The self-consistent field Hartree-Fock cluster procedure applied to B and Al adsorbed on Si(111) surface shows a greater binding energy for the B atom when it is located in the five-fold coordinated B 5 site as compared to the four-fold T 4 site. This is in contrast to Al which prefers the T 4 site. The result demonstrates strong theoretical support for recent conclusions from measurements of the B/Si(111) surface by a number of different experimental techniques including the results of our ion channeling measurements presented.