Minsi Xin

Defect Induced Electronic Structure of Uranofullerene

The interaction between the inner atoms/cluster and the outer fullerene cage is the source of various novel properties of endohedral metallofullerenes. Herein, we introduce an adatom-type spin polarization defect on the surface of a typical endohedral stable U2@C60 to predict the associated structure and electronic properties of U2@C61 based on the density functional theory method. We found that defect induces obvious changes in the electronic structure of this metallofullerene. More interestingly, the ground state of U2@C61 is nonet spin in contrast to the septet of U2@C60. Electronic structure analysis shows that the inner U atoms and the C ad-atom on the surface of the cage contribute together to this spin state, which is brought about by a ferromagnetic coupling between the spin of the unpaired electrons of the U atoms and the C ad-atom. This discovery may provide a possible approach to adapt the electronic structure properties of endohedral metallofullerenes.

Structural and electronic properties of uranium-encapsulated Au 14 cage

The structural properties of the uranium-encapsulated nano-cage U@Au14 are predicted using density functional theory. The presence of the uranium atom makes the Au14 structure more stable than the empty Au14-cage, with a triplet ground electronic state for U@Au14. Analysis of the electronic structure shows that the two frontier single-occupied molecular orbital electrons of U@Au14 mainly originate from the 5f shell of the U atom after charge transfer. Meanwhile, the bonding orbitals and charge population indicate that the designed U@Au14 nano-cage structure is stabilized by ionocovalent interactions. The current findings provide theoretical basis for future syntheses and further study of actinide doped gold nanoclusters, which might subsequently facilitate applications of such structure in radio-labeling, nanodrug carrier and other biomedical applications.

The ground state and electronic structure of Gd@C82: A systematic theoretical investigation of first principle density functionals

As a representative lanthanide endohedral metallofullerene, Gd@C82 has attracted a widespread attention among theorists and experimentalists ever since its first synthesis. Through comprehensive comparisons and discussions, as well as references to the latest high precision experiments, we evaluated the performance of different computational methods. Our results showed that the appropriate choice of the exchange-correlation functionals is the decisive factor to accurately predict both geometric and electronic structures for Gd@C82. The electronic structure of the ground state and energy gap between the septet ground state and the nonet low-lying state obtained from pure density functional methods, such as PBE and PW91, are in good agreement with current experiment. Unlike pure functionals, the popularly used hybrid functionals in previous studies, such as B3LYP, could infer the qualitative correct ground state only when small basis set for C atoms is employed. Furthermore, we also highlighted that other geometric structures of Gd@C82 with the Gd staying at different positions are either not stable or with higher energies. This work should provide some useful references for various theoretical methodologies in further density functional studies on Gd@C82 and its derivatives in the future.

Effect of ligands on the characteristics of (CdSe)13 quantum dots

The widespread applications of quantum dots (QDs) have spurred an increasing interest in the study of their coating ligands, which can not only protect the electronic structures of the central QDs, but also control their permeability through biological membranes with both size and shape. In this work, we have used density functional theory (DFT) to systematically investigate the electronic structures of (CdSe)13 passivated by OPMe2(CH2)nMe ligands with different lengths and various numbers of branches (Me = methyl group, n = 0, 1–3) as well as different number of ligands ((CdSe)13 + [OPMe2(CH2)2Me]m (m = 0, 1, 9, 10)). Our results show that the absorption peak in the ultraviolet-visible (UV-vis) spectra displays a clear blue-shift, on the scale of ∼100 nm, upon the binding of ligands. Once the total number of ligands bound with (CdSe)13 reached a saturated number (9 or 10), no more blue-shift occurred in the absorption peak in the UV-vis spectra. On the other hand, the aliphatic chain length of ligands has a negligible effect on the optical properties of the QD core. Analyses of the bonding characteristics confirm that optical transitions are dominantly governed by the central QD core rather than the organic passivation. These findings might provide insights on the material design for the passivation of quantum dots for biomedical applications.

Carbon nanotubes adsorb U atoms differently in their inner and outer surfaces

Effective clean up of radioactive waste remains one of the fundamental challenges in nuclear sciences due to the ever growing concern on the safety of nuclear power. Carbon nanotubes have recently shown encouraging promise in their potential capability of U atom adsorption and removal. In this paper, we used first-principles density functional theory (DFT) to illustrate the adsorption and interactions between U atoms and the inner/outer surfaces of a single-walled carbon nanotube. Our DFT calculations showed that when U atoms were adsorbed on each of the CNT surfaces, the ground electronic states were all quintet. However, U atoms showed differential adsorption modes depending on the surface, binding to bridge sites on the inner surface, and to hole sites on the outer surface. The interior adsorption was more stable with an interaction energy of about 1 eV greater than that of the external one, which is explained by their different ground state electronic structures. The electronic states were largely influenced by the ferromagnetic coupling between the U atoms and the net spintronics of the CNT only for the internal adsorption case, with the external adsorption mainly determined by the U atoms. Orbital and charge analysis show that compared to the external adsorption, there were about 1.0e more charge transfers between the internally adsorbed U atom and the CNT, which facilitated stronger donor–acceptor interactions. Further analysis on the density of states indicated that the internal adsorption had a larger bonding area between the U atoms and CNT, supporting the stronger internal adsorption.

Environmental‐Confinement‐Induced Stability Enhancement of Chiral Molecules

We computationally study the transition process of a chiral difluorobenzo[c]phenanthrene (DFBcPh) molecule within non-polar fullerene C(260) to explore the confinement effect. We find blue-shifts in the infrared and Raman spectra of the molecule inside the fullerene relative to those of isolated systems. Six types of spectrum features of the molecule appear in the 0-60 cm(-1) band. Interestingly, the energy barrier of the chiral transformation of the molecule is elevated by 15.88 kcal mol(-1) upon the confinement by the fullerene, indicating improvement in the stability of the enantiomers. The protection by C(260) lowers the highest occupied molecular orbital energy level and lifts the lowest unoccupied molecular orbital energy level of the chiral molecule such that the chiral molecule is further chemically stabilized. We concluded that the confinement environment has an impact at the nanoscale on the enantiomer transformation process of the chiral molecule.