The effect of light metal ion decoration of the organic linker in metal-organic framework MOF-5 on its hydrogen adsorption with respect to its hydrogen binding energy (DB.E.) and gravimetric storage capacity is examined theoretically by employing models of the form MC 6 H 6 :nH 2 where M ¼ Li þ , Na þ , Be 2þ , Mg 2þ , and Al 3þ . A systematic investigation of the suitability of DFT functionals for studying such systems is also carried out. Our results show that the interaction energy (DE) of the metal ion M with the benzene ring, DB.E., and charge transfer (Q trans ) from the metal to benzene ring exhibit the same increasing order:
. Organic linker decoration with the above metal ions strengthened H 2 -MOF-5 interactions relative to its pure state. However, amongst these ions only Mg 2þ ion resulted in DB.E. magnitudes that were optimal for allowing room temperature hydrogen storage applications of MOF-5. A much higher gravimetric storage capacity (6.15 wt.% H 2 ) is also predicted for Mg 2þ -decorated MOF-5 as compared to both pure MOF-5 and Li þ -decorated MOF-5.