Volume 129, Issue 1, 07 July 2008
Index of content:
Predictive first-principles simulations of strain-induced phenomena at water-silica nanotube interfaces129(2008); http://dx.doi.org/10.1063/1.2953457View Description Hide Description
Via ab initio simulation, we study the behavior of interfaces of water with silicananotubes. We find profound differences between zero and finite tensile strains and between unconfined (exterior) versus confined (interior) water. For these distinct cases, we characterize the fracture dynamics of the silicananotube and the underlying physical mechanisms.
129(2008); http://dx.doi.org/10.1063/1.2955460View Description Hide Description
The band energy differences of solids calculated with screened hybrid density functionals, such as the functional of Heyd–Scuseria–Ernzerhof (HSE), reproduce experimental band gaps with a high degree of accuracy. This unexpected result is here rationalized by observing that band energy differences obtained from generalized Kohn–Sham calculations with screened (short-range) Hartree–Fock–type exchange approach the excitation energies obtained via time-dependent density functional calculations with the corresponding unscreened functional. The latter are expected to be the accurate predictions of the experimental optical absorption spectra. While the optimum screening parameter is system dependent, the HSE standard value of represents a reasonable compromise across diverse systems.
A hierarchical construction scheme for accurate potential energy surface generation: An application to the reaction129(2008); http://dx.doi.org/10.1063/1.2955729View Description Hide Description
We present a hierarchical construction scheme for accurate ab initiopotential energy surface generation. The scheme is based on the observation that when molecular configuration changes, the variation in the potential energy difference between different ab initio methods is much smaller than the variation for potential energy itself. This means that it is easier to numerically represent energy difference to achieve a desired accuracy. Because the computational cost for ab initio calculations increases very rapidly with the accuracy, one can gain substantial saving in computational time by constructing a high accurate potential energy surface as a sum of a low accurate surface based on extensive ab initio data points and an energy difference surface for high and low accuracy ab initio methods based on much fewer data points. The new scheme was applied to construct an accurate ground potential energy surface for the system using the coupled-cluster method and a very large basis set. The constructed potential energy surface is found to be more accurate on describing the resonance states in the and FHD systems than the existing surfaces.
129(2008); http://dx.doi.org/10.1063/1.2955446View Description Hide Description
The composition of filmsgrown on Ge has been studied for different molecular deposition processes and after exposure to ambient air. The stoichiometry, the interaction with moisture, and the interfacial details of the films are shown to be dramatically process dependent.
Femtosecond real-time probing of transition state dynamics in a surface photoreaction: Methyl desorption from on MgO(100)129(2008); http://dx.doi.org/10.1063/1.2953578View Description Hide Description
A novel experimental approach to the investigation of surface adsorbate reactiondynamics is presented. The direct time-resolved monitoring of the surface reaction transition state and product formation dynamics were accomplished via pump-probe mass spectrometry. As an example, methyl iodide molecules adsorbed at submonolayer coverage on an ultrathin magnesia film on Mo(100) were photoexcited to the -band by ultrafast laser pulse irradiation. Employing time-delayed multiphoton ionization the dynamics of the dissociative methyl iodide transition state and of the emerging methyl photoproduct could be detected with femtosecond resolution. The reaction times deduced from the temporal evolution of the methyl ion mass signal indicate a strong interaction of the methyl fragment with the substrate surface prior to desorption.