Nodal lines and mapping to mirror Chern numbers in Ca$_2$As family

We study topological properties of materials in the Ca$_2$As family without spin-orbit coupling (SOC) by combining the first-principles calculation and a tight-binding model calculation. As a result of the calculation, we reveal that the Ca2_As family consists of one insulator phase and three nodal line phases including an intersecting nodal ring phase, though one of the phases is not found with realistic material parameters. Additionally, we discuss what kind of nontrivial topological invariants will emerge from each nodal line phase when SOC is introduced. We also find a mapping from a nodal line semimetal without SOC to a topological crystalline insulator with SOC. This mapping can be used to specify the realized topological phase from the candidates given by the previous phase classification method.