Carbonyl sulphide under strong laser field: time-dependent density functional theory

The first 52 fs of a time evolution of the electron density in OCS after an interaction with an intense sub 10 fs laser pulse are studied using the time-dependent density functional theory. The nuclear motion in this linear trimer is simulated by the classical molecular dynamics method. Laser fields of intensity 10^{13} W/cm^2 and 10^{15} W/cm^2 are used. Details of the laser induced changes of the structure, as well as the ionization rate are sensitive to the applied field intensity and its polarization. It is found that under suitable conditions the OCS molecule bends soon after an interaction with a laser pulse. A deviation from the linear geometry of up to 23.6^\circ and charged ions of up to +3 are observed. The time evolution of electric dipole moments and the time-dependent electron localization function (ELF) are also studied.Comment: pdf (included all figures): http://www.phy.hr/~goranka/Research/LaserOCS.pd

Sulfur-bearing species in molecular clouds

We study several molecules that could help in the solution of the missing sulfur problem in dense clouds and circumstellar regions, as well as in the clarification of the sulfur chemistry in comets. These sulfur molecules are: the trimer (CH2S)3 and the tetramer (CH2S)4 of thioformaldehyde, pentathian S5CH2, hexathiepan S6CH2, thiirane C2H4S, trisulfane HSSSH, and thioacetone (CH3)2CS. Infrared spectra of these species are calculated using density functional theory methods. The majority of calculated bands belong to the mid-infrared, with some of them occurring in the near and far-infrared region. We suggest that some of unidentified spectral features measured by Infrared Space Observatory in several active galactic nuclei and starburst galaxies could be caused by 1,3,5-trithiane ((CH2S)3), 1,3,5,7-tetrathiocane ((CH2S)4), and thiirane (C2H4S). The objects whose unidentified infrared features we compare with calculated bands are: NGC 253, M82, NGC 1068, Circinus, Arp 220, 30 Doradus, Orion KL, and Sgr B2.Comment: accepted for publication in MNRA

Nanometer-scale capacitors

Molecular dynamics computer simulations which employ the embedded-atom potential show that nanowires of gold exist as multishelled structures. We simulate double-walled gold nanowires and calculate the capacitance of a finite nanometer-size cylindrical capacitor. For the sizes for which multishelled nanowires appear in simulations we find the capacitances below one attofarad.Comment: 2 ps and 1 jpg figure

Multi-shell gold nanowires under compression

Deformation properties of multi-wall gold nanowires under compressive loading are studied. Nanowires are simulated using a realistic many-body potential. Simulations start from cylindrical fcc(111) structures at T=0 K. After annealing cycles axial compression is applied on multi-shell nanowires for a number of radii and lengths at T=300 K. Several types of deformation are found, such as large buckling distortions and progressive crushing. Compressed nanowires are found to recover their initial lengths and radii even after severe structural deformations. However, in contrast to carbon nanotubes irreversible local atomic rearrangements occur even under small compressions.Comment: 1 gif figure, 5 ps figure

Melting behavior of ultrathin titanium nanowires

The thermal stability and melting behavior of ultrathin titanium nanowires with multi-shell cylindrical structures are studied using molecular dynamic simulation. The melting temperatures of titanium nanowires show remarkable dependence on wire sizes and structures. For the nanowire thinner than 1.2 nm, there is no clear characteristic of first-order phase transition during the melting, implying a coexistence of solid and liquid phases due to finite size effect. An interesting structural transformation from helical multi-shell cylindrical to bulk-like rectangular is observed in the melting process of a thicker hexagonal nanowire with 1.7 nm diameter.Comment: 4 pages, 4 figure