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Lüking M, van der Spoel D, Elf J, Tribello GA. Can molecular dynamics be used to simulate biomolecular recognition? J Chem Phys 2023; 158:2889489. [PMID: 37158325 DOI: 10.1063/5.0146899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 04/19/2023] [Indexed: 05/10/2023] Open
Abstract
There are many problems in biochemistry that are difficult to study experimentally. Simulation methods are appealing due to direct availability of atomic coordinates as a function of time. However, direct molecular simulations are challenged by the size of systems and the time scales needed to describe relevant motions. In theory, enhanced sampling algorithms can help to overcome some of the limitations of molecular simulations. Here, we discuss a problem in biochemistry that offers a significant challenge for enhanced sampling methods and that could, therefore, serve as a benchmark for comparing approaches that use machine learning to find suitable collective variables. In particular, we study the transitions LacI undergoes upon moving between being non-specifically and specifically bound to DNA. Many degrees of freedom change during this transition and that the transition does not occur reversibly in simulations if only a subset of these degrees of freedom are biased. We also explain why this problem is so important to biologists and the transformative impact that a simulation of it would have on the understanding of DNA regulation.
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Affiliation(s)
- Malin Lüking
- Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden
| | - David van der Spoel
- Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden
| | - Johan Elf
- Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden
| | - Gareth A Tribello
- Centre for Quantum Materials and Technologies, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, United Kingdom
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2
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Acharya S, Bagchi B. Diffusion in a two-dimensional energy landscape in the presence of dynamical correlations and validity of random walk model. Phys Rev E 2023; 107:024127. [PMID: 36932553 DOI: 10.1103/physreve.107.024127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 01/26/2023] [Indexed: 06/18/2023]
Abstract
Diffusion in a multidimensional energy surface with minima and barriers is a problem of importance in statistical mechanics and it also has wide applications, such as protein folding. To understand it in such a system, we carry out theory and simulations of a tagged particle moving on a two-dimensional periodic potential energy surface, both in the presence and absence of noise. Langevin dynamics simulations at multiple temperatures are carried out to obtain the diffusion coefficient of a solute particle. Friction is varied from zero to large values. Diffusive motion emerges in the limit of a long time, even in the absence of noise. Noise destroys the correlations and increases diffusion at small friction. Diffusion thus exhibits a nonmonotonic friction dependence at the intermediate value of the damping, ultimately converging to our theoretically predicted value. The latter is obtained using the well-established relationship between diffusion and random walk. An excellent agreement is obtained between theory and simulations in the high-friction limit but not so in the intermediate regime. We explain the deviation in the low- to intermediate-friction regime using the modified random walk theory. The rate of escape from one cell to another is obtained from the multidimensional rate theory of Langer. We find that enhanced dimensionality plays an important role. To quantify the effects of noise on the potential-imposed coherence on the trajectories, we calculate the Lyapunov exponent. At small friction values, the Lyapunov exponent mimics the friction dependence of the rate.
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Affiliation(s)
- Subhajit Acharya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India
| | - Biman Bagchi
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India
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3
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Dutta R, Pollak E. Microscopic origin of diffusive dynamics in the context of transition path time distributions for protein folding and unfolding. Phys Chem Chem Phys 2022; 24:25373-25382. [PMID: 36239220 DOI: 10.1039/d2cp03158b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Experimentally measured transition path time distributions are usually analyzed theoretically in terms of a diffusion equation over a free energy barrier. It is though well understood that the free energy profile separating the folded and unfolded states of a protein is characterized as a transition through many stable micro-states which exist between the folded and unfolded states. Why is it then justified to model the transition path dynamics in terms of a diffusion equation, namely the Smoluchowski equation (SE)? In principle, van Kampen has shown that a nearest neighbor Markov chain of thermal jumps between neighboring microstates will lead in a continuum limit to the SE, such that the friction coefficient is proportional to the mean residence time in each micro-state. However, the practical question of how many microstates are needed to justify modeling the transition path dynamics in terms of an SE has not been addressed. This is a central topic of this paper where we compare numerical results for transition paths based on the diffusion equation on the one hand and the nearest neighbor Markov jump model on the other. Comparison of the transition path time distributions shows that one needs at least a few dozen microstates to obtain reasonable agreement between the two approaches. Using the Markov nearest neighbor model one also obtains good agreement with the experimentally measured transition path time distributions for a DNA hairpin and PrP protein. As found previously when using the diffusion equation, the Markov chain model used here also reproduces the experimentally measured long time tail and confirms that the transition path barrier height is ∼3kBT. This study indicates that in the future, when attempting to model experimentally measured transition path time distributions, one should perhaps prefer a nearest neighbor Markov model which is well defined also for rough energy landscapes. Such studies can also shed light on the minimal number of microstates needed to unravel the experimental data.
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Affiliation(s)
- Rajesh Dutta
- Chemical and Biological Physics Department, Weizmann Institute of Science, 7610001 Rehovot, Israel.
| | - Eli Pollak
- Chemical and Biological Physics Department, Weizmann Institute of Science, 7610001 Rehovot, Israel.
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4
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Mukherjee S, Bagchi B. Theoretical analyses of pressure induced glass transition in water: Signatures of surprising diffusion-entropy scaling across the transition. Mol Phys 2021. [DOI: 10.1080/00268976.2021.1930222] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Saumyak Mukherjee
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India
| | - Biman Bagchi
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India
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5
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Acharya S, Bagchi B. Study of entropy–diffusion relation in deterministic Hamiltonian systems through microscopic analysis. J Chem Phys 2020; 153:184701. [DOI: 10.1063/5.0022818] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Affiliation(s)
- Subhajit Acharya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India
| | - Biman Bagchi
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India
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6
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Banerjee P, Bagchi B. Role of local order in anomalous ion diffusion: Interrogation through tetrahedral entropy of aqueous solvation shells. J Chem Phys 2020; 153:154505. [PMID: 33092370 DOI: 10.1063/5.0022580] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Small rigid ions perturb the water structure around them significantly. At constant viscosity, alkali cations (Li+, Na+, and so on) exhibit an anomalous non-monotonic dependence of diffusivity on ion-size, in stark violation of the Stokes-Einstein expression. Although this is a well-known problem, we find that an entropic view of the problem can be developed, which provides valuable insight. The local entropy experienced by the solute ion is relevant here, which leads to the connection with local viscosity, discussed earlier by many. Due to the strong interactions with ions, the translational and rotational entropy of solvation water decreases sharply; however, an opposite effect comes from the disruption of the tetrahedral network structure of water near the charges. We compute the tetrahedral order of water molecules (qtet) around the ion and suitably defined tetrahedral entropy [S(qtet)] that is a contribution to the excess entropy of the system. Our results reveal that although the structural properties of the second shell become nearly identical to the bulk, S(qtet) of the second shell is found to play an important role in giving rise to the non-monotonic ion-size dependence. The detailed study of the static and dynamic fluctuations in qtet and the number of hydration water molecules provides interesting insights into correlation between the structure and dynamics; the smallest static fluctuation of qtet for the first hydration shell water molecules of Li+ is indicative of the iceberg picture. The study of fluctuation properties of qtet and the coordination number also reveals the role of the second hydration layer and could explain the anomalous behavior of the Rb+ ion.
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Affiliation(s)
- Puja Banerjee
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
| | - Biman Bagchi
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
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7
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Gray TH, Yong EH. Effective diffusion in one-dimensional rough potential-energy landscapes. Phys Rev E 2020; 102:022138. [PMID: 32942433 DOI: 10.1103/physreve.102.022138] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Accepted: 08/11/2020] [Indexed: 06/11/2023]
Abstract
Diffusion in spatially rough, confining, one-dimensional continuous energy landscapes is treated using Zwanzig's proposal, which is based on the Smoluchowski equation. We show that Zwanzig's conjecture agrees with Brownian dynamics simulations only in the regime of small roughness. Our correction of Zwanzig's framework corroborates well with numerical results. A numerical simulation scheme based on our coarse-grained Langevin dynamics offers significant reductions in computational time. The mean first-passage time problem in the case of random roughness is treated. Finally, we address the validity of the separation of length scales assumption for the case of polynomial backgrounds and cosine-based roughness. Our results are applicable to hierarchical energy landscapes such as that of a protein's folding and transport processes in disordered media, where there is clear separation of length scale between smooth underlying potential and its rough perturbation.
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Affiliation(s)
- Thomas H Gray
- Department of Chemical Engineering and Biotechnology, West Cambridge Site, Philippa Fawcett Drive, University of Cambridge, CB3 0AS, Cambridge, United Kingdom
- T.C.M. Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - Ee Hou Yong
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
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8
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Gray TH, Yong EH. Overdamped Brownian dynamics in piecewise-defined energy landscapes. Phys Rev E 2020; 101:052123. [PMID: 32575297 DOI: 10.1103/physreve.101.052123] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2018] [Accepted: 04/17/2020] [Indexed: 11/07/2022]
Abstract
We study the overdamped Brownian dynamics of particles moving in piecewise-defined potential energy landscapes U(x), where the height Q of each section is obtained from the exponential distribution p(Q)=aβexp(-aβQ), where β is the reciprocal thermal energy, and a>0. The averaged effective diffusion coefficient 〈D_{eff}〉 is introduced to characterize the diffusive motion: 〈x^{2}〉=2〈D_{eff}〉t. A general expression for 〈D_{eff}〉 in terms of U(x) and p(Q) is derived and then applied to three types of energy landscape: flat sections, smooth maxima, and sharp maxima. All three cases display a transition between subdiffusive and diffusive behavior at a=1, and a reduction to free diffusion as a→∞. The behavior of 〈D_{eff}〉 around the transition is investigated and found to depend heavily upon the shape of the maxima: Energy landscapes made up of flat sections or smooth maxima display power-law behavior, while for landscapes with sharp maxima, strongly divergent behavior is observed. Two aspects of the subdiffusive regime are studied: the growth of the mean squared displacement with time and the distribution of mean first-passage times. For the former, agreement between Brownian dynamics simulations and a coarse-grained equivalent was observed, but the results deviated from the random barrier model's predictions. The discrepancy could be a finite-time effect. For the latter, agreement between the characteristic exponent calculated numerically and that predicted by the random barrier model is observed in the large-amplitude limit.
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Affiliation(s)
- Thomas H Gray
- Statistical Physics Group, Department of Chemical Engineering and Biotechnology, West Cambridge Site, Philippa Fawcett Drive, University of Cambridge, CB3 0AS, Cambridge, United Kingdom.,T.C.M. Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Ee Hou Yong
- School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
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9
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Li Y, Xu Y, Kurths J, Duan J. The influences of correlated spatially random perturbations on first passage time in a linear-cubic potential. CHAOS (WOODBURY, N.Y.) 2019; 29:101102. [PMID: 31675827 DOI: 10.1063/1.5116626] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Accepted: 09/17/2019] [Indexed: 06/10/2023]
Abstract
The influences of correlated spatially random perturbations (SRPs) on the first passage problem are studied in a linear-cubic potential with a time-changing external force driven by a Gaussian white noise. First, the escape rate in the absence of SRPs is obtained by Kramers' theory. For the random potential case, we simplify the escape rate by multiplying the escape rate of smooth potentials with a specific coefficient, which is to evaluate the influences of randomness. Based on this assumption, the escape rates are derived in two scenarios, i.e., small/large correlation lengths. Consequently, the first passage time distributions (FPTDs) are generated for both smooth and random potential cases. We find that the position of the maximal FPTD has a very good agreement with that of numerical results, which verifies the validity of the proposed approximations. Besides, with increasing the correlation length, the FPTD shifts to the left gradually and tends to the smooth potential case. Second, we investigate the most probable passage time (MPPT) and mean first passage time (MFPT), which decrease with increasing the correlation length. We also find that the variation ranges of both MPPT and MFPT increase nonlinearly with increasing the intensity. Besides, we briefly give constraint conditions to guarantee the validity of our approximations. This work enables us to approximately evaluate the influences of the correlation length of SRPs in detail, which was always ignored previously.
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Affiliation(s)
- Yongge Li
- Center for Mathematical Sciences & School of Mathematics and Statistics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Yong Xu
- Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710072, China
| | - Jürgen Kurths
- Center for Mathematical Sciences & School of Mathematics and Statistics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Jinqiao Duan
- Department of Applied Mathematics, Illinois Institute of Technology, Chicago, Illinois 60616, USA
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10
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Abstract
This article gives an overview of excess-entropy scaling, the 1977 discovery by Rosenfeld that entropy determines properties of liquids like viscosity, diffusion constant, and heat conductivity. We give examples from computer simulations confirming this intriguing connection between dynamics and thermodynamics, counterexamples, and experimental validations. Recent uses in application-related contexts are reviewed, and theories proposed for the origin of excess-entropy scaling are briefly summarized. It is shown that if two thermodynamic state points of a liquid have the same microscopic dynamics, they must have the same excess entropy. In this case, the potential-energy function exhibits a symmetry termed hidden scale invariance, stating that the ordering of the potential energies of configurations is maintained if these are scaled uniformly to a different density. This property leads to the isomorph theory, which provides a general framework for excess-entropy scaling and illuminates, in particular, why this does not apply rigorously and universally. It remains an open question whether all aspects of excess-entropy scaling and related regularities reflect hidden scale invariance in one form or other.
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Affiliation(s)
- Jeppe C Dyre
- Glass and Time, IMFUFA, Department of Science and Environment, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark
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11
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Novikov SV. Diffusion of a particle in the spatially correlated exponential random energy landscape: Transition from normal to anomalous diffusion. J Chem Phys 2018; 148:024505. [PMID: 29331121 DOI: 10.1063/1.5001279] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Diffusive transport of a particle in a spatially correlated random energy landscape having exponential density of states has been considered. We exactly calculate the diffusivity in the nondispersive quasi-equilibrium transport regime for the 1D transport model and found that for slow decaying correlation functions the diffusivity becomes singular at some particular temperature higher than the temperature of the transition to the true non-equilibrium dispersive transport regime. It means that the diffusion becomes anomalous and does not follow the usual ∝ t1/2 law. In such situation, the fully developed non-equilibrium regime emerges in two stages: first, at some temperature there is the transition from the normal to anomalous diffusion, and then at lower temperature the average velocity for the infinite medium goes to zero, thus indicating the development of the true dispersive regime. Validity of the Einstein relation is discussed for the situation where the diffusivity does exist. We provide also some arguments in favor of conservation of the major features of the new transition scenario in higher dimensions.
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Affiliation(s)
- S V Novikov
- A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Leninsky Prosp. 31, 119071 Moscow, Russia and National Research University Higher School of Economics, Myasnitskaya Ulitsa 20, Moscow 101000, Russia
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12
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Li Y, Xu Y, Kurths J. Roughness-enhanced transport in a tilted ratchet driven by Lévy noise. Phys Rev E 2017; 96:052121. [PMID: 29347800 DOI: 10.1103/physreve.96.052121] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Indexed: 06/07/2023]
Abstract
The enhanced transport of particles by roughness in a tilted rough ratchet potential subject to a Lévy noise is investigated in this paper. Due to the roughness, the transport process exhibits quite different properties compared to the smooth case. We find that the roughness on the potential wall functions like a ladder to provide the convenience for particles to climb up but hinder them to slide down. The mean first passage time from one well to its right adjacent well and the mean velocity are, respectively, calculated versus the roughness, the external force, and the Lévy stability index. Our results show that the roughness is able to induce an enhancement on the mean velocity of particles and accelerate the barrier crossing process. The general conditions require a small external force and a small Lévy stability index. We find that with increasing external forces, the enhancement areas of roughness and Lévy stability index both shrink. However, for the Lévy stability index within the enhancement area, its increase will enlarge the enhancement area of roughness. On the contrary, under the same conditions we observe that for a Gaussian noise the roughness always reduces the corresponding mean velocity which is very different from the case of Lévy noise.
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Affiliation(s)
- Yongge Li
- Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710072, China
| | - Yong Xu
- Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710072, China
- Potsdam Institute for Climate Impact Research, 14412 Potsdam, Germany
- Department of Physics, Humboldt University Berlin, 12489 Berlin, Germany
| | - Jürgen Kurths
- Potsdam Institute for Climate Impact Research, 14412 Potsdam, Germany
- Department of Physics, Humboldt University Berlin, 12489 Berlin, Germany
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13
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Konincks T, Krakoviack V. Dynamics of fluids in quenched-random potential energy landscapes: a mode-coupling theory approach. SOFT MATTER 2017; 13:5283-5297. [PMID: 28677713 DOI: 10.1039/c7sm00984d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Motivated by a number of recent experimental and computational studies of the dynamics of fluids plunged in quenched-disordered external fields, we report on a theoretical investigation of this topic within the framework of the mode-coupling theory, based on the simple model of the hard-sphere fluid in a Gaussian random field. The possible dynamical arrest scenarios driven by an increase of the disorder strength and/or of the fluid density are mapped, and the corresponding evolutions of time-dependent quantities typically used for the characterization of anomalous self-diffusion are illustrated with detailed computations. Overall, a fairly reasonable picture of the dynamics of the system at hand is outlined, which in particular involves a non-monotonicity of the self-diffusion coefficient with fluid density at fixed disorder strength, in agreement with experiments. The disorder correlation length is shown to have a strong influence on the latter feature.
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Affiliation(s)
- Thomas Konincks
- Univ Lyon, ENS de Lyon, CNRS UMR 5182, Université Claude Bernard Lyon 1, Laboratoire de Chimie, F-69342, Lyon, France.
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BANERJEE ATREYEE, NANDI MANOJKUMAR, BHATTACHARYYA SARIKAMAITRA. Validity of the Rosenfeld relationship: A comparative study of the network forming NTW model and other simple liquids. J CHEM SCI 2017. [DOI: 10.1007/s12039-017-1249-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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15
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Li Y, Xu Y, Kurths J, Yue X. Lévy-noise-induced transport in a rough triple-well potential. Phys Rev E 2016; 94:042222. [PMID: 27841518 DOI: 10.1103/physreve.94.042222] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Indexed: 06/06/2023]
Abstract
Rough energy landscape and noisy environment are two common features in many subjects, such as protein folding. Due to the wide findings of bursting or spiking phenomenon in biology science, small diffusions mixing large jumps are adopted to model the noisy environment that can be properly described by Lévy noise. We combine the Lévy noise with the rough energy landscape, modeled by a potential function superimposed by a fast oscillating function, and study the transport of a particle in a rough triple-well potential excited by Lévy noise, rather than only small perturbations. The probabilities of a particle staying in the middle well are considered under different amplitudes of roughness to find out how roughness affects the steady-state probability density function. Variations in the mean first passage time from the middle well to the right well have been investigated with respect to Lévy parameters and amplitudes of the roughness. In addition, we have examined the influences of roughness on the splitting probabilities of the first escape from the middle well. We uncover that the roughness can enhance significantly the first escape of a particle from the middle well, especially for different skewness parameters, but weak differences are found for stability index and noise intensity on the probabilities a particle staying in the middle well and splitting probability to the right.
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Affiliation(s)
- Yongge Li
- Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710072, China
- Potsdam Institute for Climate Impact Research, Potsdam 14412, Germany
| | - Yong Xu
- Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710072, China
| | - Jürgen Kurths
- Potsdam Institute for Climate Impact Research, Potsdam 14412, Germany
- Institute of Applied Physics of the Russian Academy of Sciences, 603950 Nizhny Novgorod, Russia
| | - Xiaole Yue
- Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710072, China
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16
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Seki K, Bagchi K, Bagchi B. Anomalous dimensionality dependence of diffusion in a rugged energy landscape: How pathological is one dimension? J Chem Phys 2016; 144:194106. [PMID: 27208935 DOI: 10.1063/1.4948936] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Diffusion in one dimensional rugged energy landscape (REL) is predicted to be pathologically different (from any higher dimension) with a much larger chance of encountering broken ergodicity [D. L. Stein and C. M. Newman, AIP Conf. Proc. 1479, 620 (2012)]. However, no quantitative study of this difference has been reported, despite the prevalence of multidimensional physical models in the literature (like a high dimensional funnel guiding protein folding/unfolding). Paradoxically, some theoretical studies of these phenomena still employ a one dimensional diffusion description for analytical tractability. We explore the dimensionality dependent diffusion on REL by carrying out an effective medium approximation based analytical calculations and compare them with the available computer simulation results. We find that at an intermediate level of ruggedness (assumed to have a Gaussian distribution), where diffusion is well-defined, the value of the effective diffusion coefficient depends on dimensionality and changes (increases) by several factors (∼5-10) in going from 1d to 2d. In contrast, the changes in subsequent transitions (like 2d to 3d and 3d to 4d and so on) are far more modest, of the order of 10-20% only. When ruggedness is given by random traps with an exponential distribution of barrier heights, the mean square displacement (MSD) is sub-diffusive (a well-known result), but the growth of MSD is described by different exponents in one and higher dimensions. The reason for such strong ruggedness induced retardation in the case of one dimensional REL is discussed. We also discuss the special limiting case of infinite dimension (d = ∞) where the effective medium approximation becomes exact and where theoretical results become simple. We discuss, for the first time, the role of spatial correlation in the landscape on diffusion of a random walker.
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Affiliation(s)
- Kazuhiko Seki
- Nanomaterials Research Institute (NMRI), National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8565, Japan
| | - Kaushik Bagchi
- Department of Mathematics, Ohio State University, Columbus, Ohio 43201, USA and Chitrakut Annexe, 4th Main Road, Malleswaram, Bangalore 560012, India
| | - Biman Bagchi
- Institute of Molecular Science, Okazaki, Aichi 444, Japan and Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
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17
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Nandi MK, Banerjee A, Sengupta S, Sastry S, Bhattacharyya SM. Unraveling the success and failure of mode coupling theory from consideration of entropy. J Chem Phys 2016; 143:174504. [PMID: 26547173 DOI: 10.1063/1.4934986] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
We analyze the dynamics of model supercooled liquids in a temperature regime where predictions of mode coupling theory (MCT) are known to be valid qualitatively. In this regime, the Adam-Gibbs (AG) relation, based on an activation picture of dynamics, also describes the dynamics satisfactorily, and we explore the mutual consistency and interrelation of these descriptions. Although entropy and dynamics are related via phenomenological theories, the connection between MCT and entropy has not been argued for. In this work, we explore this connection and provide a microscopic derivation of the phenomenological Rosenfeld theory. At low temperatures, the overlap between the MCT power law regime and AG relation implies that the AG relation predicts an avoided divergence at Tc, the origin of which can be related to the vanishing of pair configurational entropy, which we find occurring at the same temperature. We also show that the residual multiparticle entropy plays an important role in describing the relaxation time.
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Affiliation(s)
- Manoj Kumar Nandi
- Polymer Science and Engineering Division, CSIR-National Chemical Laboratory, Pune 411008, India
| | - Atreyee Banerjee
- Polymer Science and Engineering Division, CSIR-National Chemical Laboratory, Pune 411008, India
| | - Shiladitya Sengupta
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Srikanth Sastry
- Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur Campus, Bengaluru 560 064, India
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18
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Seki K, Bagchi B. Relationship between entropy and diffusion: A statistical mechanical derivation of Rosenfeld expression for a rugged energy landscape. J Chem Phys 2016; 143:194110. [PMID: 26590530 DOI: 10.1063/1.4935969] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Diffusion-a measure of dynamics, and entropy-a measure of disorder in the system are found to be intimately correlated in many systems, and the correlation is often strongly non-linear. We explore the origin of this complex dependence by studying diffusion of a point Brownian particle on a model potential energy surface characterized by ruggedness. If we assume that the ruggedness has a Gaussian distribution, then for this model, one can obtain the excess entropy exactly for any dimension. By using the expression for the mean first passage time, we present a statistical mechanical derivation of the well-known and well-tested scaling relation proposed by Rosenfeld between diffusion and excess entropy. In anticipation that Rosenfeld diffusion-entropy scaling (RDES) relation may continue to be valid in higher dimensions (where the mean first passage time approach is not available), we carry out an effective medium approximation (EMA) based analysis of the effective transition rate and hence of the effective diffusion coefficient. We show that the EMA expression can be used to derive the RDES scaling relation for any dimension higher than unity. However, RDES is shown to break down in the presence of spatial correlation among the energy landscape values.
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Affiliation(s)
- Kazuhiko Seki
- NMRI, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8565, Japan
| | - Biman Bagchi
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
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Strong SE, Eaves JD. Tetracene Aggregation on Polar and Nonpolar Surfaces: Implications for Singlet Fission. J Phys Chem Lett 2015; 6:1209-1215. [PMID: 26262973 DOI: 10.1021/acs.jpclett.5b00141] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
In molecular crystals that exhibit singlet fission, quantum yields depend strongly on intermolecular configurations that control the relevant electronic couplings. Here, we explore how noncovalent interactions between molecules and surfaces stabilize intermolecular structures with strong singlet fission couplings. Using molecular dynamics simulations, we studied the aggregation patterns of tetracene molecules on a solid surface as a function of surface polarity. Even at low surface concentrations, tetracene self-assembled into nanocrystallites where about 10-20% of the clustered molecules were part of at least one herringbone structure. The herringbone structure is the native structure of crystalline tetracene, which exhibits a high singlet fission quantum yield. Increasing the polarity of the surface reduced both the amount of clustering and the relative number of herringbone configurations, but only when the dipoles on the surface were orientationally disordered. These results have implications for the application of singlet fission in dye-sensitized solar cells.
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Affiliation(s)
- Steven E Strong
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Joel D Eaves
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States
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