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The geometric, optical, and magnetic properties of the M@Sn12 clusters (M=Ti, V, Cr, Mn, Fe, Co, Ni) are studied using the relativistic density-functional method. The geometric optimization shows that the ground states of these clusters are probably very close to the Ih structure. Our calculations demonstrate that the optical gaps of the M@Sn12 can be tuned from infrared to green, and the magnetic moments of them vary from 2 μB to 5 μB by doping d transition metal atoms into Sn12 cage, suggesting that M@Sn12 could be a new class of potential nanomaterials with tunable magnetic and optical properties. [ABSTRACT FROM AUTHOR]

The geometric and electronic properties of the titanium carbide TiC5 cluster in its neutral and anionic charge states have been investigated using density functional theory (DFT) at the B3LYP level. The nonplanar six-membered ring-type or “butterflylike” structures are found to be the equilibrium geometric structures of TiC5 and TiC5-. Time-dependent DFT is used in the calculation of the excited states. The theoretical assignment at the B3LYP level for the features in the photoelectron spectrum is given. All results obtained are in good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

The geometric and electronic structures of metal-substituted fullerene C59Sm and exohedral fullerenes C60Sm are studied using the density-functional theory. The geometric optimization shows that the replacement of a C atom with a Sm in C60 yields a stable substitutionally doped fullerene C59Sm, and among the five possible optimized geometries for C60Sm, the most favorable exohedral sites are above the center of a hexagon and a pentagon ring. The calculations for electronic structures show that the magnetic moment of Sm is preserved for all the stable structures as tiny hybridization takes place between the orbitals of the Sm atom and those of their neighboring carbons. Because of the small energy gaps and the half occupation of the highest occupied molecular orbitals, all the stable C60Sm isomers are inferred to be conductors. [ABSTRACT FROM AUTHOR]

The generalized gradient approximation based on density functional theory is used to analyze the geometric and electronic properties of Si@C74. It is found that among the five possible optimized geometries of Si@C74, the most favorable endohedral site of Si atom is under the center of a pentagon ring on the σh plane, i.e., Si@C74-5, which is different from the center stable site for Si in C74 calculated by the semiempirical molecular orbital calculations and molecular mechanics calculations, and it is also different from the stable site, i.e., under a [6, 6] bond along the C2 axis on the σh plane in C74 for metal atoms Ba, Ca, and Eu. The deformation charge density on the σh plane reveals that the Si–C bonds in Si@C74-5 have covalent character, while the Mulliken charge analysis together with a longer Si–C bond length reveals that the Si–C bonds in Si@C74-5 have ionic character. Therefore, we infer that Si–C bonds in Si@C74-5 contain both covalent and ionic characters. [ABSTRACT FROM AUTHOR]

Charge mobilities of six DNAs and RNAs have been computed using quantum chemistry calculation combined with the Marcus-Hush theory. Based on this simulation model, we obtained quite reasonable results when compared with the experiment, and the obtained charge mobility strongly depends on the molecular reorganization and electronic coupling. Besides, we find that hole mobilities are larger than electron mobilities no matter in DNAs or in RNAs, and the hole mobility of 2L8I can reach 1.09 × 10-1 cm2 V-1 s-1 which can be applied in the molecular wire. The findings also show that our theoretical model can be regarded as a promising candidate for screening DNA- and RNA-based molecular electronic devices. [ABSTRACT FROM AUTHOR]

This paper reports a comprehensive study of (TiO2)n (n=1–3) clusters on their structures, vertical electron affinities (VEA) and adiabatic electron affinities (AEA), and excited states that are further correlated with experimental photoelectron spectra (PES). Local density functional and time-dependent density functional methods (TTDFT) with 6–31G(d) basis set are used. For (TiO2)n with n=1 and 3, the ground-state geometries are found to have C2v and Cs structures, respectively, in both neutral and anionic charge states. For neutral (TiO2)2, the most stable structure corresponds to a C2h conformation. For anionic (TiO2)2-, two isomers with C2h and C2v symmetries are identified to be nearly isoenergetic. This conclusion is supported by reoptimization at CCSD/6–31G(d) level and single-point calculation at CCSD(T)/6-311+G(d) level. Hence, they are competitive candidates for the ground-state structure of (TiO2)2-. For TiO2 and (TiO2)3, the calculated VEA and AEA values agree well with the experimental data. For (TiO2)2, the VEA and AEA obtained with the C2v structure agree well with the experimental data while those with the C2h structure do not. The subsequent assignment of PES indicates that it is the C2v isomer of (TiO2)2- that represents the structure from which the photoexcitation in experimental PES takes place. TDDFT is used to determine the excited states of (TiO2)n (n=1–3) and the calculated excitation energies are in good agreement with PES experiment. [ABSTRACT FROM AUTHOR]