Relativistic quantum chemical methods for high-accuracy calculation and prediction of heavy and superheavy atoms and molecules are developed. This requires high-order, simultaneous treatment of relativity and electron correlation; quantum electrodynamic effects are also included. The methods and computer packages developed were first applied to systems with experimentally available data; calculations agreed with experiment to a few hundredths of an eV. This made possible predictions for superheavy elements; many of their properties were found to deviate from extrapolations made on the basis of the Periodic Table. Thus, ground state electronic configurations differ in many cases from those of lighter homologues, giving different chemistry. Element 118, which will have a rare-gas electron configuration, is predicted to have positive electron affinity.
In recent years, novel experimental techniques made possible measurement of ionization potentials of very heavy elements. Experimental-theoretical collaborations yielded excellent agreement (~0.01 eV) between measurements and calculations. Joint papers were published recently for At (element 85, Nature Comm. 4, 1835, 2013) and Lr (element 103, Nature, 2015, in press).