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Comparison of molecular dynamics with classical density functional and Poisson-Boltzmann theories of the electric double layer in nanochannels

Journal of Chemical Theory and Computation

Lee, Jonathan W.; Nilson, Robert H.; Templeton, J.A.; Griffiths, Stewart K.; Kung, Andy; Wong, Bryan M.

Comparisons are made among Molecular Dynamics (MD), Classical Density Functional Theory (c-DFT), and Poisson-Boltzmann (PB) modeling of the electric double layer (EDL) for the nonprimitive three component model (3CM) in which the two ion species and solvent molecules are all of finite size. Unlike previous comparisons between c-DFT and Monte Carlo (MC), the present 3CM incorporates Lennard-Jones interactions rather than hard-sphere and hard-wall repulsions. c-DFT and MD results are compared over normalized surface charges ranging from 0.2 to 1.75 and bulk ion concentrations from 10 mM to 1 M. Agreement between the two, assessed by electric surface potential and ion density profiles, is found to be quite good. Wall potentials predicted by PB begin to depart significantly from c-DFT and MD for charge densities exceeding 0.3. Successive layers are observed to charge in a sequential manner such that the solvent becomes fully excluded from each layer before the onset of the next layer. Ultimately, this layer filling phenomenon results in fluid structures, Debye lengths, and electric surface potentials vastly different from the classical PB predictions. © 2012 American Chemical Society.

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TYPE Journal Article YEAR 2012
ScopusOSTIDOI

Rational design and synthesis of semi-conducting polymers

Cordaro, Joseph G.; Wong, Bryan M.

A rational approach was used to design polymeric materials for thin-film electronics applications, whereby theoretical modeling was used to determine synthetic targets. Time-dependent density functional theory calculations were used as a tool to predict the electrical properties of conjugated polymer systems. From these results, polymers with desirable energy levels and band-gaps were designed and synthesized. Measurements of optoelectronic properties were performed on the synthesized polymers and the results were compared to those of the theoretical model. From this work, the efficacy of the model was evaluated and new target polymers were identified.

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TYPE Conference YEAR 2010
OSTI

A long-range electric field solver for molecular dynamics of fluid-solid interfaces based on atomistic-to-continuum modeling

Templeton, J.A.; Jones, Reese E.; Zimmerman, Jonathan A.; Wong, Bryan M.

Understanding charge transport processes at a molecular level using computational techniques is currently hindered by a lack of appropriate models for incorporating anisotropic electric fields, as occur at charged fluid/solid interfaces, in molecular dynamics (MD) simulations. In this work, we develop a model for including electric fields in MD using an atomistic-to-continuum framework. Our model represents the electric potential on a finite element mesh satisfying a Poisson equation with source terms determined by the distribution of the atomic charges. The method is verified using simulations where analytical solutions are known or comparisons can be made to existing techniques. A Calculation of a salt water solution in a silicon nanochannel is performed to demonstrate the method in a target scientific application.

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TYPE Conference YEAR 2010
OSTI

LDRD final report : energy conversion using chromophore-functionalized carbon nanotubes

Leonard, Francois; Wong, Bryan M.; Krafcik, Karen; Zifer, Thomas; Katzenmeyer, Aaron M.; Kane, Alexander

With the goal of studying the conversion of optical energy to electrical energy at the nanoscale, we developed and tested devices based on single-walled carbon nanotubes functionalized with azobenzene chromophores, where the chromophores serve as photoabsorbers and the nanotube as the electronic read-out. By synthesizing chromophores with specific absorption windows in the visible spectrum and anchoring them to the nanotube surface, we demonstrated the controlled detection of visible light of low intensity in narrow ranges of wavelengths. Our measurements suggested that upon photoabsorption, the chromophores isomerize to give a large change in dipole moment, changing the electrostatic environment of the nanotube. All-electron ab initio calculations were used to study the chromophore-nanotube hybrids, and show that the chromophores bind strongly to the nanotubes without disturbing the electronic structure of either species. Calculated values of the dipole moments supported the notion of dipole changes as the optical detection mechanism.

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TYPE SAND Report YEAR 2010
DOIOSTI
Results 1–50 of 66
Results 1–50 of 66