Igor K. Petrushenko

Effect of meso-substituents on the electronic transitions of BODIPY dyes: DFT and RI-CC2 study.

In this work, the influence of substituents on the electronic transitions of model 8-R-BODIPY dyes (R=NMe2, NH2, OH, CH3, H, F, SH, Cl, Br, CF3, CN, and NO2) was investigated theoretically using time-dependent density functional theory (TD-DFT) and ab initio coupled-cluster doubles (CC2) quantum chemical calculations. Quantum chemical modeling shows a direct relationship between the electron donating and electron withdrawing character of substituents expressed by Hammett substituent constants (σp) and changes in energy of the HOMO-LUMO gap modulating spectral shifts of the S0→S1 transition. Good linear correlations of the calculated LUMO energies and σp as well as the shape of the HOMO and LUMO allow to obtain a reasonable explanation for the observed effects of substituents.

(2+1) Cycloaddition of dichlorocarbene to finite-size graphene sheets: DFT study

The [2+1] cycloaddition of dichlorocarbene to finite-size graphene has been investigated by means of the B3LYP/SVP approach. Three different sites of functionalization were studied. The results show that cycloaddition on the edge or corner positions can not significantly distort the planar framework of graphene, but center functionalization changes its structure dramatically. Reaction energies were calculated, and they show that the peripheral areas of graphene are much more reactive than the center sites. The electronic properties of graphene are weakly modified by the [2+1] cycloaddition. Finally, we propose that the [2+1] cycloaddition of dichlorocarbene, owing to its simplicity, can be a promising way to fine-tune the bandgap of graphene.Graphical abstract

DFT Study of the Elastic Properties of Pristine and Moderately Fluorinated Single-walled Carbon Nanotubes

This article presents a systematical study on structural and mechanical properties of pristine armchair single-walled carbon nanotubes (SWNTs) and fluorinated SWNTs using density functional theory. At the B3LYP/SVP and B3LYP/TZV levels, the data obtained compare with experimental and theoretical studies. The results show that fluorination in the off-axis position cannot significantly distort SWNTs framework, but axial fluorination changes the SWNT structure dramatically. It is established that there is a relatively small difference in stiffness of nanotubes which adsorbed fluorine atoms in axial and off-axis places. The permanence of general trend of Youngs modulus changes is shown.

DFT Study of the Structural and Mechanical Properties of Oxydated Single-walled Carbon Nanotubes

This paper presents a systematical analysis of the structure and mechanical properties of armchair single-walled carbon nanotubes (SWNTs) and oxidated SWNTs by using density functional theory. Our study involves Youngs modulus calculation for pristine nanotubes and oxidated models. Necessary parameters for Youngs moduli determination are obtained by calculating the optimal geometries and the optimal geometries after stretching of studied objects. It is indicated that oxygen can not significantly distort the framework of SWNTs. It is established that there is a relatively small difference in strength of nanotubes that adsorbed oxygen in axial and off-axis places. The constancy of the general trend of studied Youngs moduli is shown.

DFT Study on Adiabatic and Vertical Ionization Potentials of Graphene Sheets

Adiabatic and vertical ionization potentials (IPs) of finite-size graphene sheets as a function of size were determined by using density functional theory. In the case of graphene a very moderate gap between vertical and adiabatic IPs was observed, whereas for coronene molecule as a model compound these values differ considerably. The ionization process induces large changes in the structure of the studied sheets of graphene; “horizontal” and “vertical” bond lengths have different patterns of alternation. It was also established that the HOMO electron density distribution in the neutral graphene sheet affects its size upon ionization. The evolution of IPs of graphene sheets towards their work functions was discussed.

Effect of methyl substituents on the electronic transitions in simple meso-aniline-BODIPY based dyes: RI-CC2 and TD-CAM-B3LYP computational investigation

The S0→Si, i=1-5 electronic transitions of four 8-(4-aniline)-BODIPY and four 8-(N,N-dimethyl)-BODIPY dyes, differ by number and position of methyl substituents in the BODIPY frame, were investigated theoretically using ab initio the coupled cluster doubles (CC2) and TD-CAM-B3LYP methods. Methyl substituents in the BODIPY frame and the aniline fragment at the meso position disturb energy of local excitations S0→S1, S0→S3, and S0→S4 weakly in comparison with the fully unsubstituted BODIPY molecule. These transitions in experimental spectra form the most long-wave absorption bands at ca. 500nm as well as absorption bands in the region of 300-400nm. At the same time, the presence of aniline fragments leads to the appearance of new S0→S2 transitions of the charge transfer character in electronic spectra of BODIPYs. We also found a linear relationship between vertical energy of these charge transfer transitions and the electron donating power of an aniline fragment and electron accepting power of the BODIPY core depending on the number and position of methyl groups. The CC2 method provides the best overall description of the excitation energies in line with the experimental observations. On average, the quality of TD-CAM-B3LYP is almost equal to that of CC2, however the TD method with the CAM-B3LYP functional slightly underestimates the CT excitation energy.

Mechanical properties of carbon, silicon carbide, and boron nitride nanotubes: effect of ionization

This paper studies the effect of ionization of finite-length single-walled carbon nanotubes, boron nitride nanotubes, and silicon carbide nanotubes on their mechanical properties. The PBE/SVP calculations show that the ionization affects the elastic properties of studied models. The nanotubes demonstrate little changes in Young’s modulus upon ionization; however, the changes in bulk and shear moduli as well as in Poisson’s ratio are more pronounced. The introduction of nanotubes into composite materials, which may undergo a radiation exposure, is a promising way to enhance their performance.Graphical abstract

DFT Calculations of Hydrogen Adsorption inside Single-Walled Carbon Nanotubes

DFT calculations have been performed to study noncovalent interactions of a hydrogen molecule and single-walled carbon nanotubes (SWCNTs) of various diameters. Understanding these interactions is crucial for the development of systems for hydrogen storage and delivery. The barrier and barrier-free introduction of a hydrogen molecule into SWCNTs is observed. It has been found that hydrogen molecules bind differently onto SWCNTs, depending on their diameters and the orientation of an H2 molecule inside the SWCNT. The binding inside SWCNTs with small diameters ((3,3); (4,4)) is very unfavorable; the opposite situation is in the case of larger ((5,5); (6,6)) SWCNTs. Finally, in the case of ((7,7); (8,8)) SWCNTs, the hydrogen binding energies decrease, and their values approach to those of graphene.

Single-walled carbon nanotubes functionalized by a series of dichlorocarbenes: DFT study

The structural and elastic properties of neutral and ionized dichlorocarbene (CCl2) functionalized single-walled carbon nanotubes (SWCNTs) were studied using density functional theory (DFT). The Young’s modulus of ionized pristine SWCNTs is found to decrease in comparison to that of neutral models. The interesting effect of increase in Young’s modulus values of ionized functionalized SWCNTs is observed. We ascribe this feature to the concurrent processes of the bond elongation on ionization and the local deformation on cycloaddition. The strong dependence of the elasticity modulus on the number of addends is also observed. However, the CCl2-attached SWCNTs in their neutral and ionized forms remain strong enough to be suitable for the reinforcement of composites. In contrast to the elastic properties, the binding energies do not change significantly, irrespective of CCl2 coverage.

Theoretical study on mechanical properties of polyethylene–SWCNT complexes

This paper studies the mechanical properties of polyethylene (PE)–Single-walled carbon nanotube (SWCNT) complexes by using density functional theory (DFT). At the PBE/SVP level, the Young’s modulus of the complexes is obtained as a function of PE content. It is established that, with increasing number of PE chains attached to the SWCNTs, the Young’s modulus monotonically decreases. The density of states (DOS) results show that no orbital hybridization exists between the PE chains and nanotubes. The results of this work are of importance for the design of composite materials employing SWCNTs.