Mini Review: Quantum Confinement of Atomic and Molecular Clusters in Carbon Nanotubes

Superfluid helium droplet-mediated surface-deposition of neutral and charged silver atomic species

Experimental and theoretical work has delivered evidence of the helium nanodroplet-mediated synthesis and soft-landing of metal nanoparticles, nanowires, clusters, and single atoms on solid supports. Recent experimental advances have allowed the formation of charged metal clusters into multiply charged helium nanodroplets. The impact of the charge of immersed metal species in helium nanodroplet-mediated surface deposition is proved by considering silver atoms and cations at zero-temperature graphene as the support. By combining high-level ab initio intermolecular interaction theory with a full quantum description of the superfluid helium nanodroplet motion, evidence is presented that the fundamental mechanism of soft-deposition is preserved in spite of the much stronger interaction of charged species with surfaces, with high-density fluctuations in the helium droplet playing an essential role in braking them. Corroboration is also presented that the soft-landing becomes favored as the helium nanodroplet size increases.

Structures and Stabilities of Carbon Chain Clusters Influenced by Atomic Antimony

The C-C bond lengths of the linear magnetic neutral C_nSb, C_nSb⁺ cations and C_nSb^- anions are within 1.255-1.336 Å, which is typical for cumulene structures with moderately strong double-bonds. In this report, we found that the adiabatic ionization energy (IE) of C_nSb decreased with n. When comparing the IE~n relationship of C_nSb with that of pure C_n, we found that the latter exhibited a stair-step pattern (n ≥ 6), but the IE~n relationship of C_nSb chains took the shape of a flat curve. The IEs of C_nSb were lower than those of corresponding pure carbon chains. Different from pure carbon chains, the adiabatic electron affinity of C_nSb does not exhibit a parity effect. There is an even-odd alternation for the incremental binding energies of the open chain C_nSb (for n = 1-16) and C_nSb⁺ (n = 1-10, when n > 10, the incremental binding energies of odd (n) chain of C_nSb⁺ are larger than adjacent clusters). The difference in the incremental binding energies between the even and odd chains of both C_nSb and pure C_n diminishes with the increase in n. The incremental binding energies for C_nSb^- anions do not exhibit a parity effect. For carbon chain clusters, the most favorable binding site of atomic antimony is the terminal carbon of the carbon cluster because the terminal carbon with a large spin density bonds in an unsaturated way. The C-Sb bond is a double bond with Wiberg bond index (WBI) between 1.41 and 2.13, which is obviously stronger for a carbon chain cluster with odd-number carbon atoms. The WBI of all C-C bonds was determined to be between 1.63 and 2.01, indicating the cumulene character of the carbon chain. Generally, the alteration of WBI and, in particular, the carbon chain cluster is consistent with the bond length alteration. However, the shorter C-C distance did not indicate a larger WBI. Rather than relying on the empirical comparison of bond distance, the WBI is a meaningful quantitative indicator for predicting the bonding strength in the carbon chain.

Smolyak Algorithm Adapted to a System-Bath Separation: Application to an Encapsulated Molecule with Large-Amplitude Motions

A Smolyak algorithm adapted to system-bath separation is proposed for rigorous quantum simulations. This technique combines a sparse grid method with the system-bath concept in a specific configuration without limitations on the form of the Hamiltonian, thus achieving a highly efficient convergence of the excitation transitions for the "system" part. Our approach provides a general way to overcome the perennial convergence problem for the standard Smolyak algorithm and enables the simulation of floppy molecules with more than a hundred degrees of freedom. The efficiency of the present method is illustrated on the simulation of H₂ caged in an sII clathrate hydrate including two kinds of cage modes. The transition energies are converged by increasing the number of normal modes of water molecules. Our results confirm the triplet splittings of both translational and rotational (j = 1) transitions of the H₂ molecule. Furthermore, they show a slight increase of the translational transitions with respect to the ones in a rigid cage.