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Jang Y.,ETH Zurich | Varetto U.,Swiss National Supercomputing Center
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2010

Simulation and computation in chemistry studies have improved as computational power has increased over recent decades. Many types of chemistry simulation results are available, from atomic level bonding to volumetric representations of electron density. However, tools for the visualization of the results from quantum-chemistry computations are still limited to showing atomic bonds and isosurfaces or isocontours corresponding to certain isovalues. In this work, we study the volumetric representations of the results from quantum-chemistry computations, and evaluate and visualize the representations directly on a modern graphics processing unit without resampling the result in grid structures. Our visualization tool handles the direct evaluation of the approximated wavefunctions described as a combination of Gaussian-like primitive basis functions. For visualizations, we use a slice-based volume-rendering technique with a two-dimensional transfer function, volume clipping and illustrative rendering in order to reveal and enhance the quantum-chemistry structure. Since there is no need to resample the volume from the functional representations for the volume rendering, two issues, data transfer and resampling resolution, can be ignored; therefore, it is possible to explore interactively a large amount of different information in the computation results. © 2010 International Union of Crystallography Printed in Singapore - all rights reserved. Source


News Article
Site: http://www.nanotech-now.com/

Abstract: All materials are made up of atoms, which vibrate. These vibrations, or 'phonons', are responsible, for example, for how electric charge and heat is transported in materials. Vibrations of metals, semiconductors, and insulators in are well studied; however, now materials are being nanosized to bring better performance to applications such as displays, sensors, batteries, and catalytic membranes. What happens to vibrations when a material is nanosized has until now not been understood. Soft Surfaces Vibrate Strongly In a recent publication in Nature, ETH Professor Vanessa Wood and her colleagues explain what happens to atomic vibrations when materials are nanosized and how this knowledge can be used to systematically engineer nanomaterials for different applications. The paper shows that when materials are made smaller than about 10 to 20 nanometers -- that is, 5,000 times thinner than a human air -- the vibrations of the outermost atomic layers on surface of the nanoparticle are large and play an important role in how this material behaves. "For some applications, like catalysis, thermoelectrics, or superconductivity, these large vibrations may be good, but for other applications like LEDs or solar cells, these vibrations are undesirable," explains Wood. Indeed, the paper explains why nanoparticle-based solar cells have until now not met their full promise. The researchers showed using both experiment and theory that surface vibrations interact with electrons to reduce the photocurrent in solar cells. "Now that we have proven that surface vibrations are important, we can systematically design materials to suppress or enhance these vibrations," say Wood. Improving Solar Cells Wood's research group has worked for a long time on a particular type of nanomaterial -- colloidal nanocrystals -- semiconductors with a diameter of 2 to 10 nanometers. These materials are interesting because their optical and electrical properties are dependent on their size, which can be easily changed during their synthesis. These materials are now used commercially as red- and green-light emitters in LED-based TVs and are being explored as possible materials for low cost, solution-processed solar cells. Researchers have noticed that placing certain atoms around the surface of the nanocrystal can improve the performance of solar cells. The reason why this worked had not been understood. The work published in the Nature paper now gives the answer: a hard shell of atoms can suppress the vibrations and their interaction with electrons. This means a higher photocurrent and a higher efficiency solar cell. Big Science to Study the Nanoscale Experiments were conducted in Professor Wood's labs at ETH Zurich and at the Swiss Spallation Neutron Source at the Paul Scherrer Institute. By observing how neutrons scatter off atoms in a material, it is possible to quantify how atoms in a material vibrate. To understand the neutron measurements, simulations of the atomic vibrations were run at the Swiss National Supercomputing Center (CSCS) in Lugano. Wood says, "without access to these large facilities, this work would not have been possible. We are incredibly fortunate here in Switzerland to have these world class facilities." For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


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Site: http://www.cemag.us/rss-feeds/all/rss.xml/all

All materials are made up of atoms, which vibrate. These vibrations, or "phonons", are responsible, for example, for how electric charge and heat is transported in materials. Vibrations of metals, semiconductors, and insulators in are well studied; however, now materials are being nanosized to bring better performance to applications such as displays, sensors, batteries, and catalytic membranes. What happens to vibrations when a material is nanosized has until now not been understood. In a recent publication in Nature, ETH Zürich Professor Vanessa Wood and her colleagues explain what happens to atomic vibrations when materials are nanosized and how this knowledge can be used to systematically engineer nanomaterials for different applications. The paper shows that when materials are made smaller than about 10 to 20 nanometers — that is, 5,000 times thinner than a human air — the vibrations of the outermost atomic layers on surface of the nanoparticle are large and play an important role in how this material behaves. “For some applications, like catalysis, thermoelectrics, or superconductivity, these large vibrations may be good, but for other applications like LEDs or solar cells, these vibrations are undesirable,” explains Wood. Indeed, the paper explains why nanoparticle-based solar cells have until now not met their full promise. The researchers showed using both experiment and theory that surface vibrations interact with electrons to reduce the photocurrent in solar cells. “Now that we have proven that surface vibrations are important, we can systematically design materials to suppress or enhance these vibrations,” says Wood. Wood’s research group has worked for a long time on a particular type of nanomaterial — colloidal nanocrystals — semiconductors with a diameter of 2 to 10 nanometers. These materials are interesting because their optical and electrical properties are dependent on their size, which can be easily changed during their synthesis. These materials are now used commercially as red- and green-light emitters in LED-based TVs and are being explored as possible materials for low cost, solution-processed solar cells. Researchers have noticed that placing certain atoms around the surface of the nanocrystal can improve the performance of solar cells. The reason why this worked had not been understood. The work published in the Nature paper now gives the answer: a hard shell of atoms can suppress the vibrations and their interaction with electrons. This means a higher photocurrent and a higher efficiency solar cell. Experiments were conducted in Wood’s labs at ETH Zurich and at the Swiss Spallation Neutron Source at the Paul Scherrer Institute. By observing how neutrons scatter off atoms in a material, it is possible to quantify how atoms in a material vibrate. To understand the neutron measurements, simulations of the atomic vibrations were run at the Swiss National Supercomputing Center (CSCS) in Lugano. Wood says, “without access to these large facilities, this work would not have been possible. We are incredibly fortunate here in Switzerland to have these world class facilities.”


News Article
Site: http://www.materialstoday.com/news/

Materials are made up of atoms that vibrate, and these vibrations, or 'phonons', are responsible for how electric charge and heat is transported in the materials. Atomic vibrations in metals, semiconductors and insulators are well studied, but what happens to atomic vibrations when a material is nanosized is far less well understood. In a recent paper in Nature, Vanessa Wood at ETH Zurich in Switzerland and her colleagues explain what happens to atomic vibrations when materials are nanosized and how this knowledge can be used to systematically engineer nanomaterials for different applications. Their paper shows that for nanomaterials smaller than about 10–20nm the vibrations of the outermost atomic layers at the surface of the nanomaterial are comparatively large and play an important role in how it behaves. "For some applications, like catalysis, thermoelectrics or superconductivity, these large vibrations may be good, but for other applications like LEDs or solar cells, these vibrations are undesirable," explains Wood. Indeed, the paper helps to explain why nanoparticle-based solar cells have until now not reached their full potential. The researchers showed using both experiment and theory that these surface vibrations interact with electrons to reduce the photocurrent in solar cells. "Now that we have proven that surface vibrations are important, we can systematically design materials to suppress or enhance these vibrations," says Wood. Wood's research group has worked for some time on a particular type of nanomaterial known as colloidal nanocrystals, which are semiconductors with a diameter of 2–10nm. These materials are interesting because their optical and electrical properties are dependent on their size, which can be easily changed during their synthesis. Colloidal nanocrystals are already being used commercially as emitters of red and green light in LED-based TVs and are also being explored as possible materials for low cost, solution-processed solar cells. Researchers have noticed that placing certain atoms around the surface of the nanocrystals can improve the performance of the solar cells, but the reason why this works has not been understood. The work published in the Nature paper now provides the answer: a hard shell of atoms can suppress the surface vibrations and their interaction with electrons, producing a higher photocurrent and a higher efficiency solar cell. The experiments were conducted in Wood's labs at ETH Zurich and at the Swiss Spallation Neutron Source at the Paul Scherrer Institute, also in Switzerland. By observing how neutrons scatter off atoms in a material, it is possible to quantify how the atoms in a material vibrate. To understand the neutron measurements, simulations of the atomic vibrations were run at the Swiss National Supercomputing Center in Lugano. "Without access to these large facilities, this work would not have been possible," says Wood. "We are incredibly fortunate here in Switzerland to have these world-class facilities." This story is adapted from material from ETH Zurich, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


News Article
Site: http://phys.org/nanotech-news/

Researchers at ETH have shown for the first time what happens to atomic vibrations when materials are nanosized and how this knowledge can be used to systematically engineer nanomaterials for different applications. Using both experiment, simulation, and theory, they explain how and why vibriations at the surface of a nanomaterial (q) can interact strongly with electrons (k and k'). Credit: Deniz Bozyigit / ETH Zurich All materials are made up of atoms, which vibrate. These vibrations, or 'phonons', are responsible, for example, for how electric charge and heat is transported in materials. Vibrations of metals, semiconductors, and insulators in are well studied; however, now materials are being nanosized to bring better performance to applications such as displays, sensors, batteries, and catalytic membranes. What happens to vibrations when a material is nanosized has until now not been understood. In a recent publication in Nature, ETH Professor Vanessa Wood and her colleagues explain what happens to atomic vibrations when materials are nanosized and how this knowledge can be used to systematically engineer nanomaterials for different applications. The paper shows that when materials are made smaller than about 10 to 20 nanometers—that is, 5,000 times thinner than a human air—the vibrations of the outermost atomic layers on surface of the nanoparticle are large and play an important role in how this material behaves. "For some applications, like catalysis, thermoelectrics, or superconductivity, these large vibrations may be good, but for other applications like LEDs or solar cells, these vibrations are undesirable," explains Wood. Indeed, the paper explains why nanoparticle-based solar cells have until now not met their full promise. The researchers showed using both experiment and theory that surface vibrations interact with electrons to reduce the photocurrent in solar cells. "Now that we have proven that surface vibrations are important, we can systematically design materials to suppress or enhance these vibrations," say Wood. Wood's research group has worked for a long time on a particular type of nanomaterial—colloidal nanocrystals—semiconductors with a diameter of 2 to 10 nanometers. These materials are interesting because their optical and electrical properties are dependent on their size, which can be easily changed during their synthesis. These materials are now used commercially as red- and green-light emitters in LED-based TVs and are being explored as possible materials for low cost, solution-processed solar cells. Researchers have noticed that placing certain atoms around the surface of the nanocrystal can improve the performance of solar cells. The reason why this worked had not been understood. The work published in the Nature paper now gives the answer: a hard shell of atoms can suppress the vibrations and their interaction with electrons. This means a higher photocurrent and a higher efficiency solar cell. Experiments were conducted in Professor Wood's labs at ETH Zurich and at the Swiss Spallation Neutron Source at the Paul Scherrer Institute. By observing how neutrons scatter off atoms in a material, it is possible to quantify how atoms in a material vibrate. To understand the neutron measurements, simulations of the atomic vibrations were run at the Swiss National Supercomputing Center (CSCS) in Lugano. Wood says, "without access to these large facilities, this work would not have been possible. We are incredibly fortunate here in Switzerland to have these world class facilities." More information: Deniz Bozyigit et al. Soft surfaces of nanomaterials enable strong phonon interactions, Nature (2016). DOI: 10.1038/nature16977

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