725 research outputs found
Multiphase density functional theory parameterization of the Gupta potential for silver and gold
The ground state energies of Ag and Au in the face-centered cubic (FCC),
body-centered cubic (BCC), simple cubic (SC) and the hypothetical diamond-like
phase, and dimer were calculated as a function of bond length using density
functional theory (DFT). These energies were then used to parameterize the
many-body Gupta potential for Ag and Au. This parameterization over several
phases of Ag and Au was performed to guarantee transferability of the
potentials and to make them appropriate for studies of related nanostructures.
Depending on the structure, the energetics of the surface atoms play a crucial
role in determining the details of the nanostructure. The accuracy of the
parameters was tested by performing a 2 ns MD simulation of a cluster of 55 Ag
atoms -- a well studied cluster of Ag, the most stable structure being the
icosahedral one. Within this time scale, the initial FCC lattice was found to
transform to the icosahedral structure at room temperature. The new set of
parameters for Ag was then used in a temperature dependent atom-by-atom
deposition of Ag nanoclusters of up to 1000 atoms. We find a deposition
temperature of 500 50 K where low energy clusters are generated,
suggesting an optimal annealing temperature of 500 K for Ag cluster synthesis
Controlled propulsion and separation of helical particles at the nanoscale
Controlling the motion of nano and microscale objects in a fluid environment
is a key factor in designing optimized tiny machines that perform mechanical
tasks such as transport of drugs or genetic material in cells, fluid mixing to
accelerate chemical reactions, and cargo transport in microfluidic chips.
Directed motion is made possible by the coupled translational and rotational
motion of asymmetric particles. A current challenge in achieving directed and
controlled motion at the nanoscale lies in overcoming random Brownian motion
due to thermal fluctuations in the fluid. We use a hybrid lattice-Boltzmann
Molecular Dynamics method with full hydrodynamic interactions and thermal
fluctuations to demonstrate that controlled propulsion of individual
nanohelices in an aqueous environment is possible. We optimize the propulsion
velocity and the efficiency of externally driven nanohelices. We quantify the
importance of the thermal effects on the directed motion by calculating the
P\'eclet number for various shapes, number of turns and pitch lengths of the
helices. Consistent with the experimental microscale separation of chiral
objects, our results indicate that in the presence of thermal fluctuations at
P\'eclet numbers , chiral particles follow the direction of propagation
according to its handedness and the direction of the applied torque making
separation of chiral particles possible at the nanoscale. Our results provide
criteria for the design and control of helical machines at the nanoscale
Biopolymer Filtration in Corrugated Nanochannels
We examine pressure-driven nonequilibrium transport of linear, circular, and star polymers through a nanochannel containing a rectangular pit with full hydrodynamic interactions and thermal fluctuations. We demonstrate that with sufficiently small pressure differences, there is contour length-dependent entropic trapping of the polymer in the pit when the pit and the polymer sizes are compatible. This is due to competition between flow and chain relaxation in the pit, which leads to a nonmonotonic dependence of the polymer mobility on its size and should aid in the design of nanofiltration devices based on the polymer size and shape.Peer reviewe
Comment on ``Passage Times for Unbiased Polymer Translocation through a Narrow Pore''
One of the most fundamental quantities associated with polymer translocation
through a nanopore is the translocation time and its dependence on the
chain length . Our simulation results based on both the bond fluctuation
Monte Carlo and Molecular Dynamics methods confirm the original prediction
, which scales in the same manner as the Rouse relaxation
time of the chain except for a larger prefactor, and invalidates other scaling
claims.Comment: 1+pages, 1 Figure, Minor change
- …