the surface of Fe13Pt42nanoclusters. The Fe13Pt42nanocluster is icosahedra with Fe atoms occupying the center and Pt atoms occupying the surface, which could reduce the cost of the rare and expensive Pt. All the possible adsorption sites are taken into account on the surface of the nancluster for NH3, NH2, and H species. The results indicate that the most stable adsorption site for NH3is the edge top site, while NH2and H adsorbates favor the edge hollow site. After analyze the density of states of the NHx/nanocluster, we found that a broad band appears in the range of-5to0eV. Moreover, N2p orbital mainly hybridizes with Pt5d orbital in the energy rang of-5to0eV, and the adsorption of NH3induce a small peak around-18eV. Charge difference density and Bader charge analyses show that electrons are transferred from NH3to the Fe13Pt42nanocluster, and for NH2the electrons are transferred from the Fe13Pt42nanocluster to NH2. Compared with the bare nanocluster, the Pt atoms bonding to the NHx adsorbates lose more electrons. The nudged elastic band method was used to determine the transition state for the first dissociation step of NH3(NH3*+*â‰'NH2*+H*). The results show that the activation energy barrier is1.68eV, and the reaction energy is0.51eV. As for Fe55nanocluster, the reaction energy barrier is1.47eV for the first dehydrogenation step. Therefore, the catalyst activity of Fe13Pt42nanocluster is a little weak.