How many intramolecular hydrogen bonds does the oxalic acid dimer have?

Second-order Møller–Plesset (MP2) calculations are used to locate 69 unique minima on the potential energy surface of the oxalic acid dimer. Additional MP2 calculations, with and without scaling of the spin components of the correlation energy, are performed for 24 selected minima using larger basis sets. The global minimum is a dimer in which one of the monomers is not in its lowest-energy rotameric form. The dimer has two intermolecular and three intramolecular hydrogen bonds.