  We theoretically propose that, the single crystal formed TaS is a new type of
topological semimetal, hosting ring-shaped gapless nodal lines and triply
degenerate points (TDPs) in the absence of spin-orbit coupling (SOC). In the
presence of SOC, the each TDP splits into four TDPs along the high symmetric
line in the momentum space, and one of the nodal ring remains closed due to the
protection of the mirror reflection symmetry, while another nodal ring is fully
gapped and transforms into six pairs ofWeyl points (WPs) carrying opposite
chirality. The electronic structures of the projected surfaces are also
discussed, the unique Fermi arcs are observed and the chirality remains or
vanishes depending on the projection directions. On the (010) projected
surface, one may observe a Lifshitz transition. The new type of topological
semimetal TaS is stable and experimentally achievable, and the coexistence of
topological nodal lines, WPs and TDPs states in TaS makes it a potential
candidate to study the interplay between different types of topological
fermions.
