Atomic spin-orbit coupling is a key element in realising various exotic phases in both the weakly and strongly correlated systems. Especially, spin-orbit coupling manifests itself as a formation of the j_eff states, as suggested in several iridium oxide compounds, on which a few new phases of topological origin is based. In this talk I briefly introduce how spin-orbit coupling and the j_eff state are treated in the density functional theory calculations, and show a series of new materials - ternary chacogenide compounds GaM_4X_8 (M=Nb,Mo,Ta,W, X=S,Se,Te) - that can realise the j_eff-based physics in an ideal manner.