The eleven structural motifs studied in this work.
Bottom: Plot of the Gupta mixing energy for the four bimetallic systems as a function of the number of second-row TM atoms, . Black circles are used for Ag–Pt, red squares for Pd–Pt, green diamonds for Ag–Au, and blue triangles for Pd–Au. Top: The distribution of GM structures found in our GA search. The colors indicate the different structures: TO (white), Ino-Dh (gray), inc-Ih-AntiMackay (green), inc-Ih-Mackay (magenta), (yellow), and pIh-LS̱1 and pIh-LS̱2 (dark and light blue, respectively).
Putative GM structures found at the DFT level for the 24-14 and 32-6 compositions of all four bimetallic systems. For Pd–Au, compositions 14-24 and 6-32 are also shown. Color scheme: Pd (blue), Pt (light gray), Ag (dark gray), and Au (yellow).
Schematic representation of the DF optimization for the Oh-Ih structure of . The structural distortion, in which Au atoms (yellow) are displaced toward the surface, can be explained in terms of charge transfer effects which are not taken into account by the EP.
Cluster total energy as a function of the number of mixed bonds for several TO structures. Clusters presenting a variable number of mixed bonds are obtained by permuting the positions of the surface gold and silver atoms in the square (100) facets. The energy spread at a fixed number of mixed bonds gives an estimate of the charge transfer effects.
Gupta potential parameters used in this study (Refs. 10 and 21).
Relative energies (in eV) of the 11 structures according to DF and Gupta calculations for the Pd–Pt, Ag–Pt, and Ag–Au pairs at the 24–14 composition.
Relative energies (in eV) of selected structures according to DF and Gupta for the Pd–Pt, Ag–Pt, Pd–Au, and Ag–Au pairs at the 32–6 composition.
Segregation effects at composition 19-19 for the four pairs. Three structural motifs are investigated at the DF level (TO, Oh-Ih, and inc-Ih-Mackay̱1). In each case, two homotops are studied: “EP” is the lowest-energy homotop found using the EP; “Inverted” is the homotop formed by swapping positions of A and B atoms. Both structures are minimized at the DF level and energies (in eV) are quoted relative to the putative DF GM. The negative values for indicate that the EP predicts the wrong segregation for this system.
Relative energies (in eV) of the 11 structures according to DF and Gupta for the Pd–Au pair at the and compositions.
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