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Ronald Benjamin

Publications and source records attributed to Ronald Benjamin.

13 recordsLinked to original sources
arXiv2022

Current and diffusion of Overdamped Active Brownian Particles in a Ratchet Potential

The transport properties of a spherical active Brownian particle in a periodic potential under heavy damping are considered. The self-propelled particle is subjected to the asymmetric potential, detailed balance is lost and the particles generate a non-zero drift speed. The average current is calculated and the diffusivity of the particle is analyzed from the effective diffusion coefficient. For chiral active particles, the diffusivity decreases with increasing the angular velocity, confining the particle near the initial position, and reducing the average current.

cond-mat.soft↗
arXiv2022

Effect of roughness on the transport of an overdamped Brownian particle

We study the transport of an overdamped Brownian particle in a tilted rough potential driven by a gaussian white noise.We conisder various forms of rough potentials to analyse the effect of roughness on the diffusion and current generated.The variation of current, diffusion coefficient, and peclet number with the static tilting force, amplitude of roughness and temperature were studied. We concluded that the roughness reduces the particle current at any range of temperature. But at low temperatures, it enhances the diffusion coeffeicient of the particle

cond-mat.stat-mech↗
arXiv2015

Free energy cost of forming an interface between a crystal and its frozen version

Using a thermodynamic integration scheme, we compute the free energy cost per unit area, $\gamma$, of forming an interface between a crystal and a frozen structured wall, formed by particles frozen into the same equilibrium structure as the crystal. Even though the structure and potential energy of the crystalline phase in the vicinity of the wall is same as in the bulk, $\gamma$ has a non-zero value and increases with increasing density of the crystal and the wall. Investigating the effect of several interaction potentials between the particles, we observe a positive $\gamma$ at all crystalline densities if the potential is purely repulsive. For models with attractive interactions, such as the Lennard-Jones potential, a negative value for $\gamma$ is obtained at low densities.

cond-mat.stat-mech↗
arXiv2015

Crystal growth kinetics in Lennard-Jones and Weeks-Chandler-Andersen systems along the solid-liquid coexistence line

Kinetics of crystal-growth is investigated along the solid-liquid coexistence line for the (100), (110) and (111) orientations of the Lennard-Jones and Weeks-Chandler-Andersen fcc crystal-liquid interface, using non-equilibrium molecular dynamics simulations. A slowing down of the growth kinetics along the coexistence line is observed, which is mostly a temperature effect, with other quantities such as the melting pressure and liquid self-diffusion coefficient having a negligible impact. The growth kinetics of the two potentials become similar at large values of the melting temperature and pressure, when both resemble a purely repulsive soft-sphere potential. Classical models of crystallization from the melt are in reasonable qualitative agreement with our simulation data. Finally, several one-phase empirical melting/freezing rules are studied with respect to their validity along the coexistence line.

cond-mat.stat-mech↗
arXiv2014

Crystal-liquid interfacial free energy of hard spheres via a novel thermodynamic integration scheme

The hard sphere crystal-liquid interfacial free energy, ($\gamma_{\rm cl}$), is determined from molecular dynamics simulations using a novel thermodynamic integration (TI) scheme. The advantage of this TI scheme compared to previous methods is to successfully circumvent hysteresis effects due to the movement of the crystal-liquid interface. This is accomplished by the use of extremely short-ranged and impenetrable Gaussian flat walls which prevent the drift of the interface while imposing a negligible free-energy penalty. We find that it is crucial to analyze finite-size effects in order to obtain reliable estimates of $\gamma_{\rm cl}$ in the thermodynamic limit.

cond-mat.soft↗
arXiv2014

Excess free energy of supercooled liquids at disordered walls

Using a novel thermodynamic integration scheme, we compute the excess free energy, $\gamma$, of a glass-forming, binary Lennard-Jones liquid in contact with a frozen amorphous wall, formed by particles frozen into a similar structure as the liquid. We find that $\gamma$ is non-zero, becoming negative at low temperature. This indicates that the thermodynamics of the system is perturbed by the effect of the amorphous wall.

cond-mat.stat-mech↗
arXiv2014

Crystal-liquid interfacial free energy via thermodynamic integration

A novel thermodynamic integration (TI) scheme is presented to compute the crystal-liquid interfacial free energy ($\gamma_{\rm cl}$) from molecular dynamics simulation. The scheme is applied to a Lennard-Jones system. By using extremely short-ranged and impenetrable Gaussian flat walls to confine the liquid and crystal phases, we overcome hysteresis problems of previous TI schemes that stem from the translational movement of the crystal-liquid interface. Our technique is applied to compute $\gamma_{\rm cl}$ for the (100), (110) and (111) orientation of the crystalline phase at three temperatures under coexistence conditions. For one case, namely the (100) interface at the temperature $T=1.0$ (in reduced units), we demonstrate that finite-size scaling in the framework of capillary wave theory can be used to estimate $\gamma_{\rm cl}$ in the thermodynamic limit. Thereby, we show that our TI scheme is not associated with the suppression of capillary wave fluctuations.

cond-mat.soft↗
arXiv2013

Lennard-Jones systems near solid walls: Computing interfacial free energies from molecular simulation methods

Different computational techniques in combination with molecular dynamics computer simulation are used to to determine the wall-liquid and the wall-crystal interfacial free energies of a modified Lennard-Jones (LJ) system in contact with a solid wall. Two different kinds of solid walls are considered: a flat structureless wall and a structured wall consisting of an ideal crystal with the particles rigidly attached to fcc lattice sites. Interfacial free energies are determined by a thermodynamic integration scheme, the anisotropy of the pressure tensor, the non-equilibrium work method based on Bennett acceptance criteria, and a method using Cahn's adsorption equations based on the interfacial thermodynamics of Gibbs. For the flat wall, interfacial free energies as a function of different densities of the LJ liquid and as a function of temperature along the coexistence curve are calculated. In case of a structured wall, the interaction strength between the wall and the LJ system and the lattice constant of the structured wall are varied. Using the values of the wall-liquid and wall-crystal interfacial energies along with the value for the crystal-liquid interfacial free energy determined previously for the same system by the "cleaving potential method", we obtain the contact angle as a function of various parameters; in particular the conditions are found under which partial wetting occurs.

cond-mat.stat-mech↗
arXiv2012

Wall-liquid and wall-crystal interfacial free energies via thermodynamic integration: A molecular dynamics simulation study

A method is proposed to compute the interfacial free energy of a Lennard-Jones system in contact with a structured wall by molecular dynamics simulation. Both the bulk liquid and bulk face-centered-cubic crystal phase along the (111) orientation are considered. Our approach is based on a thermodynamic integration scheme where first the bulk Lennard-Jones system is reversibly transformed to a state where it interacts with a structureless flat wall. In a second step, the flat structureless wall is reversibly transformed into an atomistic wall with crystalline structure. The dependence of the interfacial free energy on various parameters such as the wall potential, the density and orientation of the wall is investigated. The conditions are indicated under which a Lennard-Jones crystal partially wets a flat wall.

cond-mat.stat-mech↗
arXiv2009

Stochastic energetics of a Brownian motor and refrigerator driven by non-uniform temperature

The energetics of a Brownian heat engine and heat pump driven by position dependent temperature, known as the B\"uttiker-Landauer heat engine and heat pump, is investigated by numerical simulations of the inertial Langevin equation. We identify parameter values for optimal performance of the heat engine and heat pump. Our results qualitatively differ from approaches based on the overdamped model. The behavior of the heat engine and heat pump, in the linear response regime is examined under finite time conditions and we find that the efficiency is lower than that of an endoreversible engine working under the same condition. Finally, we investigate the role of different potential and temperature profiles to enhance the efficiency of the system. Our simulations show that optimizing the potential and temperature profile leads only to a marginal enhancement of the system performance due to the large entropy production via the Brownian particle's kinetic energy.

cond-mat.stat-mech↗
arXiv2008

Inertial effects in B{ü}ttiker-Landauer Motor and Refrigerator at the Overdamped Limit

We investigate the energetics of a Brownian motor driven by position dependent temperature, commonly known as the B{ü}ttiker-Landauer motor. Overdamped models (M=0) predict that the motor can attain Carnot efficiency. However, the overdamped limit ($M\to 0$), contradicts the previous prediction due to the kinetic energy contribution to the heat transfer. Using molecular dynamics simulation and numerical solution of the inertial Langevin equation, we confirm that the motor can never achieve Carnot efficiency and verify that the heat flow via kinetic energy diverges as $M^{-1/2}$ in the overdamped limit. The reciprocal process of the motor, namely the B{ü}ttiker-Landauer refrigerator is also examined. In this case, the overdamped approach succeeds in predicting the heat transfer only when there is no temperature gradient. Its found that the Onsager symmetry between the motor and refrigerator does not suffer from the singular behavior of the kinetic energy contribution.

cond-mat.stat-mech↗
arXiv2003

Quantum spin pumping with adiabatically modulated magnetic barrier's

A quantum pump device involving magnetic barriers produced by the deposition of ferro magnetic stripes on hetero-structure's is investigated. The device for dc- transport does not provide spin-polarized currents, but in the adiabatic regime, when one modulates two independent parameters of this device, spin-up and spin-down electrons are driven in opposite directions, with the net result being that a finite net spin current is transported with negligible charge current. We also analyze our proposed device for inelastic-scattering and spin-orbit scattering. Strong spin-orbit scattering and more so inelastic scattering have a somewhat detrimental effect on spin/charge ratio especially in the strong pumping regime. Further we show our pump to be almost noiseless, implying an optimal quantum spin pump.

quant-ph↗