Sarith P. Sathian

Bio: Sarith P. Sathian is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Graphene & Interfacial thermal resistance. The author has an hindex of 14, co-authored 56 publications receiving 624 citations. Previous affiliations of Sarith P. Sathian include National Institute of Technology Calicut.

The effect of characteristic length on mean free path for confined gases

Abstract: Molecular Dynamics simulations are performed to investigate the influence of system boundaries and characteristic length (L) of the system on the mean free path (MFP) of rarefied gas confined to the walls of a nano-channel Isothermal Lennard-Jones fluid confined between Reflective walls and platinum walls at different number densities (031 atoms/nm3 and 161 atoms/nm3) are independently considered The MFP is calculated by the Lagrangian approach of tracking the trajectory of each atom and averaging the distance between successive collisions The percentage of fluid–wall collisions is observed to predominate over fluid–fluid collisions at high levels of rarefaction The influence of L (varying from 6 nm to 16 nm) on MFP is examined in this regime At lower Knudsen number (Kn), it is observed that the effect of L on MFP is minimal However, at higher rarefaction the characteristic dimension influences the MFP significantly for various wall configurations

Nanoconfinement Effects on the Kapitza Resistance at Water-CNT Interfaces.

Abstract: The Kapitza resistance (Rk) at the water-carbon nanotube (CNT) interface, with water on the inside of the nanotube, was investigated using molecular dynamics simulations We propose a new equilibrium molecular dynamics (EMD) method, also valid in the weak flow regime, to determine the Kapitza resistance in a cylindrical nanoconfinement system where nonequilibrium molecular dynamics (NEMD) methods are not suitable The proposed method is independent of the correlation time compared to Green-Kubo-based methods, which only work in short correlation time intervals Rk between the CNT and the confined water strongly depends on the diameter of the nanotube and is found to decrease with an increase in the CNT diameter, the opposite to what is reported in the literature when water is on the outside of the nanotube Rk is furthermore found to converge to the planar graphene surface value as the number of water molecules per unit surface area approaches the value in the graphene surface and a higher overlap of the vibrational spectrum A slight increase in Rk with the addition of the number of CNT walls was observed, whereas the chirality and flow do not have any impact

Tunable thermoelectric properties of SnS2 under high pressure at room temperature

Abstract: In this paper, we study the structural, electronic, vibrational, thermoelectric and elastic properties of tin disulfide (SnS2) using first principles density functional theory calculations in the pressure range 0 ≤ p ≤ 5 GPa. The variation of lattice constant along c-axis is found to be higher than that along the a-axis which significantly affects the properties. The electronic band gap is observed to decrease with the applied pressure. The Raman shift of Eg and A1g modes increases with applied pressure. Furthermore, SnS2 remains dynamically stable up to 5 GPa. Thermoelectric properties such as thermopower (S), electrical conductivity (σ), power factor (S2σ) show anisotropy. While the in-plane direction is more dominant at ambient pressure, the out-of-plane is more dominant with the increase in pressure. The calculated power factor is higher in the hole concentration than the electron concentration in the defined pressure range at room temperature. This suggests that SnS2 could be an excellent candidate material of p-type thermoelectric under high pressure conditions.

Non-isothermal flow of an electrolyte in a charged nanochannel.

Abstract: Electrokinetic flows are generally analyzed, assuming isothermal conditions even though such situations are hard to be achieved in practice. In this paper, the flow of a symmetric electrolyte in a charged nanochannel subjected to an axial temperature gradient is investigated using molecular dynamics simulations. We analyze the relative contribution of the Soret effect, the thermoelectric effect, and the double layer potential in the electrical double layer for various surface charges and temperature gradients. We find the flow driven by thermal gradient analogous to electroosmotic flow. The thermophoretic motion of the electrolyte is significant for negative surface charge than the positive surface charge. The vibrational spectrum of graphene is calculated to delineate the effect of the surface charge polarity on the observed thermophoretic motion of the electrolyte. A unique structure of interfacial water layer is observed for the positive and negative surface charges. We attribute the presence of these structures to the differences in water-carbon interactions existing for various surface charge polarity. For an applied thermal gradient in the range 2.6 K/nm to 8 K/nm, we observe a continuous net flow with average velocities reaching up to 9.4 m/s inside the channel for a negative surface charge of -0.101 C/m2. The results indicate that in a charged graphene-based nanochannel, temperature gradients can be employed to induce streaming current, depending on the relative influence of the Soret effect and the double layer potential.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Wettability effect on nanoconfined water flow

Abstract: Understanding and controlling the flow of water confined in nanopores has tremendous implications in theoretical studies and industrial applications. Here, we propose a simple model for the confined water flow based on the concept of effective slip, which is a linear sum of true slip, depending on a contact angle, and apparent slip, caused by a spatial variation of the confined water viscosity as a function of wettability as well as the nanopore dimension. Results from this model show that the flow capacity of confined water is 10 −1 ∼10 7 times that calculated by the no-slip Hagen–Poiseuille equation for nanopores with various contact angles and dimensions, in agreement with the majority of 53 different study cases from the literature. This work further sheds light on a controversy over an increase or decrease in flow capacity from molecular dynamics simulations and experiments.

Single-Layer Behavior and Its Breakdown in Twisted Graphene Layers

Abstract: We report high magnetic field scanning tunneling microscopy and Landau level spectroscopy of twisted graphene layers grown by chemical vapor deposition. For twist angles exceeding ~3° the low energy carriers exhibit Landau level spectra characteristic of massless Dirac fermions. Above 20° the layers effectively decouple and the electronic properties are indistinguishable from those in single-layer graphene, while for smaller angles we observe a slowdown of the carrier velocity which is strongly angle dependent. At the smallest angles the spectra are dominated by twist-induced van Hove singularities and the Dirac fermions eventually become localized. An unexpected electron-hole asymmetry is observed which is substantially larger than the asymmetry in either single or untwisted bilayer graphene.

Driven Polymer Translocation Through a Narrow Pore

Abstract: Motivated by experiments in which a polynucleotide is driven through a proteinaceous pore by an electric field, we study the diffusive motion of a polymer threaded through a narrow channel with which it may have strong interactions. We show that there is a range of polymer lengths in which the system is approximately translationally invariant, and we develop a coarse-grained description of this regime. From this description, general features of the distribution of times for the polymer to pass through the pore may be deduced. We also introduce a more microscopic model. This model provides a physically reasonable scenario in which, as in experiments, the polymer's speed depends sensitively on its chemical composition, and even on its orientation in the channel. Finally, we point out that the experimental distribution of times for the polymer to pass through the pore is much broader than expected from simple estimates, and speculate on why this might be.