Simulations　of　CO2　and　H2　sorption　were　performed　in　UTSA-20,　a　metal-organic　framework　(MOF)　having　zyg　topology　and　composed　of　Cu2+　ions　coordinated　to　3,3′,3′′,5,5′,5′′-benzene-1,3,5-triyl-hexabenzoate　(BHB)　linkers.　Previous　experimental　studies　have　shown　that　this　MOF　displays　remarkable　CO2　sorption　properties　and　exhibits　one　of　the　highest　gravimetric　H2　uptakes　at　77　K/1.0　atm　(2.9　wt%)　[Z.　Guo,　et　al.　Angew.　Chem.,　Int.　Ed.,　2011,　50,　3178-3181].　For　both　sorbates,　the　simulations　were　executed　with　the　inclusion　of　explicit　many-body　polarization　interactions,　which　was　necessary　to　reproduce　sorption　onto　the　open-metal　sites.　Non-polarizable　potentials　were　also　utilized　for　simulations　of　CO2　sorption　as　a　control.　The　simulated　excess　sorption　isotherms　for　both　CO2　and　H2　are　in　very　good　agreement　with　the　corresponding　experimental　data　over　a　wide　range　of　temperatures　and　pressures,　thus　demonstrating　the　accuracy　and　predictive　power　of　the　polarizable　potentials　used　herein.　The　theoretical　isosteric　heat　of　adsorption　(Qst)　values　are　also　in　good　agreement　with　the　newly　reported　experimental　Qst　values　for　the　respective　sorbates　in　UTSA-20.　Sorption　onto　the　more　positively　charged　Cu2+　ion　of　the　[Cu2(O2CR)4]　cluster　was　observed　for　both　CO2　and　H2.　However,　a　binding　site　with　energetics　comparable　to　that　for　an　open-metal　site　was　also　discovered　for　both　sorbates.　A　radial　distribution　function　(g(r))　analysis　about　the　preferential　Cu2+　ions　for　CO2　and　H2　revealed　that　both　sorbates　display　different　trends　for　the　relative　occupancy　about　such　sites　upon　increasing/decreasing　the　pressure　in　the　MOF.　Overall,　this　study　provides　insights　into　the　CO2　and　H2　sorption　mechanisms　in　this　MOF　containing　open-metal　sites　and　small　pore　sizes　for　the　first　time　through　a　classical　polarizable　force　field.　©　2017　the　Owner　Societies.