We consider slabs with N surf = 100 sites and N bulk ranging from 10 4 -10 7 . The number of hydrogen atoms is set to N H = 10 -3 N bulk to match the upper bound for H absorption in δ-Pu at room temperature. At each system size, we then vary the value of ∆E from highly positive values (corresponding to strongly favorable bulk absorption) to highly negative (corresponding to strongly favored surface adsorption) in order to determine the range of ∆E that will permit high surface coverage.