Schrödinger

About: Schrödinger is a based out in . It is known for research contribution in the topics: Sputtering & Ion. The organization has 1621 authors who have published 2200 publications receiving 81554 citations.

Optical dephasing in semiconductor mixed crystals

Abstract: The influence of disorder and localization on optical dephasing of excitons in the semiconductor mixed crystals ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$ and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As has been investigated by means of time-resolved four-wave mixing and photon echo experiments. A dephasing time of several hundreds of picoseconds is found for resonantly excited localized excitons in ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$ while the dephasing time in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As amounts to only a few picoseconds. In ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$ dephasing results mainly from hopping processes, i.e., exciton-phonon interaction. The contribution of disorder is negligible in terms of phase relaxation in ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$. In contrast, in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As elastic disorder scattering yields an essential contribution to the dephasing rate. We present a theoretical model, which treats dephasing of optical excitations in a disordered semiconductor, including the influence of disorder as well as exciton-phonon interaction. On the base of this model, the experimentally observed differences in the dephasing behavior of excitons in ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$ and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As are related to the microscopic structure of the disorder potential and the mechanism of exciton localization.

Cluster-size dependence of ranges of 100eV/atom Aun clusters

Abstract: Using molecular-dynamics simulation, we determine the ranges of Aun clusters (n = 1, 13, 43, 87, 201, 402) at fixed energy per atom, 100 eV/atom. We study three targets with different bonding properties and mass: a condensed amorphous argon sample, a gold crystal with a (1 0 0) surface and a graphite crystal with a (1 0 0 0) surface. We find that the ranges follow a power law R ∝ nα, where α ≅ 0.3 in a gold target and α ≅ 0.4 in the graphite and argon targets.

Progress in super long loop prediction.

Abstract: Sampling errors are very common in super long loop (referring here to loops that have more than thirteen residues) prediction, simply because the sampling space is vast. We have developed a dipeptide segment sampling algorithm to solve this problem. As a first step in evaluating the performance of this algorithm, it was applied to the problem of reconstructing loops in native protein structures. With a newly constructed test set of 89 loops ranging from 14 to 17 residues, this method obtains average/median global backbone root-mean-square deviations (RMSDs) to the native structure (superimposing the body of the protein, not the loop itself) of 1.46/0.68 A. Specifically, results for loops of various lengths are 1.19/0.67 A for 36 fourteen-residue loops, 1.55/0.75 A for 30 fifteen-residue loops, 1.43/0.80 A for 14 sixteen-residue loops, and 2.30/1.92 A for 9 seventeen-residue loops. In the vast majority of cases, the method locates energy minima that are lower than or equal to that of the minimized native loop, thus indicating that the new sampling method is successful and rarely limits prediction accuracy. Median RMSDs are substantially lower than the averages because of a small number of outliers. The causes of these failures are examined in some detail, and some can be attributed to flaws in the energy function, such as pi-pi interactions are not accurately accounted for by the OPLS-AA force field we employed in this study. By introducing a new energy model which has a superior description of pi-pi interactions, significantly better results were achieved for quite a few former outliers. Crystal packing is explicitly included in order to provide a fair comparison with crystal structures.

Solid-solid phase transitions and phonon softening in an embedded-atom method model for iron

Abstract: We show theoretical results concerning solid-solid phase transitions in Fe induced by pressure at 0 K and by temperature at 0 GPa. One intermediate case for 300 K at 9.8 GPa is also considered. The interatomic potential employed has been shown to be capable of describing the martensite-austenite phase transition in iron. We study the phonon dispersion curves at 0 K, and their variation by pressure. After identifying a soft phonon mode, we determine the transition pressure using several techniques. From molecular-dynamics simulations we obtain the phonon dispersion curves for 0 and 9.8 GPa at 300 K. We also study the phonon softening by temperature. We find the vibrational Gibbs free energy and compare the transition temperature with the value found by using thermodynamic integration. A calculation of the vibrational entropy demonstrates that the inclusion of anharmonicities beyond the quasiharmonic approximation has only a minor effect (10%).