Magnetic properties of two-dimensional hydrocarbon networks of sp2 and sp3 C atoms

Abstract

Based on first principles total energy calculations, we investigate geometric, electronic, and spin structures in two-dimensional polyacene-based hydrocarbon networks of sp 2 and sp 3 C atoms. Polyacenes connecting adjacent sp 3 atoms form kagome networks. The networks are stable and retain their covalent topologies up to 2000 K. They possess kagome flatbands at or near the Fermi level, depending on the size and structure of the polyacene adjoining the sp 3 C atoms. We find that the spin states of the two-dimensional covalent hydrocarbon network are changeable from antiferromagnetic to ferromagnetic by increasing the length of the sp 2 C region.

Flat bands and higher-order topology in polymerized triptycene: Tight-binding analysis on decorated star lattices

“…The physical properties in the presence of the Hubbard interaction are crudely dependent on the Fermi level. If the Fermi level is right at the flat band, one expects that flat-band ferromagnetism occurs, as is inferred from the results of studies based on the spin-dependent density functional theory for related materials [12][13][14]. In contrast, if the free-electron ground state is the HOTI phase, where the Fermi level is located at the corner-state energy, infinitesimally small on-site interaction is enough to gap out the charge excitation at the corner, i.e., double occupancy of the corner state costs the finite energy.…”

Geometric and electronic structures of two-dimensionally polymerized triptycene: covalent honeycomb networks comprising triptycene and polyphenyl

“…Indeed, our previous calculations indicated that networks comprising sp 3 C atoms and oligoacene are semiconductors with peculiar kagome bands in their valence and conductions states. 25,26) In this work, following the synthesis of triptycene polymers containing phenyl groups, we aim to investigate the energetics and electronic structure of the triptycene polymers in terms of phenyl conformations and length, using the density functional theory (DFT) with the generalized gradient approximation (GGA). Our calculation showed that the triptycene polymers are energetically stable with a total energy similar to that of an isolated benzene.…”

Electronic Structure of Two-Dimensional Hydrocarbon Networks of sp2 and sp3 C Atoms

“…Propellene [13][14][15][16] and triptycene [17][18][19][20][21] are representative examples of such three-dimensional aromatic hydrocarbon molecules with D 3h symmetry and Y-shaped ridged covalent frameworks consisting of three planar sp 2 networks connected by bridgehead sp 3 C atoms situated at the molecular axis. The ridged Y-shape networks of triptycene and propellene allow them to have a constituent unit for covalent organic frameworks: oligomerization and polymerization of triptycene and propellene result in porous and covalent architectures [22][23][24][25][26], which are expected to exhibit unusual electronic properties. In our previous work, two-dimensional covalent networks consisting of [4,4,4]propellene and sp 2 hydrocarbons possess a flat dispersion band at and around the Fermi level because the sp 2 hydrocarbon units form a Kagome lattice in the covalent network [26].…”

“…The ridged Y-shape networks of triptycene and propellene allow them to have a constituent unit for covalent organic frameworks: oligomerization and polymerization of triptycene and propellene result in porous and covalent architectures [22][23][24][25][26], which are expected to exhibit unusual electronic properties. In our previous work, two-dimensional covalent networks consisting of [4,4,4]propellene and sp 2 hydrocarbons possess a flat dispersion band at and around the Fermi level because the sp 2 hydrocarbon units form a Kagome lattice in the covalent network [26]. In addition, although triptycene can also form such two-dimensional networks, their energetics and electronic structures are still unclear.…”