Revisit of large-gap Si16 clusters encapsulating group-IV metal atoms (Ti, Zr, Hf).

Doped clusters by Si16 cage encapsulating group-IV metal atoms (M@Si16 , M = Ti, Zr and Hf) are computationally investigated by both density functional theory (DFT) and high-level CCSD(T) method. Their low-energy structures are globally searched using a genetic algorithm based on DFT. The ground state structures of neutral and anionic M@Si16 are determined by calculating the vertical and adiabatic detachment energies and comparing them with the experimental data. For neutral Ti@Si16 , the Frank-Kasper (FK) deltahedron with T d symmetry and distorted FK isomer with C3v symmetry are nearly degenerate as the ground state and may coexist in laboratory, while the distorted FK isomer is the most probable structure for Ti@Si16 - anion. For neutral and anionic Zr@Si16 and Hf@Si16 clusters, the ground states at finite temperatures up to 300 K are the fullerene-like D 4d bitruncated square trapezohedron. These theoretical results establish a more complete picture for the most stable structures of M@Si16 clusters, which possess large gaps and may serve as building blocks for electronic and optoelectronic applications.

Evaluation of bonding, electron affinity, and optical properties of M@C28 (M = Zr, Hf, Th, and U): Role of d- and f-orbitals in endohedral fullerenes from relativistic DFT calculations.

The experimentally characterized endohedral metallic fullerenes involving the small C28 cage, has shown to be able to encapsulate zirconium, hafnium, and uranium atoms, among other elements. Here, we explore the formation and nature of concentric bonds from purely d- to f-block elements, given by Zr, Hf, and uranium, along a borderline metal between such blocks, thorium. We explore the interplay of d- and f-orbitals in the chemistry of the early actinides, where the features of a d- or f-block metal can be mixed. Our results indicate that the bonding of Th@C28 involves contributions from both d- and f-type bonds, as characteristic of this early actinide element. Even uranium in U@C28 , also exhibits a contribution from d-type bonds in addition to its relevant f-block character. Electron affinity and optical properties were evaluated to gain more insights into the variation of these molecular properties in this small endohedral fullerene, along Zr, Hf, Th, and U. The current results, allows to unravel the role of (n - 1)d and (n - 2)f orbitals in confined elements ranging from d- to f-blocks, which can be useful to gain a deeper understanding of the bonding situation in other endohedral species. © 2016 Wiley Periodicals, Inc.

Biicosahedral metallaboranes: aromaticity in metal derivatives of three-dimensional analogues of naphthalene.

Consideration of the well-known very stable icosahedral B12H12(2-) as a three-dimensional analogue of benzene was extended by the recent synthesis of the biicosahedral B21H18(-) as a three-dimensional analogue of naphthalene. The preferred structures of metallaboranes derived from B21H18(-) have now been examined by density functional theory. The isoelectronic species CpNiB20H17 and CpCoCB19H17 have the 46 skeletal electrons expected by the Wade-Mingos and Jemmis rules for a structure consisting of two face-sharing fused icosahedra. The CpM units in these structures energetically prefer to be located at a meta vertex of the biicosahedron. The analogous ferraboranes CpFeB20H17 with only 44 skeletal electrons also have related biicosahedral structures. The presence of an agostic hydrogen atom bridging an Fe-B edge compensates for the two-electron deficiency in CpFeB20H17 relative to CpNiB20H17. The nucleus-independent chemical shift (NICS) values of these systems indicate them to be strongly aromatic.

Electronic and magnetic properties of manganese and iron-doped Ga(n)As(n) nanocages (n=7-12).

The electronic and magnetic properties of Mn- or Fe-doped Ga(n)As(n) (n=7-12) nanocages were studied using gradient-corrected density-functional theory considering doping at substitutional, endohedral, and exohedral sites. When doped with one atom, the most energetically favorable site gradually moves from surface (n=7-11) to interior (n=12) sites for the Mn atom, while the most preferred doping site of the Fe atom alternates between the surface (n=7,9,11) and interior (n=8,10,12) sites. All of the ground-state structures of Mn@Ga(n)As(n) have the atomlike magnetic moment of 5mu(B), while the total magnetic moments of the most stable Fe@Ga(n)As(n) cages for each size are about 2mu(B) except for the 4mu(B) magnetic moment of Fe@Ga(12)As(12). Charge transfer and hybridization between the 4s and 3d states of Mn or Fe and the 4s and 4p states of As were found. The antiferromagnetic (AFM) state of Mn(2)@Ga(n)As(n) is more energetically favorable than the ferromagnetic (FM) state. However, for Fe(2)@Ga(n)As(n) the FM state is more stable than the AFM state. The local magnetic moments of Mn and Fe atoms in the Ga(n)As(n) cages are about 4mu(B) and 3mu(B) in the FM and AFM states, respectively. For both Mn and Fe bidoping, the most energetically favorable doping sites of the transition metal atoms are located on the surface of the Ga(n)As(n) cages. The computed magnetic moments of the doped Fe and Mn atoms agree excellently with the theoretical and experimental values in the Fe(Mn)GaAs interface as well as (Ga, Mn)As dilute magnetic semiconductors.