Using density-functional calculations, we investigate the structural and magnetic properties of ultrathin Gd and Gd-carbide nanowires (NWs) encapsulated in narrow carbon nanotubes (CNTs). The equilibrium geometry of an encapsulated (2 x 2) Gd-NW is markedly different from that of bulk Gd crystals. The charge-density analysis shows pronounced spin-dependent electron transfer in the encapsulated Gd-NW in comparison with that of Gd-carbide NWs. We conclude that Gd-CNT hybridization is primarily responsible for both the structural difference and electron transfer in the encapsulated Gd-NW.

Elastic properties of prototypical CO2 polymorphs under compression are essential to understanding the nature of their pressure-induced structural changes. Despite the fundamental importance in physical chemistry and condensed matter physics and geophysical implications for the nature of fluids in the Earth and planetary interiors, the elastic properties of these polymorphs are not fully understood because of intrinsic uncertainty and difficulties in experimental estimation of elasticity. Theoretical calculations of elastic properties of high-pressure CO2 polymorphs allow us to reveal the previously unknown details of elasticity of the diverse polymorphs under extreme compression. As a step toward getting insights into the deep carbon cycle, we carried out density-functional-theory calculations and investigated the elastic constants, bulk modulus, shear modulus, Poisson ratios and acoustic wave velocities of CO2 polymorphs: II (tetragonal, P42/mnm), β-cristobalite-like V (VCR, tetragonal, I4̅2d) and tridymite-like V (VTD, orthorhombic, P2 12121) up to approximately 40 GPa. Particularly, the elastic properties and bulk moduli of all the three CO2 phases except the elastic constants of CO2–II are the first calculation results, and the elastic constants and bulk modulus calculated for CO2–II are improved. The change in elastic properties with varying pressure shows distinct trends among CO2–II, CO2–VCR, and CO2–VTD. Despite these differences, the bulk moduli for CO2 of phases I, II, VCR and VTD exhibit a gradual increase with increasing density without major discontinuity. On the basis of the calculated elastic properties of CO2–II, CO2–VCR, and CO2–VTD and a comparison between these CO2 units and SiO2 materials, we suggest that these polymorphs may be classified into two groups: (1) a weakly connected group: CO2–II, cristobalite, and tridymite and (2) a strongly connected group: CO2–VCR, CO2–VTD, and stishovite. This classification does not depend on crystal symmetry. The bulk modulus of a CO2 solid is greater than that of a SiO2 solid of the same density, and the shear modulus of a CO2 solid is smaller than that of a SiO2 solid of the same density. The elasticity of CO2 polymorphs shown here may hold some promise for investigating the elasticity of diverse solids consisting of oxide molecules under extreme pressure.

Metal atoms on graphene, when ionized, can act as a point-charge impurity to probe a charge response of graphene with the Dirac cone band structure. To understand the microscopic physics of the metal-atom-induced charge and spin polarization in graphene, we present scanning tunneling spectroscopy ͑STS͒ simulations based on density-functional theory calculations. We find that a Cs atom on graphene is fully ionized with a significant band-bending feature in the STS whereas the charge and magnetic states of Ba and La atoms on graphene appear to be complicated due to orbital hybridization and Coulomb interaction. By applying external electric field, we observe changes in charge donations and spin magnetic moments of the metal adsorbates on graphene.

The structural modifications in oxide glasses under extreme compression may account for the pressure‐induced increase in their mechanical toughness and rigidity, rendering potential for technological applications of the compressed glasses. High‐resolution solid‐state nuclear magnetic resonance has provided a structural information regarding glasses by identifying how nuclear spins behave and interact with nearby elements. However, knowledge of nuclear spins resonance in oxide glasses under extreme pressure above 1 million atmospheres has not been available, making the origins of glass densification illusive. In this article, ab initio calculations of prototypical magnesium silicate glasses quantify how structural changes in glasses affect the nature of nuclear spin interactions at high pressure beyond megabars. The calculated results establish novel correlations between pressure‐induced evolution of atomic structures, such as oxygen and cation coordination numbers, bond angle and lengths, and structurally relevant nuclear magnetic resonance parameters for Mg, Si, and O in compressed oxide glasses above megabar pressures. The established correlations highlight that the nuclear spins in glasses can serve as a new indicator to the extreme densification paths. Pressure‐induced dispersion in nuclear spin parameters also reveals an overall increase in the topological entropy. This entropy gain may weaken glasses at an elevated pressure conditions, accounting for potential softening of the compressed glasses. The proposed relationships open a new window to the evolution of diverse complex glasses under extreme stress and compression with high‐resolution solid‐state nuclear magnetic resonance.

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