Surface relaxation and reconstruction

The structure of a real (clean) surface may differ from that of an ideally truncated crystal. Two types of deviation are possible relaxation and reconstruction. 

Relaxation consists of a rigid inward or outward displacement of the uppermost planes of the surface, the s)mimetry in the surface plane being maintained. In contrast, in the case of reconstraction, the displacements, of atoms alter the 2-D symmetry of the surface. 

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An adsorbed molecule would experience different adsorption potential when attached to a terrace, step or kink. On the other hand, on some metals (platinum as an example) the heats of adsorption of simple gases (ethylene, CO, H2) vary little with surface structure. Lee, et al. [84] examined the effect of surface reconstruction and relaxation on the electronic coordination numbers of the surface atoms. They found that highly stepped surfaces relax into a configuration where the surface atoms have about the same electronic coordination number as Pt(l 11) surface atoms. It means that they lack the coordinative unsaturation of the atoms, which would take place on unaltered stepped surfaces. 

The Physics of Solid Surfaces I 2.2 Surface Reconstruction and Relaxation 987... 

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