Molecular dynamics study of the stability of a carbon nanotube atop a catalytic nanoparticle

The stability of a single-walled carbon nanotube placed on top of a catalytic nickel nanoparticle is investigated by means of molecular dynamics simulations. As a case study, we consider the $(12,0)$ nanotube consisting of 720 carbon atoms and the icosahedral Ni$_{309}$ cluster. An explicit set of constant-temperature simulations is performed in order to cover a broad temperature range from 400 to 1200 K, at which a successful growth of carbon nanotubes has been achieved experimentally by means of chemical vapor deposition. The stability of the system depending on parameters of the involved interatomic interactions is analyzed. It is demonstrated that different scenarios of the nanotube dynamics atop the nanoparticle are possible depending on the parameters of the Ni-C potential. When the interaction is weak the nanotube is stable and resembles its highly symmetric structure, while an increase of the interaction energy leads to the abrupt collapse of the nanotube in the initial stage of simulation. In order to validate the parameters of the Ni-C interaction utilized in the simulations, DFT calculations of the potential energy surface for carbon-nickel compounds are performed. The calculated dissociation energy of the Ni-C bond is in good agreement with the values, which correspond to the case of a stable and not deformed nanotube simulated within the MD approach.Comment: 11 pages, 5 figures; submitted to Eur. Phys. J.

Parity Doublet Model applied to Neutron Stars

The Parity doublet model containing the SU(2) multiplets including the baryons identified as the chiral partners of the nucleons is applied for neutron star matter. The chiral restoration is analyzed and the maximum mass of the star is calculated.Comment: Proceeding to the conference International Symposium on Exotic States of Nuclear Matte

Modelling Hybrid Stars in Quark-Hadron Approaches

The density in the core of neutron stars can reach values of about 5 to 10 times nuclear matter saturation density. It is, therefore, a natural assumption that hadrons may have dissolved into quarks under such conditions, forming a hybrid star. This star will have an outer region of hadronic matter and a core of quark matter or even a mixed state of hadrons and quarks. In order to investigate such phases, we discuss different model approaches that can be used in the study of compact stars as well as being applicable to a wider range of temperatures and densities. One major model ingredient, the role of quark interactions in the stability of massive hybrid stars is discussed. In this context, possible conflicts with lattice QCD simulations are investigated.Comment: Contribution to the EPJA Topical Issue on "Exotic Matter in Neutron Stars

Modeling Hybrid Stars

We study the so called hybrid stars, which are hadronic stars that contain a core of deconfined quarks. For this purpose, we make use of an extended version of the SU(3) chiral model. Within this approach, the degrees of freedom change naturally from hadrons (baryon octet) to quarks (u, d, s) as the temperature and/or density increases. At zero temperature we are still able to reproduce massive stars, even with the inclusion of hyperons.Comment: To appear in the proceedings of Conference C12-08-0