Krishna Muralidharan

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• Zhang, L., Frantziskonis, G. N., Muralidharan, K., & Sadat, M. R. (2021). From atomic-scale to mesoscale: A characterization of geopolymer composites using molecular dynamics and peridynamics simulations. Computational Materials Science, 186(110038). doi:https://doi.org/10.1016/j.commatsci.2020.110038
• Trzaskowski, B., Adamowicz, L., Beck, W., Muralidharan, K., & Deymier, P. A. (2014). Exploring structures and properties of new geodesic polyarenes. Chemical Physics Letters, 595-596, 6-12.
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  Abstract: We have employed the self-consistent charge density-functional tight-binding, the density functional theory and the classical molecular dynamics methods to study new geodesic polyarenes, which can be synthesized via the regiospecific cove-region closure and HF elimination. We show that the shape of new polyarenes may be altered and controlled by the presence of C 60 fullerenes. The high intrinsic curvature of the geodesic arenes facilitates fusion with C60 fullerenes. This propensity to fuse is consistent with the hypothesis of an optimal value of the bond-puckering angle at which graphene-like structures show maximum reactivity.© 2014 Elsevier B.V. All rights reserved.
• Asaduzzaman, A. M., Laref, S., Deymier, P. A., Runge, K., Cheng, H. -., Muralidharan, K., & Drake, M. J. (2013). A first-principles characterization of water adsorption on forsterite grains. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 371(1994).
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  PMID: 23734049;Abstract: Numerical simulations examining chemical interactions of water molecules with forsterite grains have demonstrated the efficacy of nebular gas adsorption as a viable mechanism for water delivery to the terrestrial planets. Nevertheless, a comprehensive picture detailing the water-adsorption mechanisms on forsterite is not yet available. Towards this end, using accurate first-principles density functional theory, we examine the adsorption mechanisms of water on the (001), (100), (010) and (110) surfaces of forsterite. While dissociative adsorption is found to be the most energetically favourable process, two stable associative adsorption configurations are also identified. In dual-site adsorption, the water molecule interacts strongly with surface magnesium and oxygen atoms, whereas single-site adsorption occurs only through the interaction with a surface Mg atom. This results in dual-site adsorption being more stable than single-site adsorption.© 2013 The Author(s) Published by the Royal Society. All rights reserved.
• Laref, S., Asaduzzaman, A. M., Beck, W., Deymier, P. A., Runge, K., Adamowicz, L., & Muralidharan, K. (2013). Characterization of graphene-fullerene interactions: Insights from density functional theory. Chemical Physics Letters, 582, 115-118.
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  Abstract: Using density functional theory (DFT) based approaches that utilize appropriate semi-empirical and nonlocal van der Waals corrections, we rigorously examine the interactions between fullerene (C60) molecules and pristine single layer graphene (SLG) sheets as well as SLG containing isolated mono-vacancy, divacancy and Stone-Wales defect-sites respectively. Our results show that chemical bonding between the C60 molecule and SLG at mono-vacancy defect-sites demonstrate predominantly sp3-like hybridization, in contrast to weaker π-π interactions that characterize C60-SLG systems containing divacancies and Stone-Wales defects. © 2013 Elsevier B.V. All rights reserved.
• Muralidharan, K., Laref, S., Cao, J., Asaduzzaman, A., Runge, K., Deymier, P., Ziolkowski, R. W., Miyawaki, M., & Muralidharan, K. -. (2013). Size-dependent permittivity and intrinsic optical anisotropy of nanometric gold thin films: a density functional theory study. Optics express, 21(10).
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  Physical properties of materials are known to be different from the bulk at the nanometer scale. In this context, the dependence of optical properties of nanometric gold thin films with respect to film thickness is studied using density functional theory (DFT). We find that the in-plane plasma frequency of the gold thin film decreases with decreasing thickness and that the optical permittivity tensor is highly anisotropic as well as thickness dependent. Quantitative knowledge of planar metal film permittivity's thickness dependence can improve the accuracy and reliability of the designs of plasmonic devices and electromagnetic metamaterials. The strong anisotropy observed may become an alternative method of realizing indefinite media.
• Proczka, J. J., Muralidharan, K., Villela, D., Simmons, J. H., & Frantziskonis, G. (2013). Guidelines for the pressure and efficient sizing of pressure vessels for compressed air energy storage. Energy Conversion and Management, 65, 597-605.
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  Abstract: The paper reports guidelines for the efficient design and sizing of Small-Scale Compressed Air Energy Storage (SS-CAES) pressure vessels, including guidelines for pressures that should be used in the SS-CAES system to minimize the cost of the pressure vessel. Under a specified energy storage capacity and specified maximum and minimum operating pressures in CAES, the volume of the vessel(s) can be evaluated. The present study provides guidelines for choosing appropriate shape and size for the vessels that minimize material and manufacturing cost for cylindrical vessels. The two main contributions of the paper are that it provides a methodology to determine: (a) an optimum pressure; (b) the shape, size, and number of vessel to be used in a particular application. Results suggest that pressure vessels with a length to diameter ratio of roughly three are the most economical, and that a system should be designed for a pressure of roughly three times the minimum pressure of the expansion device. © 2012 Elsevier Ltd. All rights reserved.
• Swinteck, N. Z., Muralidharan, K., & Deymier, P. A. (2013). Phonon scattering in one-dimensional anharmonic crystals and superlattices: Analytical and numerical study. Journal of Vibration and Acoustics, Transactions of the ASME, 135(4).
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  Abstract: Second-order perturbation theory based on multiple time scale analysis is used to illuminate three-phonon scattering processes in the one-dimensional anharmonic monoatomic crystal. Molecular dynamics simulation techniques in conjunction with spectral energy density analyses are used to quantify phonon mode lifetime in (1) the monoatomic crystal and (2) a series of superlattice configurations. It is found that the lifetime of vibrational modes in the monoatomic crystal is inherently long, because the conditions for conservation of wave vector and frequency are pathologically difficult to satisfy. Superlattice configurations, however, offer band-folding effects, whereby the availability of phonon decay channels decreases the lifetime of the vibrational modes supported by the medium. Copyright © 2013 by ASME.
• Trzaskowski, B., Adamowicz, L., Beck, W., Muralidharan, K., & Deymier, P. A. (2013). Impact of local curvature and structural defects on graphene-C₆₀ fullerene fusion reaction barriers. Journal of Physical Chemistry C, 117(38), 19664-19671.
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  Abstract: Self-consistent charge density functional tight-binding and density functional theory calculations have been employed to study the energetics of the graphene-C60 fullerene fusion. We show that there is an optimal value of the bond-puckering angle of single-layer graphene-like systems, which facilitates fusion with other low-dimension carbon systems. Specifically, chemical attachment of a C60 fullerene to a single-layer graphene sheet is not feasible from the energetic point of view due to lack of puckering of the pristine graphene surface, but may occur for systems with some surface curvature. The presence of various defects in the graphene surface, including formation of four- and five-membered rings, Stone-Wales defects, or single and double vacancies may create some surface strain leading to formation of reactive sites in graphene, which are susceptive to binding with a fullerene. As an example, we show that a single vacancy in the graphene surface can lead to formation of a stable chemical bond with a fullerene. © 2013 American Chemical Society.
• Vattuone, L., Smerieri, M., Savio, L., Asaduzzaman, A. M., Muralidharan, K., Drake, M. J., & Rocca, M. (2013). Accretion disc origin of the Earth's water. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 371(1994).
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  PMID: 23734050;Abstract: Earth's water is conventionally believed to be delivered by comets or wet asteroids after the Earth formed. However, their elemental and isotopic properties are inconsistent with those of the Earth. It was thus proposed that water was introduced by adsorption onto grains in the accretion disc prior to planetary growth, with bonding energies so high as to be stable under high-temperature conditions. Here, we show both by laboratory experiments and numerical simulations that water adsorbs dissociatively on the olivine {100} surface at the temperature (approx. 500-1500 K) and water pressure (approx. 10-8 bar) expected for the accretion disc, leaving an OH adlayer that is stable at least up to 900 K. This may result in the formation of many Earth oceans, provided that a viable mechanism to produce water from hydroxyl exists. This adsorption process must occur in all disc environments around young stars. The inevitable conclusion is thatwater should be prevalent on terrestrial planets in the habitable zone around other stars.© 2013 The Author(s) Published by the Royal Society. All rights reserved.
• Bringuier, S., Swinteck, N., Vasseur, J. O., Robillard, J. -., Runge, K., Muralidharan, K., & Deymier, P. A. (2011). Phase-controlling phononic crystals: Realization of acoustic Boolean logic gates. Journal of the Acoustical Society of America, 130(4), 1919-1925.
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  PMID: 21973346;Abstract: A phononic crystal (PC) consisting of a square array of cylindrical Polyvinylchloride inclusions in air is used to construct a variety of acoustic logic gates. In a certain range of operating frequencies, the PC band structure shows square-like equi-frequency contours centered off the Gamma point. This attribute allows for the realization of non-collinear wave and group velocity vectors in the PC wave vector space. This feature can be utilized to control with great precision, the relative phase between propagating acoustic waves in the PC. By altering the incidence angle of the impinging acoustic beams or varying the PC thickness, interferences occur between acoustic wave pairs. It is recognized that information can be encoded with this mechanism (e.g., wave amplitudes/interference patterns) and accordingly to construct a series of logic gates emulating Boolean functions. The NAND, XOR, and NOT gates are demonstrated with finite-difference time-domain simulations of acoustic waves impinging upon the PC. © 2011 Acoustical Society of America.
• Muralidharan, K., Erdmann, R. G., Runge, K., & Deymier, P. A. (2011). Asymmetric energy transport in defected boron nitride nanoribbons: Implications for thermal rectification. AIP Advances, 1(4).
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  Abstract: Using molecular dynamics simulations, the thermal transport properties of boron nitride nanoribbons (BNNR) containing geometrically-asymmetric triangular nano-vacancies were investigated. By suitably interpreting the time-evolution of spatially decomposed heat-current autocorrelation function in terms of phonon propagation characteristics, we have demonstrated the possibility of observing defect induced direction-dependent thermal transport in BNNR. This was further confirmed by appropriate analysis of direction dependent thermal diffusivity estimations in BNNR. © 2011 Copyright 2011 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License.
• Robillard, J. -., Bucay, J., Deymier, P. A., Shelke, A., Muralidharan, K., Merheb, B., Vasseur, J. O., Sukhovich, A., & Page, J. H. (2011). Resolution limit of a phononic crystal superlens. Physical Review B - Condensed Matter and Materials Physics, 83(22).
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  Abstract: We report on the subwavelength imaging capabilities of a phononic crystal (PC) flat lens consisting of a triangular array of steel cylinders in methanol, all surrounded by water. The image resolution of the PC flat lens beats the Rayleigh diffraction limit because bound modes in the lens can be excited by evanescent waves emitted by the source. These are modes that only propagate in the direction parallel to the water-lens interface. These modes resonantly amplify evanescent waves that contribute to the reconstruction of an image. By employing the finite difference time domain method and ultrasonic experiments, we also explore the effect on the image resolution and focal point on various structural and operational parameters, such as source frequency, geometry of the lens, source position, and time. The mechanisms by which these factors affect resolution are discussed in terms of the competition between the contribution of propagative modes to focusing and the ability of the source to excite bound modes of the PC lens. © 2011 American Physical Society.
• Robillard, J. -., Muralidharan, K., Bucay, J., Deymier, P. A., Beck, W., & Barker, D. (2011). Phononic metamaterials for thermal management: An atomistic computational study. Chinese Journal of Physics, 49(1), 448-461.
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  Abstract: Atomistic computational methods such as molecular dynamics and the Green-Kubo method are employed to shed light on the transport behavior of thermal phonons in models of graphene-based nanophononic crystals comprising periodic arrays of holes. We calculate the phonon lifetime and thermal conductivity as a function of the crystal filling fraction and temperature. The results are interpreted in terms of competition between elastic Bragg scat-tering and inelastic phonon-phonon scattering. We focus on the effect of the band structure on the phonon lifetime. © 2011 The Physical Society of The Republic of China.
• Runge, K., Muralidharan, K., & Deymier, P. (2011). Consistent embedding: A multi-scale approach to brittle fracture. Materials Science and Technology Conference and Exhibition 2011, MS and T'11, 1, 268-275.
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  Abstract: A method for the construction of multi-scale hierarchies that capture the behavior of more computationally demanding, accurate methods at larger length and longer time scales is presented. Consistent embedding, which provides a framework for building such multi-scale hierarchies is defined and applied to both a serial and concurrent multi-scale illustration. The failure of a 108-atom silica nanorod provides the test example for the consistent embedding hierarchies and it is shown that the concurrently modeled composite system behaves according to the more accurate quantum chemical method. A further illustration of the utility of molecular dynamics is the determination of the initiating event in brittle fracture of amorphous silica. Copyright © 2011 MS&T'11®.
• Swinteck, N., Robillard, J. -., Bringuier, S., Bucay, J., Muralidharan, K., Vasseur, J. O., Runge, K., & Deymier, P. A. (2011). Phase-controlling phononic crystal. Applied Physics Letters, 98(10).
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  Abstract: We report on a phononic crystal (PC) consisting of a square array of cylindrical polyvinylchloride inclusions in air that can be used to control the relative phase of two incident acoustic waves with different incident angles. The phase shift between waves propagating through the crystal depends on the angle of incidence of the incoming waves and the PC length. The behavior of the PC is analyzed using the finite-difference-time-domain method. The band structure and equifrequency contours calculated via the plane wave expansion method show that the distinctive phase controlling properties are attributed to noncollinear wave and group velocity vectors in the PC as well as the degree of refraction. © 2011 American Institute of Physics.
• H., N., Richard, C., King, H. E., Putnis, A., Muralidharan, K., Deymier, P., Stimpfl, M., & Drake, M. J. (2010). Where on Earth has our water come from?. Chemical Communications, 46(47), 8923-8925.
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  PMID: 20967372;Abstract: The presence of water in the Earth has long been an enigma. However, computer modelling techniques have shown that the adsorption of water onto the fractal surfaces of interplanetary dust particles, which are present in the planetary accretion disk, is sufficiently strong to provide a viable origin of terrestrial water. © 2010 The Royal Society of Chemistry.
• Mishra, S. K., Deymier, P. A., Muralidharan, K., Frantziskonis, G., Pannala, S., & Simunovic, S. (2010). Modeling the coupling of reaction kinetics and hydrodynamics in a collapsing cavity. Ultrasonics Sonochemistry, 17(1), 258-265.
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  PMID: 19520598;Abstract: We introduce a model of cavitation based on the multiphase Lattice Boltzmann method (LBM) that allows for coupling between the hydrodynamics of a collapsing cavity and supported solute chemical species. We demonstrate that this model can also be coupled to deterministic or stochastic chemical reactions. In a two-species model of chemical reactions (with a major and a minor species), the major difference observed between the deterministic and stochastic reactions takes the form of random fluctuations in concentration of the minor species. We demonstrate that advection associated with the hydrodynamics of a collapsing cavity leads to highly inhomogeneous concentration of solutes. In turn these inhomogeneities in concentration may lead to significant increase in concentration-dependent reaction rates and can result in a local enhancement in the production of minor species.
• Villela, D., Kasinathan, V. V., Valle, S. D., Alvarez, M., Frantziskonis, G., Deymier, P., & Muralidharan, K. (2010). Compressed-air energy storage systems for stand-alone off-grid photovoltaic modules. Conference Record of the IEEE Photovoltaic Specialists Conference, 962-967.
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  Abstract: In this work, a low-cost, low-volume, low-maintenance, small-scale compressed-air energy storage system (SS-CAES) is proposed, which can be used in conjunction with off-grid stand-alone photo-voltaic panels, for powering appliances and residential units in order to minimize the dependency on centralized power system grids. As a first step towards achieving this objective, we have designed and examined the compression efficiency of a single-stage, isothermal compression system that utilizes a fluid piston. Preliminary results clearly establish that the prototype holds enormous promise as energy storage systems that are compatible with renewable energy sources such as solar. © 2010 IEEE.
• Bucay, J., Roussel, E., Vasseur, J. O., Deymier, P. A., Hladky-Hennion, A., Pennec, Y., Muralidharan, K., Djafari-Rouhani, B., & Dubus, B. (2009). Positive, negative, zero refraction, and beam splitting in a solid/air phononic crystal: Theoretical and experimental study. Physical Review B - Condensed Matter and Materials Physics, 79(21).
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  Abstract: We report on a phononic crystal (PC) consisting of a square array of cylindrical polyvinylchloride inclusions in air that exhibits positive, negative, or zero refraction depending on the angle of the incident sound beam. For all three cases of refraction, the transmitted beam undergoes splitting upon exiting the crystal. These properties are analyzed theoretically using finite difference time domain method and are demonstrated experimentally. Band structures and equifrequency surfaces (EFSs) calculated with the plane-wave expansion method show that the observed properties result from the unique geometry of the PC's EFS as compared to that of the incident media. © 2009 The American Physical Society.
• Frantziskonis, G., Muralidharan, K., Deymier, P., Simunovic, S., Nukala, P., & Pannala, S. (2009). Time-parallel multiscale/multiphysics framework. Journal of Computational Physics, 228(21), 8085-8092.
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  Abstract: We introduce the time-parallel compound wavelet matrix method (tpCWM) for modeling the temporal evolution of multiscale and multiphysics systems. The method couples time parallel (TP) and CWM methods operating at different spatial and temporal scales. We demonstrate the efficiency of our approach on two examples: a chemical reaction kinetic system and a non-linear predator-prey system. Our results indicate that the tpCWM technique is capable of accelerating time-to-solution by 2-3-orders of magnitude and is amenable to efficient parallel implementation. © 2009 Elsevier Inc.
• Merheb, B., Deymier, P. A., Muralidharan, K., Bucay, J., Jain, M., Aloshyna-Lesuffleur, M., Greger, R. W., Mohanty, S., & Berker, A. (2009). Viscoelastic effect on acoustic band gaps in polymer-fluid composites. Modelling and Simulation in Materials Science and Engineering, 17(7).
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  Abstract: In this paper, we present a theoretical analysis of the propagation of acoustic waves through elastic and viscoelastic two-dimensional phononic crystal structures. Numerical calculations of transmission spectra are conducted by extending the finite-difference-time-domain method to account for linear viscoelastic materials with time-dependent moduli. We study a phononic crystal constituted of a square array of cylindrical air inclusions in a solid viscoelastic matrix. The elastic properties of the solid are those of a silicone rubber. This system exhibits very wide band gaps in its transmission spectrum that extend to frequencies in the audible range of the spectrum. These gaps are characteristic of fluid matrix/air inclusion systems and result from the very large contrast between the longitudinal and transverse speeds of sound in rubber. By treating the matrix as a viscoelastic medium within the standard linear solid (SLS) model, we demonstrate that viscoelasticity impacts the transmission properties of the rubber/air phononic crystal not only by attenuating the transmitted acoustic waves but also by shifting the passing bands frequencies toward lower values. The ranges of frequencies exhibiting attenuation or frequency shift are determined by the value of the relaxation time in the SLS model. We show that viscoelasticity can be used to decrease the frequency of pass bands (and consequently stop bands) in viscoelastic/air phononic crystals. © 2009 IOP Publishing Ltd.
• Sukhovich, A., Merheb, B., Muralidharan, K., Vasseur, J. O., Pennec, Y., Deymier, P. A., & Page, J. H. (2009). Experimental and theoretical evidence for subwavelength imaging in phononic crystals. Physical Review Letters, 102(15).
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  Abstract: We show experimentally and theoretically that super resolution can be achieved while imaging with a flat lens consisting of a phononic crystal exhibiting negative refraction. This phenomenon is related to the coupling between the incident evanescent waves and a bound slab mode of the phononic crystal lens, leading to amplification of evanescent waves by the slab mode. Super resolution is only observed when the source is located very near to the lens, and is very sensitive to the location of the source parallel to the lens surface as well as to site disorder in the phononic crystal lattice. © 2009 The American Physical Society.
• Mishra, S. K., Muralidharan, K., Deymier, P. A., Frantziskonis, G., Pannala, S., & Simunovic, S. (2008). Wavelet-based spatial scaling of coupled reaction-diffusion fields. International Journal for Multiscale Computational Engineering, 6(4), 281-297.
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  Abstract: Multiscale schemes for transferring information from fine to coarse scales are typically based on homogenization techniques. Such schemes smooth the fine scale features of the underlying fields, often resulting in the inability to accurately retain the fine scale correlations. In addition, higher-order statistical moments (beyond mean) of the relevant field variables are not necessarily preserved. As a superior alternative to averaging homogenization methods, a wavelet-based scheme for the exchange of information between a reactive and diffusive field in the context of multiscale reaction-diffusion problems is proposed and analyzed. The scheme is shown to be efficient in passing information along scales, from fine to coarse, i.e., upscaling as well as from coarse to fine, i.e., downscaling. It incorporates fine scale statistics (higher-order moments beyond mean), mainly due to the capability of wavelets to represent fields hierarchically. Critical to the success of the scheme is the identification of dominant scales containing the majority of the useful information. The dominant scales in effect specify the coarsest resolution possible. The scheme is applied in detail to the analysis of a diffusive system with a chemically reacting boundary. Reactions are simulated using kinetic Monte Carlo (kMC) and diffusion is solved by finite differences (FDs). Spatial scale differences are present at the interface of the kMC sites and the diffusion grid. The computational efficiency of the scheme is compared to results obtained by averaging homogenization, and to results from a benchmark scheme that ensures spatial scale parity between kMC and FD. © 2008 by Begell House, Inc.
• Mishra, S. K., Muralidharan, K., Deymier, P., Frantziskonis, G., Simunovic, S., & Pannala, S. (2008). Wavelet based spatial scaling of coupled reaction diffusion fields. Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 5102 LNCS(PART 2), 301-310.
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  Abstract: Multiscale schemes for transferring information from fine to coarse scales are typically based on some sort of averaging. Such schemes smooth the fine scale features of the underlying fields, thus altering the fine scale correlations. As a superior alternative to averaging, a wavelet based scheme for the exchange of information between a reactive and diffusive field in the context of multiscale reaction-diffusion problems is proposed and analyzed. The scheme is shown to be efficient in passing information along scales, from fine to coarse, i.e. up-scaling as well as from coarse to fine, i.e. down-scaling. In addition, it retains fine scale statistics, mainly due to the capability of wavelets to represent fields hierarchically. Critical to the success of the scheme is the identification of dominant scales containing the majority of useful information. The scheme is applied in detail to the analysis of a diffusive system with chemically reacting boundary. Reactions are simulated using kinetic Monte Carlo (KMC) and diffusion is solved by finite differences. Spatial scale differences are present at the interface of the KMC sites and the diffusion grid. The computational efficiency of the scheme is compared to results obtained by local averaging, and to results from a benchmark model. The spatial scaling scheme ties to wavelet based schemes for temporal scaling, presented elsewhere by the authors. © 2008 Springer-Verlag Berlin Heidelberg.
• Muralidharan, K., Deymier, P., Stimpfl, M., H., N., & Drake, M. J. (2008). Origin of water in the inner Solar System: A kinetic Monte Carlo study of water adsorption on forsterite. Icarus, 198(2), 400-407.
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  Abstract: The origin of water in the inner Solar System is not well understood. It is believed that temperatures were too high in the accretion disk in the region of the terrestrial planets for hydrous phases to be thermodynamically stable. Suggested sources of water include direct adsorption of hydrogen from the nebula into magma oceans after the terrestrial planets formed, and delivery of asteroidal or cometary material from beyond the zone of the terrestrial planets. We explore a new idea, direct adsorption of water onto grains prior to planetary accretion. This hypothesis is motivated by the observation that the accretion disk from which our planetary system formed was composed of solid grains bathed in a gas dominated by hydrogen, helium, and oxygen. Some of that hydrogen and oxygen combined to make water vapor. We examine quantitatively adsorption of water onto grains in the inner Solar System accretion disk by exploring the adsorption dynamics of water molecules onto forsterite surfaces via kinetic Monte Carlo simulations. We conclude that many Earth oceans of water could be adsorbed. © 2008 Elsevier Inc. All rights reserved.
• Muralidharan, K., Mishra, S. K., Frantziskonis, G., Deymier, P. A., Nukala, P., Simunovic, S., & Pannala, S. (2008). Dynamic compound wavelet matrix method for multiphysics and multiscale problems. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 77(2).
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  Abstract: The paper presents the dynamic compound wavelet method (dCWM) for modeling the time evolution of multiscale and/or multiphysics systems via an "active" coupling of different simulation methods applied at their characteristic spatial and temporal scales. Key to this "predictive" approach is the dynamic updating of information from the different methods in order to adaptively and accurately capture the temporal behavior of the modeled system with higher efficiency than the (nondynamic) "corrective" compound wavelet matrix method (CWM), upon which the proposed method is based. The system is simulated by a sequence of temporal increments where the CWM solution on each increment is used as the initial conditions for the next. The numerous advantages of the dCWM method such as increased accuracy and computational efficiency in addition to a less-constrained and a significantly better exploration of phase space are demonstrated through an application to a multiscale and multiphysics reaction-diffusion process in a one-dimensional system modeled using stochastic and deterministic methods addressing microscopic and macroscopic scales, respectively. © 2008 The American Physical Society.
• Muralidharan, K., Cao, C., Wan, Y., Runge, K., & Cheng, H. (2007). Environment dependent dynamic charge potential for silica: Application to nanoscale silica structures. Chemical Physics Letters, 437(1-3), 92-98.
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  Abstract: Using a potential form formally based on density functional theory (DFT), we develop a new potential for silica. Our environment dependent dynamic charge potential uses Mulliken populations obtained from ab initio calculations to describe the charge variation with respect to coordination and local strain. An embedded atom (EAM) style potential is then parameterized to yield accurate energies compared to DFT calculations for a small training set of silica nanostructures. The new potential performs well in predicting energies and relative energies of a larger suite of silica nanostructures previously studied by Bromley et al. © 2007 Elsevier B.V. All rights reserved.
• Muralidharan, K., Oh, K., Deymier, P. A., Runge, K., & Simmons, J. H. (2007). Molecular dynamics simulations of atomic-level brittle fracture mechanisms in amorphous silica. Journal of Materials Science, 42(12), 4159-4169.
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  Abstract: We have examined the atomic dynamics of the brittle fracture process in amorphous silica using molecular dynamics. Under strain, extensive atomic restructuring occur in the vicinity of voids leading to the formation of 2-membered (2-M) silica rings that are much different than the open network structure of the bulk. The sequence of events that lead to the formation of the 2-M rings was characterized by examining the change in local coordination of atoms. © Springer Science+Business Media, LLC 2007.
• Muralidharan, K., Torras, J., & Trickey, S. B. (2007). Energetics and mechanical properties of silica nanotubes. Journal of Physics Condensed Matter, 19(38).
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  Abstract: The energetically favorable structures and mechanical response to tensile and pure bending forces of single-wall and multi-wall cylindrical silica nanotubes of varying lengths and radii are predicted via classical molecular dynamics and checked, in part, by quantum mechanical studies. Two distinct parameterizations of a popular pair potential are used. One is adapted to bulk properties, the other to small nanoclusters. Predicted stable structures for single-walled tubes as a function of length at specified radii are dependent on potential parameterization. For the bulk-adapted parameterization, singlewalled tubes with large radii (12-membered rings) have an energetic preference to rearrangement into twinned parallel-column structures. Conversely, the nanobased parameterization puts such twinned structures slightly higher in energy than the corresponding single tubes. Both the mechanical properties and failure mechanisms in tension and pure bending of the single-walled tubes depend upon the nanorod dimensions. Predicted structures for the double-walled nanotubes exhibit qualitatively opposite trends for the two parameterizations. Though the potentials give different values for the tensile and bending elastic moduli for the various structures, the qualitative pictures of nanotube failure are quite similar. For comparison and insight, we also studied a small single-walled nanotube using both pure quantum forces and quantum- classical multi-scale simulations. Some distinctly different behaviors emerged. © 2007 IOP Publishing Ltd.
• Torras, J., Yao, H. e., Cao, C., Muralidharan, K., Deumens, E., Cheng, H. -., & Trickey, S. B. (2007). PUPIL: A systematic approach to software integration in multi-scale simulations. Computer Physics Communications, 177(3), 265-279.
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  Abstract: We present a relatively straightforward way to integrate existing software packages into a full multi-scale simulation package in which each application runs in its own address space and there is no run-time intervention by the researcher. The PUPIL (Program for User Package Interfacing and Linking) architectural concept is to provide a simulation Supervisor, implemented as a Manager and various Workers which involve small wrapper interfaces written and installed within each application package and various communication services. The different, autonomous packages ("Calculation Units") are plugged into the PUPIL system which one then operates as a software driver for them. Well-defined protocols are provided for communication between the different Calculation Units and the PUPIL system. The CORBA communication protocol is used to exchange information between running processes. All simulation directives from the user are stored in an XML file that is interpreted by the PUPIL Manager and Workers. An initial version has been designed using the Object Oriented (OO) paradigm and implemented in Java as a fast prototyping language. Tests of implementation ease and of operational correctness (on toy physical systems) have been carried out. In the former category, we document how interfaces to both DL_POLY and SIESTA were done relatively straightforwardly. In the latter category, the most demanding test was the joining of three different packages to do a MD calculation with pattern recognition to identify the QM-forces region and an external QM force calculation. The results show that PUPIL provides ease of operation and maintenance with little overhead. © 2007 Elsevier B.V. All rights reserved.
• Cheng, H., Wang, L., Du, M., Cao, C., Wan, Y., Yao, H. e., Muralidharan, K., Greenlee, G., & Kolchin, A. (2006). Quantum, classical, and multi-scale simulation of silica-water interaction: Molecules, clusters, and extended systems. Journal of Computer-Aided Materials Design, 13(1-3), 161-183.
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  Abstract: Over the past 6years, we have engaged in a multi-faceted computational investigation of water-silica interactions at the fundamental physical and chemical level. This effort has necessitated development and implementation of simulation methods including high-accuracy quantum mechanical approaches, classical molecular dynamics, finite element techniques, and multi-scale modeling. We have found that water and silica can interact via either hydration or hydroxylation. Depending on physical conditions, the former process can be weak (
• Deymier, P. A., Kidong, O. h., Muralidharan, K., Frantzikonis, G., & Runge, K. (2006). Selection of domains for coarse and fine levels of description in mixed-potential simulations. Journal of Computer-Aided Materials Design, 13(1-3), 17-44.
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  Abstract: An example of a mixed-potential molecular dynamics simulation is presented for amorphous silica. Pair potentials are used in the roles of embedding and embedded regions to allow us to study on-the-fly selection of a region for the more accurate description by embedded potentials. Brittle fracture with fast crack growth is the example that we choose to elucidate the characteristics of an amorphous system that lead to reliable prediction of the location of the initial fracture in the unbiased system. We conclude that a properly chosen wavelet analysis will permit such on-the-fly identification of those regions in a multi-scale simulation whose properties need to be described at the highest available accuracy. © 2006 Springer Science+Business Media, Inc.
• Muralidharan, K., Mallik, A., Runge, K., & Deymier, P. A. (2006). Implementation of consistent embedding for a larger system-Amorphous silica. Journal of Computer-Aided Materials Design, 13(1-3), 61-73.
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  Abstract: We examine the performance and behavior of the consistent embedding multi-scale simulation techniques described in the preceding article. The test is bulk amorphous silica, primarily in the small-strain regime. We also examine some practical issues that arise when the technique is used to model mechanical failure. For context, we present results of classical molecular dynamics simulations of fracture mechanisms of amorphous silica. © 2006 Springer Science+Business Media, Inc.
• Muralidharan, K., Deymier, P., & Simmons, J. H. (2005). Dynamics of brittle fracture in amorphous silica: A molecular dynamics study. Transactions of the American Nuclear Society, 92, 711-712.
• Muralidharan, K., Simmons, J. H., Deymier, P. A., & Runge, K. (2005). Molecular dynamics studies of brittle fracture in vitreous silica: Review and recent progress. Journal of Non-Crystalline Solids, 351(18), 1532-1542.
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  Abstract: The dynamics of brittle fracture in vitreous silica has been a subject of many molecular dynamics (MD) simulations and experiments. A striking similarity between both simulations and experiments is the observation of nanoscale voids that eventually coalesce leading to failure. In this work, we review the above MD simulations and carry out further MD investigations using two variations of classical 2-body potentials. We study the effect of charge-transfer, an important aspect neglected by previous simulations. Further, we examine the growth of 'critical' voids and characterize regions surrounding the voids. © 2005 Elsevier B.V. All rights reserved.
• Muralidharan, K., Deymier, P. A., & Simmons, J. H. (2003). A concurrent multiscale finite difference time domain/molecular dynamics method for bridging an elastic continuum to an atomic system. Modelling and Simulation in Materials Science and Engineering, 11(4), 487-501.
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  Abstract: A multiscale methodology that couples a finite difference time domain (FDTD) system (representing an elastic continuum) and an atomistic molecular dynamics (MD) system is proposed. The handshaking involves a parallel coupling of both the length and timescale. The FDTD-MD 'interface' is probed by a wave packet and the elastic impedance mismatch between the two systems is studied by examining the part of the probing wave packet that gets reflected from the interface. The reflected part is characterized in both temporal and frequency domains. Results show that only a small part of the wave is reflected from the interface, indicating a near seamless bridging of the two systems. Further, thermalization of the MD region results in transmission of additional energy into the FDTD region, with the transmitted energy corresponding to frequencies much higher than the central frequency of the probing wave packet. A characteristic resonant frequency exists between the MD and the FDTD regions, which is a result of a feedback between the two regions.
• Muralidharan, K., Deymier, P. A., & Simmons, J. H. (2002). Multiscale modeling of wave propagation: FDTD/MD hybrid method. Materials Research Society Symposium - Proceedings, 731, 15-20.
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  Abstract: Atomic level processes often play an important role in the way a material responds to an external field. Thus in order to model the behavior of materials accurately, it is necessary to develop simulation techniques which can effectively couple atomistic effects to the macroscopic properties of the model system and vice-versa. In other words, a multiscale methodology needs to be developed to bridge the different length and time scales. In this work we study the propagation of an elastic wave through a coupled continuum-atomistic medium. The equations of motion for the wave propagation through the continuum are solved using the Finite Difference Time Domain Method (FDTD). Simultaneously we use Molecular Dynamics (MD) to examine the effect of the wave packet on the atomic dynamics and the effect of atomic dynamics on the propagation of the wave. The handshaking between the FDTD region and the MD region is concurrent.

Proceedings Publications

• Muralidharan, K., Momayez, M., & Chaurasia, A. (2020, February). More Efficient Way to Increase Ventilation in Deep Underground Mine. In Annual Conference of the Society for Mining, Metallurgy and Exploration.
• Muralidharan, K., Momayez, M., & Rao, P. (2020, February). Heat Management Alternatives in Deep Underground Mines as a Crucial Part of Mine Ventilation. In Annual Conference of the Society for Mining, Metallurgy and Exploration.
• Frantziskonis, G. N., Muralidharan, K., & Gur, S. (2018, March 11-15). Effect of porosity on the stress-strain response and hysteretic energy dissipation capacity of NiTi SMA. In 2018 TMS Annual Meeting & Exhibition.
• Frantziskonis, G. N., Muralidharan, K., & Gur, S. (2018, March 11-15). Scale-parity Preserving Multiscale Models for Investigating the Mechanical Properties of Geopolymers. In 2018 TMS Annual Meeting & Exhibition.

Presentations

• Gur, S., Manga, V. R., Bringuier, S., Muralidharan, K., & Frantziskonis, G. N. (2016, April). The role of internal strain in the austenite phase stabilization during the martensitic phase transformation in NiTi shape memory alloys. MRS Spring meeting and exhibit. Phoenix, AZ: MRS.
• Gur, S., Manga, V. R., Bringuier, S., Muralidharan, K., & Frantziskonis, G. N. (2015, March). Anisotropy in the Transformation Dynamics of Austenite (B2) to Martensite (B19’) Associated with Superelasticity in NiTi. 2015 TMS Annual Meeting & Exhibition. Orlando, FL: TMS.