Coverage effects under atomic chemisorption: Morse-potential modeling based on bond-order conservation

Our recent analytical Morse-potential model based on bond-order conservation has been extended to treat coverage (θ) effects on the heat of atomic chemisorption Q. For highly symmetric surfaces such as fcc(111), fcc(100), and bcc(100), explicit expressions for Q versus θ have been obtained projecting regularities of Q(θ) and of the overlayer structures, in encouraging agreement with experiment. In particular, the model predicts that Q should typically decrease with θ (though at very low θ, Q can sometimes increase) and that there may be some critical coverage θ_c<1 beyond which the second-order phase transition (hollow→bridge or on-top) will occur.