Role of Strain and Ligand Effects in the Modification of the Electronic and Chemical Properties of Bimetallic Surfaces

Periodic density functional calculations are used to illustrate how the combination of strain and ligand effects modify the electronic and surface chemical properties of Ni, Pd, and Pt monolayers supported on other transition metals. Strain and the ligand effects are shown to change the width of the surface d band, which subsequently moves up or down in energy to maintain a constant band filling. Chemical properties such as the dissociative adsorption energy of hydrogen are controlled by changes induced in the average energy of the d band by modification of the d-band width.

Figure 1

Correlation between the root mean squared (rms) d-band width and d-band center for bimetallic surfaces.

Figure 2

Correlation between the rms d-band width and the matrix element. Black symbols indicate a Ni atom, gray symbols indicate Pd, and white indicates Pt. Data points labeled NiPt2.xx refer to Ni/Pt bimetallic surfaces with nearest neighbor distances of 2.77 or 2.83 Å [11]. Details for the Pt-3d surfaces can be found in Ref. 6. The keyword “Uniform” indicates the structures were strained uniformly in the unit cell lattice vector directions, otherwise, the structure was strained only in one lattice vector direction. A sheet is a single atomic layer, a slab is three layers thick and separated by five equivalent layers of vacuum. The monolayers are described in the text.

Figure 3

Correlation between the dissociative adsorption energy of ${\mathrm{H}}_2$ on bimetallic surfaces and the d-band center of those surfaces.