Structural, Magnetic, and Electronic Properties of the NiO Monolayer Epitaxially Grown on the (001) Ag Surface: An ab Initio Density Functional Study

Abstract

A periodic slab model consisting of five layers of Ag covered on both sides by NiO monolayers has been adopted to simulate the properties of ultrathin layers of nickel oxide epitaxially grown on silver (001). Different ab initio approaches have been tested including unrestricted Hartree−Fock and a variety of hybrid-exchange density functional Hamiltonians. The hybrid Becke3−Perdew−Wang functional (containing a 20% fraction of Hartree−Fock exchange) has been selected because of its satisfactory performance in describing the experimentally known properties of the two bulk systems, silver and nickel oxide. All calculations have been performed with the CRYSTAL program. In the most stable configuration (O ions directly above Ag atoms, Ni above the hollow sites), the oxide surface is corrugated (0.1 Å) and a small reduction of the work function of the metal is observed (∼0.1 eV). The AFM1 antiferromagnetic structure (alternating rows of nickel ions with opposite spin along the [11] direction) is the most stable one both in the isolated and in the supported monolayer. The Ni−Ni superexchange constant (J2) is appreciably increased (30%) by the presence of the Ag substrate. In conclusion, the presence of the metallic substrate has been found to influence the structural, electronic, and magnetic properties of the overlayer but only to a limited extent.