RESUMO
The stability of 2D all nitrogen clusters containing from 6 to 96 nitrogen atoms, terminated with CF3 groups, has been explored using two computational models: dispersion corrected B3LYP functional and scaled opposite spin Møller-Plesset perturbation theory (SOS-MP2). Single point domain-based local pair natural orbital coupled-cluster theory calculations (DLPNO-CCSD(T)) was used for further energy refinement. All systems were found to be minima, and their stability increases with CF3/N ratio. Larger clusters and anion radicals were not dynamically stable, while some of the cation radicals were found to be minima on potential energy surface. The mechanism of cluster stabilization by CF3 groups is related with interaction of orbitals holding lone electron pairs and antibonding sigma orbitals.
RESUMO
The structural variability offered by 2D materials is an essential feature in materials design. Despite its significance, obtaining assemblies with suitable stability remains a challenge. In this work, we theoretically explore novel silicon, phosphorus, and germanium, analogues of haeckelites at hybrid DFT level. Both 2D systems and nanoflakes (NF) have been studied. All materials have been found dynamically stable; Si-, P-, and Ge- analogues of haeckelites were found to be more stable in comparison to the corresponding honeycomb structure than haeckelites in comparison with graphene. All 2D materials showed metallic behavior; however, the difference between inorganic haeckelites and the corresponding honeycomb allotropes is less than that between haeckelites and graphene. Si-, P-, and Ge-, allotropes have much higher electron affinities (EAs) compared to carbon allotropes, while haeckelites have higher EAs than honeycomb structures. Furthermore, Si-, P-, and Ge-structures also exhibit low hopping activation energies for lithium atoms. It makes these materials potentially promising as a component in Li-ion batteries.
RESUMO
The electronic structure of the van der Waals heterostructures (HSs) of the phosphorene (P) nanoflakes (NFs) with graphene (G) and its allotropy (H1 and H2) NFs, and their complexes with Li have been studied using dispersion-corrected TPSS functional. According to the calculations, the attractive interactions in HSs come from dispersion. It has a relatively small contribution to the binding energy in Li complexes, especially for these forming complexes with G, H1, or H2 NF side. The binding energies between the individual NFs and Li atoms increase in the order G < H1 = H2 = P. The formation of HSs results in a synergetic effect for Li binding energies. This effect is the most notable for phosphorene binding sites; however, it also holds for G, H1, and H2 NFs. The formation of complexes with Li always leads to the almost complete charge transfer from Li to the NFs or HSs. In the case of HSs, the unpaired electron of Li is always located at the carbon NF side independently on the Li binding location. The activation energies of Li hopping for individual NFs are notably higher for P comparing with G, H1, or H2 NFs. The formation of HSs rises slightly the activation energies of Li hopping due to the increase of binding energies in Li-HS complexes. Graphical abstract.
RESUMO
The electronic structure of isomeric graphene nanoflakes (NFs) heavily doped with boron and nitrogen atoms has been explored. Dispersion-corrected B3LYP functional has been used for the geometry optimizations. A complete active space method has been used for the energy evaluations. Combined boron and nitrogen doping promotes polyradicalic antiferromagnetic ground states in the NFs and affects the nanoflake geometry. There is a charge transfer from boron to nitrogen atoms which increases with the doping level. This transfer does not involve carbon atoms. Combined doping reduces both the ionization potentials (IPs) and the electron affinities (EAs) of the NFs similar to nitrogen doping alone. Boron does not affect either IPs or EAs being neither n- nor p-type dopant for the isomeric graphene NFs. All hybrid NFs show a tendency to increase the band gaps with doping level, which is promoted by the increment of the bond length alternation with doping. Finally, the hole reorganization energies for the NFs were found to be lower than the electronic ones, positioning the hybrid NF as hole-transporting systems. Graphical Abstract Color coded natural charge differences between charged and neutral states. The excess of positive charge is green for cation radicals and the excess of negative charge is red in anion radicals.