Stability, electronic properties and chemical reactivity of palladium–vanadium(1 1 1) surface alloys

We investigate the influence of vanadium impurities on the geometric and electronic properties of palladium(111) surfaces using density-functional calculations with Perdew–Wang general gradient approximations and PAW potentials. Single layer vanadium concentrations ranging from c V=1/9 to c V=1 in and under the Pd(111) surface are considered. The calculated supercells consist of four to six layer slabs separated by several layers of vacuum, allowing the uppermost layers to relax. The most favorable vanadium superstructure over a wide concentration range is ( 3 × 3 )R30°. Adsorbed V atoms are only stable once they are incorporated into or under the Pd surface. An energy barrier of 0.7 eV for the exchange of an adsorbed V atom is determined by a nudged elastic band calculation. Vanadium impurities reduce the density of states of surface palladium atoms at the Fermi level and shift their d-bands to lower energies which reduces adsorption energies. Our findings agree very well with experimental results.