EXTRACTING CONVERGENT SURFACE FORMATION ENERGIES FROM SLAB CALCULATIONS

It is known that surface formation energies obtained as differences be tween slab energies and an independently determined bulk energy will d iverge linearly with the slab thickness. A recent paper by Fiorentini and Methfessel presented 'a solution to this problem that eliminates t he divergence and leads to rapidly convergent and accurate surface ene rgies'. Although their work is correct, the solution they propose is n ot new. In this comment, we provide some of the historical background neglected by Fiorentini and Methfessel.