3 research outputs found
TDDFT Assessment of Functionals for Optical 0–0 Transitions in Small Radicals
Using
LR-TDDFT, we calculated the 0–0 energies of 15 small
radicals for which the experimental values in gas phase are available.
We used 17 functionals. It turned out that B3LYP, M06-2X, ωB97X-D,
CAM-B3LYP, and HSE06 functionals are the most effective functionals
in terms of root-mean-square and average unsigned deviation. Using
the standard value (0.47 <i>a</i><sub>0</sub><sup>–1</sup>) of the attenuation parameter
ω, the long-range-corrected LC-GGA functionals give poor results.
However, the LC-PBE with ω = 0.25 <i>a</i><sub>0</sub><sup>–1</sup> give a
performance similar to that of B3LYP. Taking into account zero-point
correction improves the results, but the contribution of adiabatic
correction is more important than that due to the vibration. The vertical
approximation is certainly not recommended. An adiabatic calculation
seems to give a good compromise between computing time (and resources)
and reliability of the results for most of molecules investigated
in this work
Atomistic Mechanisms for the Nucleation of Aluminum Oxide Nanoparticles
A predictive
model for nanoparticle nucleation has not yet been successfully achieved.
Classical nucleation theory fails because the atomistic nature of
the seed has to be considered. Indeed, geometrical structure as well
as stoichiometry do not always match the bulk values. We present a
fully microscopic approach based on a first-principle study of aluminum
oxide clusters. We calculated stable structures of Al<sub><i>x</i></sub>O<sub><i>y</i></sub> and their associated
thermodynamic properties. From these data, the chemical composition
of a gas composed of aluminum and oxygen atoms can be calculated as
a function of temperature, pressure, and aluminum to oxygen ratio.
We demonstrate the accuracy of this approach in reproducing experimental
results obtained with time-resolved spectroscopy of a laser-induced
plasma from an Al<sub>2</sub>O<sub>3</sub> target. We thus extended
the calculation to lower temperatures, i.e., longer time scales, to
propose a scenario of composition gas evolution leading to the first
alumina seeds
Hydrogen-Induced Adsorption of Carbon Monoxide on the Gold Dimer Cation: A Joint Experimental and DFT Investigation
It
is demonstrated, using tandem mass spectrometry and radio frequency
ion trap, that the adsorption of a H atom on the gold dimer cation,
Au<sub>2</sub>H<sup>+</sup>, prevents its dissociation and allows
for adsorption of CO. Reaction kinetics are measured by employing
a radio frequency ion trap, where Au<sub>2</sub><sup>+</sup> and CO
interact for a given reaction time. The effect of a hydrogen atom
is evaluated by comparing reaction rate constants measured for Au<sub>2</sub><sup>+</sup> and Au<sub>2</sub>H<sup>+</sup>. The theoretical
results for the adsorption of CO molecules and their reaction characteristics
with Au<sub>2</sub><sup>+</sup> and Au<sub>2</sub>H<sup>+</sup> are
found to agree with the experimental findings. The joint investigations
provide insights into hydrogen atom adsorption effects and consequent
reaction mechanisms