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Department of Chemistry
University of North Dakota
151 Cornell Street Stop 9024
Grand Forks, ND 58202
    Our research is in the field of molecular modeling and simulation. More specifically, we are interested in developing and using molecular simulation methods, such as Monte Carlo methods, equilibrium and nonequilibrium molecular dynamics simulations, ab initio calculations, to analyze and understand the microscopic mechanisms underlying various nonequilibrium processes. Our recent research focuses on understanding and controlling polymorphism during crystallization. This is one of the long-standing challenges in solid-state chemistry. Polymorphism denotes the ability of a molecule to crystallize in more than one structure or packing arrangement. This phenomenon has broad practical implications for a number of industries, ranging from pharmaceuticals (drugs) to textiles (dyes and pigments) or defense (energetic materials). More generally, we develop an understanding of self-assembly on the nanoscale (studying the formation of metal and semiconductor nanoparticles or of systems of biological interest) and of transport on the nanoscale (studying the conductivity and viscosity of liquids confined in nanopores).


* Unraveling the interplay between thermodynamics and kinetics during the nucleation and growth of semiconductor, metal and molecular nanoparticles.
Sponsor: NSF CAREER Award DMR-1052808
Collaborations: Prof. L. Yu, School of Pharmacy, University of Wisconsin-Madison
      Prof. B. Garetz, Chemical and Biomolecular Engineering, NYU-Poly


Because of their size, intermediate between the dimensions of atoms and of bulk matter, nanoscale materials often exhibit very unique properties. One needs, however, to be able to control the properties of nanomaterials, such as e.g. their crystalline structure, to fully harness the powerful properties of these materials. While physicists and synthetic chemists have developed many successful strategies to this end, a complete understanding of the molecular mechanisms underlying the formation of nanomaterials has remained elusive so far. The aim of our work is two-fold. Our first goal is to elucidate these mechanisms. For this purpose, we use simulation methods appropriate for the sampling of rare events (umbrella sampling, transition path sampling methods) to simulate the crystal nucleation process. Once the critical nucleus is obtained, we simulate its growth using conventional molecular dynamics simulations. Throughout nucleation and growth, using, and developing, when necessary, appropriate order parameters, we identify how and when the selection of a specific crystalline structure (or polymorph) takes place.


* Rheology of liquid metals: equilibrium and transient-time correlation function nonequilibrium molecular dynamics simulations.
Sponsors: ACS PRF #44997-G10, NSF EPSCoR
Collaborations: Prof. D. J. Evans, Research School of Chemistry, Australian National University
      Prof. P. T. Cummings, Department of Chemical Engineering, Vanderbilt University


The knowledge of the transport properties are essential to understand the behavior of liquids and supercooled liquids. These properties are important in a wide range of applications, from biological systems to materials processing. Nonequilibrium molecular dynamics (NEMD) simulations provides a direct access to the microscopic structural changes induced by the applied shear rate. It is therefore a valuable tool to understand how the structure and in turn the transport properties of liquids are affected by shear. However, conventional NEMD methods only allow one to study systems subjected to very large shear rates, several orders of magnitude larger than the experimentally accessible rates. These methods only provide insight into the non-Newtonian behavior of liquids. We develop new simulation methods, based on the transient-time correlation function formalism, to shed light on these properties at experimentally accessible shear rates both for bulk and nanoconfined systems.

 
* Understanding the partioning behavior of elements during iron meterorite formation.
Sponsor: ND NASA EPSCoR
Collaboration: Dr. N. L. Chabot, Applied Physics Laboratory, Johns Hopkins University


Planetary materials research provides a unique approach to investigating our solar system and yields insights that would not be possible from remote observations alone. Samples of planetary materials from multiple bodies in our solar system can be examined in detail in the laboratory and as a result unravel their history. Light elements, like phosphorous, are known to have significant roles in the formation of asteroidal cores. In particular, these element influence the partitioning of siderophile trace elements and form a variety of inclusions common to iron meteorites. The aim of our research is to gain insight into the partitioning behavior of elements during iron meteorite formation by combining both theoretical and experimental efforts. This consists in carrying out classical molecular simulations on large-scale Fe-Ni-P system to (i) examine the effect of P on solidmetal/liquid metal partitioning behavior of 8 elements (Ag, As, Cu, Ga, Ge, Pd, Pt, Si,) and to (ii) explore the effect of the crystal structures of Fe alloys on partitioning behavior. The theoretical results are then compared to the predictions of current models, based on metallurgical experiments on the fractional crystallization of metallic melts.


* Adsorption and storage of environmental pollutants in carbon nanotubes and porous materials.
Sponsor: NSF EPSCoR


We use molecular simulations to shed light on the adsorption and storage of environmental pollutants in carbon nanotubes and nanoporous materials such as metal-organic frameworks. The two key features of our research are the new force field, developed to model the differnet environmental pollutants (CO2, PCBs, PAHs,...), and the new simulation methods, developed to assess the thermodynamic properties of these pollutants in the bulk as well as for confined fluids. Specific objectives include: (i) the development of a force field leading to accurate predictions of the vapor pressure and partition coefficients (ii) the generation of a database for the thermophysical properties of these pollutants to complement the few available experimental data, (iii) the thermodynamic analysis of the adsorption process from the air and from aqueous solutions. The findings, resulting from the proposed research, will suggest how to improve the capture of organic pollutants and could be potentially transformative in addressing the needs of the community for a cleaner environment.