Search

Hydrogen energy is one of promising non-polluting and renewable energy sources. In this paper, we present a first principal study of hydrogen storage in pure C 60 fullerene cage and Stone-Wales (SW) defective C 60 cages using density functional theory (DFT) with applying both the exchange functional B3LYP and the dispersion correction wb97xd at 6–31+g(d,2p) basis set. In addition, the counterpoise correction is applied, and the basis set superposition error is calculated. The calculations underscore that the hydrogenation binding energy of C 60 cages occurs through an endothermal process for C 60 H in with a hydrogen binding energy of 0.09 eV and through an exothermal process for C 60 H out , C 60 SW 66 H out , and C 60 SW 65 H out , cages with hydrogen binding energies of −2.17 eV, −2.96 eV, and −2.20 eV, respectively. Remarkably, for the first time, the intermediate hydrogen binding energy is found inside C 60 SW 66 H in fullerene, and C 60 SW 65 H in fullerene cages with energies of −0.26 eV and −0.81 eV, respectively. The hydrogen adsorption inside the cavity of C 60 SW 66 fullerene cage is thermodynamically possible below 289.8 K and entire pressure range considered. Our results highlight, for the first time, that the endohedral cavity of C 60 SW 66 is a promising new medium for hydrogen storage due to its binding energies (−0.26 eV) and its hydrogen storage weight percentage (5.3%) that are close to the optimal conditions specified by DOE for commercial use. In addition, this study opens up a new discovery of Stone-Wales defective C 60 fullerene for further endohedral cavity applications. • New insight into endohedral cavity of Stone Wales C 60 SW 66 is reported. • For the first time, a new promising medium for hydrogen storage inside cavity of C 60 SW 66 is proved. • Binding energies of −0.26 eV and hydrogen storage weight percentage up to 5.3% are achieved inside the cavity of C 60 SW 66. • This study opens a new discovery of the SW defective C 60 fullerene for further endohedral cavity applications. [ABSTRACT FROM AUTHOR]

Hydrogen is one of promising energy sources with virtually non-polluting. In this paper, the hydrogenation mechanism and hydrogen storage weight percentage of new forms of CNCs, BNNCs and SiCNCs with an apex angle of 112.9° are investigated for first time using density functional theory (DFT) and applying B3LYP level at 6–31 g(d,p) basis. The calculations underscore that for all nanocones; CNCs, BNNCs and SiCNCs the convex surface is always more energetic favorite for hydrogenation comparing with the concave surface of nanocones. Also, the hydrogen storage weight percentage is always enhanced via cross stacking nanocones. Noticeably, it is found that the electron density is widely distributed up the next neighbor atoms of pentagon ring via cross stacking, however for single nanocones is mostly concentrated on the atoms of the conical part (pentagon ring). Finally, the results show that the best candidate nanocone for hydrogen storage is the cross stacking nanocones. Image 1 • The hydrogenation mechanism of single and cross stacking nanocones is investigated. • The hydrogenation degree of nanocones is doubled for CNCs via cross stacking. • The convex surface of nanocones is the most energetic favorite for hydrogenation. • The electron density is increased and extended via cross stacking. [ABSTRACT FROM AUTHOR]

The self-interstitial carbon is the key to radiation damage in graphite moderator nuclear reactor, so an understanding of its behavior is essential for plant safety and maximized reactor lifetime. The density functional theory is applied on four different graphite unit cells, starting from of 64 carbon atoms up to 256 carbon atoms, using AIMPRO code to obtain the energetic, athermal and mechanical properties of carbon interstitial in graphite. This study presents first principles calculations of the energy of formation that prove its high barrier to athermal diffusion (1.1 eV) and the consequent large critical shear stress (39 eV–50 eV) necessary to shear graphite planes in its presence. Also, for the first time, the gamma surface of graphite in two dimensions is calculated and found to yield the critical shear stress for perfect graphite. Finally, in contrast to the extensive literature describing the interstitial of carbon in graphite as spiro interstitial, in this work the ground state of interstitial carbon is found to be canted spiro interstitial. [ABSTRACT FROM AUTHOR]

Hydrogenated fullerenes are detected in the Universe in space but their identification is still unsolved task. Therefore, this paper provides useful information about hydrogenated fullerenes (dimer, peanut and capsule) using DFT method at the B3LYP/6-31G(d) level of theory. The stability, geometric structures, hydrogen adsorption energies and NMR chemical shifts are calculated. The results show that the energy of most stable isomer of C 118 dimer is lower than the energies sum of C 60 and C 58 cages by 1.77 eV and the energy per carbon atom of C 144 capsule is more stable than C 60 cage by 126.98 meV. Also, endohedral Ti-doped C 118 dimer and C 128 peanut are found to be most stable structures than exohedral Ti-doped C 118 dimer and C 128 peanut by 2.19 eV/Ti and 3.52 eV/Ti, respectively. The hydrogenation process is found to be enhanced (especially at the caps) for endohedral Ti-doped C 118 dimer and C 128 peanut through electronic surface modifications. The most active hydrogenation sites are selected and it is found that the most stable hydrogenation sites are H out s 1   and   H out s 3 for fullerenes and endohedral Ti-doped fullerenes, respectively. [ABSTRACT FROM AUTHOR]

Ab initio DFT (density functional theory) is used to investigate the hydrogenation energy and hydrogenation mechanism of C n and C n H n fullerene cages from n = 20 to n = 60. All calculations have been performed using G03W package, with B3LYP exchange-functional and applying basis set 6–31G(d, p). It is found that the most stable hydrogenation sites on the C n fullerene cages are and sites and on the C n H n fullerene cages are , and sites. The calculations show that the required energy to initiate the hydrogen migration on the surface of C n fullerene cages between two metastable structures of C 54 H is ∼1.5 eV and on the surface of C n H n fullerene cages between metastable and stable structures of the C 60 H 61 fullerene cage is ∼2.35 eV. Also, it is found that the energy release from hydrogen migration is always enough to direct the hydrogenation process towards the most stable structures and it reduces the number of hydrogen atoms bonded to the fullerene cage via forming H 2 molecules. [ABSTRACT FROM AUTHOR]

Abstract: We present a detailed theoretical study of the behaviour of short heterogenous C/BN nanotube segments, notably the effect on band gap of introducing vacancy centres. We have introduced a complete set of band gap calculations, considering a range of different nanotube diameters and chiralities, as well as different arrangements and stoichiometries of C and BN. We have investigated three distinct distributions of BN into CNT segments using density functional theory (DFT) and applying B3LYP/6-31g(d,p): BN-random distribution, BN-row distribution, and BN-zigzag distribution. We have shown for first time a detailed study for formation energies of carbon monovacancies and how via these defects the band gaps of short heterogeneous CBNNT segments can be reduced. The reduction can reach more than 50% due to carbon vacancy in armchair CBNNTs. The wide varieties of band gaps for carbon vacancy centres may allow the fundamental control needed for designing next-generation electronic components. [Copyright &y& Elsevier]

Abstract: Using the first-principles methods, density-functional theory (DFT) and Hartree–Fock (HF), we have studied the defect fullerene cages by removing C2 units from icosahedral C60, sequentially down to C30. It is found that the band gap of defect fullerenes depends on the size considerably, and is shown for the first time that C40 cage can have very small energy gap. Also, we have investigated forty isomers of C40 cage and have selected ones with low energies and high conductivities. Therefore C40 is proposed to be an interesting unit for nanodevice applications. [Copyright &y& Elsevier]