Evolution of the vibrational spectra of doped hydrogen clusters with pressure.

The evolution of the vibrational spectra of the isoelectronic hydrogen clusters H26, H24He, and H24Li(+) is determined with pressure. We establish the vibrational modes with collective character common to the clusters, identify their individual vibrational fingerprints and discuss frequency shifts in the giga-Pascal pressure region. The results are of interest for the identification of doping elements such as inert He and ionic Li(+) in hydrogen under confinement or, conversely, establish the pressure of doped hydrogen when the vibrational spectrum is known.

Pressure-induced metallization of Li+-doped hydrogen clusters.

Endohedrally encapsulated hydrogen clusters doped with inert helium (H24He) and ionic lithium (H24Li(+)) are investigated. The confinement model is a nanoscopic analogue of the experimental compression of solid hydrogen. The structural and electronic properties of the doped hydrogen clusters are determined under the effects of pressure.

Thermodynamic states of nanoclusters at low pressure and low temperature: the case of 13 H(2).

A confinement model of finite-size systems that embodies an equation of state is presented. The temperature and pressure of the system are obtained from the positions and velocities of the enclosed particles after a number of molecular dynamics simulations. The pressure has static and dynamic (thermal) contributions, extending the Mie-Grüneisen equation of state to include weakly interacting anharmonic oscillators.

Thermal behavior of a 13-molecule hydrogen cluster under pressure.

The thermal behavior of a 13-molecule hydrogen cluster is studied as a function of pressure and temperature using a combination of trajectory and density functional theory simulations. The analysis is performed in terms of characteristic descriptors such as caloric curve, root-mean-square bond length fluctuation, pair correlation function, velocity autocorrelation function, volume thermal expansion, and diffusion coefficients. The discussion addresses on the peculiarities of the transition from the ordered-to-disordered state as exhibited by the cluster under different pressures and temperatures.

Pressure and size effects in endohedrally confined hydrogen clusters.

Density functional theory is used to carry out a systematic study of zero-temperature structural and energy properties of endohedrally confined hydrogen clusters as a function of pressure and the cluster size. At low pressures, the most stable structural forms of (H(2))(n) possess rotational symmetry that changes from C(4) through C(5) to C(6) as the cluster grows in size from n=8 through n=12 to n=15. The equilibrium configurational energy of the clusters increases with an increase of the pressure.