Trapping hydrogen atoms from a neon-gas matrix: A theoretical simulation

Structural and electronic properties of exohedrally doped neutral silicon clusters LnSin (n = 5, 10; Ln = Sm, Eu, Yb)

Lanthanide-doped silicon clusters have been extensively studied in the fields of optoelectronics, magnetism and nanomaterials during the last decade. Herein, systematic structure searches for typical neutral clusters of lanthanide-doped silicon clusters LnSin (n = 5, 10; Ln = Sm, Eu, Yb) have been performed by means of density functional theory coupled with the "stochastic kicking" global search technique. It is found that the Ln atom in LnSin prefers to locate on the surface of Sin to form an exohedral structure, and this exohedral configuration may dominate the nascent structure of LnSin. The spin density and Mulliken population analyses indicate that LnSin clusters possess remarkable magnetic moments (except for YbSin), which are mainly supplied by the Ln 4f electrons (except for Yb). Density of states visually shows the significant spin polarization for open-shell structures of SmSin and EuSin. As for the YbSin (n = 5, 10) system, it has a closed-shell electronic structure with a large HOMO-LUMO gap of 2.72 eV. Bonding analysis, including localized orbital locator and electron density difference, shows that the Si-Si covalent interaction and Sm-Si electrostatic interaction are important for the structural stability of LnSin.

The stability, electronic, and magnetic properties of rare-earth doped silicon-based clusters

The rare-earth doped silicon-based clusters exhibit remarkable structural, physical, and chemical properties, which make them attractive candidates as building units in designing of cluster-based materials with special optical, electronic, and magnetic properties. The structural, stability, electronic, and magnetic properties of pure silicon Si_n + 1 (n = 1-9) and rare-earth doped clusters Si_nEu (n = 1-9) are investigated using the "stochastic kicking" (SK) global search technique combined with density functional theory (DFT) calculations. It was found that: 1) the ground state structures of pure silicon clusters tend to form compact structures rather than cages with the increase of cluster size; 2) the ground state structures for doped species were found to be additional or substitutional sites, and the rare-earth atoms tend to locate on the surface of the silicon clusters; 3) the average binding energy of the doped clusters increased gradually and exhibited the final phenomenon of saturation with the increase of clusters size. The average binding energy of doped clusters was slightly higher than that of pure silicon clusters of the same size, which indicated that the rare-earth atom encapsulated by silicon enhanced the stability of the silicon clusters to some degree; 4) the doped clusters have strong total magnetic moments, which mainly originated from the contribution of rare-earth atoms, whereas the contribution of silicon atoms were almost negligible. As the cluster size increased, the total magnetic moments of binary mixed clusters tended to be stable.

Matrix isolation sublimation: An apparatus for producing cryogenic beams of atoms and molecules

We describe the apparatus to generate cryogenic beams of atoms and molecules based on matrix isolation sublimation. Isolation matrices of Ne and H2 are hosts for atomic and molecular species which are sublimated into vacuum at cryogenic temperatures. The resulting cryogenic beams are used for high-resolution laser spectroscopy. The technique also aims at loading atomic and molecular traps.

Energy and shape relaxation in binary atomic systems with realistic quantum cross sections

We use the spatially homogeneous linear Boltzmann equation to study the time evolution of an initial non-equilibrium distribution function of an ensemble of test particles dilutely dispersed in a background gas at thermal equilibrium. The systems considered are energetic N in He and Xe in He. We employ the quantum mechanical differential cross section to define the collision operator in the Boltzmann equation. The Boltzmann equation is solved with a moment method based on the expansion of the distribution function in the Sonine (Laguerre) polynomials as well as with a direct simulation Monte Carlo method. The moment method provides the approximate eigenvalues and eigenfunctions of the linear Boltzmann collision operator. The reciprocal of the eigenvalues is a measure of the relaxation times to equilibrium. For hard sphere cross sections, the relaxation of the average energy and the shape of the distribution function can be characterized by a single time scale determined by the momentum transfer cross section. We show that this is also the case for realistic quantum cross sections with dominant small angle scattering contributions.