Hydrogen adsorption on low-index surfaces of the PdFe alloy

The adsorption of hydrogen on the (001) and (110) surfaces of the PdFe alloy has been investigated using the projector-augmented-wave method within the generalized gradient Perdew-Burke-Ernzerhof (PBE) approximation for the exchange-correlation functional. The most preferred sites of hydrogen adsorption on the two surfaces have been determined. It has been shown that the hydrogen adsorption in hollow sites is more preferred on the (001) surface independently of its termination. The hydrogen adsorption in B1 bridge sites is energetically more favorable on the palladium-terminated (110) surface, whereas B2 bridge sites are more preferred on the iron-terminated (110) surface. The inclusion of the magnetism in the calculation leads to a decrease in the adsorption energy of hydrogen on the (001) and (110) surfaces, regardless of their termination, but does not change the tendencies revealed in variations of the binding energy in the nonmagnetic calculation. In general, the magnetism affects the position of hydrogen with respect to the surface layer and decreases the negative relaxation of interlayer distances in the cases of iron terminations of both surfaces, while hydrogen, in turn, decreases the magnetic moment of the nearest neighbor iron atoms. The paths of hydrogen diffusion from the surface deep into the material have been analyzed.