BOC-MP Formalism A Brief Reminder

The BOC-MP formalism has been extensively published (16-19) and summarized in two review articles (16-17), thus here a brief reminder will suffice. Only the latest developments leading to a more accurate treatment of the activation dissociation barriers (18i) and the heats of chemisorption of radicals (19d) will be reviewed in detail. 

To deal with quasispherical interactions, one should define a model potential relating E to r or some convenient function of r, for example, the two-center M-A bond order x, 

If we want to describe many-center M -A interactions (n is the coordination number) in the Morse-potential fashion, the simplest scheme is pairwise additivity of all the two-center M-A contributions to Q and x, namely. 

Here the simplest way to proceed is to keep the Morse parameters (Q0, / (), and a) the same for both the isolated M-A bond and each additive M-A contribution within M -A so that these contributions would differ by their bond orders x,- (i = 1,2. n) only. Experimentally, Q(n) increases less than linearly with n 

Finally, we have to choose the values of n in M -A. The simplest assumption is to limit n to nearest-neighbor metal atoms. For instance, for A/fcc(100), the maximum n = 4 can be reached in the hollow site, but n = 2 and 1 in the bridge and on-top sites, respectively. 

---