Simulations in Chemical and Condensed Matter Physics
This group studies a variety of complex many body systems providing insight at many length and time scales into the collective phenomena of interest. A current focus is on abstracted models of interacting polymer systems far from equilibrium in which they are accumulating data on the statisitcal distribution of chemical morphologies and dynamics. These models are intended to provide better understanding of how dynamic metastable states involving large molecules can emerge from a starting configuration of small molecules as is believed to have occurred in the origin of life. The researchers have studied a "well mixed reactor" version of such a model and are currently studying an extension in which spatial heterogeneity and diffusion can occur. Studies of the detailed morphological and dynamic character of the well mixed model also continue. Simulations using more chemically realistic descriptions of the atomic level are also planned.
A second focus is on the behavior of oxide water interfaces using in-house self consistent tightbinding codes. There is tremendous current interest in oxides as electrodes in a variety of technologies using aqueous electrolytes including fuel cells, batteries and electrolysers. Water-oxide interfaces are also a key component in corroding metal surfaces so such studies are also relevant to attempts to understand and inhibit corrosion. In one project the researchers are simulating at titania water interfaces with particular emphasis on new methods for calculating surface energies to understand the propensity of titania water interfaces to dissociate water. This project is a collaboration with former student Patrick Schelling, now an associate professor at the University of Central Florida, and his students. A second project in this category is a simulation of the magnetite water interface. In addition to its obvious corrosion relevance, the study is intended to provide better understanding of the mechanisms of water dissociation at a magnetite water interface, as occurs in experiments which the group is doing on the use of magnetite electrodes in electrolysers for production of gaseous hydrogen as an energy storage medium. This project is a collaboration with Professor Melissa Eblen of the Carleton College Physics Department, the Natural Resources Research Institute in Duluth, and high school physics teacher Jon Huber, who worked with the Halley Group in the Research Experiences for Teachers program at Minnesota in summer 2015 and continues experiments with students in Burnsville. In a third related project the researchers are beginning molecular dynamics simulations of membrane proteins in water at various solid aqueous interfaces. The aim is to explore the possible use of such membrane proteins to solve certain technical problems associated with the behavior of lithium-based electrodes in water in applications to batteries. This is a preliminary exploratory collaboration with Jonathan Sachs of the Department of Biomedical Engineering.
Thirdly the group simulates quantum fluid phenomena. A current emphasis is on condensate mediated transmission using Diffusion Monte Carlo methods to obtain informaton about excited scattering states in the strongly interacting helium four superfluid. The methods are unique and were developed in this group. They have published results in Physical Review B using a guiding wave function which did not conserve particle current. The current project is to use an improved guiding wave function which removes that defect. The project is relevant to an experiment they proposed more than a decade ago and which has been tried in various laboratories, still without a definitive result, to observe the condensate mediated transmission effect. Another quantum fluids project, carried on at a low intensity level, is the exploration of effects of disorder, and in particular of disorder induced pairing, in superconductors.
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