(HX)2 species (X=F through At) in the groups of the periodic system:: MP2 and CCSD(T) ab initio quantum chemical calculations

(XH)2 species (X=F through At) were studied ab initio using the CCSD(T) and MP2 procedures. All-electron calculations were performed for X=F, Cl and Br while average relativistic effective potentials were used consistently for all the halogens. All (HX)2 structures are H-bonded; the HX…XH structures are less stable.