Range-separated density functional theory: A 4-component relativistic study of the rare gas dimers He2, Ne2, Ar2, Kr2, Xe2, Rn2 and Uuo2

► First implementation of 4-component relativistic long-range MP2/short-range DFT. ► First complete study of spectroscopic constants of the rare gas dimers He2-Uuo2. ► MP2-srLDA has a performance similar to pure MP2, but the overbinding of MP2 can be tuned by the range-separation parameter.