Metal‐intercalated organic crystals exhibit a large variety of interesting phenomena such as superconductivity, magnetism, and metallic conductivity because of which they could find wide technological applications. Here, the electronic, magnetic, and conducting properties of two polymorphs of naphthalene molecular crystals such as naphthalene‐I and naphthalene‐II are studied within first principle calculations by intercalating a potassium atom (K). The most stable structure of K‐intercalated naphthalene in each crystal phase is identified by estimating the stabilization energy. In naphthalene‐I, the most stable structure of single K atom doped naphthalene shows a fully compensated ferrimagnetic ground state, whereas K‐doped naphthalene‐II prefers a nonmagnetic ground state. The electronic band structure of K‐intercalated naphthalene shows a shift in the Fermi level due to the charge transfer from the K atom to the host molecule, making the system conducting. However, an interesting half‐metallic behavior with anisotropic charge transport along one crystallographic direction is observed in the stable structure of K‐intercalated naphthalene‐I crystal.

Potassium‐intercalated naphthalene crystal with P21/a symmetry shows anisotropic spin transport along one crystallographic direction mediated through naphthalene–potassium–naphthalene packing. Localized up‐spins and conducting down‐spins result in a half‐metallic behavior in this intercalated crystal. In addition, the asymmetric spin density distribution leads to a fully compensated ferrimagnetic ground state, as discussed by Sasmita Mohakud and co‐workers in article number http://doi.wiley.com/10.1002/pssb.202000398.