Gabriel Bester

The mechanism of proton conduction in phosphoric acid

Neat liquid phosphoric acid (H(3)PO(4)) has the highest intrinsic proton conductivity of any known substance and is a useful model for understanding proton transport in other phosphate-based systems in biology and clean energy technologies. Here, we present an ab initio molecular dynamics study that reveals, for the first time, the microscopic mechanism of this high proton conductivity. Anomalously fast proton transport in hydrogen-bonded systems involves a structural diffusion mechanism in which intramolecular proton transfer is driven by specific hydrogen bond rearrangements in the surrounding environment. Aqueous media transport excess charge defects through local hydrogen bond rearrangements that drive individual proton transfer reactions. In contrast, strong, polarizable hydrogen bonds in phosphoric acid produce coupled proton motion and a pronounced protic dielectric response of the medium, leading to the formation of extended, polarized hydrogen-bonded chains. The interplay between these chains and a frustrated hydrogen-bond network gives rise to the high proton conductivity.

Importance of Second-Order Piezoelectric Effects in Zinc-Blende Semiconductors

We show that the piezoelectric effect that describes the emergence of an electric field in response to a crystal deformation in III-V semiconductors such as GaAs and InAs has strong contributions from second-order effects that have been neglected so far. We calculate the second-order piezoelectric tensors using density-functional theory and obtain the piezoelectric field for [111]-oriented In(x)Ga(1-x)As quantum wells of realistic dimensions and concentration x. We find that the linear and the quadratic piezoelectric coefficients have the opposite effect on the field, and for large strains (large In concentration) the quadratic terms even dominate. Thus, the piezoelectric field turns out to be a rare example of a physical quantity for which the first-order and second-order contributions are of comparable magnitude.

Carrier relaxation mechanisms in self-assembled ( In , Ga ) As ∕ Ga As quantum dots: Efficient P → S Auger relaxation of electrons

We calculate the

Excitons, biexcitons, and trions in self-assembled ( In , Ga ) As ∕ Ga As quantum dots: Recombination energies, polarization, and radiative lifetimes versus dot height

P

Theory of excitonic spectra and entanglement engineering in dot molecules.

-shell\char21{}to\char21{}

Interpretation of ab initio total energy results in a chemical language: I. Formalism and implementation into a mixed-basis pseudopotential code

S

Dependence of the electronic structure of self-assembled (In,Ga)As∕GaAs quantum dots on height and composition

-shell decay lifetime

Effective formation energies of atomic defects in D03Fe3Al: an ab-initio study

\ensuremath{\tau}\phantom{\rule{0.2em}{0ex}}(P\ensuremath{\rightarrow}S)

Experimental imaging and atomistic modeling of electron and hole quasiparticle wave functions in InAs/GaAs quantum dots

of electrons in lens-shaped self-assembled

Prediction of an Excitonic Ground State in InAs/InSb Quantum Dots

(\mathrm{In},\mathrm{Ga})\mathrm{As}∕\mathrm{Ga}\mathrm{As}