A computational study on the BN-yne sheet application in the Na-ion batteries.

Although Li-ion batteries are extensively applied, short lifetime, high cost, and safety problems limit their application. Na-ion batteries (NIB) might be an alternative to the Li-ion owing to wide availability, low cost, and nontoxicity of Na. Here, we performed density functional theory calculations to investigate the possible application of a graphyne-like BN layer (BN-yne) in the anode of NIBs. The adsorption energies of Na and Na+ on the BN-yne are predicted to be -15.3 and -54.6 kcal/mol, respectively. It was found that the maximum barrier energy for migration of Na atom and Na+ ion through BN-yne surface is about 20.2 and 16.5 kcal/mol, respectively. The calculated cell voltage for the BN-yne are predicted to be and 1.70 V. Using an electric field of -0.02 a. u. much more strengthens the interaction of Na+ with the BN-yne compared to the Na atom, increasing the cell voltage of NIB to 2.10 eV. We showed that a high Na storage capacity (Na4B2N2), high cell voltage and diffusion ability of BN-yne make it a promising candidate for the NIB anode material.

Evaluating Minnesota 2006 density functionals against some challenging problems in DFT.

We tested the ability of Minnesota 2006 exchange-correlation functionals entailing M06-HF, M06-2X, M06 and M06-L in solving some challenging problems for density functional (DF) theory. It was found that these DFs cannot calculate the energy of a hydrogen atom well. Also, they show a smaller energy for stretched H2+, which becomes much smaller by decreasing the %Hartree-Fock (HF) exact exchange. Unlike the case of H2+, by increasing the %HF, the DFs overestimate by more the energy of H2 molecule at infinity. For a coronene molecule, by enlarging %HF exchange, the LUMO and HOMO shift to higher and lower energies, respectively, widening the gap. We found that M06-HF and M06-2X are not suitable for electronic property calculations, and may not precisely represent the strong bonds in the dimers of metals. In summary, there is no systematic trend indicating that one Minnesota DF predicts acceptable distances and energies for rare gas dimers, and just M06-HF gives acceptable distances for all dimers. For the F atom and F2 molecule, upon increasing the %HF, the electron affinity decreases and the results of M06-HF are much closer to experimental values. Compared to experimental results, the calculated adiabatic electron affinities are much more accurate than the vertical electron affinities.

A theoretical study on monoatomic BN nanochains and nanorings.

Boron nitride (BN) nanochains were successfully synthesized recently. In this work, we investigate the electronic, energetic, and structural properties of BN nanochains and nanorings by means of density functional theory calculations. Our calculations support the experimental findings and offer additional physical insights into these new nanostructured materials. We show that BN nanochains are biracial compounds that tend to be closed and form a ring. They have single and double bonds alternately throughout the chain. The boron atoms are not saturated and are strong Lewis acids. Increase in the length of the chain tends to result in the conversion from a semiconductor to a semimetal material. The ring structures are stabler than the corresponding chains, and unlike the chains these structures are predicted to be insulators. The binding energy of the chains and rings increases with an increase in their size. Rings with odd or even numbers of BN units show different electronic properties.

Functionalization of the pristine and stone-wales defected BC3 graphenes with pyrene.

The functionalization of pristine and Stone-Wales defected BC3 nanosheets with a pyrene molecule was investigated using density functional theory. Frontier molecular analysis shows that the main interaction is π-π stacking, releasing energies in the range of 143.6 to 169.1 kJ mol(-1). We predicted that after the functionalization process, the electrical conductance of the pristine sheet may be increased. Also, it modifies the work function of the pristine sheet and, as a consequence, its field-emission current densities may significantly enhance. However, the pyrene functionalization results in little change in the electronic properties of the defected sheet.

Fluorination of BC3 nanotubes: DFT studies.

We have studied the adsorption of atomic and molecular fluorines on a BC3 nanotube by using density functional calculations. It was found that the adsorption of atomic fluorine on a C atom of the tube surface is energetically more favorable than that on a B atom by about 0.97 eV. The adsorption of atomic fluorine on both C and B atoms significantly affects the electronic properties of the BC3 tube. The HOMO-LUMO energy gap is considerably reduced from 2.37 to 1.50 and 1.14 eV upon atomic F adsorption on B and C atoms, respectively. Molecular fluorine energetically tends to be dissociated on B atoms of the tube surface. The associative and dissociative adsorption energies of F2 were calculated to be about -0.42 and -4.79 eV, respectively. Electron emission density from BC3 nanotube surface will be increased upon both atomic and molecular fluorine adsorptions due to work function decrement.

A DFT study on the sensing behavior of a BC2N nanotube toward formaldehyde.

We investigated the viability of using a BC2N nanotube to detect formaldehyde (H2CO) molecule by means of B3LYP and M06 density functionals. The results indicate that the molecule is weakly adsorbed on the intrinsic BC2N nanotube releasing energy of 0.8 kcal mol(-1) (at B3LYP/6-31G(d)) without significant effect on the HOMO-LUMO energy gap and electrical conductivity of the tube. Thus, H2CO cannot be detected using this intrinsic nanotube. To overcome this problem, a carbon atom of the tube wall was substituted by a Si atom. It was demonstrated that the Si-doped tube cannot only strongly adsorb the H2CO molecule, but also may effectively detect its presence because of the increase in the electric conductivity of the tube.

A large gap opening of graphene induced by the adsorption of CO on the Al-doped site.

We investigated CO adsorption on the pristine, Stone-Wales (SW) defected, Al- and Si- doped graphenes by using density functional calculations in terms of geometric, energetic and electronic properties. It was found that CO molecule is weakly adsorbed on the pristine and SW defected graphenes and their electronic properties were slightly changed. The Al- and Si- doped graphenes show high reactivity toward CO, so calculated adoption energies are about -11.40 and -13.75 kcal mol(-1) in the most favorable states. It was found that, among all the structures, the electronic properties of Al-doped graphene are strongly sensitive to the presence of CO molecule. We demonstrate the existence of a large Eg opening of 0.87 eV in graphene which is induced by Al-doping and CO adsorption.