45 research outputs found
Coupling atomistic and continuum hydrodynamics through a mesoscopic model: application to liquid water
We have conducted a triple-scale simulation of liquid water by concurrently
coupling atomistic, mesoscopic, and continuum models of the liquid. The
presented triple-scale hydrodynamic solver for molecular liquids enables the
insertion of large molecules into the atomistic domain through a mesoscopic
region. We show that the triple-scale scheme is robust against the details of
the mesoscopic model owing to the conservation of linear momentum by the
adaptive resolution forces. Our multiscale approach is designed for molecular
simulations of open domains with relatively large molecules, either in the
grand canonical ensemble or under non-equilibrium conditions.Comment: triple-scale simulation, molecular dynamics, continuum, wate
Comparison of Molecular Dynamics with Hybrid Continuum-Molecular Dynamics for a Single Tethered Polymer in a Solvent
We compare a newly developed hybrid simulation method which combines
classical molecular dynamics (MD) and computational fluid dynamics (CFD) to a
simulation consisting only of molecular dynamics. The hybrid code is composed
of three regions: a classical MD region, a continuum domain where the dynamical
equations are solved by standard CFD methods, and an overlap domain where
transport information from the other two domains is exchanged. The exchange of
information in the overlap region ensures that momentum, energy and mass are
conserved. The validity of the hybrid code is demonstrated by studying a single
polymer tethered to a hard wall immersed in explicit solvent and undergoing
shear flow. In classical molecular dynamics simulation a great deal of
computational time is devoted to simulating solvent molecules, although the
solvent itself is of no direct interest. By contrast, the hybrid code simulates
the polymer and surrounding solvent explicitly, whereas the solvent farther
away from the polymer is modeled using a continuum description. In the hybrid
simulations the MD domain is an open system whose number of particles is
controlled to filter the perturbative density waves produced by the polymer
motion.We compare conformational properties of the polymer in both simulations
for various shear rates. In all cases polymer properties compare extremely well
between the two simulation scenarios, thereby demonstrating that this hybrid
method is a useful way to model a system with polymers and under nonzero flow
conditions. There is also good agreement between the MD and hybrid schemes and
experimental data on tethered DNA in flow. The computational cost of the hybrid
protocol can be reduced to less than 6% of the cost of updating the MD forces,
confirming the practical value of the method.Comment: 13 pages, 8 figure
Monte Carlo adaptive resolution simulation of multicomponent molecular liquids
Complex soft matter systems can be efficiently studied with the help of
adaptive resolution simulation methods, concurrently employing two levels of
resolution in different regions of the simulation domain. The non-matching
properties of high- and low-resolution models, however, lead to thermodynamic
imbalances between the system's subdomains. Such inhomogeneities can be healed
by appropriate compensation forces, whose calculation requires nontrivial
iterative procedures. In this work we employ the recently developed Hamiltonian
Adaptive Resolution Simulation method to perform Monte Carlo simulations of a
binary mixture, and propose an efficient scheme, based on Kirkwood
Thermodynamic Integration, to regulate the thermodynamic balance of
multi-component systems
Hamiltonian adaptive resolution simulation for molecular liquids
Adaptive resolution schemes allow the simulation of a molecular fluid
treating simultaneously different subregions of the system at different levels
of resolution. In this work we present a new scheme formulated in terms of a
global Hamiltonian. Within this approach equilibrium states corresponding to
well defined statistical ensembles can be generated making use of all standard
Molecular Dynamics or Monte Carlo methods. Models at different resolutions can
thus be coupled, and thermodynamic equilibrium can be modulated keeping each
region at desired pressure or density without disrupting the Hamiltonian
framework.Comment: 11 pages, 3 Figure
The Stokes-Einstein Relation at Moderate Schmidt Number
The Stokes-Einstein relation for the self-diffusion coefficient of a
spherical particle suspended in an incompressible fluid is an asymptotic result
in the limit of large Schmidt number, that is, when momentum diffuses much
faster than the particle. When the Schmidt number is moderate, which happens in
most particle methods for hydrodynamics, deviations from the Stokes-Einstein
prediction are expected. We study these corrections computationally using a
recently-developed minimally-resolved method for coupling particles to an
incompressible fluctuating fluid in both two and three dimensions. We find that
for moderate Schmidt numbers the diffusion coefficient is reduced relative to
the Stokes-Einstein prediction by an amount inversely proportional to the
Schmidt number in both two and three dimensions. We find, however, that the
Einstein formula is obeyed at all Schmidt numbers, consistent with linear
response theory. The numerical data is in good agreement with an approximate
self-consistent theory, which can be used to estimate finite-Schmidt number
corrections in a variety of methods. Our results indicate that the corrections
to the Stokes-Einstein formula come primarily from the fact that the particle
itself diffuses together with the momentum. Our study separates effects coming
from corrections to no-slip hydrodynamics from those of finite separation of
time scales, allowing for a better understanding of widely observed deviations
from the Stokes-Einstein prediction in particle methods such as molecular
dynamics.Comment: Submitte