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In this paper, the heterofullerenes made of the smallest fullerene, C20were investigated by quantum chemistry calculations based on density functional theory. The geometrical structures, energies, electronic properties, and the aromaticities of the C19X (X = B, N, O, Al, Si, P, S, Ga, Ge, As, and Se) cages were studied systemically and compared with those of the pristine C20cage. It is found that the doped cages with different heteroatoms exhibit various structural, electronic, and aromatic properties. Several doping behaviors of the C19X cages are different from those of the C59X cages. These results imply the possibility to modulate the physical properties of heterofullerenes by tuning the sizes of the carbon cages as well as the substitution elements. [ABSTRACT FROM PUBLISHER]

In this article, the nanotubes obtained by silicon atoms substitutionally doping the single-walled carbon nanotubes were investigated by quantum chemistry calculations under the framework of density functional theory. The geometrical structures, relative stabilities and electronic properties of the Si-doped tubes were studied in details and compared with those of the pristine (12, 0) tubes. It is found that the Si atoms in the doped tubes have obviously larger π-orbital axis vector angles than carbon atoms, and they also tend to “pop out” from the original positions. The Si-doped nanotubes exhibit lower thermodynamic stability than those of the undoped tubes from the viewpoint of both cohesive energy and Gibbs free energy. The energy levels of the frontier orbitals vary within 0.25 eV when the silicon atom is introduced into the nanotubes. However, most hybrid nanotubes present larger energy gaps than those of the pristine ones. [ABSTRACT FROM AUTHOR]

This work reveals first principle results of the endohedral fullerenes made from neutral or charged single atomic lithium (Li or Li+) encapsulated in fullerenes with various cage sizes. According to the calculated binding energies, it is found that the encapsulation of a single lithium atom is energetically more favorable than that of lithium cation. Lithium, in both atomic and cationic forms, exhibits a clear tendency to depart from the center in large cages. Interaction effects dominate the whole encapsulation process of lithium to carbon cages. Further, the nature of the interaction between Li (or Li+) and carbon cages is discussed based on reduced density gradient, energy decomposition analysis, and charge transfer. [ABSTRACT FROM AUTHOR]

Efficient and safe hydrogen storage is a pivotal challenge for the advancement of hydrogen energy technologies. To address this, the engineering of high-performance solid-state hydrogen storage materials through the loading of transition metals (TM) on carbon-based solids has gained considerable interest. However, the mechanics for TM such as Palladium that bolster hydrogen storage have not well addressed yet. This work presents hydrogen absorptions with metal Pd nanoparticles loaded on reduced graphene oxide (Pd-rGO), including material preparation, structural characterization, hydrogen storage performance, and quantum chemical mechanistic insights. A simple material synthesis strategy has been explored and Pd-rGO composites are successfully prepared with graphite powder as raw materials by an easy reduction-oxidation process. Then, Pd-rGO composites are characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, Raman, transmission electron microscopy, and nitrogen adsorption-desorption isotherms methods to clarify the detailed structural characteristics of Pd-rGO with different loading amounts. It is found that Pd nanoparticles with an average particle size of 10 nm are uniformly dispersed on the surface of rGO. The materials have high defect severity and increased specific surface areas with Pd loading. The hydrogen adsorption capacity of Pd-rGO can be increased by 64 % compared with that without Pd loading due to the hydrogen spillover effect. In addition, the intensification mechanism of hydrogen storage of Pd-rGO composites is further understood by using density functional theory calculations and surface interaction analysis. • Prepared Pd-rGO composites materials for hydrogen storage from graphite powder. • Pd loading improves hydrogen storage capacity for rGO. • Elucidated mechanism of Pd enhancing hydrogen storage through DFT calculations. [ABSTRACT FROM AUTHOR]

• Revealed microscopic characteristics and structural parameters of taixi anthracite. • Conceptualized single molecular description of taixi anthracite as C 763 H 397 O 21 N 8. • Summarized microstructure features of coal with various metamorphism. This work presents insights into the molecular structure of Chinese Taixi anthracite (TXA) at atomic scales. The comprehensive analysis of materials characterizations and data fitting & calculations are performed to reveal microscopic characteristics and structural parameters of TXA. Then the planar and three-dimensional molecular structure models of TXA are con with the help of computer-aided molecular design and multi-scale molecular simulation calculations. The chemical structure characteristics of TXA are systematically analyzed, such as the carbon framework, main functional groups, and typical chemical bonding features. It is found that aromatic carbons are the main skeleton of organic matter, combined with some aliphatic carbons mainly in form of methyl, methylene and methine. Conceptualized single molecular description of TXA is determined to be C 763 H 397 O 21 N 8. Representative two-dimensional and three-dimensional molecular structural models are also constructed to describe the apparent molecular structural features of TXA. Finally, molecular structural models are further verified by the elemental composition, nuclear magnetic resonance, Fourier transform infrared, and bond concentration of TXA. In addition, we summarized microstructure features of coal with various metamorphism. This work could provide theoretical guidance for understanding the microstructure of TXA and building the correlation between coal structure and functional properties to achieve efficient utilization of coal resources. [ABSTRACT FROM AUTHOR]

Abstract The four new modified nucleobases (NBs), 5-mC, 5-hmC, 5-fC and 5-caC , besides the regular adenine, thymine, cytosine, guanine and uracil, are important in expression and regulation of genetic information. These four new major NBs are all derived from base cytosine by adding various functional groups, and their identification from the regular ones are much desired currently. However, the four new major NBs interacted with graphene on its surface have not been well considered, though a number of studies of regular NBs adsorbed on low-dimensional carbon materials are available to identify different NBs. This work reveals the interaction between the four new major NBs and graphene nanoflake substrate by using first-principle calculations based on density functional theory. The structure, energy and non-covalent interaction of the graphene/NBs complex are calculated and explored in details. The energy decomposition analysis, reduced density gradient, charge transfer and projected density of states are also performed to investigate the nature of the interaction between NBs and graphene nanoflake. Electrostatic and orbital interaction are found to be important to stabilize the interaction between NBs and graphene nanoflake, though orbital interaction is less significant. It is very noticed that the proportion of dispersion interaction could be more than half of the sum attractive contributions. Thus, dispersion interaction is the most dominating factor in stabilizing graphene/NBs complexes. The results of reduced density gradient further confirm that the interaction between the graphene nanoflake and NBs is mainly the van der Waals type. Besides, much attention is paid to the interaction differences between the four new major NBs and the pristine cytosine, and the impact of the introduced functional groups of the four new major NBs on the structure, energy and interaction is also discussed. Graphical abstract Image 1 Highlights • The nature of the interaction between four modified nucleobases and graphene is revealed to be different from the pristine cytosine. • The interaction between four modified nucleobases and graphene can be analyzed quantitatively by decomposing into Pauli, electrostatic, orbital and dispersion parts. • Reduced density gradient, electrostatic potential and projected density of states can directly depict the physical image of the interaction between four modified nucleobases and graphene. [ABSTRACT FROM AUTHOR]