Li-Li Sun

Structural stability and electronic property of C68X4 (X = H, F, and Cl) fullerene compounds

A systematic study on the geometrical structures and electronic properties of C(68)X(4) (X=H, F, and Cl) fullerene compounds has been carried out on the basis of density functional theory. In all classical C(68)X(4) isomers with two adjacent pentagons and one quasifullerene isomer [C(s):C(68)(f)] containing a heptagon in the framework, the C(s):0064 isomers are most favorable in energy. The addition reaction energies of C(68)X(4) (C(s):0064) are high exothermic, and C(68)F(4) is more thermodynamically accessible. The C(68)X(4) (C(s):0064) possess strong aromatic character, with nucleus independent chemical shifts ranging from -22.0 to -26.1 ppm. Further investigations on electronic properties indicate that C(68)F(4) and C(68)Cl(4) could be excellent electron-acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities (3.29 and 3.15 eV, respectively). The Mulliken charge populations and partial density of states are also calculated, which show that decorating C(68) fullerene with various X atoms will cause remarkably different charge distributions in C(68)X(4) (C(s):0064) and affect their electronic properties distinctly. Finally, the infrared spectra of the most stable C(68)X(4) (C(s):0064) molecules are simulated to assist further experimental characterization.

Searching for stable hept‐C62X2 (X = F, Cl, and Br): Structures and stabilities of heptagon‐containing C62 halogenated derivatives

To determine the geometries of the most stable hept‐C62X2 (X = F, Cl, and Br) isomers, all 967 possible hept‐C62F2 isomers have been orderly optimized using AM1, HF/STO‐3G, B3LYP/3‐21G, and B3LYP/6‐31G* methods, and chlorofullerenes and bromofullerenes, which are isostructural with five most stable hept‐C62F2 isomers, were regarded as candidates of the most stable isomer, and optimized at the B3LYP/6‐31G* level. The results reveal that 2,9‐ and 9,62‐hept‐C62X2 (X = F, Cl, and Br) are the two most stable isomers with slight energy difference. The halogenation releases strain energy of hept‐C62, and all halogenated fullerenes are more chemically stable than hept‐C62 with lower EHOMO and higher ELUMO. All five most stable hept‐C62X2 (X = F, Cl, and Br) isomers are energetically favorable, and their thermodynamic stability decreases along with the increase of sizes of addends. Only hept‐C62F2 isomers show high thermodynamic stability, and they are potentially synthesized in experiments. 59,62‐squ‐C62X2 (X = F, Cl, and Br) were computed for comparison, and they are found to be more stable than their heptagon‐containing isomers.

Search for the most stable Ca@C44 isomer: Structural stability and electronic property investigations

Stimulated by the mass spectroscopic observation of the metallofullerene Ca@C(44), we have performed a systematic investigation to search for the most stable isomer using HF/3-21G approximately LanL2DZ, HF/6-31+G(d), B3LYP/6-31+G(d), and MP2/6-31+G(d)//B3LYP/6-31+G(d) methods. The Ca@C(44) (D(2):53) isomer with eight adjacent pentagons in the fullerene framework is predicted to possess the lowest energy. The thermodynamics stability explorations of Ca@C(44) isomers at different temperatures show that Ca@C(44) (D(2):53) is the most thermodynamically stable in the temperature range of absolute zero to 4000 K. The encapsulation of Ca atom in C(44) fullerene is exothermic, and the electronic structure of Ca@C(44) (D(2):53) can be described formally as Ca(2+)@C(44) (2-). Further analysis on the frontier molecular orbitals and density of states of Ca@C(44) (D(2):53) suggests that both highest occupied molecular orbital and lowest unoccupied molecular orbital are carbonlike with low Ca character, and the carbon cage possesses high chemical activity. In addition, the vibrational spectrum of Ca@C(44) (D(2):53) has been simulated and analyzed to gain an insight into the metal-cage vibrations.

Structures and stabilities of neutral and charged D 5 h X@C50 endohedral complexes

Equilibrium geometries and stabilities of endohedral complexes formed by H, Li, Na, K, Be, Mg, Ca and D 5 h C50, as well as their charged states, are computed using B3LYP/6-31G* method, and bond lengths of H@C50 are nearly unchanged compared with those of bare C50, indicating interaction between them is almost negligible. However, C–C bonds change significantly when metals are encapsulated. Following the increase of the extra charges on the complexes, the structural distortions decrease for Li, Na, K, Mg, and Ca series endohedral derivatives, but increase for Be series endohedral derivatives, which change in the same way with C50 → → . Most endohedral complexes investigated are energetically favorable, except for H@C50, Be@C50, and Mg@C50. E HOMO and E LUMO are nearly unchanged when atoms are encapsulated, but significantly decrease following the increase of extra positive charges, and both are determined by the number of extra charges. Frequency calculations show that K@ and Be@ are local minima. The D 3 endohedral complexes are optimized for comparison, and their structural and energetic parameters change in the same tendency with these of D 5 h isomers. Only D 3 K@C50 is a local minimum, and the D 3 complexes are not necessarily more stable than the corresponding D 5 h isomers.

Theoretical Studies on Structures and Properties of Endohedral Fullerenes Complexes: XHn@C32(X=F, O, N, C; n=1—4)

Theoretical studies on structures and properties of endohedral fullerene complexes formed by encapsulating small molecules of HF, H2O, NH3, and CH4 in a C32 fullerene cage, were carried out by ab initio method. Current calculations reveal that these processes to encase them in fullerene are energetically unfavorable because of the small cavity size of C32. The red shift in the F-H stretching frequency indicates the potential existence of hydrogen bonding between the HF molecule and the carbon cage.

Structures and stabilities of endo- and exohedral Si20H20 derivatives: X@Si20H20 and XSi20H20, X = H + , H, N, P, C − , and Si −

Geometries, relative energies, and stabilities of endo- and exohedral complexes, X@Si20H20 and XSi20H20, (X = H+, H, N, P, C−, and Si−) are calculated at B3LYP/6-31G* level. The energy minimum structure of Si20H21 + shows that the proton cannot be positioned in the Si20H20 centre, but prefers attach to Si20H20 exohedrally with C2v symmetry. Most investigated Ih endohedral complexes X@Si20H20 (X = H, N, P, C−, and Si−) are local minima, except for 2N@Si20H20, which is a high-order saddle point. Inclusions energies of the endohedral complexes are calculated, and it reveals that energy penalties caused by encapsulation are rather small. Exohedral complexes XSi20H20 (X = H, N, P, C−, and Si−) have C2v or Cs local minima, and most of them are more stable than their endohedral isomers with the exception of C2v 4PSi20H20 and 4Si−Si20H20.