Motivated by the highly one-dimensional edge state due to a Dirac nodal line the system in single-component molecular conductor [Pt(dmdt)₂], we investigate the magnetic properties of both [Pt(dmdt)₂] and [Ni(dmdt)₂], which are related materials by element substitution, by real-space-dependent random-phase approximation (RPA) in three-orbital Hubbard models with spin–orbit coupling, where these models are constructed using first-principles calculations. We calculate longitudinal and transverse spin susceptibilities by three-dimensional real-space-dependent RPA. We find that the helical spin-density wave (SDW) with incommensurate nesting of the Fermi arcs is induced at the edge by the Coulomb repulsion. We also find that the magnetic structure of the helical SDW can be changed by extremely small carrier doping, which is controllable in molecular conductors.

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