Quantum-chemistry calculations of hydrogen adsorption

See Table 4, main manuscript. The results of periodic calculations with high loadings (n=16×8=128) were compared with the previous calculation (periodic, n=16), and with a calculation without periodic boundary conditions (cluster, n=16), in order to test the dependence of the PM6 results with the model employed (Table S2). From the values reported in Table S2 it can be observed the total similarity between the adsorption energies, coincident at -1.3 kcal/mol on a 'per hydrogen molecule' basis. This indicates that the loading at one IBU can be extrapolated to eight IBUs (full unit cell), and that the IBU-cluster (Figure S1a) is as valid as the periodic model for studying the hydrogen adsorption.