Ngn (Ng= Ne, Ar, Kr, Xe, and Rn; n=1, 2) encapsulated porphyrin-like porous C24N24 fullerene: A quantum chemical study.

This study focused on the theoretical viability of Ngn@C24N24 (Ng = Ne, Ar, Kr, Xe, and Rn; n = 1, 2) complexes using density functional theory at the computational level of ωB97X-D/def2-TZVP. Thermodynamic and kinetic stabilities of these complexes have been evaluated by calculating the interaction energy of Ng atoms encapsulated C24N24 cage (ΔEint), and the corresponding dissociation energy barrier (ΔG‡), respectively. The obtained results predict that although these complexes are thermodynamically unstable compared to their dissociation into free Ng atoms and the bare C24N24 cage, but once formed, they are protected by the activation energy barrier of the corresponding dissociation process. Furthermore, natural population analysis (NPA) and topological analysis of the electron density have been employed to investigate the nature of Ng-Ng and Ng-cage interactions. The results demonstrate that these interactions are highly significant compared to similar cases in the free state; and the amounts of energy of the interaction gradually increases as the Ng atom becomes heavier. Surprisingly in the Kr2@C24N24 complex the Kr-Kr bond is somewhat covalent in nature relative to non-bonded interaction in Kr2 free dimer.

A density functional theory analysis for the adsorption of the amine group on graphene and boron nitride nanosheets.

In this paper first principles total energy calculations to study the adsorption of amine group (NH2) on graphene (G) and boron nitride (hBN) nanosheets are developed; the density functional theory, within the local density approximation and Perdew-Wang functional was employed. The sheets were modeled with a sufficiently proved CnHm-like cluster with armchair edge. The optimized geometry was obtained following the minimum energy criterion, searching on four positions for each nanosheet: perpendicular to the carbon atom, on the hexagon, inside the hexagon and on the bridge C-C, for the G-amine interaction; and, perpendicular to the B, perpendicular to the N, on the hexagon, and inside the hexagon, for the hBN-amine interaction. A physisorption, with amine parallel to the C-C-C bond with a distance graphene-amine of 2.56 Å, was found. For the case of BN a B-N bond, with bond length equal to 1.56 Å, was found; the amine lies perpendicular to the nanosheet. When the graphene is doped with B and Al atoms a chemisorption with B-N (1.57 Å) and Al-N (1.78 Å) bonds is observed; the bond angle in the amine group is also incremented, 5.5° and 8.1°, respectively. In the presence of point defects (monovacancies) of B in the hBN-amine and C in the G-amine, there exists chemisorption, increasing the reactivity of the sheets.

First principles studies of the graphene-phenol interactions.

Studies of the interaction between phenol and intrinsic graphene, as well as phenol and aluminum doped graphene layer are performed using first principles total energy calculations within the periodic density functional theory. A 4x4 periodic structure is used to explore the adsorption of a phenol molecule on the intrinsic graphene and on aluminum doped graphene layer. The electron-ion interactions are modeled using ultra-soft pseudo-potentials, and the exchange-correlation energies are treated according to the generalized gradient approximation (GGA) with the PBE parameterization. We consider different molecule orientations: parallel and perpendicular to the graphene layer to relax the atomic structure. To explain the optimized atomic geometry we determine binding energies for all cases and the density of states (DOS) and partial DOS for the most relevant configurations. Results indicate that the direct interaction of oxygen with aluminum yields the ground state geometry with the phenol molecule adsorbed on the graphene layer. Binding energies and DOS structures also demonstrate that the ground state configuration is that where the O and Al atoms interact with a separation distance of 1.97 Å.

DFT studies of the phenol adsorption on boron nitride sheets.

We perform first principles total energy calculations to investigate the atomic structures of the adsorption of phenol (C(6)H(5)OH) on hexagonal boron nitride (BN) sheets. Calculations are done within the density functional theory as implemented in the DMOL code. Electron-ion interactions are modeled according to the local-spin-density-approximation (LSDA) method with the Perdew-Wang parametrization. Our studies take into account the hexagonal h-BN sheets and the modified by defects d-BN sheets. The d-BN sheets are composed of one hexagon, three pentagons and three heptagons. Five different atomic structures are investigated: parallel to the sheet, perpendicular to the sheet at the B site, perpendicular to the sheet at the N site, perpendicular to the central hexagon and perpendicular to the B-N bond (bridge site). To determine the structural stability we apply the criteria of minimum energy and vibration frequency. After the structural relaxation phenol molecules adsorb on both h-BN and d-BN sheets. Results of the binding energies indicate that phenol is chemisorbed. The polarity of the system increases as a consequence of the defects presence which induces transformation from an ionic to covalent bonding. The elastic properties on the BN structure present similar behavior to those reported in the literature for graphene.

On the electronic properties of two-dimensional honeycomb GaInN and GaAlN alloys: a molecular analysis.

We have performed first principles total energy calculations to investigate the structural and the electronic properties of two-dimensional honeycomb GaAlN and GaInN alloys. Calculations were done using a coronene-like (C(24)H(12)) cluster and for different numbers of Ga, Al, and In atoms. The exchange and correlation potential energies were treated within the generalized gradient approximation (GGA). The bond length, dipole moment, binding energy, and gap between the HOMO and the LUMO are reported as a function of x. The stability of the structures depends on the site of the substituted atom; for example, when three Ga atoms are substituted, the GaInN alloy becomes unstable. The gap in the GaAlN increases from 3.76 eV (GaN) to 4.51 eV (AlN), and in the GaInN decreases to 2.11 eV. The biggest polarity occurs when eight and four Ga atoms are substituted, for GaAlN and GaInN, respectively.

Influence of point defects on the electronic properties of boron nitride nanosheets.

Density functional theory was utilized to study the electronic properties of boron nitride (BN) sheets, taking into account the presence of defects. The structure considered consisted of a central hexagon surrounded by alternating pentagons (three) and heptagons (three). The isocoronene cluster model with an armchair edge was used with three different chemical compositions. In the first structure, three B-B bonds were formed where one B in the dimer was part of the central hexagon. In the second structure, three N-N-N bonds were formed at the periphery of the cluster, around the central hexagon. In the third structure, three N-N bonds were formed in a similar fashion to the first model. Our results indicated that the third structure was the most stable configuration; this exhibited planar geometry, semiconductor behavior, and ionic character. To explore the effects of doping, we replaced B and N atoms with C atoms, considering different atomic positions in the central hexagon. When an N atom was replaced with a C atom, the new structure was a semiconductor, but when a B atom was replaced with a C atom, the new structure was a semimetal. At the same time, the polarity increased, inducing covalent behavior. Replacing two N atoms with two C atoms also resulted in a semiconductor, while replacing two B atoms with two C atoms yielded a semimetal; in both cases the bonding was covalent. When three B (three N) atoms of the central hexagon were replaced with three C atoms, the new structure exhibited a transition to a conductor (remained a semiconductor) with low polarity. When monovacancies (N) and divacancies (B and N) were inserted into the lattice, the system was transformed into a covalent semiconductor. Finally, the electrostatic potential surface was calculated in order to explore intermolecular properties such as the charge distribution, which showed how the reactivity of the boron nitride sheets was affected by doping and orbital hybridization.

Theoretical study of the electronic properties of fluorographene.

First-principles calculations were performed for fluorine-decorated graphene (fluorographene). Three different hexagonal clusters were used-circular (C(24)H(12)), triangular (C(23)H(10)) and rectangular (C(24)H(12))-and the fluorine atoms were randomly distributed in the mesh. Graphene is structurally stable in the three geometries, but fluorographene stability is only attained for the circular and triangular clusters. Gaps of the circular graphene and the corresponding fluorographene are 2.94 and 1.13 eV, respectively; in the triangular case, the values are zero and 0.47 eV. Both the circular and triangular structures show a transition from ionic to covalent character.