Associate Dean for the Natural Sciences
University of Delaware
202 4 Kent Way
Newark, DE 19716
(b. 1955) B.S., 1979, University of California, Berkeley; M.A., 1981, Ph.D., 1986, Harvard University; Postdoctoral Member of Technical Staff, 1986 – 1988, AT&T Bell Laboratories
My group applies theoretical and computational methods to a wide range of problems in chemistry and materials science. These problems include semiconductor surface chemistry, electron conduction through molecules, solar fuel production, formation of atmospheric aerosols, and solvation in supercritical water. Our work concentrates on problems of current interest to experimenters and many of these projects involve direct collaborations with experimental groups. However, we are primarily interested in predicting new chemistry that has not yet been studied experimentally, or extending our understanding to situations where experiments are not possible. Most of our work involves first-principles electronic structure methods (also known as quantum chemistry), but we generally apply these methods in novel ways, often in combination with other methods.
As an example of our approach, we are currently studying how electrical currents are conducted through organic molecules attached to semiconductor surfaces. Our goal is to support development of materials for new generations of electronic devices, as well as to build a fundamental understanding of electrical conductivity at the atomic scale. The figure illustrates one application in which rows of styrene molecules are bonded to a silicon surface (of which only a small part is shown in the upper figure).
The electrical conductance of these molecules can be measured with a scanning tunneling microscope (STM) and we have developed theoretical tools for predicting how the electrical current measured with STM is related to the molecular structure.For styrene on silicon, we find that the current depends strongly on the orientation of the phenyl ring, so that the molecule at the end of the row has a brighter feature in the STM image (lower figure) than the others. This enhanced conductance at the end of styrene rows has been seen experimentally, but its connection to molecular geometry could only be uncovered with theory. This result suggests that subtle changes in molecular structure can be used to control flow of electrical currents.
In related work, we are studying how the electronic properties of photocatalysts such as zinc gallium oxynitride may be modified by controlling their composition or doping with impurities. The goal is to develop new materials for generating chemical fuels from solar energy.
We also develop new theoretical methods to make useful predictions in regimes that are not accessible to experiment. For example, in collaboration with Prof. Wood, we are developing a new method for modeling solvation energies, combining the ability of molecular dynamics to model the structural variety in solutions and the ability of first-principles calculations to determine accurate energies for those structures. This method has allowed us to predict solvation energies in supercritical water, where other methods fail. Our method can be applied to very high temperatures and pressures, which are important for understanding geochemical and industrial processes, but which cannot be reproduced in the laboratory. We are using the same idea to model the kinetics of aerosol formation, an important process in atmospheric chemistry that contributes to cloud formation and is an essential component in determining the global climate.
- A. M. Shough, D. J. Doren and R. F. Lobo “A Visible Light Photocatalyst: Effects of Vanadium Substitution on ETS-10,” Phys. Chem. Chem. Phys., (2007) 9, 5096.
- L. Yang and D.J. Doren “Structure of Styrene Molecular Lines on Si(100)-2x1:H,” J. Phys. Chem. C, (2008) 112, 781.
- W. Liu, R.H. Wood and D.J. Doren “Sodium Chloride in Supercritical Water as a Function of Density: Potentials of Mean Force and an Equation for the Dissociation Constant from 723 to 1073 K and from 0 to 0.9 g/cm3,” J. Phys. Chem. B, (2008) 112, 7289.
- A.M. Shough, D. J. Doren and D.M. Di Toro “Polyfunctional Methodology for Improved DFT Thermochemical Predictions,” J. Phys. Chem., (2008) 112, 10624.
- A.M. Shough, D.J. Doren and B. Ogunnaike “Transition Metal Substitution in ETS-10: DFT Calculations and a Simple Model for Electronic Structure Prediction,”Chem. Materials, (2009) 21, 1232.
- O. Rahaman, A.C.T. van Duin, V.S. Bryantsev, J.E. Mueller, S.D. Solares, W.A. Goddard and D.J. Doren “Development of a ReaxFF Reactive Force Field for Aqueous Chloride and Copper Chloride,” J. Phys. Chem. A, (2010) 114, 3556.
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