Recent Publications

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Singlet fission for quantum information and quantum computing: the parallel JDE model

Singlet fission is a photoconversion process that generates a doubly excited, maximally spin entangled pair... Read more
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The Dynamics of Water in Porous Two-Dimensional Crystals

Porous two-dimensional crystals offer many promises for water desalination applications. For computer simulation to play... Read more
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The Motion of Trapped Holes on Nanocrystal Surfaces

This Perspective discusses the phenomenon of trapped-hole diffusion in colloidal semiconductor nanocrystals. Surface charge-carrier traps... Read more
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Surface-Trapped Hole Diffusion in CdS and CdSe: The Superexchange Mechanism

In contrast to the conventional view that surface-trapped holes in CdS and CdSe nanoparticles are... Read more
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Linear Response Theory for Water Transport Through Dry Nanopores

Porous two-dimensional crystals like graphene have the potential to revolutionize reverse-osmosis membrane technology. The permeability... Read more
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Nanocrystalline Iron Monosulfides Near Stoichiometry

Solids composed of iron and sulfur are earth abundant and nontoxic, and can exhibit interesting... Read more

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art

Singlet fission for quantum information and quantum computing: the parallel JDE model

Singlet fission is a photoconversion process that generates a doubly excited, maximally spin entangled pair state. This state has applications to quantum information and computing that are only beginning to be realized. In this article, we construct and analyze a spin-exciton hamiltonian to describe the dynamics of the two-triplet state...

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Polarizable molecules in the vibrational spectroscopy of water

We examine the role of electronic polarizability in water on short (tens of femtoseconds), intermediate (hundreds of femtoseconds), and long (≈1 ps) time scales by comparing molecular dynamics results to experimental data for vibrational spectroscopy of HOD in liquid D 2 O. Because the OH absorption frequency is sensitive to...

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The subdiffusive targeting problem

Recent experiments in living cells have observed subdiffusive motion, where the mean squared displacement of a molecule grows sublinearly with time as 〈 x 2 〉∼ t α . Motivated by these experiments, we develop a theory for subdiffusion-limited bimolecular enzyme kinetics. As in normal diffusion, the statistics of the...

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Carrier transport in heterojunction nanocrystals under strain

We present a theory for carrier transport in semiconducting nanoscale heterostructures that emphasizes the effects of strain at the interface between two different crystal structures. An exactly solvable model shows that the interface region, or junction, acts as a scattering potential that facilitates charge separation. As a case study, we...

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A microscopic model of singlet fission

Singlet fission, where an electronically excited singlet on one chromophore converts into a doubly excited state on two, has gone from a curiosity in organic photophysics to a potential pathway for increasing solar energy conversion efficiencies. Focusing on the role of solvent-induced energy level fluctuations that would be present in...

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The tunable hydrophobic effect on electrically doped graphene

Using molecular dynamics simulations, we study the hydrophobic effect on electrically doped single layer graphene. With doping levels measured in volts, large changes in contact angle occur for modest voltages applied to the sheet. The effect can be understood as a renormalization of the surface tension between graphene and water...

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Tetracene aggregation on polar and nonpolar surfaces: Implications for singlet fission

In molecular crystals that exhibit singlet fission, quantum yields depend strongly on intermolecular configurations that control the relevant electronic couplings. Here, we explore how noncovalent interactions between molecules and surfaces stabilize intermolecular structures with strong singlet fission couplings. Using molecular dynamics simulations, we studied the aggregation patterns of tetracene molecules...

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Collective aspects of singlet fission in molecular crystals

We present a model to describe collective features of singlet fission in molecular crystals and analyze it using many-body theory. The model we develop allows excitonic states to delocalize over several chromophores which is consistent with the character of the excited states in many molecular crystals, such as the acenes,...

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The Dynamics of Water in Porous Two-Dimensional Crystals

Porous two-dimensional crystals offer many promises for water desalination applications. For computer simulation to play a predictive role in this area, however, one needs to have reliable methods for simulating an atomistic system with hydrodynamic currents and interpretative tools to relate microscopic interactions to emergent macroscopic dynamical quantities, such as...

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The Motion of Trapped Holes on Nanocrystal Surfaces

This Perspective discusses the phenomenon of trapped-hole diffusion in colloidal semiconductor nanocrystals. Surface charge-carrier traps are ubiquitous in nanocrystals and often dictate the fate of photoexcited carriers. New measurements and calculations are unveiling the nature of the nanocrystal surface, but many challenges to understanding the dynamics of trapped carriers remain...

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