WorldWideScience

Sample records for all-atom molecular dynamics

  1. Coupling all-atom molecular dynamics simulations of ions in water with Brownian dynamics

    CERN Document Server

    Erban, Radek

    2015-01-01

    Molecular dynamics (MD) simulations of ions (K$^+$, Na$^+$, Ca$^{2+}$ and Cl$^-$) in aqueous solutions are investigated. Water is described using the SPC/E model. A stochastic coarse-grained description for ion behaviour is presented and parameterized using MD simulations. It is given as a system of coupled stochastic and ordinary differential equations, describing the ion position, velocity and acceleration. The stochastic coarse-grained model provides an intermediate description between all-atom MD simulations and Brownian dynamics (BD) models. It is used to develop a multiscale method which uses all-atom MD simulations in parts of the computational domain and (less detailed) BD simulations in the remainder of the domain.

  2. Combining Coarse-Grained Protein Models with Replica-Exchange All-Atom Molecular Dynamics

    OpenAIRE

    Andrzej Koliński; Maksim Kouza; Dominik Gront; Sebastian Kmiecik; Jacek Wabik

    2013-01-01

    We describe a combination of all-atom simulations with CABS, a well-established coarse-grained protein modeling tool, into a single multiscale protocol. The simulation method has been tested on the C-terminal beta hairpin of protein G, a model system of protein folding. After reconstructing atomistic details, conformations derived from the CABS simulation were subjected to replica-exchange molecular dynamics simulations with OPLS-AA and AMBER99sb force fields in explicit solvent. Such a combi...

  3. Combining Coarse-Grained Protein Models with Replica-Exchange All-Atom Molecular Dynamics

    Directory of Open Access Journals (Sweden)

    Andrzej Koliński

    2013-05-01

    Full Text Available We describe a combination of all-atom simulations with CABS, a well-established coarse-grained protein modeling tool, into a single multiscale protocol. The simulation method has been tested on the C-terminal beta hairpin of protein G, a model system of protein folding. After reconstructing atomistic details, conformations derived from the CABS simulation were subjected to replica-exchange molecular dynamics simulations with OPLS-AA and AMBER99sb force fields in explicit solvent. Such a combination accelerates system convergence several times in comparison with all-atom simulations starting from the extended chain conformation, demonstrated by the analysis of melting curves, the number of native-like conformations as a function of time and secondary structure propagation. The results strongly suggest that the proposed multiscale method could be an efficient and accurate tool for high-resolution studies of protein folding dynamics in larger systems.

  4. Combining Coarse-Grained Protein Models with Replica-Exchange All-Atom Molecular Dynamics

    CERN Document Server

    Wabik, Jacek; Gront, Dominik; Kouza, Maksim; Kolinski, Andrzej

    2013-01-01

    We describe a combination of all-atom simulations with CABS, a well-established coarse-grained protein modeling tool, into a single multiscale protocol. The simulation method has been tested on the C-terminal beta hairpin of protein G, a model system of protein folding. After reconstructing atomistic details, conformations derived from the CABS simulation were subjected to replica-exchange molecular dynamics simulations with OPLS-AA and AMBER99sb force fields in explicit solvent. Such a combination accelerates system convergence several times in comparison with all-atom simulations starting from the extended chain conformation, demonstrated by the analysis of melting curves, the number of native-like conformations as a function of time and secondary structure propagation. The results strongly suggest that the proposed multiscale method could be an efficient and accurate tool for high-resolution studies of protein folding dynamics in larger systems.

  5. Picosecond infrared laser-induced all-atom nonequilibrium molecular dynamics simulation of dissociation of viruses.

    Science.gov (United States)

    Hoang Man, Viet; Van-Oanh, Nguyen-Thi; Derreumaux, Philippe; Li, Mai Suan; Roland, Christopher; Sagui, Celeste; Nguyen, Phuong H

    2016-04-28

    Since the discovery of the plant pathogen tobacco mosaic virus as the first viral entity in the late 1800s, viruses traditionally have been mainly thought of as pathogens for disease-resistances. However, viruses have recently been exploited as nanoplatforms with applications in biomedicine and materials science. To this aim, a large majority of current methods and tools have been developed to improve the physical stability of viral particles, which may be critical to the extreme physical or chemical conditions that viruses may encounter during purification, fabrication processes, storage and use. However, considerably fewer studies are devoted to developing efficient methods to degrade or recycle such enhanced stability biomaterials. With this in mind, we carry out all-atom nonequilibrium molecular dynamics simulation, inspired by the recently developed mid-infrared free-electron laser pulse technology, to dissociate viruses. Adopting the poliovirus as a representative example, we find that the primary step in the dissociation process is due to the strong resonance between the amide I vibrational modes of the virus and the tuned laser frequencies. This process is determined by a balance between the formation and dissociation of the protein shell, reflecting the highly plasticity of the virus. Furthermore, our method should provide a feasible approach to simulate viruses, which is otherwise too expensive for conventional equilibrium all-atom simulations of such very large systems. Our work shows a proof of concept which may open a new, efficient way to cleave or to recycle virus-based materials, provide an extremely valuable tool for elucidating mechanical aspects of viruses, and may well play an important role in future fighting against virus-related diseases. PMID:27071540

  6. All-atom molecular dynamics calculation study of entire poliovirus empty capsids in solution

    Energy Technology Data Exchange (ETDEWEB)

    Andoh, Y.; Yoshii, N.; Yamada, A.; Kojima, H.; Mizutani, K.; Okazaki, S., E-mail: okazaki@apchem.nagoya-u.ac.jp [Department of Applied Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Fujimoto, K. [Department of Pharmacy, College of Pharmaceutical Sciences, Ritsumeikan University, Nojihigashi, Kusatsu, Shiga 525-8577 (Japan); Nakagawa, A. [Institute for Protein Research, Osaka University, Yamadaoka, Suita, Osaka 565-0871 (Japan); Nomoto, A. [Institute of Microbial Chemistry, Kamiosaki, Shinagawa-ku, Tokyo 141-0021 (Japan)

    2014-10-28

    Small viruses that belong, for example, to the Picornaviridae, such as poliovirus and foot-and-mouth disease virus, consist simply of capsid proteins and a single-stranded RNA (ssRNA) genome. The capsids are quite stable in solution to protect the genome from the environment. Here, based on long-time and large-scale 6.5 × 10{sup 6} all-atom molecular dynamics calculations for the Mahoney strain of poliovirus, we show microscopic properties of the viral capsids at a molecular level. First, we found equilibrium rapid exchange of water molecules across the capsid. The exchange rate is so high that all water molecules inside the capsid (about 200 000) can leave the capsid and be replaced by water molecules from the outside in about 25 μs. This explains the capsid's tolerance to high pressures and deactivation by exsiccation. In contrast, the capsid did not exchange ions, at least within the present simulation time of 200 ns. This implies that the capsid can function, in principle, as a semipermeable membrane. We also found that, similar to the xylem of trees, the pressure of the solution inside the capsid without the genome was negative. This is caused by coulombic interaction of the solution inside the capsid with the capsid excess charges. The negative pressure may be compensated by positive osmotic pressure by the solution-soluble ssRNA and the counter ions introduced into it.

  7. All-atom molecular dynamics calculation study of entire poliovirus empty capsids in solution

    International Nuclear Information System (INIS)

    Small viruses that belong, for example, to the Picornaviridae, such as poliovirus and foot-and-mouth disease virus, consist simply of capsid proteins and a single-stranded RNA (ssRNA) genome. The capsids are quite stable in solution to protect the genome from the environment. Here, based on long-time and large-scale 6.5 × 106 all-atom molecular dynamics calculations for the Mahoney strain of poliovirus, we show microscopic properties of the viral capsids at a molecular level. First, we found equilibrium rapid exchange of water molecules across the capsid. The exchange rate is so high that all water molecules inside the capsid (about 200 000) can leave the capsid and be replaced by water molecules from the outside in about 25 μs. This explains the capsid's tolerance to high pressures and deactivation by exsiccation. In contrast, the capsid did not exchange ions, at least within the present simulation time of 200 ns. This implies that the capsid can function, in principle, as a semipermeable membrane. We also found that, similar to the xylem of trees, the pressure of the solution inside the capsid without the genome was negative. This is caused by coulombic interaction of the solution inside the capsid with the capsid excess charges. The negative pressure may be compensated by positive osmotic pressure by the solution-soluble ssRNA and the counter ions introduced into it

  8. All-Atom Molecular Dynamics Simulation of Protein Translocation through an α-Hemolysin Nanopore

    KAUST Repository

    Di Marino, Daniele

    2015-08-06

    © 2015 American Chemical Society. Nanopore sensing is attracting the attention of a large and varied scientific community. One of the main issues in nanopore sensing is how to associate the measured current signals to specific features of the molecule under investigation. This is particularly relevant when the translocating molecule is a protein and the pore is sufficiently narrow to necessarily involve unfolding of the translocating protein. Recent experimental results characterized the cotranslocational unfolding of Thioredoxin (Trx) passing through an α-hemolisin pore, providing evidence for the existence of a multistep process. In this study we report the results of all-atom molecular dynamics simulations of the same system. Our data indicate that Trx translocation involves two main barriers. The first one is an unfolding barrier associated with a translocation intermediate where the N-terminal region of Trx is stuck at the pore entrance in a conformation that strongly resembles the native one. After the abrupt unfolding of the N-terminal region, the Trx enters the α-hemolisin vestibule. During this stage, the constriction is occupied not only by the translocating residue but also by a hairpin-like structure forming a tangle in the constriction. The second barrier is associated with the disentangling of this region.

  9. Application of principal component analysis in protein unfolding: An all-atom molecular dynamics simulation study

    Science.gov (United States)

    Das, Atanu; Mukhopadhyay, Chaitali

    2007-10-01

    We have performed molecular dynamics (MD) simulation of the thermal denaturation of one protein and one peptide—ubiquitin and melittin. To identify the correlation in dynamics among various secondary structural fragments and also the individual contribution of different residues towards thermal unfolding, principal component analysis method was applied in order to give a new insight to protein dynamics by analyzing the contribution of coefficients of principal components. The cross-correlation matrix obtained from MD simulation trajectory provided important information regarding the anisotropy of backbone dynamics that leads to unfolding. Unfolding of ubiquitin was found to be a three-state process, while that of melittin, though smaller and mostly helical, is more complicated.

  10. Effects of Lipid Composition on Bilayer Membranes Quantified by All-Atom Molecular Dynamics.

    Science.gov (United States)

    Ding, Wei; Palaiokostas, Michail; Wang, Wen; Orsi, Mario

    2015-12-10

    Biological bilayer membranes typically contain varying amounts of lamellar and nonlamellar lipids. Lamellar lipids, such as dioleoylphosphatidylcholine (DOPC), are defined by their tendency to form the lamellar phase, ubiquitous in biology. Nonlamellar lipids, such as dioleoylphosphatidylethanolamine (DOPE), prefer instead to form nonlamellar phases, which are mostly nonbiological. However, nonlamellar lipids mix with lamellar lipids in biomembrane structures that remain overall lamellar. Importantly, changes in the lamellar vs nonlamellar lipid composition are believed to affect membrane function and modulate membrane proteins. In this work, we employ atomistic molecular dynamics simulations to quantify how a range of bilayer properties are altered by variations in the lamellar vs nonlamellar lipid composition. Specifically, we simulate five DOPC/DOPE bilayers at mixing ratios of 1/0, 3/1, 1/1, 1/3, and 0/1. We examine properties including lipid area and bilayer thickness, as well as the transmembrane profiles of electron density, lateral pressure, electric field, and dipole potential. While the bilayer structure is only marginally altered by lipid composition changes, dramatic effects are observed for the lateral pressure, electric field, and dipole potential profiles. Possible implications for membrane function are discussed. PMID:26560961

  11. Structure and Function of Photosystem I-[FeFe] Hydrogenase Protein Fusions: An All-Atom Molecular Dynamics Study.

    Science.gov (United States)

    Harris, Bradley J; Cheng, Xiaolin; Frymier, Paul

    2016-02-01

    All-atom molecular dynamics (MD) simulation was used to study the solution dynamics and protein-protein interactions of protein fusions of photosystem I (PSI) from Thermosynechococcus elongatus and an [FeFe]-hydrogenase (FeFe H2ase) from Clostridium pasteurianum, a unique complex capable of photocatalytic hydrogen production. This study involved fusions of these two proteins via dithiol linkers of different length including decanedithiol, octanedithiol, and hexanedithiol, for which experimental data had previously been obtained. Evaluation of root-mean-squared deviations (RMSDs) relative to the respective crystal structures of PSI and the FeFe H2ase shows that these fusion complexes approach stable equilibrium conformations during the MD simulations. Investigating protein mobility via root-mean-squared fluctuations (RMSFs) reveals that tethering via the shortest hexanedithiol linker results in increased atomic fluctuations of both PSI and the hydrogenase in these fusion complexes. Evaluation of the inter- and intraprotein electron transfer distances in these fusion complexes indicates that the structural changes in the FeFe H2ase arising from ligation to PSI via the shortest hexanedithiol linker may hinder electron transport in the hydrogenase, thus providing a molecular level explanation for the observation that the medium-length octanedithiol linker gives the highest hydrogen production rate. PMID:26671167

  12. Membrane Binding and Insertion of a pHLIP Peptide Studied by All-Atom Molecular Dynamics Simulations

    Directory of Open Access Journals (Sweden)

    Guanghong Wei

    2013-07-01

    Full Text Available Recent experiments in function mechanism study reported that a pH low-insertion peptide (pHLIP can insert into a zwitterionic palmitoyloleoylphosphatidylcholine (POPC lipid bilayer at acidic pH while binding to the bilayer surface at basic pH. However, the atomic details of the pH-dependent interaction of pHLIP with a POPC bilayer are not well understood. In this study, we investigate the detailed interactions of pHLIP with a POPC bilayer at acidic and basic pH conditions as those used in function mechanism study, using all-atom molecular dynamics (MD simulations. Simulations have been performed by employing the initial configurations, where pHLIP is placed in aqueous solution, parallel to bilayer surface (system S, partially-inserted (system P, or fully-inserted (system F in POPC bilayers. On the basis of multiple 200-ns MD simulations, we found (1 pHLIP in system S can spontaneously insert into a POPC bilayer at acidic pH, while binding to the membrane surface at basic pH; (2 pHLIP in system P can insert deep into a POPC bilayer at acidic pH, while it has a tendency to exit, and stays at bilayer surface at basic pH; (3 pHLIP in system F keeps in an α-helical structure at acidic pH while partially unfolding at basic pH. This study provides at atomic-level the pH-induced insertion of pHLIP into POPC bilayer.

  13. All-Atom Molecular Dynamics Simulations Reveal Significant Differences in Interaction between Antimycin and Conserved Amino Acid Residues in Bovine and Bacterial bc1 Complexes

    OpenAIRE

    Kokhan, Oleksandr; Shinkarev, Vladimir P.

    2011-01-01

    Antimycin A is the most frequently used specific and powerful inhibitor of the mitochondrial respiratory chain. We used all-atom molecular dynamics (MD) simulations to study the dynamic aspects of the interaction of antimycin A with the Qi site of the bacterial and bovine bc1 complexes embedded in a membrane. The MD simulations revealed considerable conformational flexibility of antimycin and significant mobility of antimycin, as a whole, inside the Qi pocket. We conclude that many of the dif...

  14. A-Site Residues Move Independently from P-Site Residues in all-Atom Molecular Dynamics Simulations of the 70S Bacterial Ribosome

    OpenAIRE

    Relly Brandman; Yigal Brandman; Pande, Vijay S.

    2012-01-01

    The ribosome is a large macromolecular machine, and correlated motion between residues is necessary for coordinating function across multiple protein and RNA chains. We ran two all-atom, explicit solvent molecular dynamics simulations of the bacterial ribosome and calculated correlated motion between residue pairs by using mutual information. Because of the short timescales of our simulation (ns), we expect that dynamics are largely local fluctuations around the crystal structure. We hypothes...

  15. Mechanism of PhosphoThreonine/Serine Recognition and Specificity for Modular Domains from All-atom Molecular Dynamics

    OpenAIRE

    Huang, Yu-ming M; Chang, Chia-en A.

    2011-01-01

    Abstract Background Phosphopeptide-binding domains mediate many vital cellular processes such as signal transduction and protein recognition. We studied three well-known domains important for signal transduction: BRCT repeats, WW domain and forkhead-associated (FHA) domain. The first two recognize both phosphothreonine (pThr) and phosphoserine (pSer) residues, but FHA has high specificity for pThr residues. Here we used molecular dynamics (MD) simulations to reveal how FHA exclusive...

  16. Mechanism of PhosphoThreonine/Serine Recognition and Specificity for Modular Domains from All-atom Molecular Dynamics

    OpenAIRE

    Huang Yu-ming M; Chang Chia-en A

    2011-01-01

    Abstract Background Phosphopeptide-binding domains mediate many vital cellular processes such as signal transduction and protein recognition. We studied three well-known domains important for signal transduction: BRCT repeats, WW domain and forkhead-associated (FHA) domain. The first two recognize both phosphothreonine (pThr) and phosphoserine (pSer) residues, but FHA has high specificity for pThr residues. Here we used molecular dynamics (MD) simulations to reveal how FHA exclusively chooses...

  17. Effect of water on structure and dynamics of [BMIM][PF6] ionic liquid: An all-atom molecular dynamics simulation investigation

    Science.gov (United States)

    Sharma, Anirban; Ghorai, Pradip Kr.

    2016-03-01

    Composition dependent structural and dynamical properties of aqueous hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid (IL) have been investigated by using all-atom molecular dynamics simulation. We observe that addition of water does not increase significant number of dissociated ions in the solution over the pure state. As a consequence, self-diffusion coefficient of the cation and anion is comparable to each other at all water concentration similar to that is observed for the pure state. Voronoi polyhedra analysis exhibits strong dependence on the local environment of IL concentration. Void and neck distributions in Voronoi tessellation are approximately Gaussian for pure IL but upon subsequent addition of water, we observe deviation from the Gaussian behaviour with an asymmetric broadening with long tail of exponential decay at large void radius, particularly at higher water concentrations. The increase in void space and neck size at higher water concentration facilitates ionic motion, thus, decreasing dynamical heterogeneity and IL reorientation time and increases self-diffusion coefficient significantly.

  18. All-atom Molecular Dynamic Simulations and NMR Spectra Study on Intermolecular Interactions of N,N-dimethylacetamide-Water System

    Institute of Scientific and Technical Information of China (English)

    Rong Zhang; Zai-you Tan; San-lai Luo

    2008-01-01

    N,N-dimethylacetamide (DMA) has been investigated extensively in studying models of peptide bonds. An all-atom MD simulation and the NMR spectra were performed to investigate the interactions in the DMA- water system. The radial distribution functions (RDFs) and the hydrogen-bonding network were used in MD simulations. There are strong hydrogen bonds and weak C-H…O contacts in the mixtures, as shown by the analysis of the RDFs. The insight structures in the DMA-water mixtures can be classified into different regions by the analysis of the hydrogen-bonding network. Chemical shifts of the hydrogen atom of water molecule with concentration and temperatures are adopted to study the interactions in the mixtures. The results of NMR spectra show good agreement with the statistical results of hydrogen bonds in MD simulations.

  19. Mechanism of PhosphoThreonine/Serine Recognition and Specificity for Modular Domains from All-atom Molecular Dynamics

    Directory of Open Access Journals (Sweden)

    Huang Yu-ming M

    2011-05-01

    Full Text Available Abstract Background Phosphopeptide-binding domains mediate many vital cellular processes such as signal transduction and protein recognition. We studied three well-known domains important for signal transduction: BRCT repeats, WW domain and forkhead-associated (FHA domain. The first two recognize both phosphothreonine (pThr and phosphoserine (pSer residues, but FHA has high specificity for pThr residues. Here we used molecular dynamics (MD simulations to reveal how FHA exclusively chooses pThr and how BRCT and WW recognize both pThr/pSer. The work also investigated the energies and thermodynamic information of intermolecular interactions. Results Simulations carried out included wide-type and mutated systems. Through analysis of MD simulations, we found that the conserved His residue defines dual loops feature of the FHA domain, which creates a small cavity reserved for only the methyl group of pThr. These well-organized loop interactions directly response to the pThr binding selectivity, while single loop (the 2nd phosphobinding site of FHA or in combination with α-helix (BRCT repeats or β-sheet (WW domain fail to differentiate pThr/pSer. Conclusions Understanding the domain pre-organizations constructed by conserved residues and the driving force of domain-phosphopeptide recognition provides structural insight into pThr specific binding, which also helps in engineering proteins and designing peptide inhibitors.

  20. Structural Interpretation of the Large Slowdown of Water Dynamics at Stacked Phospholipid Membranes for Decreasing Hydration Level: All-Atom Molecular Dynamics

    Directory of Open Access Journals (Sweden)

    Carles Calero

    2016-04-01

    Full Text Available Hydration water determines the stability and function of phospholipid membranes as well as the interaction of membranes with other molecules. Experiments and simulations have shown that water dynamics slows down dramatically as the hydration decreases, suggesting that the interfacial water that dominates the average dynamics at low hydration is slower than water away from the membrane. Here, based on all-atom molecular dynamics simulations, we provide an interpretation of the slowdown of interfacial water in terms of the structure and dynamics of water–water and water–lipid hydrogen bonds (HBs. We calculate the rotational and translational slowdown of the dynamics of water confined in stacked phospholipid membranes at different levels of hydration, from completely hydrated to poorly hydrated membranes. For all hydrations, we analyze the distribution of HBs and find that water–lipids HBs last longer than water–water HBs and that at low hydration most of the water is in the interior of the membrane. We also show that water–water HBs become more persistent as the hydration is lowered. We attribute this effect (i to HBs between water molecules that form, in turn, persistent HBs with lipids; (ii to the hindering of the H-bonding switching between water molecules due to the lower water density at the interface; and (iii to the higher probability of water–lipid HBs as the hydration decreases. Our interpretation of the large dynamic slowdown in water under dehydration is potentially relevant in understanding membrane biophysics at different hydration levels.

  1. Predicting novel binding modes of agonists to β adrenergic receptors using all-atom molecular dynamics simulations.

    Directory of Open Access Journals (Sweden)

    Stefano Vanni

    Full Text Available Understanding the binding mode of agonists to adrenergic receptors is crucial to enabling improved rational design of new therapeutic agents. However, so far the high conformational flexibility of G protein-coupled receptors has been an obstacle to obtaining structural information on agonist binding at atomic resolution. In this study, we report microsecond classical molecular dynamics simulations of β(1 and β(2 adrenergic receptors bound to the full agonist isoprenaline and in their unliganded form. These simulations show a novel agonist binding mode that differs from the one found for antagonists in the crystal structures and from the docking poses reported by in silico docking studies performed on rigid receptors. Internal water molecules contribute to the stabilization of novel interactions between ligand and receptor, both at the interface of helices V and VI with the catechol group of isoprenaline as well as at the interface of helices III and VII with the ethanolamine moiety of the ligand. Despite the fact that the characteristic N-C-C-OH motif is identical in the co-crystallized ligands and in the full agonist isoprenaline, the interaction network between this group and the anchor site formed by Asp(3.32 and Asn(7.39 is substantially different between agonists and inverse agonists/antagonists due to two water molecules that enter the cavity and contribute to the stabilization of a novel network of interactions. These new binding poses, together with observed conformational changes in the extracellular loops, suggest possible determinants of receptor specificity.

  2. Studies of base pair sequence effects on DNA solvation based on all-atom molecular dynamics simulations

    Indian Academy of Sciences (India)

    Surjit B Dixit; Mihaly Mezei; David L Beveridge

    2012-07-01

    Detailed analyses of the sequence-dependent solvation and ion atmosphere of DNA are presented based on molecular dynamics (MD) simulations on all the 136 unique tetranucleotide steps obtained by the ABC consortium using the AMBER suite of programs. Significant sequence effects on solvation and ion localization were observed in these simulations. The results were compared to essentially all known experimental data on the subject. Proximity analysis was employed to highlight the sequence dependent differences in solvation and ion localization properties in the grooves of DNA. Comparison of the MD-calculated DNA structure with canonical A- and B-forms supports the idea that the G/C-rich sequences are closer to canonical A- than B-form structures, while the reverse is true for the poly A sequences, with the exception of the alternating ATAT sequence. Analysis of hydration density maps reveals that the flexibility of solute molecule has a significant effect on the nature of observed hydration. Energetic analysis of solute–solvent interactions based on proximity analysis of solvent reveals that the GC or CG base pairs interactmore strongly with watermolecules in the minor groove of DNA that the AT or TA base pairs, while the interactions of the AT or TA pairs in the major groove are stronger than those of the GC or CG pairs. Computation of solvent-accessible surface area of the nucleotide units in the simulated trajectories reveals that the similarity with results derived from analysis of a database of crystallographic structures is excellent. The MD trajectories tend to follow Manning’s counterion condensation theory, presenting a region of condensed counterions within a radius of about 17 Å from the DNA surface independent of sequence. The GC and CG pairs tend to associate with cations in the major groove of the DNA structure to a greater extent than the AT and TA pairs. Cation association is more frequent in the minor groove of AT than the GC pairs. In general

  3. Density relaxation and particle motion characteristics in a non-ionic deep eutectic solvent (acetamide + urea): Time-resolved fluorescence measurements and all-atom molecular dynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    Das, Anuradha; Das, Suman; Biswas, Ranjit, E-mail: ranjit@bose.res.in [Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata, West Bengal 700098 (India)

    2015-01-21

    Temperature dependent relaxation dynamics, particle motion characteristics, and heterogeneity aspects of deep eutectic solvents (DESs) made of acetamide (CH{sub 3}CONH{sub 2}) and urea (NH{sub 2}CONH{sub 2}) have been investigated by employing time-resolved fluorescence measurements and all-atom molecular dynamics simulations. Three different compositions (f) for the mixture [fCH{sub 3}CONH{sub 2} + (1 − f)NH{sub 2}CONH{sub 2}] have been studied in a temperature range of 328-353 K which is ∼120-145 K above the measured glass transition temperatures (∼207 K) of these DESs but much lower than the individual melting temperature of either of the constituents. Steady state fluorescence emission measurements using probe solutes with sharply different lifetimes do not indicate any dependence on excitation wavelength in these metastable molten systems. Time-resolved fluorescence anisotropy measurements reveal near-hydrodynamic coupling between medium viscosity and rotation of a dissolved dipolar solute. Stokes shift dynamics have been found to be too fast to be detected by the time-resolution (∼70 ps) employed, suggesting extremely rapid medium polarization relaxation. All-atom simulations reveal Gaussian distribution for particle displacements and van Hove correlations, and significant overlap between non-Gaussian (α{sub 2}) and new non-Gaussian (γ) heterogeneity parameters. In addition, no stretched exponential relaxations have been detected in the simulated wavenumber dependent acetamide dynamic structure factors. All these results are in sharp contrast to earlier observations for ionic deep eutectics with acetamide [Guchhait et al., J. Chem. Phys. 140, 104514 (2014)] and suggest a fundamental difference in interaction and dynamics between ionic and non-ionic deep eutectic solvent systems.

  4. Molecular dynamics study of human carbonic anhydrase II in complex with Zn(2+) and acetazolamide on the basis of all-atom force field simulations.

    Science.gov (United States)

    Wambo, Thierry O; Chen, Liao Y; McHardy, Stanton F; Tsin, Andrew T

    2016-01-01

    Human carbonic anhydrase II (hCAII) represents an ultimate example of the perfectly efficient metalloenzymes, which is capable of catalyzing the hydration of carbon dioxide with a rate approaching the diffusion controlled limit. Extensive experimental studies of this physiologically important metalloprotein have been done to elucidate the fundamentals of its enzymatic actions: what residues anchor the Zn(2+) (or another divalent cation) at the bottom of the binding pocket; how the relevant residues work concertedly with the divalent cation in the reversible conversions between CO2 and HCO3(-); what are the protonation states of the relevant residues and acetazolamide, an inhibitor complexed with hCAII, etc. In this article, we present a detailed computational study on the basis of the all-atom CHARMM force field where Zn(2+) is represented with a simple model of divalent cation using the transferrable parameters available from the current literature. We compute the hydration free energy of Zn(2+), the characteristics of hCAII-Zn(2+) complexation, and the absolute free energy of binding acetazolamide to the hCAII-Zn(2+) complex. In each of these three problems, our computed results agree with the experimental data within the known margin of error without making any case-by-case adjustments to the parameters. The quantitatively accurate insights we gain in this all-atom molecular dynamics study should be helpful in the search and design of more specific inhibitors of this and other carbonic anhydrases. PMID:27232456

  5. Energetics of nonpolar and polar compounds in cationic, anionic, and nonionic micelles studied by all-atom molecular dynamics simulation combined with a theory of solutions.

    Science.gov (United States)

    Date, Atsushi; Ishizuka, Ryosuke; Matubayasi, Nobuyuki

    2016-05-21

    Energetic analysis was conducted for nonpolar and polar solutes bound in a cationic micelle of dodecyl trimethyl ammonium bromide (DTAB), an anionic micelle of sodium dodecyl sulfate (SDS), and a nonionic micelle of tetraethylene glycol monododecyl ether (Brij30). All-atom molecular dynamics simulation was performed, and the free energies of binding the solutes in the hydrophobic-core and headgroup regions of the micelles were computed using the energy-representation method. It was found in all the micelles examined that aromatic naphthalene is preferably located more outward than aliphatic propane and that the polar solutes are localized at the interface of the hydrophobic and hydrophilic regions. The roles of the surfactant and water were then elucidated by decomposing the free energy into the contributions from the respective species. Water was observed to play a decisive role in determining the binding location of the solute, while the surfactant was found to be more important for the overall stabilization of the solute within the micelle. The effects of attractive and repulsive interactions of the solute with the surfactant and water were further examined, and their competition was analyzed in connection with the preferable location of the solute in the micellar system. PMID:27117093

  6. Free energetics of carbon nanotube association in aqueous inorganic NaI salt solutions: Temperature effects using all-atom molecular dynamics simulations.

    Science.gov (United States)

    Ou, Shu-Ching; Cui, Di; Wezowicz, Matthew; Taufer, Michela; Patel, Sandeep

    2015-06-15

    In this study, we examine the temperature dependence of free energetics of nanotube association using graphical processing unit-enabled all-atom molecular dynamics simulations (FEN ZI) with two (10,10) single-walled carbon nanotubes in 3 m NaI aqueous salt solution. Results suggest that the free energy, enthalpy and entropy changes for the association process are all reduced at the high temperature, in agreement with previous investigations using other hydrophobes. Via the decomposition of free energy into individual components, we found that solvent contribution (including water, anion, and cation contributions) is correlated with the spatial distribution of the corresponding species and is influenced distinctly by the temperature. We studied the spatial distribution and the structure of the solvent in different regions: intertube, intratube and the bulk solvent. By calculating the fluctuation of coarse-grained tube-solvent surfaces, we found that tube-water interfacial fluctuation exhibits the strongest temperature dependence. By taking ions to be a solvent-like medium in the absence of water, tube-anion interfacial fluctuation shows similar but weaker dependence on temperature, while tube-cation interfacial fluctuation shows no dependence in general. These characteristics are discussed via the malleability of their corresponding solvation shells relative to the nanotube surface. Hydrogen bonding profiles and tetrahedrality of water arrangement are also computed to compare the structure of solvent in the solvent bulk and intertube region. The hydrophobic confinement induces a relatively lower concentration environment in the intertube region, therefore causing different intertube solvent structures which depend on the tube separation. This study is relevant in the continuing discourse on hydrophobic interactions (as they impact generally a broad class of phenomena in biology, biochemistry, and materials science and soft condensed matter research), and

  7. Molecular jamming - the cystine slipknot mechanical clamp in all-atom simulations

    OpenAIRE

    Peplowski, Lukasz; Sikora, Mateusz; Nowak, Wieslaw; Cieplak, Marek

    2011-01-01

    A recent survey of 17 134 proteins has identified a new class of proteins which are expected to yield stretching induced force-peaks in the range of 1 nN. Such high force peaks should be due to forcing of a slip-loop through a cystine ring, i.e. by generating a cystine slipknot. The survey has been performed in a simple coarse grained model. Here, we perform all-atom steered molecular dynamics simulations on 15 cystine knot proteins and determine their resistance to stretching. In agreement w...

  8. Molecular jamming--the cystine slipknot mechanical clamp in all-atom simulations.

    Science.gov (United States)

    Pepłowski, Lukasz; Sikora, Mateusz; Nowak, Wiesław; Cieplak, Marek

    2011-02-28

    A recent survey of 17 134 proteins has identified a new class of proteins which are expected to yield stretching induced force peaks in the range of 1 nN. Such high force peaks should be due to forcing of a slip-loop through a cystine ring, i.e., by generating a cystine slipknot. The survey has been performed in a simple coarse grained model. Here, we perform all-atom steered molecular dynamics simulations on 15 cystine knot proteins and determine their resistance to stretching. In agreement with previous studies within a coarse grained structure based model, the level of resistance is found to be substantially higher than in proteins in which the mechanical clamp operates through shear. The large stretching forces arise through formation of the cystine slipknot mechanical clamp and the resulting steric jamming. We elucidate the workings of such a clamp in an atomic detail. We also study the behavior of five top strength proteins with the shear-based mechanostability in which no jamming is involved. We show that in the atomic model, the jamming state is relieved by moving one amino acid at a time and there is a choice in the selection of the amino acid that advances the first. In contrast, the coarse grained model also allows for a simultaneous passage of two amino acids. PMID:21361557

  9. Molecular jamming—The cystine slipknot mechanical clamp in all-atom simulations

    Science.gov (United States)

    Pepłowski, Łukasz; Sikora, Mateusz; Nowak, Wiesław; Cieplak, Marek

    2011-02-01

    A recent survey of 17 134 proteins has identified a new class of proteins which are expected to yield stretching induced force peaks in the range of 1 nN. Such high force peaks should be due to forcing of a slip-loop through a cystine ring, i.e., by generating a cystine slipknot. The survey has been performed in a simple coarse grained model. Here, we perform all-atom steered molecular dynamics simulations on 15 cystine knot proteins and determine their resistance to stretching. In agreement with previous studies within a coarse grained structure based model, the level of resistance is found to be substantially higher than in proteins in which the mechanical clamp operates through shear. The large stretching forces arise through formation of the cystine slipknot mechanical clamp and the resulting steric jamming. We elucidate the workings of such a clamp in an atomic detail. We also study the behavior of five top strength proteins with the shear-based mechanostability in which no jamming is involved. We show that in the atomic model, the jamming state is relieved by moving one amino acid at a time and there is a choice in the selection of the amino acid that advances the first. In contrast, the coarse grained model also allows for a simultaneous passage of two amino acids.

  10. Probing the global and local dynamics of aminoacyl-tRNA synthetases using all-atom and coarse-grained simulations

    OpenAIRE

    Strom, Alexander M.; Fehling, Samuel C.; Bhattacharyya, Sudeep; Hati, Sanchita

    2014-01-01

    Coarse-grained simulations have emerged as invaluable tools for studying conformational changes in biomolecules. To evaluate the effectiveness of computationally inexpensive coarse-grained models in studying global and local dynamics of large protein systems like aminoacyl-tRNA synthetases, we have performed coarse-grained normal mode analysis, as well as principle component analysis on trajectories of all-atom and coarse-grained molecular dynamics simulations for three aminoacyl-tRNA synthet...

  11. Molecular insights into diphenylalanine nanotube assembly: all-atom simulations of oligomerization.

    Science.gov (United States)

    Jeon, Joohyun; Mills, Carolyn E; Shell, M Scott

    2013-04-18

    Self-assembling peptides represent a growing class of inexpensive, environmentally benign, nanostructured materials. In particular, diphenylalanine (FF) self-assembles into nanotubes with remarkable strength and thermal stability that have found use in a wide variety of applications, including as sacrificial templates and scaffolds for structuring inorganic materials and as interfacial "nanoforests" for superhydrophobic surfaces and high-performance supercapacitors and biosensors. However, little is known about the assembly mechanisms of FF nanotubes or the forces underlying their stability. Here, we perform a variety of molecular dynamics simulations on both zwitterionic and capped (uncharged) versions of the FF peptide to understand the early stages of self-assembly. We compare these results to simulations of the proposed nanotube X-ray crystal structure. When comparing the zwitterionic and uncharged FF peptides, we find that, while electrostatic interactions steer the former into more ordered dimers and trimers, the hydrophobic side chain interactions play a strong role in determining the structures of larger oligomers. Simulations of the crystal structure fragment also suggest that the strongest interactions occur between side chains, not between the charged termini that form salt bridges. We conclude that the amphiphilic nature of FF is key to understanding its self-assembly, and that the early precursors to nanotube structures are likely to involve substantial hydrophobic clustering, rather than hexamer ring motifs as has been previously suggested. PMID:23521630

  12. Probing the folded state and mechanical unfolding pathways of T4 lysozyme using all-atom and coarse-grained molecular simulation

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Wenjun, E-mail: wjzheng@buffalo.edu; Glenn, Paul [Department of Physics, University at Buffalo, Buffalo, New York 14260 (United States)

    2015-01-21

    The Bacteriophage T4 Lysozyme (T4L) is a prototype modular protein comprised of an N-terminal and a C-domain domain, which was extensively studied to understand the folding/unfolding mechanism of modular proteins. To offer detailed structural and dynamic insights to the folded-state stability and the mechanical unfolding behaviors of T4L, we have performed extensive equilibrium and steered molecular dynamics simulations of both the wild-type (WT) and a circular permutation (CP) variant of T4L using all-atom and coarse-grained force fields. Our all-atom and coarse-grained simulations of the folded state have consistently found greater stability of the C-domain than the N-domain in isolation, which is in agreement with past thermostatic studies of T4L. While the all-atom simulation cannot fully explain the mechanical unfolding behaviors of the WT and the CP variant observed in an optical tweezers study, the coarse-grained simulations based on the Go model or a modified elastic network model (mENM) are in qualitative agreement with the experimental finding of greater unfolding cooperativity in the WT than the CP variant. Interestingly, the two coarse-grained models predict different structural mechanisms for the observed change in cooperativity between the WT and the CP variant—while the Go model predicts minor modification of the unfolding pathways by circular permutation (i.e., preserving the general order that the N-domain unfolds before the C-domain), the mENM predicts a dramatic change in unfolding pathways (e.g., different order of N/C-domain unfolding in the WT and the CP variant). Based on our simulations, we have analyzed the limitations of and the key differences between these models and offered testable predictions for future experiments to resolve the structural mechanism for cooperative folding/unfolding of T4L.

  13. Probing the folded state and mechanical unfolding pathways of T4 lysozyme using all-atom and coarse-grained molecular simulation

    International Nuclear Information System (INIS)

    The Bacteriophage T4 Lysozyme (T4L) is a prototype modular protein comprised of an N-terminal and a C-domain domain, which was extensively studied to understand the folding/unfolding mechanism of modular proteins. To offer detailed structural and dynamic insights to the folded-state stability and the mechanical unfolding behaviors of T4L, we have performed extensive equilibrium and steered molecular dynamics simulations of both the wild-type (WT) and a circular permutation (CP) variant of T4L using all-atom and coarse-grained force fields. Our all-atom and coarse-grained simulations of the folded state have consistently found greater stability of the C-domain than the N-domain in isolation, which is in agreement with past thermostatic studies of T4L. While the all-atom simulation cannot fully explain the mechanical unfolding behaviors of the WT and the CP variant observed in an optical tweezers study, the coarse-grained simulations based on the Go model or a modified elastic network model (mENM) are in qualitative agreement with the experimental finding of greater unfolding cooperativity in the WT than the CP variant. Interestingly, the two coarse-grained models predict different structural mechanisms for the observed change in cooperativity between the WT and the CP variant—while the Go model predicts minor modification of the unfolding pathways by circular permutation (i.e., preserving the general order that the N-domain unfolds before the C-domain), the mENM predicts a dramatic change in unfolding pathways (e.g., different order of N/C-domain unfolding in the WT and the CP variant). Based on our simulations, we have analyzed the limitations of and the key differences between these models and offered testable predictions for future experiments to resolve the structural mechanism for cooperative folding/unfolding of T4L

  14. Quantum Mechanics/Molecular Mechanics Method Combined with Hybrid All-Atom and Coarse-Grained Model: Theory and Application on Redox Potential Calculations.

    Science.gov (United States)

    Shen, Lin; Yang, Weitao

    2016-04-12

    We developed a new multiresolution method that spans three levels of resolution with quantum mechanical, atomistic molecular mechanical, and coarse-grained models. The resolution-adapted all-atom and coarse-grained water model, in which an all-atom structural description of the entire system is maintained during the simulations, is combined with the ab initio quantum mechanics and molecular mechanics method. We apply this model to calculate the redox potentials of the aqueous ruthenium and iron complexes by using the fractional number of electrons approach and thermodynamic integration simulations. The redox potentials are recovered in excellent accordance with the experimental data. The speed-up of the hybrid all-atom and coarse-grained water model renders it computationally more attractive. The accuracy depends on the hybrid all-atom and coarse-grained water model used in the combined quantum mechanical and molecular mechanical method. We have used another multiresolution model, in which an atomic-level layer of water molecules around redox center is solvated in supramolecular coarse-grained waters for the redox potential calculations. Compared with the experimental data, this alternative multilayer model leads to less accurate results when used with the coarse-grained polarizable MARTINI water or big multipole water model for the coarse-grained layer. PMID:26930454

  15. Open boundary molecular dynamics

    Science.gov (United States)

    Delgado-Buscalioni, R.; Sablić, J.; Praprotnik, M.

    2015-09-01

    This contribution analyzes several strategies and combination of methodologies to perform molecular dynamic simulations in open systems. Here, the term open indicates that the total system has boundaries where transfer of mass, momentum and energy can take place. This formalism, which we call Open Boundary Molecular Dynamics (OBMD), can act as interface of different schemes, such as Adaptive Resolution Scheme (AdResS) and Hybrid continuum-particle dynamics to link atomistic, coarse-grained (CG) and continuum (Eulerian) fluid dynamics in the general framework of fluctuating Navier-Stokes equations. The core domain of the simulation box is solved using all-atom descriptions. The CG layer introduced using AdResS is located at the outer part of the open box to make feasible the insertion of large molecules into the system. Communications between the molecular system and the outer world are carried out in the outer layers, called buffers. These coupling preserve momentum and mass conservation laws and can thus be linked with Eulerian hydro- dynamic solvers. In its simpler form, OBMD allows, however, to impose a local pressure tensor and a heat flux across the system's boundaries. For a one component molecular system, the external normal pressure and temperature determine the external chemical potential and thus the independent parameters of a grand-canonical ensemble simulation. Extended ensembles under non-equilibrium stationary states can also be simulated as well as time dependent forcings (e.g. oscillatory rheology). To illustrate the robustness of the combined OBMD-AdResS method, we present simulations of star-polymer melts at equilibrium and in sheared flow.

  16. Molecular Dynamics Simulations of Protein Dynamics and their relevance to drug discovery

    OpenAIRE

    Salsbury, Freddie R.

    2010-01-01

    Molecular dynamics simulations have become increasingly useful in studying biological systems of biomedical interest, and not just in the study of model or toy systems. In this article, the methods and principles of all-atom molecular dynamics will be elucidated with several examples provided of their utility to investigators interested on drug discovery.

  17. An Evaluation of Explicit Receptor Flexibility in Molecular Docking Using Molecular Dynamics and Torsion Angle Molecular Dynamics

    OpenAIRE

    Armen, Roger S.; Chen, Jianhan; Brooks, Charles L.

    2009-01-01

    Incorporating receptor flexibility into molecular docking should improve results for flexible proteins. However, the incorporation of explicit all-atom flexibility with molecular dynamics for the entire protein chain may also introduce significant error and “noise” that could decrease docking accuracy and deteriorate the ability of a scoring function to rank native-like poses. We address this apparent paradox by comparing the success of several flexible receptor models in cross-docking and mu...

  18. Nonequilibrium and generalized-ensemble molecular dynamics simulations for amyloid fibril

    International Nuclear Information System (INIS)

    Amyloids are insoluble and misfolded fibrous protein aggregates and associated with more than 20 serious human diseases. We perform all-atom molecular dynamics simulations of amyloid fibril assembly and disassembly

  19. Nonequilibrium and generalized-ensemble molecular dynamics simulations for amyloid fibril

    Energy Technology Data Exchange (ETDEWEB)

    Okumura, Hisashi [Research Center for Computational Science, Institute for Molecular Science, Okazaki, Aichi 444-8585 (Japan); Department of Structural Molecular Science, The Graduate University for Advanced Studies, Okazaki, Aichi 444-8585 (Japan)

    2015-12-31

    Amyloids are insoluble and misfolded fibrous protein aggregates and associated with more than 20 serious human diseases. We perform all-atom molecular dynamics simulations of amyloid fibril assembly and disassembly.

  20. Nonequilibrium and generalized-ensemble molecular dynamics simulations for amyloid fibril

    Science.gov (United States)

    Okumura, Hisashi

    2015-12-01

    Amyloids are insoluble and misfolded fibrous protein aggregates and associated with more than 20 serious human diseases. We perform all-atom molecular dynamics simulations of amyloid fibril assembly and disassembly.

  1. Molecular Dynamics Simulation of Amyloid Beta Dimer Formation

    CERN Document Server

    Urbanc, B; Ding, F; Sammond, D; Khare, S; Buldyrev, S V; Stanley, H E; Dokholyan, N V

    2004-01-01

    Recent experiments with amyloid-beta (Abeta) peptide suggest that formation of toxic oligomers may be an important contribution to the onset of Alzheimer's disease. The toxicity of Abeta oligomers depends on their structure, which is governed by assembly dynamics. Due to limitations of current experimental techniques, a detailed knowledge of oligomer structure at the atomic level is missing. We introduce a molecular dynamics approach to study Abeta dimer formation: (1) we use discrete molecular dynamics simulations of a coarse-grained model to identify a variety of dimer conformations, and (2) we employ all-atom molecular mechanics simulations to estimate the thermodynamic stability of all dimer conformations. Our simulations of a coarse-grained Abeta peptide model predicts ten different planar beta-strand dimer conformations. We then estimate the free energies of all dimer conformations in all-atom molecular mechanics simulations with explicit water. We compare the free energies of Abeta(1-42) and Abeta(1-40...

  2. Accelerating Fermionic Molecular Dynamics

    OpenAIRE

    Clark, M. A.; Kennedy, A. D.

    2004-01-01

    We consider how to accelerate fermionic molecular dynamics algorithms by introducing n pseudofermion fields coupled with the nth root of the fermionic kernel. This reduces the maximum pseudofermionic force, and thus allows a larger molecular dynamics integration step size without hitting an instability in the integrator.

  3. Polymer friction Molecular Dynamics

    OpenAIRE

    Sivebæk, Ion Marius; Samoilov, Vladimir N.; Persson, Bo N. J.

    2010-01-01

    We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: a) polymer sliding against a hard substrate, and b) polymer sliding on polymer. In the first setup the shear stresses are relatively independent of molecular length. For polymer sliding on polymer the friction is significantly larger, and dependent on the molecular chain length. In both cases, the shear stresses are proportional to ...

  4. An All-atom Structure-Based Potential for Proteins: Bridging Minimal Models with All-atom Empirical Forcefields

    OpenAIRE

    Whitford, Paul C.; Jeffrey K Noel; Gosavi, Shachi; Schug, Alexander; Sanbonmatsu, Kevin Y.; Onuchic, José N.

    2009-01-01

    Protein dynamics take place on many time and length scales. Coarse-grained structure-based (Gō) models utilize the funneled energy landscape theory of protein folding to provide an understanding of both long time and long length scale dynamics. All-atom empirical forcefields with explicit solvent can elucidate our understanding of short time dynamics with high energetic and structural resolution. Thus, structure-based models with atomic details included can be used to bridge our understanding...

  5. Nonequilibrium molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Hoover, W.G. (California Univ., Davis, CA (USA). Dept. of Applied Science Lawrence Livermore National Lab., CA (USA))

    1990-11-01

    The development of nonequilibrium molecular dynamics is described, with emphasis on massively-parallel simulations involving the motion of millions, soon to be billions, of atoms. Corresponding continuum simulations are also discussed. 14 refs., 8 figs.

  6. Molecular dynamics simulations

    OpenAIRE

    Tarmyshov, Konstantin B.

    2007-01-01

    Molecular simulations can provide a detailed picture of a desired chemical, physical, or biological process. It has been developed over last 50 years and is being used now to solve a large variety of problems in many different fields. In particular, quantum calculations are very helpful to study small systems at a high resolution where electronic structure of compounds is accounted for. Molecular dynamics simulations, in turn, are employed to study development of a certain molecular ensemble ...

  7. Polymer friction Molecular Dynamics

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, Vladimir N.; Persson, Bo N. J.

    We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: a) polymer sliding against a hard substrate, and b) polymer sliding on polymer. In the first setup the shear stresses are relatively...... independent of molecular length. For polymer sliding on polymer the friction is significantly larger, and dependent on the molecular chain length. In both cases, the shear stresses are proportional to the squeezing pressure and finite at zero load, indicating an adhesional contribution to the friction force....

  8. Simulation of lipid bilayer self-assembly using all-atom lipid force fields.

    Science.gov (United States)

    Skjevik, Åge A; Madej, Benjamin D; Dickson, Callum J; Lin, Charles; Teigen, Knut; Walker, Ross C; Gould, Ian R

    2016-04-21

    In this manuscript we expand significantly on our earlier communication by investigating the bilayer self-assembly of eight different types of phospholipids in unbiased molecular dynamics (MD) simulations using three widely used all-atom lipid force fields. Irrespective of the underlying force field, the lipids are shown to spontaneously form stable lamellar bilayer structures within 1 microsecond, the majority of which display properties in satisfactory agreement with the experimental data. The lipids self-assemble via the same general mechanism, though at formation rates that differ both between lipid types, force fields and even repeats on the same lipid/force field combination. In addition to zwitterionic phosphatidylcholine (PC) and phosphatidylethanolamine (PE) lipids, anionic phosphatidylserine (PS) and phosphatidylglycerol (PG) lipids are represented. To our knowledge this is the first time bilayer self-assembly of phospholipids with negatively charged head groups is demonstrated in all-atom MD simulations. PMID:27034995

  9. Molecular Mechanism of Allosteric Communication in Hsp70 Revealed by Molecular Dynamics Simulations

    OpenAIRE

    Chiappori, Federica; Merelli, Ivan; Colombo, Giorgio; Milanesi, Luciano; Morra, Giulia

    2012-01-01

    Author Summary Allostery, or the capability of proteins to respond to ligand binding events with a variation in structure or dynamics at a distant site, is a common feature for biomolecular function and regulation in a large number of proteins. Intra-protein connections and inter-residue coordinations underlie allosteric mechanisms and react to binding primarily through a finely tuned modulation of motions and structures at the microscopic scale. Hence, all-atom molecular dynamics simulations...

  10. MOLECULAR REPLICATOR DYNAMICS

    OpenAIRE

    BÄRBEL M. R. STADLER; Stadler, Peter F

    2003-01-01

    Template-dependent replication at the molecular level is the basis of reproduction in nature. A detailed understanding of the peculiarities of the chemical reaction kinetics associated with replication processes is therefore an indispensible prerequisite for any understanding of evolution at the molecular level. Networks of interacting self-replicating species can give rise to a wealth of different dynamical phenomena, from competitive exclusion to permanent coexistence, from global stability...

  11. Substructured multibody molecular dynamics.

    Energy Technology Data Exchange (ETDEWEB)

    Grest, Gary Stephen; Stevens, Mark Jackson; Plimpton, Steven James; Woolf, Thomas B. (Johns Hopkins University, Baltimore, MD); Lehoucq, Richard B.; Crozier, Paul Stewart; Ismail, Ahmed E.; Mukherjee, Rudranarayan M. (Rensselaer Polytechnic Institute, Troy, NY); Draganescu, Andrei I.

    2006-11-01

    We have enhanced our parallel molecular dynamics (MD) simulation software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator, lammps.sandia.gov) to include many new features for accelerated simulation including articulated rigid body dynamics via coupling to the Rensselaer Polytechnic Institute code POEMS (Parallelizable Open-source Efficient Multibody Software). We use new features of the LAMMPS software package to investigate rhodopsin photoisomerization, and water model surface tension and capillary waves at the vapor-liquid interface. Finally, we motivate the recipes of MD for practitioners and researchers in numerical analysis and computational mechanics.

  12. Molecular Dynamics/Order Parameter eXtrapolation (MD/OPX) for Bionanosystem Simulations

    OpenAIRE

    Miao, Yinglong; Ortoleva, Peter J.

    2009-01-01

    A multiscale approach, Molecular Dynamics/Order Parameter eXtrapolation (MD/OPX), to the all-atom simulation of large bionanosystems is presented. The approach starts with the introduction of a set of order parameters (OPs) automatically generated with orthogonal polynomials to characterize the nanoscale features of bionanosystems. The OPs are shown to evolve slowly via Newton’s equations and the all-atom multiscale analysis (AMA) developed earlier1 demonstrates the existence of their stochas...

  13. Molecular dynamics for fermions

    International Nuclear Information System (INIS)

    The time-dependent variational principle for many-body trial states is used to discuss the relation between the approaches of different molecular dynamics models to describe indistinguishable fermions. Early attempts to include effects of the Pauli principle by means of nonlocal potentials as well as more recent models which work with antisymmetrized many-body states are reviewed under these premises. (orig.)

  14. Explicit all-atom modeling of realistically sized ligand-capped nanocrystals

    KAUST Repository

    Kaushik, Ananth P.

    2012-01-01

    We present a study of an explicit all-atom representation of nanocrystals of experimentally relevant sizes (up to 6 nm), capped with alkyl chain ligands, in vacuum. We employ all-atom molecular dynamics simulation methods in concert with a well-tested intermolecular potential model, MM3 (molecular mechanics 3), for the studies presented here. These studies include determining the preferred conformation of an isolated single nanocrystal (NC), pairs of isolated NCs, and (presaging studies of superlattice arrays) unit cells of NC superlattices. We observe that very small NCs (3 nm) behave differently in a superlattice as compared to larger NCs (6 nm and above) due to the conformations adopted by the capping ligands on the NC surface. Short ligands adopt a uniform distribution of orientational preferences, including some that lie against the face of the nanocrystal. In contrast, longer ligands prefer to interdigitate. We also study the effect of changing ligand length and ligand coverage on the NCs on the preferred ligand configurations. Since explicit all-atom modeling constrains the maximum system size that can be studied, we discuss issues related to coarse-graining the representation of the ligands, including a comparison of two commonly used coarse-grained models. We find that care has to be exercised in the choice of coarse-grained model. The data provided by these realistically sized ligand-capped NCs, determined using explicit all-atom models, should serve as a reference standard for future models of coarse-graining ligands using united atom models, especially for self-assembly processes. © 2012 American Institute of Physics.

  15. Accelerating Molecular Dynamic Simulation on Graphics Processing Units

    OpenAIRE

    Friedrichs, Mark S.; Eastman, Peter; Vaidyanathan, Vishal; Houston, Mike; Legrand, Scott; Beberg, Adam L.; Ensign, Daniel L.; Bruns, Christopher M.; Pande, Vijay S.

    2009-01-01

    We describe a complete implementation of all-atom protein molecular dynamics running entirely on a graphics processing unit (GPU), including all standard force field terms, integration, constraints, and implicit solvent. We discuss the design of our algorithms and important optimizations needed to fully take advantage of a GPU. We evaluate its performance, and show that it can be more than 700 times faster than a conventional implementation running on a single CPU core.

  16. Orbital free molecular dynamics

    International Nuclear Information System (INIS)

    The microscopic properties of hot and dense plasmas stay a field essentially studied thanks to classical theories like the One Component Plasma, models which rely on free parameters, particularly ionization. In order to investigate these systems, we have used, in this PhD work, a semi-classical model, without free parameters, that is based on coupling consistently classical molecular dynamics for the nuclei and orbital free density functional theory for the electrons. The electronic fluid is represented by a free energy entirely determined by the local density. This approximation was validated by a comparison with an ab initio technique, quantum molecular dynamics. This one is identical to the previous except for the description of the free energy that depends on a quantum-independent-particle model. Orbital free molecular dynamics was then used to compute equation of state of boron and iron plasmas in the hot and dense regime. Furthermore, comparisons with classical theories were performed on structural and dynamical properties. Finally, equation of state and transport coefficients mixing laws were studied by direct simulation of a plasma composed of deuterium and copper. (author)

  17. Molecular Dynamics of Acetylcholinesterase

    Energy Technology Data Exchange (ETDEWEB)

    Shen, T Y.; Tai, Kaihsu; Henchman, Richard H.; Mccammon, Andy

    2002-06-01

    Molecular dynamics simulations are leading to a deeper understanding of the activity of the enzyme acetylcholinesterase. Simulations have shown how breathing motions in the enzyme facilitate the displacement of substrate from the surface of the enzyme to the buried active site. The most recent work points to the complex and spatially extensive nature of such motions and suggests possible modes of regulation of the activity of the enzyme.

  18. From Molecular Dynamics to Dissipative Particle Dynamics

    OpenAIRE

    Flekkoy, Eirik G.; Coveney, Peter V.

    1999-01-01

    A procedure is introduced for deriving a coarse-grained dissipative particle dynamics from molecular dynamics. The rules of the dissipative particle dynamics are derived from the underlying molecular interactions, and a Langevin equation is obtained that describes the forces experienced by the dissipative particles and specifies the associated canonical Gibbs distribution for the system.

  19. Interactive molecular dynamics

    CERN Document Server

    Schroeder, Daniel V

    2015-01-01

    Physics students now have access to interactive molecular dynamics simulations that can model and animate the motions of hundreds of particles, such as noble gas atoms, that attract each other weakly at short distances but repel strongly when pressed together. Using these simulations, students can develop an understanding of forces and motions at the molecular scale, nonideal fluids, phases of matter, thermal equilibrium, nonequilibrium states, the Boltzmann distribution, the arrow of time, and much more. This article summarizes the basic features and capabilities of such a simulation, presents a variety of student exercises using it at the introductory and intermediate levels, and describes some enhancements that can further extend its uses. A working simulation code, in HTML5 and JavaScript for running within any modern Web browser, is provided as an online supplement.

  20. Interactive molecular dynamics

    Science.gov (United States)

    Schroeder, Daniel V.

    2015-03-01

    Physics students now have access to interactive molecular dynamics simulations that can model and animate the motions of hundreds of particles, such as noble gas atoms, that attract each other weakly at short distances but repel strongly when pressed together. Using these simulations, students can develop an understanding of forces and motions at the molecular scale, nonideal fluids, phases of matter, thermal equilibrium, nonequilibrium states, the Boltzmann distribution, the arrow of time, and much more. This article summarizes the basic features and capabilities of such a simulation, presents a variety of student exercises using it at the introductory and intermediate levels, and describes some enhancements that can further extend its uses. A working simulation code, in html5 and javascript for running within any modern Web browser, is provided as an online supplement.

  1. Order parameter prediction from molecular dynamics simulations in proteins

    CERN Document Server

    Perilla, Juan R

    2011-01-01

    A molecular understanding of how protein function is related to protein structure will require an ability to understand large conformational changes between multiple states. Unfortunately these states are often separated by high free energy barriers and within a complex energy landscape. This makes it very difficult to reliably connect, for example by all-atom molecular dynamics calculations, the states, their energies and the pathways between them. A major issue needed to improve sampling on the intermediate states is an order parameter -- a reduced descriptor for the major subset of degrees of freedom -- that can be used to aid sampling for the large conformational change. We present a novel way to combine information from molecular dynamics using non-linear time series and dimensionality reduction, in order to quantitatively determine an order parameter connecting two large-scale conformationally distinct protein states. This new method suggests an implementation for molecular dynamics calculations that ma...

  2. The nonequilibrium molecular dynamics

    International Nuclear Information System (INIS)

    MOLECULAR DYNAMICS has been generalized in order to simulate a variety of NONEQUILIBRIUM systems. This generalization has been achieved by adopting microscopic mechanical definitions of macroscopic thermodynamic and hydrodynamic variables, such as temperature and stress. Some of the problems already treated include rapid plastic deformation, intense heat conduction, strong shockwaves simulation, and far-from-equilibrium phase transformations. Continuing advances in technique and in the modeling of interatomic forces, coupled with qualitative improvements in computer hardware, are enabling such simulations to approximate real-world microscale and nanoscale experiments

  3. Electronic continuum model for molecular dynamics simulations.

    Science.gov (United States)

    Leontyev, I V; Stuchebrukhov, A A

    2009-02-28

    A simple model for accounting for electronic polarization in molecular dynamics (MD) simulations is discussed. In this model, called molecular dynamics electronic continuum (MDEC), the electronic polarization is treated explicitly in terms of the electronic continuum (EC) approximation, while the nuclear dynamics is described with a fixed-charge force field. In such a force-field all atomic charges are scaled to reflect the screening effect by the electronic continuum. The MDEC model is rather similar but not equivalent to the standard nonpolarizable force-fields; the differences are discussed. Of our particular interest is the calculation of the electrostatic part of solvation energy using standard nonpolarizable MD simulations. In a low-dielectric environment, such as protein, the standard MD approach produces qualitatively wrong results. The difficulty is in mistreatment of the electronic polarizability. We show how the results can be much improved using the MDEC approach. We also show how the dielectric constant of the medium obtained in a MD simulation with nonpolarizable force-field is related to the static (total) dielectric constant, which includes both the nuclear and electronic relaxation effects. Using the MDEC model, we discuss recent calculations of dielectric constants of alcohols and alkanes, and show that the MDEC results are comparable with those obtained with the polarizable Drude oscillator model. The applicability of the method to calculations of dielectric properties of proteins is discussed. PMID:19256627

  4. Introduction to Accelerated Molecular Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Perez, Danny [Los Alamos National Laboratory

    2012-07-10

    Molecular Dynamics is the numerical solution of the equations of motion of a set of atoms, given an interatomic potential V and some boundary and initial conditions. Molecular Dynamics is the largest scale model that gives unbiased dynamics [x(t),p(t)] in full atomistic detail. Molecular Dynamics: is simple; is 'exact' for classical dynamics (with respect to a given V); can be used to compute any (atomistic) thermodynamical or dynamical properties; naturally handles complexity -- the system does the right thing at the right time. The physics derives only from the interatomic potential.

  5. Molecular Dynamics Calculations

    Science.gov (United States)

    1996-01-01

    The development of thermodynamics and statistical mechanics is very important in the history of physics, and it underlines the difficulty in dealing with systems involving many bodies, even if those bodies are identical. Macroscopic systems of atoms typically contain so many particles that it would be virtually impossible to follow the behavior of all of the particles involved. Therefore, the behavior of a complete system can only be described or predicted in statistical ways. Under a grant to the NASA Lewis Research Center, scientists at the Case Western Reserve University have been examining the use of modern computing techniques that may be able to investigate and find the behavior of complete systems that have a large number of particles by tracking each particle individually. This is the study of molecular dynamics. In contrast to Monte Carlo techniques, which incorporate uncertainty from the outset, molecular dynamics calculations are fully deterministic. Although it is still impossible to track, even on high-speed computers, each particle in a system of a trillion trillion particles, it has been found that such systems can be well simulated by calculating the trajectories of a few thousand particles. Modern computers and efficient computing strategies have been used to calculate the behavior of a few physical systems and are now being employed to study important problems such as supersonic flows in the laboratory and in space. In particular, an animated video (available in mpeg format--4.4 MB) was produced by Dr. M.J. Woo, now a National Research Council fellow at Lewis, and the G-VIS laboratory at Lewis. This video shows the behavior of supersonic shocks produced by pistons in enclosed cylinders by following exactly the behavior of thousands of particles. The major assumptions made were that the particles involved were hard spheres and that all collisions with the walls and with other particles were fully elastic. The animated video was voted one of two

  6. Molecular dynamics simulations

    International Nuclear Information System (INIS)

    The molecular dynamics computer simulation discovery of the slow decay of the velocity autocorrelation function in fluids is briefly reviewed in order to contrast that long time tail with those observed for the stress autocorrelation function in fluids and the velocity autocorrelation function in the Lorentz gas. For a non-localized particle in the Lorentz gas it is made plausible that even if it behaved quantum mechanically its long time tail would be the same as the classical one. The generalization of Fick's law for diffusion for the Lorentz gas, necessary to avoid divergences due to the slow decay of correlations, is presented. For fluids, that generalization has not yet been established, but the region of validity of generalized hydrodynamics is discussed. 20 refs., 5 figs

  7. Free energy calculations on Transthyretin dissociation and ligand binding from Molecular Dynamics Simulations

    DEFF Research Database (Denmark)

    Sørensen, Jesper; Hamelberg, Donald; McCammon, J. Andrew

    experimental results have helped to explain this aberrant behavior of TTR, however, structural insights of the amyloidgenic process are still lacking. Therefore, we have used all-atom molecular dynamics simulation and free energy calculations to study the initial phase of this process. We have calculated the...... free energy changes of the initial tetramer dissociation under different conditions and in the presence of thyroxine....

  8. Multiscale approach for the construction of equilibrated all-atom models of a poly(ethylene glycol)-based hydrogel.

    Science.gov (United States)

    Li, Xianfeng; Murthy, N Sanjeeva; Becker, Matthew L; Latour, Robert A

    2016-06-01

    A multiscale modeling approach is presented for the efficient construction of an equilibrated all-atom model of a cross-linked poly(ethylene glycol) (PEG)-based hydrogel using the all-atom polymer consistent force field (PCFF). The final equilibrated all-atom model was built with a systematic simulation toolset consisting of three consecutive parts: (1) building a global cross-linked PEG-chain network at experimentally determined cross-link density using an on-lattice Monte Carlo method based on the bond fluctuation model, (2) recovering the local molecular structure of the network by transitioning from the lattice model to an off-lattice coarse-grained (CG) model parameterized from PCFF, followed by equilibration using high performance molecular dynamics methods, and (3) recovering the atomistic structure of the network by reverse mapping from the equilibrated CG structure, hydrating the structure with explicitly represented water, followed by final equilibration using PCFF parameterization. The developed three-stage modeling approach has application to a wide range of other complex macromolecular hydrogel systems, including the integration of peptide, protein, and/or drug molecules as side-chains within the hydrogel network for the incorporation of bioactivity for tissue engineering, regenerative medicine, and drug delivery applications. PMID:27013229

  9. Nanoscale deicing by molecular dynamics simulation

    Science.gov (United States)

    Xiao, Senbo; He, Jianying; Zhang, Zhiliang

    2016-07-01

    Deicing is important to human activities in low-temperature circumstances, and is critical for combating the damage caused by excessive accumulation of ice. The aim of creating anti-icing materials, surfaces and applications relies on the understanding of fundamental nanoscale ice adhesion mechanics. Here in this study, we employ all-atom modeling and molecular dynamics simulation to investigate ice adhesion. We apply force to detach and shear nano-sized ice cubes for probing the determinants of atomistic adhesion mechanics, and at the same time investigate the mechanical effect of a sandwiched aqueous water layer between ice and substrates. We observe that high interfacial energy restricts ice mobility and increases both ice detaching and shearing stresses. We quantify up to a 60% decrease in ice adhesion strength by an aqueous water layer, and provide atomistic details that support previous experimental studies. Our results contribute quantitative comparison of nanoscale adhesion strength of ice on hydrophobic and hydrophilic surfaces, and supply for the first time theoretical references for understanding the mechanics at the atomistic origins of macroscale ice adhesion.Deicing is important to human activities in low-temperature circumstances, and is critical for combating the damage caused by excessive accumulation of ice. The aim of creating anti-icing materials, surfaces and applications relies on the understanding of fundamental nanoscale ice adhesion mechanics. Here in this study, we employ all-atom modeling and molecular dynamics simulation to investigate ice adhesion. We apply force to detach and shear nano-sized ice cubes for probing the determinants of atomistic adhesion mechanics, and at the same time investigate the mechanical effect of a sandwiched aqueous water layer between ice and substrates. We observe that high interfacial energy restricts ice mobility and increases both ice detaching and shearing stresses. We quantify up to a 60% decrease in ice

  10. Physical adsorption and molecular dynamics

    International Nuclear Information System (INIS)

    Some aspects of noble gases adsorption (except He) on graphite substracts are reviewed. Experimental results from this adsorption are analyzed and compared with molecular dynamics calculations. (L.C.)

  11. ACEMD: Accelerating bio-molecular dynamics in the microsecond time-scale

    CERN Document Server

    Harvey, M J; De Fabritiis, G

    2009-01-01

    The high arithmetic performance and intrinsic parallelism of recent graphical processing units (GPUs) can offer a technological edge for molecular dynamics simulations. ACEMD is a production-class bio-molecular dynamics (MD) simulation program designed specifically for GPUs which is able to achieve supercomputing scale performance of 40 nanoseconds/day for all-atom protein systems with over 23,000 atoms. We illustrate the characteristics of the code, its validation and performance. We also run a microsecond-long trajectory for an all-atom molecular system in explicit TIP3P water on a single workstation computer equipped with just 3 GPUs. This performance on cost effective hardware allows ACEMD to reach microsecond timescales routinely with important implications in terms of scientific applications.

  12. Galilei invariant molecular dynamics

    International Nuclear Information System (INIS)

    We construct a C*-dynamical model for a chemical reaction. Galilei invariance of our nonrelativistic model is demonstrated by defining it directly on a Galilean space-time fibrebundle with C*-algebra valued fibre, i.e. without reference to any coordinate system. The existence of equilibrium states in this model is established and some of their properties are discussed. (orig.)

  13. Ab-Initio Molecular Dynamics

    CERN Document Server

    Kühne, Thomas D

    2012-01-01

    Computer simulations and molecular dynamics in particular, is a very powerful method to provide detailed and essentially exact informations of classical many-body problems. With the advent of \\textit{ab-initio} molecular dynamics, where the forces are computed on-the-fly by accurate electronic structure calculations, the scope of either method has been greatly extended. This new approach, which unifies Newton's and Schr\\"odinger's equations, allows for complex simulations without relying on any adjustable parameter. This review is intended to outline the basic principles as well as a survey of the field. Beginning with the derivation of Born-Oppenheimer molecular dynamics, the Car-Parrinello method as well as novel hybrid scheme that unifies best of either approach are discussed. The predictive power is demonstrated by a series of applications ranging from insulators to semiconductors and even metals in condensed phases.

  14. State-Dependent Molecular Dynamics

    Directory of Open Access Journals (Sweden)

    Ciann-Dong Yang

    2014-10-01

    Full Text Available This paper proposes a new mixed quantum mechanics (QM—molecular mechanics (MM approach, where MM is replaced by quantum Hamilton mechanics (QHM, which inherits the modeling capability of MM, while preserving the state-dependent nature of QM. QHM, a single mechanics playing the roles of QM and MM simultaneously, will be employed here to derive the three-dimensional quantum dynamics of diatomic molecules. The resulting state-dependent molecular dynamics including vibration, rotation and spin are shown to completely agree with the QM description and well match the experimental vibration-rotation spectrum. QHM can be incorporated into the framework of a mixed quantum-classical Bohmian method to enable a trajectory interpretation of orbital-spin interaction and spin entanglement in molecular dynamics.

  15. A sampling of molecular dynamics

    Science.gov (United States)

    Sindhikara, Daniel Jon

    The sheer vastness of the number of computations required to simulate a biological molecule puts incredible pressure on algorithms to be efficient while maintaining sufficient accuracy. This dissertation summarizes various projects whose purposes address the large span of types of problems in molecular dynamics simulations of biological systems including: increasing efficiency, measuring convergence, avoiding pitfalls, and an application and analysis of a biological system. Chapters 3 and 4 deal with an enhanced sampling algorithm called "replica exchange molecular dynamics" which is designed to speed-up molecular dynamics simulations. The optimization of a key parameter of these simulations is analyzed. In these successive projects, it was found conclusively that maximizing "exchange attempt frequency" is the most efficient way to run a replica exchange molecular dynamics simulation. Chapter 5 describes an enhanced metric for convergence in parallel simulations called the normalized ergodic measure. The metric is applied to several properties for several replica exchange simulations. Advantages of this metric over other methods are described. Chapter 6 describes the implementation and optimization of an enhanced sampling algorithm similar to replica exchange molecular dynamics called multicanonical algorithm replica exchange molecular dynamics. The algorithm was implemented into a biomolecular simulation suite called AMBER. Additionally several parameters were analyzed and optimized. In Chapter 7, a pitfall in molecular dynamics is observed in biological systems that is caused by negligent use of a simulation's "thermostat". It was found that if the same pseudorandom number seed were used for multiple systems, they eventually synchronize. In this project, synchronization was observed in biological molecules. Various negative effects including corruption of data are pointed out. Chapter 8 describes molecular dynamics simulation of NikR, a homotetrameric nickel

  16. Gas Phase Molecular Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Hall, G.E.; Prrese, J.M.; Sears, T.J.; Weston, R.E.

    1999-05-21

    The goal of this research is the understanding of elementary chemical and physical processes important in the combustion of fossil fuels. Interest centers on reactions involving short-lived chemical intermediates and their properties. High-resolution high-sensitivity laser absorption methods are augmented by high temperature flow-tube reaction kinetics studies with mass spectrometric sampling. These experiments provide information on the energy levels, structures and reactivity of molecular flee radical species and, in turn, provide new tools for the study of energy flow and chemical bond cleavage in the radicals in chemical systems. The experimental work is supported by theoretical and computational work using time-dependent quantum wavepacket calculations that provide insights into energy flow between the vibrational modes of the molecule.

  17. Molecular dynamics simulation of diffusivity

    Institute of Scientific and Technical Information of China (English)

    Juanfang LIU; Danling ZENG; Qin LI; Hong GAO

    2008-01-01

    Equilibrium molecular dynamics simulation was performed on water to calculate its diffusivity by adopting different potential models. The results show that the potential models have great influence on the simulated results. In addition, the diffusivities obtained by the SPCE model conform well to the experimental values.

  18. Progress in quantum molecular dynamics

    International Nuclear Information System (INIS)

    In this paper a microscopic simulation method of the quantum molecular dynamics (QMD) and its extensions to high- and low-energy regions are reported. Combined with the statistical decay calculation, QMD can reproduce experimental data with fixed and very few parameters. (J.P.N.)

  19. Towards Molecular Dynamics Simulations of Chiral Room-Temperature Ionic Liquids

    Czech Academy of Sciences Publication Activity Database

    Lísal, Martin; Chval, Z.; Storch, Jan; Izák, Pavel

    2014-01-01

    Roč. 189, SI (2014), s. 85-94. ISSN 0167-7322 R&D Projects: GA ČR(CZ) GAP106/12/0569; GA MŠk LH12020 Institutional support: RVO:67985858 Keywords : chiral room-temperature ionic liquid * molecular dynamics simulation * non-polarizable fully flexible all- atom force field Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 2.515, year: 2014

  20. Molecular Dynamics Simulations of a Pulmonary Surfactant Protein B Peptide in a Lipid Monolayer

    OpenAIRE

    Freites, J. Alfredo; Choi, Yunsoo; Tobias, Douglas J.

    2003-01-01

    Pulmonary surfactant is a complex mixture of lipids and proteins that lines the air/liquid interface of the alveolar hypophase and confers mechanical stability to the alveoli during the breathing process. The desire to formulate synthetic mixtures for low-cost prophylactic and therapeutic applications has motivated the study of the specific roles and interactions of the different components. All-atom molecular dynamics simulations were carried out on a model system composed of a monolayer of ...

  1. Amino acids and proteins at ZnO-water interfaces in molecular dynamics simulations

    OpenAIRE

    Nawrocki, Grzegorz; Cieplak, Marek

    2014-01-01

    We determine potentials of the mean force for interactions of amino acids with four common surfaces of ZnO in aqueous solutions. The method involves all-atom molecular dynamics simulations combined with the umbrella sampling technique. The profiled nature of the density of water with the strongly adsorbed first layer affects the approach of amino acids to the surface and generates either repulsion or weak binding. The largest binding energy is found for tyrosine interacting with the surface i...

  2. Ab initio based force field and molecular dynamics simulations of crystalline TATB.

    Science.gov (United States)

    Gee, Richard H; Roszak, Szczepan; Balasubramanian, Krishnan; Fried, Laurence E

    2004-04-15

    An all-atom force field for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is presented. The classical intermolecular interaction potential for TATB is based on single-point energies determined from high-level ab initio calculations of TATB dimers. The newly developed potential function is used to examine bulk crystalline TATB via molecular dynamics simulations. The isobaric thermal expansion and isothermal compression under hydrostatic pressures obtained from the molecular dynamics simulations are in good agreement with experiment. The calculated volume-temperature expansion is almost one dimensional along the c crystallographic axis, whereas under compression, all three unit cell axes participate, albeit unequally. PMID:15267608

  3. Relation of centroid molecular dynamics and ring-polymer molecular dynamics to exact quantum dynamics

    OpenAIRE

    Hele, Timothy J. H.; Willatt, Michael J.; Muolo, Andrea; Althorpe, Stuart C.

    2015-01-01

    We recently obtained a quantum-Boltzmann-conserving classical dynamics by making a single change to the derivation of the `Classical Wigner' approximation. Here, we show that the further approximation of this `Matsubara dynamics' gives rise to two popular heuristic methods for treating quantum Boltzmann time-correlation functions: centroid molecular dynamics (CMD) and ring-polymer molecular dynamics (RPMD). We show that CMD is a mean-field approximation to Matsubara dynamics, obtained by disc...

  4. Combining optimal control theory and molecular dynamics for protein folding.

    Directory of Open Access Journals (Sweden)

    Yaman Arkun

    Full Text Available A new method to develop low-energy folding routes for proteins is presented. The novel aspect of the proposed approach is the synergistic use of optimal control theory with Molecular Dynamics (MD. In the first step of the method, optimal control theory is employed to compute the force field and the optimal folding trajectory for the Cα atoms of a Coarse-Grained (CG protein model. The solution of this CG optimization provides an harmonic approximation of the true potential energy surface around the native state. In the next step CG optimization guides the MD simulation by specifying the optimal target positions for the Cα atoms. In turn, MD simulation provides an all-atom conformation whose Cα positions match closely the reference target positions determined by CG optimization. This is accomplished by Targeted Molecular Dynamics (TMD which uses a bias potential or harmonic restraint in addition to the usual MD potential. Folding is a dynamical process and as such residues make different contacts during the course of folding. Therefore CG optimization has to be reinitialized and repeated over time to accomodate these important changes. At each sampled folding time, the active contacts among the residues are recalculated based on the all-atom conformation obtained from MD. Using the new set of contacts, the CG potential is updated and the CG optimal trajectory for the Cα atoms is recomputed. This is followed by MD. Implementation of this repetitive CG optimization-MD simulation cycle generates the folding trajectory. Simulations on a model protein Villin demonstrate the utility of the method. Since the method is founded on the general tools of optimal control theory and MD without any restrictions, it is widely applicable to other systems. It can be easily implemented with available MD software packages.

  5. From Molecular Dynamics to Brownian Dynamics

    CERN Document Server

    Erban, Radek

    2014-01-01

    Three coarse-grained molecular dynamics (MD) models are investigated with the aim of developing and analyzing multiscale methods which use MD simulations in parts of the computational domain and (less detailed) Brownian dynamics (BD) simulations in the remainder of the domain. The first MD model is formulated in one spatial dimension. It is based on elastic collisions of heavy molecules (e.g. proteins) with light point particles (e.g. water molecules). Two three-dimensional MD models are then investigated. The obtained results are applied to a simplified model of protein binding to receptors on the cellular membrane. It is shown that modern BD simulators of intracellular processes can be used in the bulk and accurately coupled with a (more detailed) MD model of protein binding which is used close to the membrane.

  6. Molecular Dynamics for Dense Matter

    CERN Document Server

    Maruyama, Toshiki; Chiba, Satoshi

    2012-01-01

    We review a molecular dynamics method for nucleon many-body systems called the quantum molecular dynamics (QMD) and our studies using this method. These studies address the structure and the dynamics of nuclear matter relevant to the neutron star crusts, supernova cores, and heavy-ion collisions. A key advantage of QMD is that we can study dynamical processes of nucleon many-body systems without any assumptions on the nuclear structure. First we focus on the inhomogeneous structures of low-density nuclear matter consisting not only of spherical nuclei but also of nuclear "pasta", i.e., rod-like and slab-like nuclei. We show that the pasta phases can appear in the ground and equilibrium states of nuclear matter without assuming nuclear shape. Next we show our simulation of compression of nuclear matter which corresponds to the collapsing stage of supernovae. With increase of density, a crystalline solid of spherical nuclei change to a triangular lattice of rods by connecting neighboring nuclei. Finally, we dis...

  7. Implementation of a protein reduced point charge model toward molecular dynamics applications.

    Science.gov (United States)

    Leherte, Laurence; Vercauteren, Daniel P

    2011-11-17

    A reduced point charge model was developed in a previous work from the study of extrema in smoothed charge density distribution functions generated from the Amber99 molecular electrostatic potential. In the present work, such a point charge distribution is coupled with the Amber99 force field and implemented in the program TINKER to allow molecular dynamics (MD) simulations of proteins. First applications to two polypeptides that involve α-helix and β-sheet motifs are analyzed and compared to all-atom MD simulations. Two types of coarse-grained (CG)-based trajectories are generated using, on one hand, harmonic bond stretching terms and, on the other hand, distance restraints. Results show that the use of the unrestrained CG conditions are sufficient to preserve most of the secondary structure characteristics but restraints lead to a better agreement between CG and all-atom simulation results such as rmsd, dipole moment, and time-dependent mean square deviation functions. PMID:21800922

  8. Molecular dynamics simulation study of the binding of purine bases to the aptamer domain of the guanine sensing riboswitch

    OpenAIRE

    Villa, Alessandra; Wöhnert, Jens; Stock, Gerhard

    2009-01-01

    Riboswitches are a novel class of genetic control elements that function through the direct interaction of small metabolite molecules with structured RNA elements. The ligand is bound with high specificity and affinity to its RNA target and induces conformational changes of the RNA's secondary and tertiary structure upon binding. To elucidate the molecular basis of the remarkable ligand selectivity and affinity of one of these riboswitches, extensive all-atom molecular dynamics simulations in...

  9. Rheology via nonequilibrium molecular dynamics

    International Nuclear Information System (INIS)

    The equilibrium molecular dynamics formulated by Newton, Lagrange, and Hamilton has been modified in order to simulate rheologial molecular flows with fast computers. This modified Nonequilibrium Molecular Dynamics (NEMD) has been applied to fluid and solid deformations, under both homogeneous and shock conditions, as well as to the transport of heat. The irreversible heating associated with dissipation could be controlled by carrying out isothermal NEMD calculations. The new isothermal NEMD equations of motion are consistent with Gauss' 1829 Least-Constraint principle as well as certain microscopic equilibrium and nonequilibrium statistical formulations due to Gibbs and Boltzmann. Application of isothermal NEMD revealed high-frequency and high-strain-rate behavior for simple fluids which resembled the behavior of polymer solutions and melts at lower frequencies and strain rates. For solids NEMD produces plastic flows consistent with experimental observations at much lower strain rates. The new nonequilibrium methods also suggest novel formulations of thermodynamics in nonequilibrium systems and shed light on the failure of the Principle of Material Frame Indifference

  10. Rheology via nonequilibrium molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Hoover, W.G.

    1982-10-01

    The equilibrium molecular dynamics formulated by Newton, Lagrange, and Hamilton has been modified in order to simulate rheologial molecular flows with fast computers. This modified Nonequilibrium Molecular Dynamics (NEMD) has been applied to fluid and solid deformations, under both homogeneous and shock conditions, as well as to the transport of heat. The irreversible heating associated with dissipation could be controlled by carrying out isothermal NEMD calculations. The new isothermal NEMD equations of motion are consistent with Gauss' 1829 Least-Constraint principle as well as certain microscopic equilibrium and nonequilibrium statistical formulations due to Gibbs and Boltzmann. Application of isothermal NEMD revealed high-frequency and high-strain-rate behavior for simple fluids which resembled the behavior of polymer solutions and melts at lower frequencies and strain rates. For solids NEMD produces plastic flows consistent with experimental observations at much lower strain rates. The new nonequilibrium methods also suggest novel formulations of thermodynamics in nonequilibrium systems and shed light on the failure of the Principle of Material Frame Indifference.

  11. Coarse-grained molecular dynamics simulations of nanopatterning with multivalent inks

    Science.gov (United States)

    Cieplak, Marek; Thompson, Damien

    2008-06-01

    A coarse-grained molecular dynamics (MD) model is developed to study the multivalent, or multisite, binding of small functionalized dendrimer molecules to β-cyclodextrin-terminated self-assembled monolayers, the so-called ``molecular printboards'' used to print ``ink'' molecules on surfaces with a high degree of positional control and specificity. Some current and future bionanotechnology applications are in the creation of nanoparticle assemblies, directed protein assembly, platforms for biosensing, and cell:surface attachment. The coarse-grained model allows us to probe up to microsecond timescales and model ink diffusion, crucial for the application of the printboard in, for example, medical diagnostics. Recent all-atom MD simulations identified and quantified the molecular strain limiting the stability of nanopatterns created with small dendrimer inks, and explained the different patterns obtained experimentally with different dendrimer inks. In the present work, the all-atom simulations are ``scaled up'' to longer timescales via coarse graining, without incurring significant additional computational expense, and, crucially, without significant loss in atom-scale detail, the coarse-grained MD simulations yielding properties similar to those obtained from the all-atom simulations. The anchoring of the ink molecules to the monolayer is of multivalent nature and the degree of multivalency shows a sharp dependence on temperature, control of temperature thus providing a further operational ``switch'' for directed molecular assembly. The computational protocol developed can, in principle, be extended to model any multivalent assembly, for example, virus-cell complexation.

  12. Laser Controlled Molecular Orientation Dynamics

    International Nuclear Information System (INIS)

    Molecular orientation is a challenging control issue covering a wide range of applications from reactive collisions, high order harmonic generation, surface processing and catalysis, to nanotechnologies. The laser control scenario rests on the following three steps: (i) depict some basic mechanisms producing dynamical orientation; (ii) use them both as computational and interpretative tools in optimal control schemes involving genetic algorithms; (iii) apply what is learnt from optimal control to improve the basic mechanisms. The existence of a target molecular rotational state combining the advantages of efficient and post-pulse long duration orientation is shown. A strategy is developed for reaching such a target in terms of a train of successive short laser pulses applied at predicted time intervals. Each individual pulse imparts a kick to the molecule which orients. Transposition of such strategies to generic systems is now under investigation

  13. Better, Cheaper, Faster Molecular Dynamics

    Science.gov (United States)

    Pohorille, Andrew; DeVincenzi, Donald L. (Technical Monitor)

    2001-01-01

    Recent, revolutionary progress in genomics and structural, molecular and cellular biology has created new opportunities for molecular-level computer simulations of biological systems by providing vast amounts of data that require interpretation. These opportunities are further enhanced by the increasing availability of massively parallel computers. For many problems, the method of choice is classical molecular dynamics (iterative solving of Newton's equations of motion). It focuses on two main objectives. One is to calculate the relative stability of different states of the system. A typical problem that has' such an objective is computer-aided drug design. Another common objective is to describe evolution of the system towards a low energy (possibly the global minimum energy), "native" state. Perhaps the best example of such a problem is protein folding. Both types of problems share the same difficulty. Often, different states of the system are separated by high energy barriers, which implies that transitions between these states are rare events. This, in turn, can greatly impede exploration of phase space. In some instances this can lead to "quasi non-ergodicity", whereby a part of phase space is inaccessible on time scales of the simulation. To overcome this difficulty and to extend molecular dynamics to "biological" time scales (millisecond or longer) new physical formulations and new algorithmic developments are required. To be efficient they should account for natural limitations of multi-processor computer architecture. I will present work along these lines done in my group. In particular, I will focus on a new approach to calculating the free energies (stability) of different states and to overcoming "the curse of rare events". I will also discuss algorithmic improvements to multiple time step methods and to the treatment of slowly decaying, log-ranged, electrostatic effects.

  14. Error and efficiency of replica exchange molecular dynamics simulations.

    Science.gov (United States)

    Rosta, Edina; Hummer, Gerhard

    2009-10-28

    We derive simple analytical expressions for the error and computational efficiency of replica exchange molecular dynamics (REMD) simulations (and by analogy replica exchange Monte Carlo simulations). The theory applies to the important case of systems whose dynamics at long times is dominated by the slow interconversion between two metastable states. As a specific example, we consider the folding and unfolding of a protein. The efficiency is defined as the rate with which the error in an estimated equilibrium property, as measured by the variance of the estimator over repeated simulations, decreases with simulation time. For two-state systems, this rate is in general independent of the particular property. Our main result is that, with comparable computational resources used, the relative efficiency of REMD and molecular dynamics (MD) simulations is given by the ratio of the number of transitions between the two states averaged over all replicas at the different temperatures, and the number of transitions at the single temperature of the MD run. This formula applies if replica exchange is frequent, as compared to the transition times. High efficiency of REMD is thus achieved by including replica temperatures in which the frequency of transitions is higher than that at the temperature of interest. In tests of the expressions for the error in the estimator, computational efficiency, and the rate of equilibration we find quantitative agreement with the results both from kinetic models of REMD and from actual all-atom simulations of the folding of a peptide in water. PMID:19894977

  15. Molecular dynamics investigation of dynamic crack stability

    International Nuclear Information System (INIS)

    A series of molecular-dynamics simulations has been performed in order to evaluate the effects of several physical factors on dynamic crack stability. These factors are the crystalline structure and the interatomic interaction modeled by various empirical potentials. For brittle crack propagation at low temperature we find that steady-state crack velocities are limited to a band of accessible values. Increasing the overload beyond KIc, the crack can propagate with a steady-state velocity, which quickly reaches the terminal velocity of about 0.4 of the Rayleigh wave speed. The magnitude of the terminal velocity can be related to the nonlinearity of the interatomic interaction. Further increasing the overload does not change the steady-state velocity dramatically, but significantly increases the amplitude of acoustic emission from the crack tip. Loading the crack even further leads to instabilities which take the form of cleavage steps, dislocation emission, or branching. The instability is closely related to the buildup of a localized coherent, phononlike field generated by the bond-breaking events. The form of the instability depends critically on crystal structure and on the crystallographic orientation of the crack system but can also be correlated with the relative ease of dislocation generation (and motion). copyright 1997 The American Physical Society

  16. Molecular dynamics of interface rupture

    Science.gov (United States)

    Koplik, Joel; Banavar, Jayanth R.

    1993-01-01

    Several situations have been studied in which a fluid-vapor or fluid-fluid interface ruptures, using molecular dynamics simulations of 3000 to 20,000 Lennard-Jones molecules in three dimensions. The cases studied are the Rayleigh instability of a liquid thread, the burst of a liquid drop immersed in a second liquid undergoing shear, and the rupture of a liquid sheet in an extensional flow. The late stages of the rupture process involve the gradual withdrawal of molecules from a thinning neck, or the appearance and growth of holes in a sheet. In all cases, it is found that despite the small size of the systems studied, tens of angstroms, the dynamics is in at least qualitative accord with the behavior expected from continuum calculations, and in some cases the agreement is to within tens of percent. Remarkably, this agreement occurs even though the Eulerian velocity and stress fields are essentially unmeasurable - dominated by thermal noise. The limitations and prospects for such molecular simulation techniques are assessed.

  17. Molecular potentials and relaxation dynamics

    International Nuclear Information System (INIS)

    The use of empirical pseudopotentials, in evaluating interatomic potentials, provides an inexpensive and convenient method for obtaining highly accurate potential curves and permits the modeling of core-valence correlation, and the inclusion of relativistic effects when these are significant. Recent calculations of the X1Σ+ and a3Σ+ states of LiH, NaH, KH, RbH, and CsH and the X2Σ+ states of their anions are discussed. Pseudopotentials, including core polarization terms, have been used to replace the core electrons, and this has been coupled with the development of compact, higly-optimized basis sets for the corresponding one- and two-electron atoms. Comparisons of the neutral potential curves with experiment and other ab initio calculations show good agreement (within 1000 cm-1 over most of the potential curves) with the difference curves being considerably more accurate. In the method of computer molecular dynamics, the force acting on each particle is the resultant of all interactions with other atoms in the neighborhood and is obtained as the derivative of an effective many-body potential. Exploiting the pseudopotential approach, in obtaining the appropriate potentials may be very fruitful in the future. In the molecular dynamics example considered here, the conventional sum-of-pairwise-interatomic-potentials (SPP) approximation is used with the potentials derived either from experimental spectroscopic data or from Hartree-Fock calculations. The problem is the collisional de-excitation of vibrationally excited molecular hydrogen at an Fe surface. The calculations have been carried out for an initial vibrotational state v = 8, J = 1 and a translational temperature corresponding to a gas temperature of 5000K. Different angles of approach and different initial random impact points on the surface have been selected. For any given collision with the wall, the molecule may pick up or lose vibrotatonal and translational energy

  18. Overcoming potential energy distortions in constrained internal coordinate molecular dynamics simulations

    Science.gov (United States)

    Kandel, Saugat; Salomon-Ferrer, Romelia; Larsen, Adrien B.; Jain, Abhinandan; Vaidehi, Nagarajan

    2016-01-01

    The Internal Coordinate Molecular Dynamics (ICMD) method is an attractive molecular dynamics (MD) method for studying the dynamics of bonded systems such as proteins and polymers. It offers a simple venue for coarsening the dynamics model of a system at multiple hierarchical levels. For example, large scale protein dynamics can be studied using torsional dynamics, where large domains or helical structures can be treated as rigid bodies and the loops connecting them as flexible torsions. ICMD with such a dynamic model of the protein, combined with enhanced conformational sampling method such as temperature replica exchange, allows the sampling of large scale domain motion involving high energy barrier transitions. Once these large scale conformational transitions are sampled, all-torsion, or even all-atom, MD simulations can be carried out for the low energy conformations sampled via coarse grained ICMD to calculate the energetics of distinct conformations. Such hierarchical MD simulations can be carried out with standard all-atom forcefields without the need for compromising on the accuracy of the forces. Using constraints to treat bond lengths and bond angles as rigid can, however, distort the potential energy landscape of the system and reduce the number of dihedral transitions as well as conformational sampling. We present here a two-part solution to overcome such distortions of the potential energy landscape with ICMD models. To alleviate the intrinsic distortion that stems from the reduced phase space in torsional MD, we use the Fixman compensating potential. To additionally alleviate the extrinsic distortion that arises from the coupling between the dihedral angles and bond angles within a force field, we propose a hybrid ICMD method that allows the selective relaxing of bond angles. This hybrid ICMD method bridges the gap between all-atom MD and torsional MD. We demonstrate with examples that these methods together offer a solution to eliminate the potential

  19. Overcoming potential energy distortions in constrained internal coordinate molecular dynamics simulations

    International Nuclear Information System (INIS)

    The Internal Coordinate Molecular Dynamics (ICMD) method is an attractive molecular dynamics (MD) method for studying the dynamics of bonded systems such as proteins and polymers. It offers a simple venue for coarsening the dynamics model of a system at multiple hierarchical levels. For example, large scale protein dynamics can be studied using torsional dynamics, where large domains or helical structures can be treated as rigid bodies and the loops connecting them as flexible torsions. ICMD with such a dynamic model of the protein, combined with enhanced conformational sampling method such as temperature replica exchange, allows the sampling of large scale domain motion involving high energy barrier transitions. Once these large scale conformational transitions are sampled, all-torsion, or even all-atom, MD simulations can be carried out for the low energy conformations sampled via coarse grained ICMD to calculate the energetics of distinct conformations. Such hierarchical MD simulations can be carried out with standard all-atom forcefields without the need for compromising on the accuracy of the forces. Using constraints to treat bond lengths and bond angles as rigid can, however, distort the potential energy landscape of the system and reduce the number of dihedral transitions as well as conformational sampling. We present here a two-part solution to overcome such distortions of the potential energy landscape with ICMD models. To alleviate the intrinsic distortion that stems from the reduced phase space in torsional MD, we use the Fixman compensating potential. To additionally alleviate the extrinsic distortion that arises from the coupling between the dihedral angles and bond angles within a force field, we propose a hybrid ICMD method that allows the selective relaxing of bond angles. This hybrid ICMD method bridges the gap between all-atom MD and torsional MD. We demonstrate with examples that these methods together offer a solution to eliminate the potential

  20. Overcoming potential energy distortions in constrained internal coordinate molecular dynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    Kandel, Saugat; Salomon-Ferrer, Romelia; Larsen, Adrien B.; Vaidehi, Nagarajan, E-mail: nvaidehi@coh.org [Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, California 91010 (United States); Jain, Abhinandan, E-mail: Abhi.Jain@jpl.nasa.gov [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109 (United States)

    2016-01-28

    The Internal Coordinate Molecular Dynamics (ICMD) method is an attractive molecular dynamics (MD) method for studying the dynamics of bonded systems such as proteins and polymers. It offers a simple venue for coarsening the dynamics model of a system at multiple hierarchical levels. For example, large scale protein dynamics can be studied using torsional dynamics, where large domains or helical structures can be treated as rigid bodies and the loops connecting them as flexible torsions. ICMD with such a dynamic model of the protein, combined with enhanced conformational sampling method such as temperature replica exchange, allows the sampling of large scale domain motion involving high energy barrier transitions. Once these large scale conformational transitions are sampled, all-torsion, or even all-atom, MD simulations can be carried out for the low energy conformations sampled via coarse grained ICMD to calculate the energetics of distinct conformations. Such hierarchical MD simulations can be carried out with standard all-atom forcefields without the need for compromising on the accuracy of the forces. Using constraints to treat bond lengths and bond angles as rigid can, however, distort the potential energy landscape of the system and reduce the number of dihedral transitions as well as conformational sampling. We present here a two-part solution to overcome such distortions of the potential energy landscape with ICMD models. To alleviate the intrinsic distortion that stems from the reduced phase space in torsional MD, we use the Fixman compensating potential. To additionally alleviate the extrinsic distortion that arises from the coupling between the dihedral angles and bond angles within a force field, we propose a hybrid ICMD method that allows the selective relaxing of bond angles. This hybrid ICMD method bridges the gap between all-atom MD and torsional MD. We demonstrate with examples that these methods together offer a solution to eliminate the potential

  1. Molecular dynamics simulation of benzene

    Science.gov (United States)

    Trumpakaj, Zygmunt; Linde, Bogumił B. J.

    2016-03-01

    Intermolecular potentials and a few models of intermolecular interaction in liquid benzene are tested by Molecular Dynamics (MD) simulations. The repulsive part of the Lennard-Jones 12-6 (LJ 12-6) potential is too hard, which yields incorrect results. The exp-6 potential with a too hard repulsive term is also often used. Therefore, we took an expa-6 potential with a small Gaussian correction plus electrostatic interactions. This allows to modify the curvature of the potential. The MD simulations are carried out in the temperature range 280-352 K under normal pressure and at experimental density. The Rayleigh scattering of depolarized light is used for comparison. The results of MD simulations are comparable with the experimental values.

  2. Molecular dynamics studies of palladium

    International Nuclear Information System (INIS)

    Equilibrium bulk properties of Pd are examined using molecular dynamics technique based on the embedded atom potential. We calculate the total energy and the lattice parameter as a function of temperature. Melting temperature is determined from the discontinuous transition in the energy and lattice parameter. Specific heat and linear coefficient of thermal expansion are calculated from the energy and lattice parameters respectively and results show good agreement with experimental values. Finally the mean square displacements of thermal expansion are calculated form the energy and lattice parameters respectively and results show good agreement with the experimental values. Finally the mean square displacements of the atoms in bulk Pd are compared with the mean square displacements on the three low-index faces (100), (110) and (III). (author)

  3. Molecular energetics in the capsomere of virus-like particle revealed by molecular dynamics simulations.

    Science.gov (United States)

    Zhang, Lin; Tang, Ronghong; Bai, Shu; Connors, Natalie K; Lua, Linda H L; Chuan, Yap P; Middelberg, Anton P J; Sun, Yan

    2013-05-01

    Virus-like particles (VLPs) are highly organized nanoparticles that have great potential in vaccinology, gene therapy, drug delivery, and materials science. However, the application of VLPs is hindered by obstacles in their design and production due to low efficiency of self-assembly. In the present study, all-atom (AA) molecular dynamics (MD) simulations coupled with the molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) method are utilized to examine the molecular interactions in the capsomere of a murine polyomavirus (MPV) VLP. It is found that both low ionic strength and the intracapsomere disulfide bonds are favorable for maintaining a stable capsomere. Simulation results examining the effects of solution conditions on the stabilization of a capsomere were verified by calorimetry experiments. Simulation results of free energy decomposition indicate that hydrophobic interaction is favorable for the formation of a capsomere, whereas electrostatic interaction is unfavorable. With increasing ionic strength, the dominant interaction for the stabilization of a capsomere changes from hydrophobic to electrostatic. By comprehensive analyses, the key amino acid residues (hot spots) in VP1 protein aiding formation of a capsomere in different solution conditions have been identified. These results provide molecular insights into the stabilization of building blocks for VLP and are expected to have implications in their partitioning between the correct and off-pathway reactions in VLP assembly. PMID:23586433

  4. Rigid-body molecular dynamics of DNA inside a nucleosome.

    Science.gov (United States)

    Fathizadeh, Arman; Berdy Besya, Azim; Reza Ejtehadi, Mohammad; Schiessel, Helmut

    2013-03-01

    The majority of eukaryotic DNA, about three quarter, is wrapped around histone proteins forming so-called nucleosomes. To study nucleosomal DNA we introduce a coarse-grained molecular dynamics model based on sequence-dependent harmonic rigid base pair step parameters of DNA and nucleosomal binding sites. Mixed parametrization based on all-atom molecular dynamics and crystallographic data of protein-DNA structures is used for the base pair step parameters. The binding site parameters are adjusted by experimental B-factor values of the nucleosome crystal structure. The model is then used to determine the energy cost for placing a twist defect into the nucleosomal DNA which allows us to use Kramers theory to calculate nucleosome sliding caused by such defects. It is shown that the twist defect scenario together with the sequence-dependent elasticity of DNA can explain the slow time scales observed for nucleosome mobility along DNA. With this method we also show how the twist defect mechanism leads to a higher mobility of DNA in the presence of sin mutations near the dyad axis. Finally, by performing simulations on 5s rDNA, 601, and telomeric base pair sequences, it is demonstrated that the current model is a powerful tool to predict nucleosome positioning. PMID:23475204

  5. Petascale molecular dynamics simulation using the fast multipole method on K computer

    KAUST Repository

    Ohno, Yousuke

    2014-10-01

    In this paper, we report all-atom simulations of molecular crowding - a result from the full node simulation on the "K computer", which is a 10-PFLOPS supercomputer in Japan. The capability of this machine enables us to perform simulation of crowded cellular environments, which are more realistic compared to conventional MD simulations where proteins are simulated in isolation. Living cells are "crowded" because macromolecules comprise ∼30% of their molecular weight. Recently, the effects of crowded cellular environments on protein stability have been revealed through in-cell NMR spectroscopy. To measure the performance of the "K computer", we performed all-atom classical molecular dynamics simulations of two systems: target proteins in a solvent, and target proteins in an environment of molecular crowders that mimic the conditions of a living cell. Using the full system, we achieved 4.4 PFLOPS during a 520 million-atom simulation with cutoff of 28 Å. Furthermore, we discuss the performance and scaling of fast multipole methods for molecular dynamics simulations on the "K computer", as well as comparisons with Ewald summation methods. © 2014 Elsevier B.V. All rights reserved.

  6. How can a beta-sheet peptide be both a potent antimicrobial and harmfully toxic? Molecular dynamics simulations of protegrin-1 in micelles

    DEFF Research Database (Denmark)

    Langham, Allison A; Khandelia, Himanshu; Kaznessis, Yiannis N

    2006-01-01

    In this work, the naturally occurring beta-hairpin antimicrobial peptide protegrin-1 (PG-1) is studied by molecular dynamics simulation in all-atom sodium dodecylsulfate and dodecylphosphocholine micelles. These simulations provide a high-resolution picture of the interactions between the peptide...

  7. Theoretical Concepts in Molecular Photodissociation Dynamics

    DEFF Research Database (Denmark)

    Henriksen, Niels Engholm

    This chapter contains sections titled: Introduction Quantum Dynamics of Molecular Photofragmentation The Total Reaction Probability Final Product Distributions Time-Independent Approach, Stationary Scattering States Gaussian Wave Packet Dynamics Wigner Phase Space Representation The Diatomic Mole...

  8. Theoretical Concepts in Molecular Photodissociation Dynamics

    DEFF Research Database (Denmark)

    Henriksen, Niels Engholm

    1995-01-01

    This chapter contains sections titled: Introduction Quantum Dynamics of Molecular Photofragmentation The Total Reaction Probability Final Product Distributions Time-Independent Approach, Stationary Scattering States Gaussian Wave Packet Dynamics Wigner Phase Space Representation The Diatomic...

  9. Molecular dynamics of membrane proteins.

    Energy Technology Data Exchange (ETDEWEB)

    Woolf, Thomas B. (Johns Hopkins University School of Medicine, Baltimore, MD); Crozier, Paul Stewart; Stevens, Mark Jackson

    2004-10-01

    Understanding the dynamics of the membrane protein rhodopsin will have broad implications for other membrane proteins and cellular signaling processes. Rhodopsin (Rho) is a light activated G-protein coupled receptor (GPCR). When activated by ligands, GPCRs bind and activate G-proteins residing within the cell and begin a signaling cascade that results in the cell's response to external stimuli. More than 50% of all current drugs are targeted toward G-proteins. Rho is the prototypical member of the class A GPCR superfamily. Understanding the activation of Rho and its interaction with its Gprotein can therefore lead to a wider understanding of the mechanisms of GPCR activation and G-protein activation. Understanding the dark to light transition of Rho is fully analogous to the general ligand binding and activation problem for GPCRs. This transition is dependent on the lipid environment. The effect of lipids on membrane protein activity in general has had little attention, but evidence is beginning to show a significant role for lipids in membrane protein activity. Using the LAMMPS program and simulation methods benchmarked under the IBIG program, we perform a variety of allatom molecular dynamics simulations of membrane proteins.

  10. Molecular dynamics simulations data of the twenty encoded amino acids in different force fields.

    Science.gov (United States)

    Vitalini, F; Noé, F; Keller, B G

    2016-06-01

    We present extensive all-atom Molecular Dynamics (MD) simulation data of the twenty encoded amino acids in explicit water, simulated with different force fields. The termini of the amino acids have been capped to ensure that the dynamics of the Φ and ψ torsion angles are analogues to the dynamics within a peptide chain. We use representatives of each of the four major force field families: AMBER ff-99SBILDN [1], AMBER ff-03 [2], OPLS-AA/L [3], CHARMM27 [4] and GROMOS43a1 [5], [6]. Our data represents a library and test bed for method development for MD simulations and for force fields development. Part of the data set has been previously used for comparison of the dynamic properties of force fields (Vitalini et al., 2015) [7] and for the construction of peptide basis functions for the variational approach to molecular kinetics [8]. PMID:27054161

  11. A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants

    Directory of Open Access Journals (Sweden)

    James P. Ewen

    2016-08-01

    Full Text Available For the successful development and application of lubricants, a full understanding of their complex nanoscale behavior under a wide range of external conditions is required, but this is difficult to obtain experimentally. Nonequilibrium molecular dynamics (NEMD simulations can be used to yield unique insights into the atomic-scale structure and friction of lubricants and additives; however, the accuracy of the results depend on the chosen force-field. In this study, we demonstrate that the use of an accurate, all-atom force-field is critical in order to; (i accurately predict important properties of long-chain, linear molecules; and (ii reproduce experimental friction behavior of multi-component tribological systems. In particular, we focus on n-hexadecane, an important model lubricant with a wide range of industrial applications. Moreover, simulating conditions common in tribological systems, i.e., high temperatures and pressures (HTHP, allows the limits of the selected force-fields to be tested. In the first section, a large number of united-atom and all-atom force-fields are benchmarked in terms of their density and viscosity prediction accuracy of n-hexadecane using equilibrium molecular dynamics (EMD simulations at ambient and HTHP conditions. Whilst united-atom force-fields accurately reproduce experimental density, the viscosity is significantly under-predicted compared to all-atom force-fields and experiments. Moreover, some all-tom force-fields yield elevated melting points, leading to significant overestimation of both the density and viscosity. In the second section, the most accurate united-atom and all-atom force-field are compared in confined NEMD simulations which probe the structure and friction of stearic acid adsorbed on iron oxide and separated by a thin layer of n-hexadecane. The united-atom force-field provides an accurate representation of the structure of the confined stearic acid film; however, friction coefficients are

  12. Molecular dynamics simulation by atomic mass weighting

    OpenAIRE

    Mao, Boryeu; Friedman, Alan R.

    1990-01-01

    A molecular dynamics-based simulation method in which atomic masses are weighted is described. Results from this method showed that the capability for conformation search in molecular dynamics simulation of a short peptide (FMRF-amide) is significantly increased by mass weighting.

  13. Beyond Modeling: All-Atom Olfactory Receptor Model Simulations

    Directory of Open Access Journals (Sweden)

    Peter C Lai

    2012-05-01

    Full Text Available Olfactory receptors (ORs are a type of GTP-binding protein-coupled receptor (GPCR. These receptors are responsible for mediating the sense of smell through their interaction with odor ligands. OR-odorant interactions marks the first step in the process that leads to olfaction. Computational studies on model OR structures can validate experimental functional studies as well as generate focused and novel hypotheses for further bench investigation by providing a view of these interactions at the molecular level. Here we have shown the specific advantages of simulating the dynamic environment that is associated with OR-odorant interactions. We present a rigorous methodology that ranges from the creation of a computationally-derived model of an olfactory receptor to simulating the interactions between an OR and an odorant molecule. Given the ubiquitous occurrence of GPCRs in the membranes of cells, we anticipate that our OR-developed methodology will serve as a model for the computational structural biology of all GPCRs.

  14. A Real-Time All-Atom Structural Search Engine for Proteins

    OpenAIRE

    Gonzalez, Gabriel; Hannigan, Brett; DeGrado, William F.

    2014-01-01

    Protein designers use a wide variety of software tools for de novo design, yet their repertoire still lacks a fast and interactive all-atom search engine. To solve this, we have built the Suns program: a real-time, atomic search engine integrated into the PyMOL molecular visualization system. Users build atomic-level structural search queries within PyMOL and receive a stream of search results aligned to their query within a few seconds. This instant feedback cycle enables a new “designabilit...

  15. Hemolytic mechanism of dioscin proposed by molecular dynamics simulations.

    Science.gov (United States)

    Lin, Fu; Wang, Renxiao

    2010-01-01

    Saponins are a class of compounds containing a triterpenoid or steroid core with some attached carbohydrate modules. Many saponins cause hemolysis. However, the hemolytic mechanism of saponins at the molecular level is not yet fully understood. In an attempt to explore this issue, we have studied dioscin-a saponin with high hemolytic activity-through extensive molecular dynamics (MD) simulations. Firstly, all-atom MD simulations of 8 ns duration were conducted to study the stability of the dioscin-cholesterol complex and the cholesterol-cholesterol complex in water and in decane, respectively. MM-GB/SA computations indicate that the dioscin-cholesterol complex is energetically more favorable than the cholesterol-cholesterol complex in a non-polar environment. Next, several coarse-grained MD simulations of 400 ns duration were conducted to directly observe the distribution of multiple dioscin molecules on a DPPC-POPC-PSM-CHOL lipid bilayer. Our results indicate that dioscin can penetrate into the lipid bilayer, accumulate in the lipid raft micro-domain, and then bind cholesterol. This leads to the destabilization of lipid raft and consequent membrane curvature, which may eventually result in the hemolysis of red cells. This possible mechanism of hemolysis can well explain some experimental observations on hemolysis. PMID:19513766

  16. Small molecule interactions with lipid bilayers: a molecular dynamics study of chlorhexidine

    Science.gov (United States)

    van Oosten, Brad; Marquardt, Drew; Sternin, Edward; Harroun, Thad

    2013-03-01

    Chlorhexidine presents an interesting modelling challenge with a hydrophobic hexane connecting two biguanides (arginine analogues) and two aromatic rings. We conducted molecular dynamic simulations using the GROMACS simulation software to reproduce the experimental environment of chlorhexidine in a 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC) bilayer to produce atomic-level information. We constructed an all-atom force field of chlorhexidine from the CHARMM36 force field using well established parameters of certain amino acids. Partial charges were treated differently, which were calculated using GAUSSIAN software. We will compare and contrast the results of our model to that of our neutron scattering experiments previously done in our lab.

  17. Mechanism resulting in chemical imbalance due to cellular damage associated with mechanoporation: A molecular dynamics study

    Science.gov (United States)

    Sliozberg, Yelena R.; Chantawansri, Tanya L.

    2016-05-01

    To elucidate the mechanism of ion transport through a transmembrane pore, all-atom molecular dynamics simulations were employed. A model membrane where a pore connects the intra- and extra-cellular compartment was considered. Pores with radii of 1.5 nm or less exhibited resealing over the course of 135 ns simulations, and ionic disturbance is minimal. Ion transport through a larger pore (2 nm radius) leads to a substantial change in the intra- and extra-cellular ionic concentrations. The influx of Na+ and Cl- ions down their concentration gradients is greater than the efflux of K+ leading to an osmotic influx of water.

  18. Thermally driven molecular linear motors - A molecular dynamics study

    DEFF Research Database (Denmark)

    Zambrano, Harvey A; Walther, Jens Honore; Jaffe, Richard Lawrence

    2009-01-01

    We conduct molecular dynamics simulations of a molecular linear motor consisting of coaxial carbon nanotubes with a long outer carbon nanotube confining and guiding the motion of an inner short, capsule-like nanotube. The simulations indicate that the motion of the capsule can be controlled by th...

  19. Communication: Relation of centroid molecular dynamics and ring-polymer molecular dynamics to exact quantum dynamics

    International Nuclear Information System (INIS)

    We recently obtained a quantum-Boltzmann-conserving classical dynamics by making a single change to the derivation of the “Classical Wigner” approximation. Here, we show that the further approximation of this “Matsubara dynamics” gives rise to two popular heuristic methods for treating quantum Boltzmann time-correlation functions: centroid molecular dynamics (CMD) and ring-polymer molecular dynamics (RPMD). We show that CMD is a mean-field approximation to Matsubara dynamics, obtained by discarding (classical) fluctuations around the centroid, and that RPMD is the result of discarding a term in the Matsubara Liouvillian which shifts the frequencies of these fluctuations. These findings are consistent with previous numerical results and give explicit formulae for the terms that CMD and RPMD leave out

  20. Quantum dynamics of complex molecular systems

    OpenAIRE

    Miller, William H.

    2005-01-01

    This Perspective presents a broad overview of the present status of theoretical capabilities for describing quantum dynamics in molecular systems with many degrees of freedom, e.g., chemical reactions in solution, clusters, solids, or biomolecular environments.

  1. Dynamical processes in atomic and molecular physics

    CERN Document Server

    Ogurtsov, Gennadi

    2012-01-01

    Atomic and molecular physics underlie a basis for our knowledge of fundamental processes in nature and technology and in such applications as solid state physics, chemistry and biology. In recent years, atomic and molecular physics has undergone a revolutionary change due to great achievements in computing and experimental techniques. As a result, it has become possible to obtain information both on atomic and molecular characteristics and on dynamics of atomic and molecular processes. This e-book highlights the present state of investigations in the field of atomic and molecular physics. Rece

  2. Ab initio mass tensor molecular dynamics

    OpenAIRE

    Tsuchida, Eiji

    2010-01-01

    Mass tensor molecular dynamics was first introduced by Bennett [J. Comput. Phys. 19, 267 (1975)] for efficient sampling of phase space through the use of generalized atomic masses. Here, we show how to apply this method to ab initio molecular dynamics simulations with minimal computational overhead. Test calculations on liquid water show a threefold reduction in computational effort without making the fixed geometry approximation. We also present a simple recipe for estimating the optimal ato...

  3. Accelerated molecular dynamics simulations of protein folding

    OpenAIRE

    Miao, Y.; Feixas, F; Eun, C; McCammon, JA

    2015-01-01

    © 2015 Wiley Periodicals, Inc. Folding of four fast-folding proteins, including chignolin, Trp-cage, villin headpiece and WW domain, was simulated via accelerated molecular dynamics (aMD). In comparison with hundred-of-microsecond timescale conventional molecular dynamics (cMD) simulations performed on the Anton supercomputer, aMD captured complete folding of the four proteins in significantly shorter simulation time. The folded protein conformations were found within 0.2-2.1 Å of the native ...

  4. Molecular Dynamic Simulation on High Performance Infrastrucutres

    OpenAIRE

    Bergant, Anže

    2016-01-01

    This thesis covers comparison between different computer platforms of high performance computing while performing molecular dynamics simulations, which falls under very complex problems and needs lots of processing power. Our goal was to critically evaluate different platforms while solving molecular dynamics, so we used 1 to 16 processor cores on a computer cluster and one and two graphics processing units (GPU) for simulations. The results will be used while planning on buying new computer ...

  5. Atomic dynamics of alumina melt: A molecular dynamics simulation study

    OpenAIRE

    Jahn, S.; P. A. Madden

    2008-01-01

    The atomic dynamics of Al2O3 melt are studied by molecular dynamics simulation. The particle interactions are described by an advanced ionic interaction model that includes polarization effects and ionic shape deformations. The model has been shown to reproduce accurately the static structure factors S(Q) from neutron and x-ray diffraction and the dynamic structure factor S(Q,ω) from inelastic x-ray scattering. Analysis of the partial dynamic structure factors shows inelastic features in the ...

  6. A Molecular Dynamics Study of the Structural and Dynamical Properties of Putative Arsenic Substituted Lipid Bilayers

    Directory of Open Access Journals (Sweden)

    Ratna Juwita

    2013-04-01

    Full Text Available Cell membranes are composed mainly of phospholipids which are in turn, composed of five major chemical elements: carbon, hydrogen, nitrogen, oxygen, and phosphorus. Recent studies have suggested the possibility of sustaining life if the phosphorus is substituted by arsenic. Although this issue is still controversial, it is of interest to investigate the properties of arsenated-lipid bilayers to evaluate this possibility. In this study, we simulated arsenated-lipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-arsenocholine (POAC, lipid bilayers using all-atom molecular dynamics to understand basic structural and dynamical properties, in particular, the differences from analogous 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, (POPC lipid bilayers. Our simulations showed that POAC lipid bilayers have distinct structural and dynamical properties from those of native POPC lipid bilayers. Relative to POPC lipid bilayers, POAC lipid bilayers have a more compact structure with smaller lateral areas and greater order. The compact structure of POAC lipid bilayers is due to the fact that more inter-lipid salt bridges are formed with arsenate-choline compared to the phosphate-choline of POPC lipid bilayers. These inter-lipid salt bridges bind POAC lipids together and also slow down the head group rotation and lateral diffusion of POAC lipids. Thus, it would be anticipated that POAC and POPC lipid bilayers would have different biological implications.

  7. Modeling the Hydrogen Bond within Molecular Dynamics

    Science.gov (United States)

    Lykos, Peter

    2004-01-01

    The structure of a hydrogen bond is elucidated within the framework of molecular dynamics based on the model of Rahman and Stillinger (R-S) liquid water treatment. Thus, undergraduates are exposed to the powerful but simple use of classical mechanics to solid objects from a molecular viewpoint.

  8. Molecular Dynamics Simulations of Simple Liquids

    Science.gov (United States)

    Speer, Owner F.; Wengerter, Brian C.; Taylor, Ramona S.

    2004-01-01

    An experiment, in which students were given the opportunity to perform molecular dynamics simulations on a series of molecular liquids using the Amber suite of programs, is presented. They were introduced to both physical theories underlying classical mechanics simulations and to the atom-atom pair distribution function.

  9. Fermionic Molecular Dynamics for nuclear dynamics and thermodynamics

    CERN Document Server

    Hasnaoui, K H O; Gulminelli, F

    2008-01-01

    A new Fermionic Molecular Dynamics (FMD) model based on a Skyrme functional is proposed in this paper. After introducing the basic formalism, some first applications to nuclear structure and nuclear thermodynamics are presented

  10. Folding peptides and proteins with all-atom physics: methods and applications

    Science.gov (United States)

    Shell, M. Scott

    2008-03-01

    Computational methods offer powerful tools for investigating proteins and peptides at the molecular-level; however, it has proven challenging to reproduce the long time scale folding processes of these molecules at a level that is both faithful to the atomic driving forces and attainable with modern commodity cluster computing. Alternatively, the past decade has seen significant progress in using bioinformatics-based approaches to infer the three dimensional native structures of proteins, drawing upon extensive knowledge databases of known protein structures [1]. These methods work remarkably well when a homologous protein can be found to provide a structural template for a candidate sequence. However, in cases where homology to database proteins is low, where the folding pathway is of interest, or where conformational flexibility is substantial---as in many emerging protein and peptide technologies---bioinformatics methods perform poorly. There is therefore great interest in seeing purely physics-based approaches succeed. We discuss a purely physics-based, database-free folding method, relying on proper thermal sampling (replica exchange molecular dynamics) and molecular potential energy functions. In order to surmount the tremendous computational demands of all-atom folding simulations, our approach implements a conformational search strategy based on a putative protein folding mechanism called zipping and assembly [2-4]. That is, we explicitly seek out potential folding pathways inferred from short simulations, and iteratively pursue all such routes by coaxing a polypeptide chain along them. The method is called the Zipping and Assembly Method (ZAM) and it works in two parts: (1) the full polypeptide chain is broken into small fragments that are first simulated independently and then successively re-assembled into larger segments with further sampling, and (2) consistently stable structure in fragments is detected and locked into place, in order to avoid re

  11. Comparison of pathways from the geometric targeting method and targeted molecular dynamics in nitrogen regulatory protein C

    International Nuclear Information System (INIS)

    Geometric targeting (GT) is a recently introduced method for rapidly generating all-atom pathways from one protein state to another, based on geometric rather than energetic considerations. To generate pathways, a bias is applied that gradually moves atoms toward a target structure, while a set of geometric constraints between atoms is enforced to keep the structure stereochemically acceptable. In this work, we compare conformational pathways generated from GT to pathways from the much more computationally intensive and commonly used targeted molecular dynamics (TMD) technique, for a complicated conformational change in the signaling protein nitrogen regulatory protein C. We show that the all-atom pathways from GT are similar to previously reported TMD pathways for this protein, by comparing motion along six progress variables that describe the various structural changes. The results suggest that for nitrogen regulatory protein C, finding an all-atom pathway is primarily a problem of geometry, and that a detailed force field in this case constitutes an unnecessary extra layer of detail. We also show that the pathway snapshots from GT have good structure quality, by measuring various structure quality metrics. Transient hydrogen bonds detected by the two methods show some similarities but also some differences. The results justify the usage of GT as a rapid, approximate alternative to TMD for generating stereochemically acceptable all-atom pathways in highly constrained protein systems

  12. New ways to boost molecular dynamics simulations.

    Science.gov (United States)

    Krieger, Elmar; Vriend, Gert

    2015-05-15

    We describe a set of algorithms that allow to simulate dihydrofolate reductase (DHFR, a common benchmark) with the AMBER all-atom force field at 160 nanoseconds/day on a single Intel Core i7 5960X CPU (no graphics processing unit (GPU), 23,786 atoms, particle mesh Ewald (PME), 8.0 Å cutoff, correct atom masses, reproducible trajectory, CPU with 3.6 GHz, no turbo boost, 8 AVX registers). The new features include a mixed multiple time-step algorithm (reaching 5 fs), a tuned version of LINCS to constrain bond angles, the fusion of pair list creation and force calculation, pressure coupling with a "densostat," and exploitation of new CPU instruction sets like AVX2. The impact of Intel's new transactional memory, atomic instructions, and sloppy pair lists is also analyzed. The algorithms map well to GPUs and can automatically handle most Protein Data Bank (PDB) files including ligands. An implementation is available as part of the YASARA molecular modeling and simulation program from www.YASARA.org. PMID:25824339

  13. Equilibrium conformational dynamics in an RNA tetraloop from massively parallel molecular dynamics.

    Science.gov (United States)

    DePaul, Allison J; Thompson, Erik J; Patel, Sarav S; Haldeman, Kristin; Sorin, Eric J

    2010-08-01

    Conformational equilibrium within the ubiquitous GNRA tetraloop motif was simulated at the ensemble level, including 10 000 independent all-atom molecular dynamics trajectories totaling over 110 micros of simulation time. This robust sampling reveals a highly dynamic structure comprised of 15 conformational microstates. We assemble a Markov model that includes transitions ranging from the nanosecond to microsecond timescales and is dominated by six key loop conformations that contribute to fluctuations around the native state. Mining of the Protein Data Bank provides an abundance of structures in which GNRA tetraloops participate in tertiary contact formation. Most predominantly observed in the experimental data are interactions of the native loop structure within the minor groove of adjacent helical regions. Additionally, a second trend is observed in which the tetraloop assumes non-native conformations while participating in multiple tertiary contacts, in some cases involving multiple possible loop conformations. This tetraloop flexibility can act to counterbalance the energetic penalty associated with assuming non-native loop structures in forming tertiary contacts. The GNRA motif has thus evolved not only to readily participate in simple tertiary interactions involving native loop structure, but also to easily adapt tetraloop secondary conformation in order to participate in larger, more complex tertiary interactions. PMID:20223768

  14. Dynamics and Thermodynamics of Molecular Machines

    DEFF Research Database (Denmark)

    Golubeva, Natalia

    2014-01-01

    to their microscopic size, molecular motors are governed by principles fundamentally different from those describing the operation of man-made motors such as car engines. In this dissertation the dynamic and thermodynamic properties of molecular machines are studied using the tools of nonequilibrium......Molecular machines, or molecular motors, are small biophysical devices that perform a variety of essential metabolic processes such as DNA replication, protein synthesis and intracellular transport. Typically, these machines operate by converting chemical energy into motion and mechanical work. Due...... statistical mechanics. The first part focuses on noninteracting molecular machines described by a paradigmatic continuum model with the aim of comparing and contrasting such a description to the one offered by the widely used discrete models. Many molecular motors, for example, kinesin involved in cellular...

  15. Advances in molecular vibrations and collision dynamics molecular clusters

    CERN Document Server

    Bacic, Zatko

    1998-01-01

    This volume focuses on molecular clusters, bound by van der Waals interactions and hydrogen bonds. Twelve chapters review a wide range of recent theoretical and experimental advances in the areas of cluster vibrations, spectroscopy, and reaction dynamics. The authors are leading experts, who have made significant contributions to these topics.The first chapter describes exciting results and new insights in the solvent effects on the short-time photo fragmentation dynamics of small molecules, obtained by combining heteroclusters with femtosecond laser excitation. The second is on theoretical work on effects of single solvent (argon) atom on the photodissociation dynamics of the solute H2O molecule. The next two chapters cover experimental and theoretical aspects of the energetics and vibrations of small clusters. Chapter 5 describes diffusion quantum Monte Carlo calculations and non additive three-body potential terms in molecular clusters. The next six chapters deal with hydrogen-bonded clusters, refle...

  16. Fast dynamics of molecular bridges

    Czech Academy of Sciences Publication Activity Database

    Špička, Václav; Kalvová, Anděla; Velický, B.

    T151, č. 1 (2012), s. 1-17. ISSN 0031-8949 R&D Projects: GA ČR GAP204/12/0897 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z10100520 Keywords : time quantum dynamics * nonequilibrium Green-functions * Kadanoff-Baym equations * initial correlations * transportequations * mesoscopic systems Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.032, year: 2012

  17. Scalable Molecular Dynamics for Large Biomolecular Systems

    Directory of Open Access Journals (Sweden)

    Robert K. Brunner

    2000-01-01

    Full Text Available We present an optimized parallelization scheme for molecular dynamics simulations of large biomolecular systems, implemented in the production-quality molecular dynamics program NAMD. With an object-based hybrid force and spatial decomposition scheme, and an aggressive measurement-based predictive load balancing framework, we have attained speeds and speedups that are much higher than any reported in literature so far. The paper first summarizes the broad methodology we are pursuing, and the basic parallelization scheme we used. It then describes the optimizations that were instrumental in increasing performance, and presents performance results on benchmark simulations.

  18. Molecular Scale Dynamics of Large Ring Polymers

    Science.gov (United States)

    Gooßen, S.; Brás, A. R.; Krutyeva, M.; Sharp, M.; Falus, P.; Feoktystov, A.; Gasser, U.; Pyckhout-Hintzen, W.; Wischnewski, A.; Richter, D.

    2014-10-01

    We present neutron scattering data on the structure and dynamics of melts from polyethylene oxide rings with molecular weights up to ten times the entanglement mass of the linear counterpart. The data reveal a very compact conformation displaying a structure approaching a mass fractal, as hypothesized by recent simulation work. The dynamics is characterized by a fast Rouse relaxation of subunits (loops) and a slower dynamics displaying a lattice animal-like loop displacement. The loop size is an intrinsic property of the ring architecture and is independent of molecular weight. This is the first experimental observation of the space-time evolution of segmental motion in ring polymers illustrating the dynamic consequences of their topology that is unique among all polymeric systems of any other known architecture.

  19. Methane in carbon nanotube - molecular dynamics simulation

    OpenAIRE

    Bartuś, Katarzyna; Bródka, Aleksander

    2011-01-01

    Abstract The behaviour of methane molecules inside carbon nanotube at room temperature is studied using classical molecular dynamics simulations. A methane molecule is represented either by a shapeless super-atom or by rigid set of 5 interaction centres localised on atoms. Different loadings of methane molecules ranging from the dense gas density to the liquid density, and the influence of flexibility of the CNT on structural and dynamics properties of confined molecules are consid...

  20. Neutron Star Crust and Molecular Dynamics Simulation

    CERN Document Server

    Horowitz, C J; Schneider, A; Berry, D K

    2011-01-01

    In this book chapter we review plasma crystals in the laboratory, in the interior of white dwarf stars, and in the crust of neutron stars. We describe a molecular dynamics formalism and show results for many neutron star crust properties including phase separation upon freezing, diffusion, breaking strain, shear viscosity and dynamics response of nuclear pasta. We end with a summary and discuss open questions and challenges for the future.

  1. Molecular dynamics simulation of impact test

    Energy Technology Data Exchange (ETDEWEB)

    Akahoshi, Y. [Kyushu Inst. of Tech., Kitakyushu, Fukuoka (Japan); Schmauder, S.; Ludwig, M. [Stuttgart Univ. (Germany). Staatliche Materialpruefungsanstalt

    1998-11-01

    This paper describes an impact test by molecular dynamics (MD) simulation to evaluate embrittlement of bcc Fe at different temperatures. A new impact test model is developed for MD simulation. The typical fracture behaviors show transition from brittle to ductile fracture, and a history of the impact loads also demonstrates its transition. We conclude that the impact test by MD could be feasible. (orig.)

  2. Molecular dynamic simulation of directional crystal growth

    OpenAIRE

    Costa, B. V.; Coura, P. Z.; Mesquita, O. N.

    1999-01-01

    We use molecular dynamic to simulate the directional growth of binary mixtures. our results compare very well with analitical and experimental results. This opens up the possibility to probe growth situations which are difficult to reach experimentally, being an important tool for further experimental and theoretical developments in the area of crystal growth.

  3. Molecular dynamics - NMR experiments and simulations

    Czech Academy of Sciences Publication Activity Database

    Dračínský, Martin; Hodgkinson, P.; Kessler, Jiří; Bouř, Petr

    Brno : Masaryk University Press, 2015 - (Sklenář, V.). s. 277-278 ISBN 978-80-210-7890-1. [EUROMAR 2015. 05.07.2015-10.07.2015, Praha] Institutional support: RVO:61388963 Keywords : molecular dynamics * NMR spectroscopy * MD simulations Subject RIV: CF - Physical ; Theoretical Chemistry

  4. Reaction dynamics in polyatomic molecular systems

    Energy Technology Data Exchange (ETDEWEB)

    Miller, W.H. [Lawrence Berkeley Laboratory, CA (United States)

    1993-12-01

    The goal of this program is the development of theoretical methods and models for describing the dynamics of chemical reactions, with specific interest for application to polyatomic molecular systems of special interest and relevance. There is interest in developing the most rigorous possible theoretical approaches and also in more approximate treatments that are more readily applicable to complex systems.

  5. Molecular dynamics simulations of weak detonations.

    Science.gov (United States)

    Am-Shallem, Morag; Zeiri, Yehuda; Zybin, Sergey V; Kosloff, Ronnie

    2011-12-01

    Detonation of a three-dimensional reactive nonisotropic molecular crystal is modeled using molecular dynamics simulations. The detonation process is initiated by an impulse, followed by the creation of a stable fast reactive shock wave. The terminal shock velocity is independent of the initiation conditions. Further analysis shows supersonic propagation decoupled from the dynamics of the decomposed material left behind the shock front. The dependence of the shock velocity on crystal nonlinear compressibility resembles solitary behavior. These properties categorize the phenomena as a weak detonation. The dependence of the detonation wave on microscopic potential parameters was investigated. An increase in detonation velocity with the reaction exothermicity reaching a saturation value is observed. In all other respects the model crystal exhibits typical properties of a molecular crystal. PMID:22304055

  6. Protein Kinase A (PKA) Phosphorylation of Na+/K+-ATPase Opens Intracellular C-terminal Water Pathway Leading to Third Na+-binding site in Molecular Dynamics Simulations

    OpenAIRE

    Poulsen, H.; Nissen, P.; Mouritsen, O G; Khandelia, H.

    2012-01-01

    Phosphorylation is one of the major mechanisms for posttranscriptional modification of proteins. The addition of a compact, negatively charged moiety to a protein can significantly change its function and localization by affecting its structure and interaction network. We have used all-atom Molecular Dynamics (MD) simulations to investigate the structural consequences of phosphorylating the Na+/K+- ATPase (NKA) residue S936, which is the best characterized phosphorylation site in NKA, targete...

  7. Dynamical quenching of tunneling in molecular magnets

    International Nuclear Information System (INIS)

    It is shown that a single molecular magnet placed in a rapidly oscillating magnetic field displays the phenomenon of quenching of tunneling processes. The results open a way to manipulate the quantum states of molecular magnets by means of radiation in the terahertz range. Our analysis separates the time evolution into slow and fast components thereby obtaining an effective theory for the slow dynamics. This effective theory presents quenching of the tunnel effect, in particular, stands out its difference with the so-called coherent destruction of tunneling. We support our prediction with numerical evidence based on an exact solution of Schrödinger's equation. - Highlights: • Single molecular magnets under rapidly oscillating magnetic fields is studied. • It is shown that this system displays the quenching of tunneling processes. • Our findings provide a control of quantum molecular magnets via terahertz radiation

  8. Dynamical quenching of tunneling in molecular magnets

    Energy Technology Data Exchange (ETDEWEB)

    José Santander, María, E-mail: maria.jose.noemi@gmail.com [Recursos Educativos Quántica, Santiago (Chile); Departamento de Física, Universidad de Santiago de Chile and CEDENNA, Avda. Ecuador 3493, Santiago (Chile); Nunez, Alvaro S., E-mail: alnunez@dfi.uchile.cl [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Casilla 487-3, Santiago (Chile); Roldán-Molina, A. [Instituto de Física, Pontificia Universidad Católica de Valparaíso, Avenida Universidad 330, Curauma, Valparaíso (Chile); Troncoso, Roberto E., E-mail: r.troncoso.c@gmail.com [Centro para el Desarrollo de la Nanociencia y la Nanotecnología, CEDENNA, Avda. Ecuador 3493, Santiago 9170124 (Chile); Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso (Chile)

    2015-12-15

    It is shown that a single molecular magnet placed in a rapidly oscillating magnetic field displays the phenomenon of quenching of tunneling processes. The results open a way to manipulate the quantum states of molecular magnets by means of radiation in the terahertz range. Our analysis separates the time evolution into slow and fast components thereby obtaining an effective theory for the slow dynamics. This effective theory presents quenching of the tunnel effect, in particular, stands out its difference with the so-called coherent destruction of tunneling. We support our prediction with numerical evidence based on an exact solution of Schrödinger's equation. - Highlights: • Single molecular magnets under rapidly oscillating magnetic fields is studied. • It is shown that this system displays the quenching of tunneling processes. • Our findings provide a control of quantum molecular magnets via terahertz radiation.

  9. Molecular dynamics simulations of biological membranes and membrane proteins using enhanced conformational sampling algorithms.

    Science.gov (United States)

    Mori, Takaharu; Miyashita, Naoyuki; Im, Wonpil; Feig, Michael; Sugita, Yuji

    2016-07-01

    This paper reviews various enhanced conformational sampling methods and explicit/implicit solvent/membrane models, as well as their recent applications to the exploration of the structure and dynamics of membranes and membrane proteins. Molecular dynamics simulations have become an essential tool to investigate biological problems, and their success relies on proper molecular models together with efficient conformational sampling methods. The implicit representation of solvent/membrane environments is reasonable approximation to the explicit all-atom models, considering the balance between computational cost and simulation accuracy. Implicit models can be easily combined with replica-exchange molecular dynamics methods to explore a wider conformational space of a protein. Other molecular models and enhanced conformational sampling methods are also briefly discussed. As application examples, we introduce recent simulation studies of glycophorin A, phospholamban, amyloid precursor protein, and mixed lipid bilayers and discuss the accuracy and efficiency of each simulation model and method. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov. PMID:26766517

  10. The MOLDY short-range molecular dynamics package

    Science.gov (United States)

    Ackland, G. J.; D'Mellow, K.; Daraszewicz, S. L.; Hepburn, D. J.; Uhrin, M.; Stratford, K.

    2011-12-01

    measuring thermodynamic properities, diffusion, radiation damage, fracture, twinning deformation, nucleation and growth of phase transitions, sputtering etc. In the vast majority of materials, the interactions are non-pairwise, and the code must be able to deal with many-body forces. Solution method: Molecular dynamics involves integrating Newton's equations of motion. MOLDY uses verlet (for good energy conservation) or predictor-corrector (for accurate trajectories) algorithms. It is parallelised using open MP. It also includes a static minimisation routine to find the lowest energy structure. Boundary conditions for surfaces, clusters, grain boundaries, thermostat (Nose), barostat (Parrinello-Rahman), and externally applied strain are provided. The initial configuration can be either a repeated unit cell or have all atoms given explictly. Initial velocities are generated internally, but it is also possible to specify the velocity of a particular atom. A wide range of interatomic force models are implemented, including embedded atom, Morse or Lennard-Jones. Thus the program is especially well suited to calculations of metals. Restrictions: The code is designed for short-ranged potentials, and there is no Ewald sum. Thus for long range interactions where all particles interact with all others, the order- N scaling will fail. Different interatomic potential forms require recompilation of the code. Additional comments: There is a set of associated open-source analysis software for postprocessing and visualisation. This includes local crystal structure recognition and identification of topological defects. Running time: A set of test modules for running time are provided. The code scales as order N. The parallelisation shows near-linear scaling with number of processors in a shared memory environment. A typical run of a few tens of nanometers for a few nanoseconds will run on a timescale of days on a multiprocessor desktop.

  11. Exciton dynamics in perturbed vibronic molecular aggregates.

    Science.gov (United States)

    Brüning, C; Wehner, J; Hausner, J; Wenzel, M; Engel, V

    2016-07-01

    A site specific perturbation of a photo-excited molecular aggregate can lead to a localization of excitonic energy. We investigate this localization dynamics for laser-prepared excited states. Changing the parameters of the electric field significantly influences the exciton localization which offers the possibility for a selective control of this process. This is demonstrated for aggregates possessing a single vibrational degree of freedom per monomer unit. It is shown that the effects identified for the molecular dimer can be generalized to larger aggregates with a high density of vibronic states. PMID:26798840

  12. Convergence of Molecular Dynamics Simulation of Protein Native States: Feasibility vs Self-Consistency Dilemma.

    Science.gov (United States)

    Sawle, Lucas; Ghosh, Kingshuk

    2016-02-01

    All-atom molecular dynamics simulations need convergence tests to evaluate the quality of data. The notion of "true" convergence is elusive, and one can only hope to satisfy self-consistency checks (SCC). There are multiple SCC criteria, and their assessment of all-atom simulations of the native state for real globular proteins is sparse. Here, we present a systematic study of different SCC algorithms, both in terms of their ability to detect the lack of self-consistency and their computational demand, for the all-atom native state simulations of four globular proteins (CSP, CheA, CheW, and BPTI). Somewhat surprisingly, we notice some of the most stringent SCC criteria, e.g., the criteria demanding similarity of the cluster probability distribution between the first and the second halves of the trajectory or the comparison of fluctuations between different blocks using covariance overlap measure, can require tens of microseconds of simulation even for proteins with less than 100 amino acids. We notice such long simulation times can sometimes be associated with traps, but these traps cannot be detected by some of the common SCC methods. We suggest an additional, and simple, SCC algorithm to quickly detect such traps by monitoring the constancy of the cluster entropy (CCE). CCE is a necessary but not sufficient criteria, and additional SCC algorithms must be combined with it. Furthermore, as seen in the explicit solvent simulation of 1 ms long trajectory of BPTI,1 passing self-consistency checks at an earlier stage may be misleading due to conformational changes taking place later in the simulation, resulting in different, but segregated regions of SCC. Although there is a hierarchy of complex SCC algorithms, caution must be exercised in their application with the knowledge of their limitations and computational expense. PMID:26765584

  13. Open quantum system parameters from molecular dynamics

    CERN Document Server

    Wang, Xiaoqing; Wüster, Sebastian; Eisfeld, Alexander

    2015-01-01

    We extract the site energies and spectral densities of the Fenna-Matthews-Olson (FMO) pigment protein complex of green sulphur bacteria from simulations of molecular dynamics combined with energy gap calculations. Comparing four different combinations of methods, we investigate the origin of quantitative differences regarding site energies and spectral densities obtained previously in the literature. We find that different forcefields for molecular dynamics and varying local energy minima found by the structure relaxation yield significantly different results. Nevertheless, a picture averaged over these variations is in good agreement with experiments and some other theory results. Throughout, we discuss how vibrations external- or internal to the pigment molecules enter the extracted quantities differently and can be distinguished. Our results offer some guidance to set up more computationally intensive calculations for a precise determination of spectral densities in the future. These are required to determ...

  14. Towards the molecular bases of polymerase dynamics

    International Nuclear Information System (INIS)

    One aspect of the strong relationship that is known to exist between the processes of DNA replication and transcription is manifest in the coupling of the rates of movement of the replication fork (rf) and RNA polymerase (rt). We address two issues concerning the largely unexplored area of polymerase dynamics: (i) The validity of an approximate kinematic formula linking rf and rt suggested by experiments in which transcription is initiated in some prokaryotes with the antibiotic streptolydigin, and (ii) What are the molecular bases of the kinematic formula? An analysis of the available data suggests possible molecular bases for polymerase dynamics. In particular, we are led to a hypothesis: In active chromatin rt may depend on the length (λt) of the transcript of the primary messenger RNA (pre-mRNA). This new effect is subject to experimental verification. We discuss possible experiments that may be performed in order to test this prediction. (author). Refs, 6 tabs

  15. Nonadiabatic Molecular Dynamics Based on Trajectories

    Directory of Open Access Journals (Sweden)

    Felipe Franco de Carvalho

    2013-12-01

    Full Text Available Performing molecular dynamics in electronically excited states requires the inclusion of nonadiabatic effects to properly describe phenomena beyond the Born-Oppenheimer approximation. This article provides a survey of selected nonadiabatic methods based on quantum or classical trajectories. Among these techniques, trajectory surface hopping constitutes an interesting compromise between accuracy and efficiency for the simulation of medium- to large-scale molecular systems. This approach is, however, based on non-rigorous approximations that could compromise, in some cases, the correct description of the nonadiabatic effects under consideration and hamper a systematic improvement of the theory. With the help of an in principle exact description of nonadiabatic dynamics based on Bohmian quantum trajectories, we will investigate the origin of the main approximations in trajectory surface hopping and illustrate some of the limits of this approach by means of a few simple examples.

  16. Molecular dynamics study of cyclohexane interconversion

    Science.gov (United States)

    Wilson, Michael A.; Chandler, David

    1990-12-01

    Classical molecular dynamics calculations are reported for one C 6H 12 molecule in a bath of 250 CS 2 molecules at roomtemperature and liquid densities of 1.0, 1.3, 1.4 and 1.5 g/cm 3. The solvent contribution to the free energy of activation for the chair-boat isomerization has been determined to high accuracy. The transmission coefficient and reactive flux correlation functions have also been computed. The results obtained agree with earlier conclusions drawn from RISM integral equation calculations and stochastic molecular dynamics calculations. Namely, the solvent effect on the rate manifests a qualitative breakdown of transition state theory and the RRKM picture of unimolecular kinetics. Analysis of the activated trajectories indicate a significant degree of quasiperiodicity.

  17. Molecular dynamics at constant Cauchy stress

    Science.gov (United States)

    Miller, Ronald E.; Tadmor, Ellad B.; Gibson, Joshua S.; Bernstein, Noam; Pavia, Fabio

    2016-05-01

    The Parrinello-Rahman algorithm for imposing a general state of stress in periodic molecular dynamics simulations is widely used in the literature and has been implemented in many readily available molecular dynamics codes. However, what is often overlooked is that this algorithm controls the second Piola-Kirchhoff stress as opposed to the true (Cauchy) stress. This can lead to misinterpretation of simulation results because (1) the true stress that is imposed during the simulation depends on the deformation of the periodic cell, (2) the true stress is potentially very different from the imposed second Piola-Kirchhoff stress, and (3) the true stress can vary significantly during the simulation even if the imposed second Piola-Kirchhoff is constant. We propose a simple modification to the algorithm that allows the true Cauchy stress to be controlled directly. We then demonstrate the efficacy of the new algorithm with the example of martensitic phase transformations under applied stress.

  18. Molecular dynamics simulation for modelling plasma spectroscopy

    CERN Document Server

    Talin, B; Calisti, A; Gigosos, M A; González, M A; Gaztelurrutia, T R; Dufty, J W

    2003-01-01

    The ion-electron coupling properties for an ion impurity in an electron gas and for a two-component plasma are carried out on the basis of a regularized electron-ion potential removing the short-range Coulomb divergence. This work is largely motivated by the study of radiator dipole relaxation in plasmas which makes a real link between models and experiments. Current radiative property models for plasmas include single electron collisions neglecting charge-charge correlations within the classical quasi-particle approach commonly used in this field. The dipole relaxation simulation based on electron-ion molecular dynamics proposed here will provide a means to benchmark and improve model developments. Benefiting from a detailed study of a single ion embedded in an electron plasma, the challenging two-component ion-electron molecular dynamics simulations are proved accurate. They open new possibilities of obtaining reference lineshape data.

  19. New ways to boost molecular dynamics simulations

    NARCIS (Netherlands)

    Krieger, E.; Vriend, G.

    2015-01-01

    We describe a set of algorithms that allow to simulate dihydrofolate reductase (DHFR, a common benchmark) with the AMBER all-atom force field at 160 nanoseconds/day on a single Intel Core i7 5960X CPU (no graphics processing unit (GPU), 23,786 atoms, particle mesh Ewald (PME), 8.0 A cutoff, correct

  20. Molecular quantum dynamics. From theory to applications

    International Nuclear Information System (INIS)

    An educational and accessible introduction to the field of molecular quantum dynamics. Illustrates the importance of the topic for broad areas of science: from astrophysics and the physics of the atmosphere, over elementary processes in chemistry, to biological processes. Presents chosen examples of striking applications, highlighting success stories, summarized by the internationally renowned experts. Including a foreword by Lorenz Cederbaum (University Heidelberg, Germany). This book focuses on current applications of molecular quantum dynamics. Examples from all main subjects in the field, presented by the internationally renowned experts, illustrate the importance of the domain. Recent success in helping to understand experimental observations in fields like heterogeneous catalysis, photochemistry, reactive scattering, optical spectroscopy, or femto- and attosecond chemistry and spectroscopy underline that nuclear quantum mechanical effects affect many areas of chemical and physical research. In contrast to standard quantum chemistry calculations, where the nuclei are treated classically, molecular quantum dynamics can cover quantum mechanical effects in their motion. Many examples, ranging from fundamental to applied problems, are known today that are impacted by nuclear quantum mechanical effects, including phenomena like tunneling, zero point energy effects, or non-adiabatic transitions. Being important to correctly understand many observations in chemical, organic and biological systems, or for the understanding of molecular spectroscopy, the range of applications covered in this book comprises broad areas of science: from astrophysics and the physics and chemistry of the atmosphere, over elementary processes in chemistry, to biological processes (such as the first steps of photosynthesis or vision). Nevertheless, many researchers refrain from entering this domain. The book ''Molecular Quantum Dynamics'' offers them an accessible introduction. Although the

  1. Simulation of Abrasive Machining Using Molecular Dynamics

    OpenAIRE

    Oluwajobi, Akinjide O.; Chen, Xun

    2009-01-01

    The development of ultra–precision processes which can achieve excellent surface finish and tolerance at nanometre level is now a critical requirement for many applications in medical, electronics and energy industry. Presently, it is very difficult to observe the diverse microscopic physical phenomena occurring in nanometric machining through experiments. The use of Molecular Dynamics (MD) simulation has proved to be an effective tool for the prediction and the analysis ...

  2. Modelling abrasive machining techniques using molecular dynamics

    OpenAIRE

    Oluwajobi, Akinjide O.; Chen, Xun

    2008-01-01

    The development of ultra–precision processes which can achieve nanometre surface finishes and tolerances is now a critical requirement for many applications in medical, electronics and energy industry. Presently, it is very difficult to observe the diverse microscopic physical phenomena occurring in nanometric machining through experiments. The use Molecular Dynamics (MD) simulation has proved to be an effective tool for the prediction and the analysis of these processes at the nanometre scal...

  3. Molecular dynamics simulation of a chemical reaction

    International Nuclear Information System (INIS)

    Molecular dynamics is used to study the chemical reaction A+A→B+B. It is shown that the reaction rate constant follows the Arrhenius law both for Lennard-Jones and hard sphere interaction potentials between substrate particles. A. For the denser systems the reaction rate is proportional to the value of the radial distribution function at the contact point of two hard spheres. 10 refs, 4 figs

  4. Molecular dynamics modelling of solidification in metals

    Energy Technology Data Exchange (ETDEWEB)

    Boercker, D.B.; Belak, J.; Glosli, J. [Lawrence Livermore National Lab., CA (United States)

    1997-12-31

    Molecular dynamics modeling is used to study the solidification of metals at high pressure and temperature. Constant pressure MD is applied to a simulation cell initially filled with both solid and molten metal. The solid/liquid interface is tracked as a function of time, and the data are used to estimate growth rates of crystallites at high pressure and temperature in Ta and Mg.

  5. Molecular dynamics simulation of expanding infinite matter

    International Nuclear Information System (INIS)

    Multi-fragmentation occurred in an expanding infinite system is studied by using molecular dynamics simulation. To evaluate the secondary decay effect, the time evolution of expanding system is proceeded till all fragments are stabilized completely. The fragment mass distribution from the expansion is compared with a percolation model and the cause of the exponential shape is clarified. The cause of small critical temperature is also discussed. (author)

  6. Molecular Dynamics with Helical Periodic Boundary Conditions

    Czech Academy of Sciences Publication Activity Database

    Kessler, Jiří; Bouř, Petr

    2014-01-01

    Roč. 35, č. 21 (2014), s. 1552-1559. ISSN 0192-8651 R&D Projects: GA ČR GAP208/11/0105; GA MŠk(CZ) LH11033 Grant ostatní: GA AV ČR(CZ) M200551205; GA MŠk(CZ) LM2010005 Institutional support: RVO:61388963 Keywords : periodic boundary conditions * helical symmetry * molecular dynamics * protein structure * amyloid fibrils Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.589, year: 2014

  7. Implementation of Accelerated Molecular Dynamics in NAMD

    OpenAIRE

    Wang, Yi; Harrison, Christopher B.; Schulten, Klaus; McCammon, J. Andrew

    2011-01-01

    Accelerated molecular dynamics (aMD) is an enhanced-sampling method that improves the conformational space sampling by reducing energy barriers separating different states of a system. Here we present the implementation of aMD in the parallel simulation program NAMD. We show that aMD simulations performed with NAMD have only a small overhead compared with classical MD simulations. Through example applications to the alanine dipeptide, we discuss the choice of acceleration parameters, the inte...

  8. Temperature Dependent Molecular Dynamic Simulation of Friction

    CERN Document Server

    Dias, R A; Coura, P Z; Costa, B V

    2006-01-01

    In this work we present a molecular dynamics simulation of a FFM experiment. The tip-sample interaction is studied by varying the normal force in the tip and the temperature of the surface. The friction force, cA, at zero load and the friction coefficient, $\\mu$, were obtained. Our results strongly support the idea that the effective contact area, A, decreases with increasing temperature and the friction coefficient presents a clear signature of the premelting process of the surface.

  9. Simulating granular flow with molecular dynamics

    OpenAIRE

    Ristow, Gerald

    1992-01-01

    We investigate by means of Molecular Dynamics simulations an assembly of spheres to model a granular medium flowing from an upper rectangular chamber through a hole into a lower chamber. Two different two dimensional models are discussed one of them including rotations of the individual spheres. The outflow properties are investigated and compared to experimental data. The qualitative agreement suggests that our models contain the necessary ingredients to describe the outflow properties of gr...

  10. Molecular dynamics simulations using graphics processing units

    OpenAIRE

    Baker, J.A.; Hirst, J.D.

    2011-01-01

    It is increasingly easy to develop software that exploits Graphics Processing Units (GPUs). The molecular dynamics simulation community has embraced this recent opportunity. Herein, we outline the current approaches that exploit this technology. In the context of biomolecular simulations, we discuss some of the algorithms that have been implemented and some of the aspects that distinguish the GPU from previous parallel environments. The ubiquity of GPUs and the ingenuity of the simulation com...

  11. Molecular Dynamics Studies of Nanofluidic Devices

    DEFF Research Database (Denmark)

    Zambrano Rodriguez, Harvey Alexander

    of transport mechanism to drive fluids and solids at the nanoscale. Specifically, we present the results of three different research projects. Throughout the first part of this thesis, we include a comprenhensive introduction to computational nanofluidics and to molecular simulations, and describe...... the molecular dynamics methodology. In the second part of this thesis, we present the results of three different research projects. Fristly, we present a computational study of thermophoresis as a suitable mechanism to drive water droplets confined in different types of carbon nanotubes. We observe a...... motion of the water droplet in opposite direction to the imposed thermal gradient also we measure higher velocities as higher thermal gradients are imposed. Secondly, we present an atomistic analysis of a molecular linear motor fabricated of coaxial carbon nanotubes and powered by thermal gradients. The...

  12. Optimally designed fields for controlling molecular dynamics

    Science.gov (United States)

    Rabitz, Herschel

    1991-10-01

    This research concerns the development of molecular control theory techniques for designing optical fields capable of manipulating molecular dynamic phenomena. Although is has been long recognized that lasers should be capable of manipulating dynamic events, many frustrating years of intuitively driven laboratory studies only serve to illustrate the point that the task is complex and defies intuition. The principal new component in the present research is the recognition that this problem falls into the category of control theory and its inherent complexities require the use of modern control theory tools largely developed in the engineering disciplines. Thus, the research has initiated a transfer of the control theory concepts to the molecular scale. Although much contained effort will be needed to fully develop these concepts, the research in this grant set forth the basic components of the theory and carried out illustrative studies involving the design of optical fields capable of controlling rotational, vibrational and electronic degrees of freedom. Optimal control within the quantum mechanical molecular realm represents a frontier area with many possible ultimate applications. At this stage, the theoretical tools need to be joined with merging laboratory optical pulse shaping capabilities to illustrate the power of the concepts.

  13. Control Volume Representation of Molecular Dynamics

    CERN Document Server

    Smith, E R; Dini, D; Zaki, T A

    2012-01-01

    A Molecular Dynamics (MD) parallel to the Control Volume (CV) formulation of fluid mechanics is developed by integrating the formulas of [1] Irving and Kirkwood, J. Chem. Phys. 18, 817 (1950) over a finite cubic volume of molecular dimensions. The Lagrangian molecular system is expressed in terms of an Eulerian CV, which yields an equivalent to Reynolds' Transport Theorem for the discrete system. This approach casts the dynamics of the molecular system into a form that can be readily compared to the continuum equations. The MD equations of motion are reinterpreted in terms of a Lagrangian-to-Control-Volume (LCV) conversion function \\vartheta_{i}, for each molecule i. The LCV function and its spatial derivatives are used to express fluxes and relevant forces across the control surfaces. The relationship between the local pressures computed using the Volume Average (VA, [2] Lutsko, J. Appl. Phys 64, 1152 (1988)) techniques and the Method of Planes (MOP, [3] Todd et al, Phys. Rev. E 52, 1627 (1995)) emerges natu...

  14. Atomic dynamics of alumina melt: A molecular dynamics simulation study

    Directory of Open Access Journals (Sweden)

    S.Jahn

    2008-03-01

    Full Text Available The atomic dynamics of Al2O3 melt are studied by molecular dynamics simulation. The particle interactions are described by an advanced ionic interaction model that includes polarization effects and ionic shape deformations. The model has been shown to reproduce accurately the static structure factors S(Q from neutron and x-ray diffraction and the dynamic structure factor S(Q,ω from inelastic x-ray scattering. Analysis of the partial dynamic structure factors shows inelastic features in the spectra up to momentum transfers, Q, close to the principal peaks of partial static structure factors. The broadening of the Brillouin line widths is discussed in terms of a frequency dependent viscosity η(ω.

  15. A Concurrent Multiscale Micromorphic Molecular Dynamics. Part I. Theoretical Formulation

    CERN Document Server

    Li, Shaofan

    2014-01-01

    Based on a novel concept of multiplicative multiscale decomposition, we have derived a multiscale micromorphic molecular dynamics (MMMD)to extent the (Andersen)-Parrinello-Rahman molecular dynamics to mesoscale and macroscale. The multiscale micromorphic molecular dynamics is a con-current three-scale particle dynamics that couples a fine scale molecular dynamics, a mesoscale particle dynamics of micromorphic medium, and a coarse scale nonlocal particle dynamics of nonlinear continuum. By choosing proper statistical closure conditions, we have shown that the original Andersen-Parrinello-Rahman molecular dynamics can be rigorously formulated and justified from first principle, and it is a special case of the proposed multiscale micromorphic molecular dynamics. The discovered mutiscale structure and the corresponding multiscale dynamics reveal a seamless transition channel from atomistic scale to continuum scale and the intrinsic coupling relation among them, and it can be used to solve finite size nanoscale sc...

  16. Molecular Dynamics Studies of Initiation in Energetic Materials

    OpenAIRE

    Haskins, P.

    1995-01-01

    In this paper an overview of Molecular Dynamics simulations of chemically reacting systems is described. In particular, molecular dynamics simulations of shock initiation in a model energetic material are reported. The use of Molecular Dynamics to model thermal initiation and determine reactions rates in energetic materials is also discussed. Finally, the future potential of MD techniques for energetic materials applications is considered.

  17. Dynamical structure of fluid mercury: Molecular-dynamics simulations

    OpenAIRE

    Hoshino, Kozo; Tanaka, Shunichiro; Shimojo, Fuyuki

    2007-01-01

    We have carried out molecular-dynamics simulations for nonmetallic fluid mercury in liquid and vapor phases using a Lennard-Jones type effective potential and shown that the structure factors S(Q) and the dynamic structure factors S(Q, omega) of nonmetallic fluid mercury obtained by our MD simulations are in good agreement with recent X-ray diffraction and inelastic X-ray scattering experiments. We conclude from these results that, though the fluid mercury which shows a metal-nonmetal transit...

  18. Application of optimal prediction to molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Barber IV, John Letherman

    2004-12-01

    Optimal prediction is a general system reduction technique for large sets of differential equations. In this method, which was devised by Chorin, Hald, Kast, Kupferman, and Levy, a projection operator formalism is used to construct a smaller system of equations governing the dynamics of a subset of the original degrees of freedom. This reduced system consists of an effective Hamiltonian dynamics, augmented by an integral memory term and a random noise term. Molecular dynamics is a method for simulating large systems of interacting fluid particles. In this thesis, I construct a formalism for applying optimal prediction to molecular dynamics, producing reduced systems from which the properties of the original system can be recovered. These reduced systems require significantly less computational time than the original system. I initially consider first-order optimal prediction, in which the memory and noise terms are neglected. I construct a pair approximation to the renormalized potential, and ignore three-particle and higher interactions. This produces a reduced system that correctly reproduces static properties of the original system, such as energy and pressure, at low-to-moderate densities. However, it fails to capture dynamical quantities, such as autocorrelation functions. I next derive a short-memory approximation, in which the memory term is represented as a linear frictional force with configuration-dependent coefficients. This allows the use of a Fokker-Planck equation to show that, in this regime, the noise is {delta}-correlated in time. This linear friction model reproduces not only the static properties of the original system, but also the autocorrelation functions of dynamical variables.

  19. Molecular dynamics simulations of the helical antimicrobial peptide ovispirin-1 in a zwitterionic dodecylphosphocholine micelle

    DEFF Research Database (Denmark)

    Khandelia, Himanshu; Kaznessis, Yiannis N

    2005-01-01

    We have carried out a 40-ns all-atom molecular dynamics simulation of the helical antimicrobial peptide ovispirin-1 (OVIS) in a zwitterionic diphosphocholine (DPC) micelle. The DPC micelle serves as an economical and effective model for a cellular membrane owing to the presence of a choline....... The final conformation, orientation, and the structure of OVIS are in excellent agreement with the experimentally observed properties of the peptide in the presence of lipid bilayers composed of 75% zwitterionic lipids. The amphipathic peptide binds to the micelle with its hydrophobic face buried in...... the micellar core and the polar side chains protruding into the aqueous phase. There is overwhelming evidence that points to the significant and indispensable participation of hydrophobic residues in binding to the zwitterionic interface. The simulation starts with a conformation that is unbiased...

  20. Coarse Grained Molecular Dynamics Simulations of Transmembrane Protein-Lipid Systems

    Directory of Open Access Journals (Sweden)

    Peter Spijker

    2010-06-01

    Full Text Available Many biological cellular processes occur at the micro- or millisecond time scale. With traditional all-atom molecular modeling techniques it is difficult to investigate the dynamics of long time scales or large systems, such as protein aggregation or activation. Coarse graining (CG can be used to reduce the number of degrees of freedom in such a system, and reduce the computational complexity. In this paper the first version of a coarse grained model for transmembrane proteins is presented. This model differs from other coarse grained protein models due to the introduction of a novel angle potential as well as a hydrogen bonding potential. These new potentials are used to stabilize the backbone. The model has been validated by investigating the adaptation of the hydrophobic mismatch induced by the insertion of WALP-peptides into a lipid membrane, showing that the first step in the adaptation is an increase in the membrane thickness, followed by a tilting of the peptide.

  1. Nano-tribology through molecular dynamics simulations

    Institute of Scientific and Technical Information of China (English)

    WANG; Hui(

    2001-01-01

    [1]Burkert, U., Allinger, N. L., Molecular Mechanics, York: Maple Press Company, 1982.[2]Daw, M. S. , Baskes, M. I., Embedded-atom method: derivation and application to impurities, surface and other defects in metals, Phys. Rev. B, 1984, 29: 6443-6453.[3]Frenke, D., Smit, B., Understanding Molecular Simulation, San Diego: Academic Press, 1996, 60-67, 125-140.[4]Granick, S., Motions and relaxation of confined liquids, Science, 1991, 253: 1374-1379.[5]Koplik, J., Banavar, J., Willemsen, J., Molecular dynamics of Poisewulle flow and moving contact line, Phys. Rev.Lett., 1988, 60: 1282-1285.[6]Hu, Y. Z., Wang, H., Guo, Y. et al., Simulation of lubricant rheology in thin film lubrication, Part I: simulation of Poiseuille flow, Wear, 1996, 196: 243-259.[7]Zou, K., Li, Z. J, Leng, Y. S. et al. , Surface force apparatus and its application in the study of solid contacts, Chinese Science Bulletin, 1999, 44: 268-271.[8]Stevens, M. , Mondello, M., Grest, G. et al. , Comparison of shear flow of hexadecane in a confined geometry and in bulk,J. Chem. Phys., 1997, 106: 7303-7314.[9]Huang, P., Luo, J. B., Wen, S. Z., Theoretical study on the lubrication failure for tthe lubricants with a limiting shear stress, Tribology International, 1999, 32: 421-426.[10]Ryckaert, J. P. , Bellemans. , A molecular dynamics of alkanes, Faraday Soc. , 1978, 66: 95-106.[11]Wang, H. , Hu, Y. Z., A molecular dynamics study on slip phenomenon at solid-liquid interface, in Proceedings of tthe First AICT, Beijing: Tsinghua University Press, 1998, 295-299.[12]Landman, U., Luedtke, W., Burnham, N. et al., Mechanisms and dynamics of adhesion, nanoindentation, and fracture, Science, 1990, 248: 454-461.[13]Leng, Y. S., Hu, Y. Z., Zheng, L. Q., Adhesive contact of flat-ended wedges: theory and computer experiments, Journal of Tribology, 1999, 121: 128-132.

  2. xMDFF: molecular dynamics flexible fitting of low-resolution X-ray structures

    International Nuclear Information System (INIS)

    A new real-space refinement method for low-resolution X-ray crystallography is presented. The method is based on the molecular dynamics flexible fitting protocol targeted at addressing large-scale deformations of the search model to achieve refinement with minimal manual intervention. An explanation of the method is provided, augmented by results from the refinement of both synthetic and experimental low-resolution data, including an independent electrophysiological verification of the xMDFF-refined crystal structure of a voltage-sensor protein. X-ray crystallography remains the most dominant method for solving atomic structures. However, for relatively large systems, the availability of only medium-to-low-resolution diffraction data often limits the determination of all-atom details. A new molecular dynamics flexible fitting (MDFF)-based approach, xMDFF, for determining structures from such low-resolution crystallographic data is reported. xMDFF employs a real-space refinement scheme that flexibly fits atomic models into an iteratively updating electron-density map. It addresses significant large-scale deformations of the initial model to fit the low-resolution density, as tested with synthetic low-resolution maps of d-ribose-binding protein. xMDFF has been successfully applied to re-refine six low-resolution protein structures of varying sizes that had already been submitted to the Protein Data Bank. Finally, via systematic refinement of a series of data from 3.6 to 7 Å resolution, xMDFF refinements together with electrophysiology experiments were used to validate the first all-atom structure of the voltage-sensing protein Ci-VSP

  3. A real-time all-atom structural search engine for proteins.

    Directory of Open Access Journals (Sweden)

    Gabriel Gonzalez

    2014-07-01

    Full Text Available Protein designers use a wide variety of software tools for de novo design, yet their repertoire still lacks a fast and interactive all-atom search engine. To solve this, we have built the Suns program: a real-time, atomic search engine integrated into the PyMOL molecular visualization system. Users build atomic-level structural search queries within PyMOL and receive a stream of search results aligned to their query within a few seconds. This instant feedback cycle enables a new "designability"-inspired approach to protein design where the designer searches for and interactively incorporates native-like fragments from proven protein structures. We demonstrate the use of Suns to interactively build protein motifs, tertiary interactions, and to identify scaffolds compatible with hot-spot residues. The official web site and installer are located at http://www.degradolab.org/suns/ and the source code is hosted at https://github.com/godotgildor/Suns (PyMOL plugin, BSD license, https://github.com/Gabriel439/suns-cmd (command line client, BSD license, and https://github.com/Gabriel439/suns-search (search engine server, GPLv2 license.

  4. Molecular dynamic results on transport properties

    Energy Technology Data Exchange (ETDEWEB)

    Alder, B.J.; Alley, W.E.

    1978-06-01

    Following a broad discussion of generalized hydrodynamics, three examples are given to illustrate how useful this approach is in extending hydrodynamics to nearly the scale of molecular dimensions and the time between collisions, principally by including viscoelastic effects. The three examples concern the behavior of the velocity autocorrelation function, the decay of fluctuations in a resonating system, and the calculation of the dynamic structure factor obtained from neutron scattering. In the latter case the molecular dynamics results are also compared to the predictions of generalized kinetic theory. Finally it is shown how to implement generalized hydrodynamics both on a microscopic and macroscopic level. Hydrodynamics is unable to account for the long time tails in the velocity autocorrelation functions and the divergent Burnett coefficients observed for the Lorentz gas. Instead, the long time behavior of the Burnett coefficient and the distribution of displacements (the self part of the dynamic structure factor) can be accounted for by a random walk with a waiting time distribution which is chosen to give the correct velocity autocorrelation function. This random walk predicts, in agreement with the observations, that this displacement distribution is Gaussian at long times for the Lorentz gas, while for hard disks it has been found not to be so.

  5. Molecular dynamic results on transport properties

    International Nuclear Information System (INIS)

    Following a broad discussion of generalized hydrodynamics, three examples are given to illustrate how useful this approach is in extending hydrodynamics to nearly the scale of molecular dimensions and the time between collisions, principally by including viscoelastic effects. The three examples concern the behavior of the velocity autocorrelation function, the decay of fluctuations in a resonating system, and the calculation of the dynamic structure factor obtained from neutron scattering. In the latter case the molecular dynamics results are also compared to the predictions of generalized kinetic theory. Finally it is shown how to implement generalized hydrodynamics both on a microscopic and macroscopic level. Hydrodynamics is unable to account for the long time tails in the velocity autocorrelation functions and the divergent Burnett coefficients observed for the Lorentz gas. Instead, the long time behavior of the Burnett coefficient and the distribution of displacements (the self part of the dynamic structure factor) can be accounted for by a random walk with a waiting time distribution which is chosen to give the correct velocity autocorrelation function. This random walk predicts, in agreement with the observations, that this displacement distribution is Gaussian at long times for the Lorentz gas, while for hard disks it has been found not to be so

  6. Molecular dynamics studies of aromatic hydrocarbon liquids

    International Nuclear Information System (INIS)

    This project mainly involves a molecular dynamics and Monte Carlo study of the effect of molecular shape on thermophysical properties of bulk fluids with an emphasis on the aromatic hydrocarbon liquids. In this regard we have studied the modeling, simulation methodologies, and predictive and correlating methods for thermodynamic properties of fluids of nonspherical molecules. In connection with modeling we have studied the use of anisotropic site-site potentials, through a modification of the Gay-Berne Gaussian overlap potential, to successfully model the aromatic rings after adding the necessary electrostatic moments. We have also shown these interaction sites should be located at the geometric centers of the chemical groups. In connection with predictive methods, we have shown two perturbation type theories to work well for fluids modeled using one-center anisotropic potentials and the possibility exists for extending these to anisotropic site-site models. In connection with correlation methods, we have studied, through simulations, the effect of molecular shape on the attraction term in the generalized van der Waals equation of state for fluids of nonspherical molecules and proposed a possible form which is to be studied further. We have successfully studied the vector and parallel processing aspects of molecular simulations for fluids of nonspherical molecules

  7. Molecular dynamics simulations and 2D NOESY spectrum study on the different behaviors of glutathione disulfide in different solutions

    International Nuclear Information System (INIS)

    Highlights: ► Different behaviors of GSSG are observed in aqueous and DMSO solutions. ► The interesting phenomena have been proved by the MD simulations and 2D NMR experiment. ► The NOESY spectroscopy show good agreement with the MD simulations. - Abstract: All-atom molecular dynamics simulations and 2D nuclear Overhauser effect spectroscopy (NOESY) were used to study the interactions and conformations of glutathione disulfide (GSSG) in aqueous and DMSO solutions. GSSG showed variations in conformation in the two solutions, shifting between extended and folded states. Showing preference for extension in aqueous solution and folding for a long time in DMSO are observed by the simulations. The interesting phenomena have been proved by the 2D NMR experiment. The NMR experimental results show agreement with the molecular dynamics simulations.

  8. Continuous Finite Element Methods of Molecular Dynamics Simulations

    OpenAIRE

    Qiong Tang; Luohua Liu; Yujun Zheng

    2015-01-01

    Molecular dynamics simulations are necessary to perform very long integration times. In this paper, we discuss continuous finite element methods for molecular dynamics simulation problems. Our numerical results about AB diatomic molecular system and A2B triatomic molecules show that linear finite element and quadratic finite element methods can better preserve the motion characteristics of molecular dynamics, that is, properties of energy conservation and long-term stability. So finite elemen...

  9. Parallelization of quantum molecular dynamics simulation code

    International Nuclear Information System (INIS)

    A quantum molecular dynamics simulation code has been developed for the analysis of the thermalization of photon energies in the molecule or materials in Kansai Research Establishment. The simulation code is parallelized for both Scalar massively parallel computer (Intel Paragon XP/S75) and Vector parallel computer (Fujitsu VPP300/12). Scalable speed-up has been obtained with a distribution to processor units by division of particle group in both parallel computers. As a result of distribution to processor units not only by particle group but also by the particles calculation that is constructed with fine calculations, highly parallelization performance is achieved in Intel Paragon XP/S75. (author)

  10. Ab Initio Molecular Dynamics: A Virtual Laboratory

    OpenAIRE

    Hobbi Mobarhan, Milad

    2014-01-01

    In this thesis, we perform ab initio molecular dynamics (MD) simulations at the Hartree-Fock level, where the forces are computed on-the-fly using the Born-Oppenheimer approximation. The theory behind the Hartree-Fock method is discussed in detail and an implementation of this method based on Gaussian basis functions is explained. We also demonstrate how to calculate the analytic energy derivatives needed for obtaining the forces acting on the nuclei. Hartree-Fock calculations on the ground s...

  11. Molecular dynamics simulation of ribosome jam

    KAUST Repository

    Matsumoto, Shigenori

    2011-09-01

    We propose a coarse-grained molecular dynamics model of ribosome molecules to study the dependence of translation process on environmental parameters. We found the model exhibits traffic jam property, which is consistent with an ASEP model. We estimated the influence of the temperature and concentration of molecules on the hopping probability used in the ASEP model. Our model can also treat environmental effects on the translation process that cannot be explained by such cellular automaton models. © 2010 Elsevier B.V. All rights reserved.

  12. Electrostatic Energy Calculations for Molecular Dynamics

    CERN Document Server

    Love, M J; Comment, Henri J.F. Jansen; Love, Michael J.

    1995-01-01

    The evaluation of Coulomb forces is a difficult task. The summations that are involved converge only conditionally and care has to be taken in selecting the appropriate procedure to define the limits. The Ewald method is a standard method for obtaining Coulomb forces, but this method is rather slow, since it depends on the square of the number of atoms in a unit cell. In this paper we have adapted the plane-wise summation method for the evaluation of Coulomb forces. The use of this method allows for larger computational cells in molecular dynamics calculations.

  13. Molecular beam studies of reaction dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Y.T.

    1987-03-01

    Purpose of this research project is two-fold: (1) to elucidate detailed dynamics of simple elementary reactions which are theoretically important and to unravel the mechanism of complex chemical reactions or photo chemical processes which play an important role in many macroscopic processes and (2) to determine the energetics of polyatomic free radicals using microscopic experimental methods. Most of the information is derived from measurement of the product fragment translational energy and angular distributions using unique molecular beam apparati designed for these purposes.

  14. Molecular dynamics at constant temperature and pressure

    Science.gov (United States)

    Toxvaerd, S.

    1993-01-01

    Algorithms for molecular dynamics (MD) at constant temperature and pressure are investigated. The ability to remain in a regular orbit in an intermittent chaotic regime is used as a criterion for long-time stability. A simple time-centered algorithm (leap frog) is found to be the most stable of the commonly used algorithms in MD. A model of N one-dimensional dimers with a double-well intermolecular potential, for which the distribution functions at constant temperature T and pressure P can be calculated, is used to investigate MD-NPT dynamics. A time-centered NPT algorithm is found to sample correctly and to be very robust with respect to volume scaling.

  15. Fermionic Molecular Dynamics and short range correlations

    CERN Document Server

    Feldmeier, H; Roth, R S; Schnack, J

    1998-01-01

    Fermionic Molecular Dynamics (FMD) models a system of fermions by means of many-body states which are composed of antisymmetrized products of single-particle states. These consist of one or several Gaussians localized in coordinate and momentum space. The parameters specifying them are the dynamical variables of the model. As the repulsive core of the nucleon-nucleon interaction induces short range correlations which cannot be accommodated by a Slater determinant, a novel approach, the unitary correlation operator method (UCOM), is applied. The unitary correlator moves two particles away from each other whenever their relative distance is within the repulsive core. The time-dependent variational principle yields the equations of motion for the variables. Energies of the stationary ground states are calculated and compared to exact many-body results for nuclei up to Ca 48. Time-dependent solutions are shown for collisions between nuclei.

  16. The Dependence of All-Atom Statistical Potentials on Structural Training Database

    OpenAIRE

    Zhang, Chi; Liu, Song; Zhou, Hongyi; Zhou, Yaoqi

    2004-01-01

    An accurate statistical energy function that is suitable for the prediction of protein structures of all classes should be independent of the structural database used for energy extraction. Here, two high-resolution, low-sequence-identity structural databases of 333 α-proteins and 271 β-proteins were built for examining the database dependence of three all-atom statistical energy functions. They are RAPDF (residue-specific all-atom conditional probability discriminatory function), atomic KBP ...

  17. Protein simulations combining an all-atom force field with a Go term

    International Nuclear Information System (INIS)

    Using a variant of parallel tempering, we study the changes in sampling within a simulation, when the all-atom model is coupled to a Go-like potential. We find that the native structure is not the lowest-energy configuration in the all-atom force field. Adding a Go term deforms the energy landscape in such a way that the native configuration becomes the global minimum but does not lead to faster thermalization

  18. GOAP: A Generalized Orientation-Dependent, All-Atom Statistical Potential for Protein Structure Prediction

    OpenAIRE

    Zhou, Hongyi; Skolnick, Jeffrey

    2011-01-01

    An accurate scoring function is a key component for successful protein structure prediction. To address this important unsolved problem, we develop a generalized orientation and distance-dependent all-atom statistical potential. The new statistical potential, generalized orientation-dependent all-atom potential (GOAP), depends on the relative orientation of the planes associated with each heavy atom in interacting pairs. GOAP is a generalization of previous orientation-dependent potentials th...

  19. Dynamic Shear Modulus of Polymers from Molecular Dynamics Simulations

    Science.gov (United States)

    Byutner, Oleksiy; Smith, Grant

    2001-03-01

    In this work we describe the methodology for using equilibrium molecular dynamics simulations (MD) simulations to obtain the viscoelastic properties of polymers in the glassy regime. Specifically we show how the time dependent shear stress modulus and frequency dependent complex shear modulus in the high-frequency regime can be determined from the off-diagonal terms of the stress-tensor autocorrelation function obtained from MD trajectories using the Green-Kubo method and appropriate Fourier transforms. In order to test the methodology we have performed MD simulations of a low-molecular-weight polybutadiene system using quantum chemistry based potential functions. Values of the glassy modulus and the maximum loss frequency were found to be in good agreement with experimental data for polybutadiene at 298 K.

  20. Multiple branched adaptive steered molecular dynamics

    Science.gov (United States)

    Ozer, Gungor; Keyes, Thomas; Quirk, Stephen; Hernandez, Rigoberto

    2014-08-01

    Steered molecular dynamics, SMD, [S. Park and K. Schulten, J. Chem. Phys. 120, 5946 (2004)] combined with Jarzynski's equality has been used widely in generating free energy profiles for various biological problems, e.g., protein folding and ligand binding. However, the calculated averages are generally dominated by "rare events" from the ensemble of nonequilibrium trajectories. The recently proposed adaptive steered molecular dynamics, ASMD, introduced a new idea for selecting important events and eliminating the non-contributing trajectories, thus decreasing the overall computation needed. ASMD was shown to reduce the number of trajectories needed by a factor of 10 in a benchmarking study of decaalanine stretching. Here we propose a novel, highly efficient "multiple branching" (MB) version, MB-ASMD, which obtains a more complete enhanced sampling of the important trajectories, while still eliminating non-contributing segments. Compared to selecting a single configuration in ASMD, MB-ASMD offers to select multiple configurations at each segment along the reaction coordinate based on the distribution of work trajectories. We show that MB-ASMD has all benefits of ASMD such as faster convergence of the PMF even when pulling 1000 times faster than the reversible limit while greatly reducing the probability of getting trapped in a non-significant path. We also analyze the hydrogen bond breaking within the decaalanine peptide as we force the helix into a random coil and confirm ASMD results with less noise in the numerical averages.

  1. Dynamics of Ag clusters on complex surfaces: Molecular dynamics simulations

    Science.gov (United States)

    Alkis, S.; Krause, J. L.; Fry, J. N.; Cheng, H.-P.

    2009-03-01

    We study the diffusion of silver nanoparticles on self-assembled monolayers (SAMs). Silver clusters Agn of sizes n=55 , 147, and 1289 were evolved in contact with an alkanethiol (12 carbon, dodecanethiol) SAM deposited on a gold (111) surface. Analysis based on classical molecular dynamics simulations reveals that these systems exhibit a rich variety of behaviors, from superdiffusive for the lightest cluster to pinned for the heaviest, evolution self-similar in lengths and times for the lightest cluster but with characteristic time scales and directional anisotropies emerging for the heavier clusters.

  2. Molecular Dynamics Simulations of Janus Particle Dynamics in Uniform Flow

    CERN Document Server

    Archereau, Aurelien Y M; Willmott, Geoff R

    2016-01-01

    We use molecular dynamics simulations to study the dynamics of Janus particles, micro- or nanoparticles which are not spherically symmetric, in the uniform flow of a simple liquid. In particular we consider spheres with an asymmetry in the solid-liquid interaction over their surfaces and calculate the forces and torques experienced by the particles as a function of their orientation with respect to the flow. We also examine particles that are deformed slightly from a spherical shape. We compare the simulation results to the predictions of a previously introduced theoretical approach, which computes the forces and torques on particles with variable slip lengths or aspherical deformations that are much smaller than the particle radius. We find that there is good agreement between the forces and torques computed from our simulations and the theoretical predictions, when the slip condition is applied to the first layer of liquid molecules adjacent to the surface.

  3. Parametrizing linear generalized Langevin dynamics from explicit molecular dynamics simulations

    CERN Document Server

    Gottwald, Fabian; Ivanov, Sergei D; Kühn, Oliver

    2015-01-01

    Fundamental understanding of complex dynamics in many-particle systems on the atomistic level is of utmost importance. Often the systems of interest are of macroscopic size but can be partitioned into few important degrees of freedom which are treated most accurately and others which constitute a thermal bath. Particular attention in this respect attracts the linear generalized Langevin equation (GLE), which can be rigorously derived by means of a linear projection (LP) technique. Within this framework a complicated interaction with the bath can be reduced to a single memory kernel. This memory kernel in turn is parametrized for a particular system studied, usually by means of time-domain methods based on explicit molecular dynamics data. Here we discuss that this task is most naturally achieved in frequency domain and develop a Fourier-based parametrization method that outperforms its time-domain analogues. Very surprisingly, the widely used rigid bond method turns out to be inappropriate in general. Importa...

  4. The 2011 Dynamics of Molecular Collisions Conference

    Energy Technology Data Exchange (ETDEWEB)

    Nesbitt, David J. [JILA, NIST

    2011-07-11

    The Dynamics of Molecular Collisions Conference focuses on all aspects of molecular collisions--experimental & theoretical studies of elastic, inelastic, & reactive encounters involving atoms, molecules, ions, clusters, & surfaces--as well as half collisions--photodissociation, photo-induced reaction, & photodesorption. The scientific program for the meeting in 2011 included exciting advances in both the core & multidisciplinary forefronts of the study of molecular collision processes. Following the format of the 2009 meeting, we also invited sessions in special topics that involve interfacial dynamics, novel emerging spectroscopies, chemical dynamics in atmospheric, combustion & interstellar environments, as well as a session devoted to theoretical & experimental advances in ultracold molecular samples. Researchers working inside & outside the traditional core topics of the meeting are encouraged to join the conference. We invite contributions of work that seeks understanding of how inter & intra-molecular forces determine the dynamics of the phenomena under study. In addition to invited oral sessions & contributed poster sessions, the scientific program included a formal session consisting of five contributed talks selected from the submitted poster abstracts. The DMC has distinguished itself by having the Herschbach Medal Symposium as part of the meeting format. This tradition of the Herschbach Medal was first started in the 2007 meeting chaired by David Chandler, based on a generous donation of funds & artwork design by Professor Dudley Herschbach himself. There are two such awards made, one for experimental & one for theoretical contributions to the field of Molecular Collision Dynamics, broadly defined. The symposium is always held on the last night of the meeting & has the awardees are asked to deliver an invited lecture on their work. The 2011 Herschbach Medal was dedicated to the contributions of two long standing leaders in Chemical Physics, Professor

  5. Evaluation of reduced point charge models of proteins through Molecular Dynamics simulations: application to the Vps27 UIM-1-Ubiquitin complex.

    Science.gov (United States)

    Leherte, Laurence; Vercauteren, Daniel P

    2014-02-01

    Reduced point charge models of amino acids are designed, (i) from local extrema positions in charge density distribution functions built from the Poisson equation applied to smoothed molecular electrostatic potential (MEP) functions, and (ii) from local maxima positions in promolecular electron density distribution functions. Corresponding charge values are fitted versus all-atom Amber99 MEPs. To easily generate reduced point charge models for protein structures, libraries of amino acid templates are built. The program GROMACS is used to generate stable Molecular Dynamics trajectories of an Ubiquitin-ligand complex (PDB: 1Q0W), under various implementation schemes, solvation, and temperature conditions. Point charges that are not located on atoms are considered as virtual sites with a nul mass and radius. The results illustrate how the intra- and inter-molecular H-bond interactions are affected by the degree of reduction of the point charge models and give directions for their implementation; a special attention to the atoms selected to locate the virtual sites and to the Coulomb-14 interactions is needed. Results obtained at various temperatures suggest that the use of reduced point charge models allows to probe local potential hyper-surface minima that are similar to the all-atom ones, but are characterized by lower energy barriers. It enables to generate various conformations of the protein complex more rapidly than the all-atom point charge representation. PMID:24316938

  6. A scheme to combine molecular dynamics and dislocation dynamics

    International Nuclear Information System (INIS)

    Many engineering challenges occur on multiple interacting length scales, e.g. during fracture atoms separate on the atomic scale while plasticity develops on the micrometer scale. To investigate the details of these events, a concurrent multiscale model is required which studies the problem at appropriate length- and time-scales: the atomistic scale and the dislocation dynamics scale. The AtoDis multiscale model is introduced, which combines atomistics and dislocation dynamicsinto a fully dynamic model that is able to simulate deformation mechanisms at finite temperature. The model uses point forces to ensure mechanical equilibrium and kinematic continuity at the interface. By resolving each interface atom analytically, and not numerically, the framework uses a coarse FEM mesh and intrinsically filters out atomistic vibrations. This multiscale model allows bi-directional dislocation transition at the interface of both models with no remnant atomic disorder. Thereby, the model is able to simulate a larger plastic zone than conventional molecular dynamics while reducing the need for constitutive dislocation dynamics equations. This contribution studies dislocation nucleation at finite temperature and investigates the absorption of dislocations into the crack wake. (paper)

  7. Color Molecular-Dynamics for High Density Matter

    OpenAIRE

    Maruyama, Toshiki; Hatsuda, Tetsuo

    1999-01-01

    We propose a microscopic simulation for quark many-body system based on molecular dynamics. Using color confinement and one-gluon exchange potentials together with the meson exchange potentials between quarks, we construct nucleons and nuclear/quark matter. Statistical feature and the dynamical change between confinement and deconfinement phases are studied with this molecular dynamics simulation.

  8. Preformed template fluctuations promote fibril formation: Insights from lattice and all-atom models

    Energy Technology Data Exchange (ETDEWEB)

    Kouza, Maksim, E-mail: mkouza@chem.uw.edu.pl; Kolinski, Andrzej [Faculty of Chemistry, University of Warsaw, ul. Pasteura 1, 02-093 Warszaw (Poland); Co, Nguyen Truong [Department of Physics, Institute of Technology, National University of HCM City, 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City (Viet Nam); Institute for Computational Science and Technology, Quang Trung Software City, Tan Chanh Hiep Ward, District 12, Ho Chi Minh City (Viet Nam); Nguyen, Phuong H. [Laboratoire de Biochimie Theorique, UPR 9080 CNRS, IBPC, Universite Paris 7, 13 rue Pierre et Marie Curie, 75005 Paris (France); Li, Mai Suan, E-mail: masli@ifpan.edu.pl [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland)

    2015-04-14

    Fibril formation resulting from protein misfolding and aggregation is a hallmark of several neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases. Despite the fact that the fibril formation process is very slow and thus poses a significant challenge for theoretical and experimental studies, a number of alternative pictures of molecular mechanisms of amyloid fibril formation have been recently proposed. What seems to be common for the majority of the proposed models is that fibril elongation involves the formation of pre-nucleus seeds prior to the creation of a critical nucleus. Once the size of the pre-nucleus seed reaches the critical nucleus size, its thermal fluctuations are expected to be small and the resulting nucleus provides a template for sequential (one-by-one) accommodation of added monomers. The effect of template fluctuations on fibril formation rates has not been explored either experimentally or theoretically so far. In this paper, we make the first attempt at solving this problem by two sets of simulations. To mimic small template fluctuations, in one set, monomers of the preformed template are kept fixed, while in the other set they are allowed to fluctuate. The kinetics of addition of a new peptide onto the template is explored using all-atom simulations with explicit water and the GROMOS96 43a1 force field and simple lattice models. Our result demonstrates that preformed template fluctuations can modulate protein aggregation rates and pathways. The association of a nascent monomer with the template obeys the kinetics partitioning mechanism where the intermediate state occurs in a fraction of routes to the protofibril. It was shown that template immobility greatly increases the time of incorporating a new peptide into the preformed template compared to the fluctuating template case. This observation has also been confirmed by simulation using lattice models and may be invoked to understand the role of template fluctuations in

  9. Preformed template fluctuations promote fibril formation: Insights from lattice and all-atom models

    International Nuclear Information System (INIS)

    Fibril formation resulting from protein misfolding and aggregation is a hallmark of several neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases. Despite the fact that the fibril formation process is very slow and thus poses a significant challenge for theoretical and experimental studies, a number of alternative pictures of molecular mechanisms of amyloid fibril formation have been recently proposed. What seems to be common for the majority of the proposed models is that fibril elongation involves the formation of pre-nucleus seeds prior to the creation of a critical nucleus. Once the size of the pre-nucleus seed reaches the critical nucleus size, its thermal fluctuations are expected to be small and the resulting nucleus provides a template for sequential (one-by-one) accommodation of added monomers. The effect of template fluctuations on fibril formation rates has not been explored either experimentally or theoretically so far. In this paper, we make the first attempt at solving this problem by two sets of simulations. To mimic small template fluctuations, in one set, monomers of the preformed template are kept fixed, while in the other set they are allowed to fluctuate. The kinetics of addition of a new peptide onto the template is explored using all-atom simulations with explicit water and the GROMOS96 43a1 force field and simple lattice models. Our result demonstrates that preformed template fluctuations can modulate protein aggregation rates and pathways. The association of a nascent monomer with the template obeys the kinetics partitioning mechanism where the intermediate state occurs in a fraction of routes to the protofibril. It was shown that template immobility greatly increases the time of incorporating a new peptide into the preformed template compared to the fluctuating template case. This observation has also been confirmed by simulation using lattice models and may be invoked to understand the role of template fluctuations in

  10. Performance Analysis on Molecular Dynamics Simulation of Protein Using GROMACS

    OpenAIRE

    Astuti, A. D.; Mutiara, A. B.

    2009-01-01

    Development of computer technology in chemistry, bring many application of chemistry. Not only the application to visualize the structure of molecule but also to molecular dynamics simulation. One of them is Gromacs. Gromacs is an example of molecular dynamics application developed by Groningen University. This application is a non-commercial and able to work in the operating system Linux. The main ability of Gromacs is to perform molecular dynamics simulation and minimization energy. In this...

  11. Development of semiclassical molecular dynamics simulation method.

    Science.gov (United States)

    Nakamura, Hiroki; Nanbu, Shinkoh; Teranishi, Yoshiaki; Ohta, Ayumi

    2016-04-28

    Various quantum mechanical effects such as nonadiabatic transitions, quantum mechanical tunneling and coherence play crucial roles in a variety of chemical and biological systems. In this paper, we propose a method to incorporate tunneling effects into the molecular dynamics (MD) method, which is purely based on classical mechanics. Caustics, which define the boundary between classically allowed and forbidden regions, are detected along classical trajectories and the optimal tunneling path with minimum action is determined by starting from each appropriate caustic. The real phase associated with tunneling can also be estimated. Numerical demonstration with use of a simple collinear chemical reaction O + HCl → OH + Cl is presented in order to help the reader to well comprehend the method proposed here. Generalization to the on-the-fly ab initio version is rather straightforward. By treating the nonadiabatic transitions at conical intersections by the Zhu-Nakamura theory, new semiclassical MD methods can be developed. PMID:27067383

  12. DMS: A Package for Multiscale Molecular Dynamics

    CERN Document Server

    Somogyi, Endre; Ortoleva, Peter J

    2013-01-01

    Advances in multiscale theory and computation provide a novel paradigm for simulating many-classical particle systems. The Deductive Multiscale Simulator (DMS) is a multiscale molecular dynamics (MD) program built on two of these advances, i.e., multiscale Langevin (ML) and multiscale factorization (MF). Both capture the coevolution of the the coarse-grained (CG) state and the microstate. This provides these methods with great efficiency over conventional MD. Neither involve the introduction of phenomenological governing equations for the CG state with attendant uncertainty in both their form of the governing equations and the data needed to calibrate them. The design and implementation of DMS as an open source computational platform is presented here. DMS is written in Python, uses Gromacs to achieve the microphase, and then advances the microstate via a CG-guided evolution. DMS uses MDAnalysis, a Python library for analyzing MD trajectories, to perform computations required to construct CG-related variables...

  13. Molecular dynamics simulations of shock compressed graphite

    International Nuclear Information System (INIS)

    We present molecular dynamic simulations of the shock compression of graphite with the LCBOPII potential. The range of shock intensities covers the full range of available experimental data, including near-tera-pascal pressures. The results are in excellent agreement with the available DFT data and point to a graphite-diamond transition for shock pressures above 65 GPa, a value larger than the experimental data (20 to 50 GPa). The transition mechanism leads preferentially to hexagonal diamond through a diffusion-less process but is submitted to irreversible re-graphitization upon release: this result is in good agreement with the lack of highly ordered diamond observed in post-mortem experimental samples. Melting is found for shock pressures ranging from 200 to 300 GPa, close to the approximate LCBOPII diamond melting line. A good overall agreement is found between the calculated and experimental Hugoniot data up to 46% compression rate. (authors)

  14. Assessing Molecular Dynamics Simulations with Solvatochromism Modeling.

    Science.gov (United States)

    Schwabe, Tobias

    2015-08-20

    For the modeling of solvatochromism with an explicit representation of the solvent molecules, the quality of preceding molecular dynamics simulations is crucial. Therefore, the possibility to apply force fields which are derived with as little empiricism as possible seems desirable. Such an approach is tested here by exploiting the sensitive solvatochromism of p-nitroaniline, and the use of reliable excitation energies based on approximate second-order coupled cluster results within a polarizable embedding scheme. The quality of the various MD settings for four different solvents, water, methanol, ethanol, and dichloromethane, is assessed. In general, good agreement with the experiment is observed when polarizable force fields and special treatment of hydrogen bonding are applied. PMID:26220273

  15. Nano-tribology through molecular dynamics simulations

    Institute of Scientific and Technical Information of China (English)

    王慧; 胡元中; 邹鲲; 冷永胜

    2001-01-01

    The solidification and interfacial slip in nanometer-scale lubricating films as well as the contact and adhesion of metal crystals have been studied via molecular dynamics simulations. Results show that the critical pressure for the solid-liquid transition declines as the film thickness decreases, in-dicating that the lubricant in the thin films may exist in a solid-like state. It is also found that the interfa-cial slip may occur in thin films at relatively low shear rate, and there is a good correlation between the slip phenomenon and the lubricant solidification. The simulations reveal that a micro-scale adhesion may take place due to the atomic jump during the process of approaching or separating of two smooth crystal surfaces, which provides important information for understanding the origin of interfacial friction.

  16. Molecular dynamics simulation of laser shock phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Fukumoto, Ichirou [Japan Atomic Energy Research Inst., Kansai Research Establishment, Advanced Photon Research Center, Neyagawa, Osaka (Japan).

    2001-10-01

    Recently, ultrashort-pulse lasers with high peak power have been developed, and their application to materials processing is expected as a tool of precision microfabrication. When a high power laser irradiates, a shock wave propagates into the material and dislocations are generated. In this paper, laser shock phenomena of the metal were analyzed using the modified molecular dynamics method, which has been developed by Ohmura and Fukumoto. The main results obtained are summarized as follows: (1) The shock wave induced by the Gaussian beam irradiation propagates radially from the surface to the interior. (2) A lot of dislocations are generated at the solid-liquid interface by the propagation of a shock wave. (3) Some dislocations are moved instantaneously with the velocity of the longitudinal wave when the shock wave passes, and their velocity is not larger than the transverse velocity after the shock wave has passed. (author)

  17. Statistical mechanics and dynamics of molecular fragmentation

    Energy Technology Data Exchange (ETDEWEB)

    Quack, M. (Goettingen Univ. (Germany, F.R.). Inst. fuer Physikalische Chemie)

    1981-05-11

    The foundations of the use of statistical-mechanical equations of motion, in particular the Pauli equation, for the description of intramolecular processes and molecular fragmentation are discussed briefly. Quantum-mechanical trajectories for model systems illustrate how the statistical behaviour may emerge from the dynamical equations of motion. Product state distributions resulting from the fragmentation of strongly coupled, metastable intermediates in chemical-activation experiments can be calculated by using restricted equipartition, which applies as the long-time limit of the Pauli equation. A simple Pauli-equation model is proposed to calculate lifetimes of metastable intermediates. The consequences of the finite rate of intramolecular relaxation processes for the specific rate constants for fragmentation and possible deviations from microcanonical equilibrium are explored.

  18. Statistical mechanics and dynamics of molecular fragmentation

    International Nuclear Information System (INIS)

    The foundations of the use of statistical-mechanical equations of motion, in particular the Pauli equation, for the description of intramolecular processes and molecular fragmentation are discussed briefly. Quantum-mechanical trajectories for model systems illustrate how the statistical behaviour may emerge from the dynamical equations of motion. Product state distributions resulting from the fragmentation of strongly coupled, metastable intermediates in chemical-activation experiments can be calculated by using restricted equipartition, which applies as the long-time limit of the Pauli equation. A simple Pauli-equation model is proposed to calculate lifetimes of metastable intermediates. The consequences of the finite rate of intramolecular relaxation processes for the specific rate constants for fragmentation and possible deviations from microcanonical equilibrium are explored. (author)

  19. Cell list algorithms for nonequilibrium molecular dynamics

    Science.gov (United States)

    Dobson, Matthew; Fox, Ian; Saracino, Alexandra

    2016-06-01

    We present two modifications of the standard cell list algorithm that handle molecular dynamics simulations with deforming periodic geometry. Such geometry naturally arises in the simulation of homogeneous, linear nonequilibrium flow modeled with periodic boundary conditions, and recent progress has been made developing boundary conditions suitable for general 3D flows of this type. Previous works focused on the planar flows handled by Lees-Edwards or Kraynik-Reinelt boundary conditions, while the new versions of the cell list algorithm presented here are formulated to handle the general 3D deforming simulation geometry. As in the case of equilibrium, for short-ranged pairwise interactions, the cell list algorithm reduces the computational complexity of the force computation from O(N2) to O(N), where N is the total number of particles in the simulation box. We include a comparison of the complexity and efficiency of the two proposed modifications of the standard algorithm.

  20. Superdeformed $\\Lambda$ hypernuclei with antisymmetrized molecular dynamics

    CERN Document Server

    Isaka, Masahiro; Kimura, Masaaki; Hiyama, Emiko; Sagawa, Hiroyuki; Yamamoto, Yasuo

    2014-01-01

    The response to the addition of a $\\Lambda$ hyperon is investigated for the deformed states such as superdeformation in $^{41}_\\Lambda$Ca, $^{46}_\\Lambda $Sc and $^{48}_\\Lambda$Sc. In the present study, we use the antisymmetrized molecular dynamics (AMD) model. It is pointed out that many kinds of deformed bands appear in $^{45}$Sc and $^{47}$Sc. Especially, it is found that there exists superdeformed states in $^{45}$Sc. By the addition of a $\\Lambda$ particle to $^{40}$Ca, $^{45}$Sc and $^{47}$Sc, it is predicted, for the first time, that the superdeformed states exist in the hypernuclei $^{41}_\\Lambda$Ca and $^{46}_\\Lambda$Sc. The manifestation of the dependence of the $\\Lambda$-separation energy on nuclear deformation such as spherical, normal deformation and superdeformation is shown in the energy spectra of $^{41}_\\Lambda$Ca, $^{46}_\\Lambda $Sc and $^{48}_\\Lambda$Sc hypernuclei.

  1. Molecular Dynamics Simulations for Predicting Surface Wetting

    Directory of Open Access Journals (Sweden)

    Jing Chen

    2014-06-01

    Full Text Available The investigation of wetting of a solid surface by a liquid provides important insights; the contact angle of a liquid droplet on a surface provides a quantitative measurement of this interaction and the degree of attraction or repulsion of that liquid type by the solid surface. Molecular dynamics (MD simulations are a useful way to examine the behavior of liquids on solid surfaces on a nanometer scale. Thus, we surveyed the state of this field, beginning with the fundamentals of wetting calculations to an examination of the different MD methodologies used. We highlighted some of the advantages and disadvantages of the simulations, and look to the future of computer modeling to understand wetting and other liquid-solid interaction phenomena.

  2. Nonequilibrium molecular dynamics: The first 25 years

    International Nuclear Information System (INIS)

    Equilibrium Molecular Dynamics has been generalized to simulate Nonequilibrium systems by adding sources of thermodynamic heat and work. This generalization incorporates microscopic mechanical definitions of macroscopic thermodynamic and hydrodynamic variables, such as temperature and stress, and augments atomistic forces with special boundary, constraint, and driving forces capable of doing work on, and exchanging heat with, an otherwise Newtonian system. The underlying Lyapunov instability of these nonequilibrium equations of motion links microscopic time-reversible deterministic trajectories to macroscopic time-irreversible hydrodynamic behavior as described by the Second Law of Thermodynamics. Green-Kubo linear-response theory has been checked. Nonlinear plastic deformation, intense heat conduction, shockwave propagation, and nonequilibrium phase transformation have all been simulated. The nonequilibrium techniques, coupled with qualitative improvements in parallel computer hardware, are enabling simulations to approximate real-world microscale and nanoscale experiments

  3. Dynamics of dewetting at the nanoscale using molecular dynamics.

    Science.gov (United States)

    Bertrand, E; Blake, T D; Ledauphin, V; Ogonowski, G; Coninck, J De; Fornasiero, D; Ralston, J

    2007-03-27

    Large-scale molecular dynamics simulations are used to model the dewetting of solid surfaces by partially wetting thin liquid films. Two levels of solid-liquid interaction are considered that give rise to large equilibrium contact angles. The initial length and thickness of the films are varied over a wide range at the nanoscale. Spontaneous dewetting is initiated by removing a band of molecules either from each end of the film or from its center. As observed experimentally and in previous simulations, the films recede at an initially constant speed, creating a growing rim of liquid with a constant receding dynamic contact angle. Consistent with the current understanding of wetting dynamics, film recession is faster on the more poorly wetted surface to an extent that cannot be explained solely by the increase in the surface tension driving force. In addition, the rates of recession of the thinnest films are found to increase with decreasing film thickness. These new results imply not only that the mobility of the liquid molecules adjacent to the solid increases with decreasing solid-liquid interactions, but also that the mobility adjacent to the free surface of the film is higher than in the bulk, so that the effective viscosity of the film decreases with thickness. PMID:17328565

  4. Continuous Finite Element Methods of Molecular Dynamics Simulations

    Directory of Open Access Journals (Sweden)

    Qiong Tang

    2015-01-01

    Full Text Available Molecular dynamics simulations are necessary to perform very long integration times. In this paper, we discuss continuous finite element methods for molecular dynamics simulation problems. Our numerical results about AB diatomic molecular system and A2B triatomic molecules show that linear finite element and quadratic finite element methods can better preserve the motion characteristics of molecular dynamics, that is, properties of energy conservation and long-term stability. So finite element method is also a reliable method to simulate long-time classical trajectory of molecular systems.

  5. Extracting Conformational Ensembles of Small Molecules from Molecular Dynamics Simulations: Ampicillin as a Test Case

    Directory of Open Access Journals (Sweden)

    Giuliano Malloci

    2016-01-01

    Full Text Available The accurate and exhaustive description of the conformational ensemble sampled by small molecules in solution, possibly at different physiological conditions, is of primary interest in many fields of medicinal chemistry and computational biology. Recently, we have built an on-line database of compounds with antimicrobial properties, where we provide all-atom force-field parameters and a set of molecular properties, including representative structures extracted from cluster analysis over μs-long molecular dynamics (MD trajectories. In the present work, we used a medium-sized antibiotic from our sample, namely ampicillin, to assess the quality of the conformational ensemble. To this aim, we compared the conformational landscape extracted from previous unbiased MD simulations to those obtained by means of Replica Exchange MD (REMD and those originating from three freely-available conformer generation tools widely adopted in computer-aided drug-design. In addition, for different charge/protonation states of ampicillin, we made available force-field parameters and static/dynamic properties derived from both Density Functional Theory and MD calculations. For the specific system investigated here, we found that: (i the conformational statistics extracted from plain MD simulations is consistent with that obtained from REMD simulations; (ii overall, our MD-based approach performs slightly better than any of the conformer generator tools if one takes into account both the diversity of the generated conformational set and the ability to reproduce experimentally-determined structures.

  6. The Folding of de Novo Designed Protein DS119 via Molecular Dynamics Simulations.

    Science.gov (United States)

    Wang, Moye; Hu, Jie; Zhang, Zhuqing

    2016-01-01

    As they are not subjected to natural selection process, de novo designed proteins usually fold in a manner different from natural proteins. Recently, a de novo designed mini-protein DS119, with a βαβ motif and 36 amino acids, has folded unusually slowly in experiments, and transient dimers have been detected in the folding process. Here, by means of all-atom replica exchange molecular dynamics (REMD) simulations, several comparably stable intermediate states were observed on the folding free-energy landscape of DS119. Conventional molecular dynamics (CMD) simulations showed that when two unfolded DS119 proteins bound together, most binding sites of dimeric aggregates were located at the N-terminal segment, especially residues 5-10, which were supposed to form β-sheet with its own C-terminal segment. Furthermore, a large percentage of individual proteins in the dimeric aggregates adopted conformations similar to those in the intermediate states observed in REMD simulations. These results indicate that, during the folding process, DS119 can easily become trapped in intermediate states. Then, with diffusion, a transient dimer would be formed and stabilized with the binding interface located at N-terminals. This means that it could not quickly fold to the native structure. The complicated folding manner of DS119 implies the important influence of natural selection on protein-folding kinetics, and more improvement should be achieved in rational protein design. PMID:27128902

  7. Hybrid Atomistic and Coarse-Grained Molecular Dynamics Simulations of Polyethylene Glycol (PEG) in Explicit Water.

    Science.gov (United States)

    Stanzione, Francesca; Jayaraman, Arthi

    2016-05-01

    In-silico design of polymeric biomaterials requires molecular dynamics (MD) simulations that retain essential atomistic/molecular details (e.g., explicit water around the biofunctional macromolecule) while simultaneously achieving large length and time scales pertinent to macroscale function. Such large-scale atomistically detailed macromolecular MD simulations with explicit solvent representation are computationally expensive. One way to overcome this limitation is to use an adaptive resolution scheme (AdResS) in which the explicit solvent molecules dynamically adopt either atomistic or coarse-grained resolution depending on their location (e.g., near or far from the macromolecule) in the system. In this study we present the feasibility and the limitations of AdResS methodology for studying polyethylene glycol (PEG) in adaptive resolution water, for varying PEG length and architecture. We first validate the AdResS methodology for such systems, by comparing PEG and solvent structure with that from all-atom simulations. We elucidate the role of the atomistic zone size and the need for calculating thermodynamic force correction within this AdResS approach to correctly reproduce the structure of PEG and water. Lastly, by varying the PEG length and architecture, we study the hydration of PEG, and the effect of PEG architectures on the structural properties of water. Changing the architecture of PEG from linear to multiarm star, we observe reduction in the solvent accessible surface area of the PEG, and an increase in the order of water molecules in the hydration shells. PMID:27108869

  8. The Folding of de Novo Designed Protein DS119 via Molecular Dynamics Simulations

    Directory of Open Access Journals (Sweden)

    Moye Wang

    2016-04-01

    Full Text Available As they are not subjected to natural selection process, de novo designed proteins usually fold in a manner different from natural proteins. Recently, a de novo designed mini-protein DS119, with a βαβ motif and 36 amino acids, has folded unusually slowly in experiments, and transient dimers have been detected in the folding process. Here, by means of all-atom replica exchange molecular dynamics (REMD simulations, several comparably stable intermediate states were observed on the folding free-energy landscape of DS119. Conventional molecular dynamics (CMD simulations showed that when two unfolded DS119 proteins bound together, most binding sites of dimeric aggregates were located at the N-terminal segment, especially residues 5–10, which were supposed to form β-sheet with its own C-terminal segment. Furthermore, a large percentage of individual proteins in the dimeric aggregates adopted conformations similar to those in the intermediate states observed in REMD simulations. These results indicate that, during the folding process, DS119 can easily become trapped in intermediate states. Then, with diffusion, a transient dimer would be formed and stabilized with the binding interface located at N-terminals. This means that it could not quickly fold to the native structure. The complicated folding manner of DS119 implies the important influence of natural selection on protein-folding kinetics, and more improvement should be achieved in rational protein design.

  9. Molecular Dynamic Simulation of Failure of Ettringite

    International Nuclear Information System (INIS)

    Ettringite is an important component in the hydration products of cement paste. To better understand the failure modes under tensile loading of cement-based materials, mechanical properties of each individual hydration product needs to be evaluated at atomic scale. This paper presents a molecular dynamic (MD) method to characterize and understand the mechanical properties of ettringite and its failure modes. The molecular structure of ettringite is established using ReaxFF force field package in LAMMPS. To characterize the atomic failure modes of cement paste, MD simulations were conducted by applying tensile strain load and shear strain load, respectively. In each MD failure simulation, the stress-strain relationship was plotted to quantify the mechanical properties at atomic scale. Then elastic constants of the ettringite crystal structure were calculated from these stress-strain relationships. MD simulations were validated by comparing the mechanical properties calculated from LAMMPS and those acquired from experiments. Future research should be performed on bridging-relationships of mechanical properties between atomic scale and macroscale to provide insights into further understanding the influence of mechanical properties at atomic scale on the performance of cement-based materials at macroscale.

  10. Molecular Dynamic Simulation of Failure of Ettringite

    Science.gov (United States)

    Sun, W.; Wang, D.; Wang, L.

    2013-03-01

    Ettringite is an important component in the hydration products of cement paste. To better understand the failure modes under tensile loading of cement-based materials, mechanical properties of each individual hydration product needs to be evaluated at atomic scale. This paper presents a molecular dynamic (MD) method to characterize and understand the mechanical properties of ettringite and its failure modes. The molecular structure of ettringite is established using ReaxFF force field package in LAMMPS. To characterize the atomic failure modes of cement paste, MD simulations were conducted by applying tensile strain load and shear strain load, respectively. In each MD failure simulation, the stress-strain relationship was plotted to quantify the mechanical properties at atomic scale. Then elastic constants of the ettringite crystal structure were calculated from these stress-strain relationships. MD simulations were validated by comparing the mechanical properties calculated from LAMMPS and those acquired from experiments. Future research should be performed on bridging-relationships of mechanical properties between atomic scale and macroscale to provide insights into further understanding the influence of mechanical properties at atomic scale on the performance of cement-based materials at macroscale.

  11. Molecular beam studies of reaction dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Y.T. [Lawrence Berkeley Laboratory, CA (United States)

    1993-12-01

    The major thrust of this research project is to elucidate detailed dynamics of simple elementary reactions that are theoretically important and to unravel the mechanism of complex chemical reactions or photochemical processes that play important roles in many macroscopic processes. Molecular beams of reactants are used to study individual reactive encounters between molecules or to monitor photodissociation events in a collision-free environment. Most of the information is derived from measurement of the product fragment energy, angular, and state distributions. Recent activities are centered on the mechanisms of elementary chemical reactions involving oxygen atoms with unsaturated hydrocarbons, the dynamics of endothermic substitution reactions, the dependence of the chemical reactivity of electronically excited atoms on the alignment of excited orbitals, the primary photochemical processes of polyatomic molecules, intramolecular energy transfer of chemically activated and locally excited molecules, the energetics of free radicals that are important to combustion processes, the infrared-absorption spectra of carbonium ions and hydrated hydronium ions, and bond-selective photodissociation through electric excitation.

  12. All-atom normal-mode analysis reveals an RNA-induced allostery in a bacteriophage coat protein

    Science.gov (United States)

    Dykeman, Eric C.; Twarock, Reidun

    2010-03-01

    Assembly of the T=3 bacteriophage MS2 is initiated by the binding of a 19 nucleotide RNA stem loop from within the phage genome to a symmetric coat protein dimer. This binding event effects a folding of the FG loop in one of the protein subunits of the dimer and results in the formation of an asymmetric dimer. Since both the symmetric and asymmetric forms of the dimer are needed for the assembly of the protein container, this allosteric switch plays an important role in the life cycle of the phage. We provide here details of an all-atom normal-mode analysis of this allosteric effect. The results suggest that asymmetric contacts between the A -duplex RNA phosphodiester backbone of the stem loop with the EF loop in one coat protein subunit results in an increased dynamic behavior of its FG loop. The four lowest-frequency modes, which encompass motions predominantly on the FG loops, account for over 90% of the increased dynamic behavior due to a localization of the vibrational pattern on a single FG loop. Finally, we show that an analysis of the allosteric effect using an elastic network model fails to predict this localization effect, highlighting the importance of using an all-atom full force field method for this problem.

  13. On the composition dependence of thermodynamic, dynamic and dielectric properties of water-methanol model mixtures. Molecular dynamics simulation results

    Directory of Open Access Journals (Sweden)

    E. Galicia-Andrés

    2015-12-01

    Full Text Available We have investigated thermodynamic and dynamic properties as well as the dielectric constant of water-methanol model mixtures in the entire range of composition by using constant pressure molecular dynamics simulations at ambient conditions. The SPC/E and TIP4P/Ew water models are used in combination with the OPLS united atom modelling for methanol. Changes of the average number of hydrogen bonds between particles of different species and of the fractions of differently bonded molecules are put in correspondence with the behavior of excess mixing volume and enthalpy, of self-diffusion coefficients and rotational relaxation times. From the detailed analyses of the results obtained in this work, we conclude that an improvement of the description of an ample set of properties of water-methanol mixtures can possibly be reached, if a more sophisticated, carefully parameterized, e.g., all atom, model for methanol is used. Moreover, exploration of parametrization of the methanol force field, with simultaneous application of different combination rules for methanol-water cross interactions, is required.

  14. Molecular dynamics studies on nanoscale gas transport

    Science.gov (United States)

    Barisik, Murat

    Three-dimensional molecular dynamics (MD) simulations of nanoscale gas flows are studied to reveal surface effects. A smart wall model that drastically reduces the memory requirements of MD simulations for gas flows is introduced. The smart wall molecular dynamics (SWMD) represents three-dimensional FCC walls using only 74 wall Molecules. This structure is kept in the memory and utilized for each gas molecule surface collision. Using SWMD, fluid behavior within nano-scale confinements is studied for argon in dilute gas, dense gas, and liquid states. Equilibrium MD method is employed to resolve the density and stress variations within the static fluid. Normal stress calculations are based on the Irving-Kirkwood method, which divides the stress tensor into its kinetic and virial parts. The kinetic component recovers pressure based on the ideal gas law. The particle-particle virial increases with increased density, while the surface-particle virial develops due to the surface force field effects. Normal stresses within nano-scale confinements show anisotropy induced primarily by the surface force-field and local variations in the fluid density near the surfaces. For dilute and dense gas cases, surface-force field that extends typically 1nm from each wall induces anisotropic normal stress. For liquid case, this effect is further amplified by the density fluctuations that extend beyond the three field penetration region. Outside the wall force-field penetration and density fluctuation regions the normal stress becomes isotropic and recovers the thermodynamic pressure, provided that sufficiently large force cut-off distances are utilized in the computations. Next, non-equilibrium SWMD is utilized to investigate the surface-gas interaction effects on nanoscale shear-driven gas flows in the transition and free molecular flow regimes. For the specified surface properties and gas-surface pair interactions, density and stress profiles exhibit a universal behavior inside the

  15. Molecular Dynamics in the Multicanonical Ensemble: Equivalence of Wang-Landau Sampling, Statistical Temperature Molecular Dynamics, and Metadynamics

    OpenAIRE

    Junghans, Christoph; Perez, Danny; Vogel, Thomas

    2014-01-01

    We show direct formal relationship between the Wang-Landau iteration [PRL 86, 2050 (2001)], metadynamics [PNAS 99, 12562 (2002)] and statistical temperature molecular dynamics [PRL 97, 050601 (2006)], the major Monte Carlo and molecular dynamics work-horses for sampling from a generalized, multicanonical ensemble. We demonstrate that statistical temperature molecular dynamics (which is formally derived from the Wang-Landau method), augmented by the introduction of kernel updates of the statis...

  16. Gas-Phase Molecular Dynamics: Vibrational Dynamics of Polyatomic Molecules

    International Nuclear Information System (INIS)

    The goal of this research is the understanding of elementary chemical and physical processes important in the combustion of fossil fuels. Interest centers on reactions and properties of short-lived chemical intermediates. High-resolution, high-sensitivity, laser absorption methods are augmented by high- temperature, flow-tube reaction kinetics studies with mass-spectrometric sampling. These experiments provide information on the energy levels, structures and reactivity of molecular free radical species and in turn, provide new tools for the study of energy flow and chemical bond cleavage in the radicals involved in chemical systems. The experimental work is supported by theoretical studies using time-dependent quantum wave packet calculations, which provide insight into energy flow among the vibrational modes of polyatomic molecules and interference effects in multiple-surface dynamics

  17. Molecular Dynamics Investigated by Neutron Scattering

    International Nuclear Information System (INIS)

    A short review of the present state of the problem of applicability of the Krieger-Nelkin theory as well as of the Griffing theory to gases is made. Then, on the basis of experiments with liquid methane, the applicability of the mass-tensor concept to molecules in condensed states is criticized. Strong arguments against the application of the Krieger-Nelkin theory to condensed states are: a shift of neutron energy distribution after scattering towards higher energies and the lack of dependence of the Inelastic part on the scattering angle. Further sections deal with the rotational dynamics of ammonium groups in ammonium compounds. Most of the experimental material is discussed in connection with ammonium halides on the basis of experiments by different authors. For some substances a freedom of rotation of NH4 groups was obtained from neutron measurements, whereas for some others the rotation goes over into torsional vibration. In this case, frequencies of torsional vibrations obtained by various authors from neutron experiments were compared with those obtained from infrared spectroscopy and specific heat measurements. The barrier-to-rotation evaluation from total neutron cross-section measurements is also discussed. Further a comparison is made of the rotational dynamics of NH4 groups in NH4CIO4 and H3O groups in H3OCIO4 on the basis of neutron inelastic scattering experiments. A free rotation of the NH4 group in ammonium perchlorate was obtained even at temperatures as low as liquid nitrogen temperature. For H3OCIO4 a torsional vibration of the H3O group with a frequency of 497 cm-1 was obtained. So in spite of the identity of the crystal lattices of NH4CIO4 and H3OCIO4 the dynamics of the NH4 and H3O groups are different. The results are compared with those known from Raman spectroscopy and nuclear magnetic resonance. Finally, a number of other substances is discussed from the point of view of molecular dynamics. (author)

  18. Parametrizing linear generalized Langevin dynamics from explicit molecular dynamics simulations

    International Nuclear Information System (INIS)

    Fundamental understanding of complex dynamics in many-particle systems on the atomistic level is of utmost importance. Often the systems of interest are of macroscopic size but can be partitioned into a few important degrees of freedom which are treated most accurately and others which constitute a thermal bath. Particular attention in this respect attracts the linear generalized Langevin equation, which can be rigorously derived by means of a linear projection technique. Within this framework, a complicated interaction with the bath can be reduced to a single memory kernel. This memory kernel in turn is parametrized for a particular system studied, usually by means of time-domain methods based on explicit molecular dynamics data. Here, we discuss that this task is more naturally achieved in frequency domain and develop a Fourier-based parametrization method that outperforms its time-domain analogues. Very surprisingly, the widely used rigid bond method turns out to be inappropriate in general. Importantly, we show that the rigid bond approach leads to a systematic overestimation of relaxation times, unless the system under study consists of a harmonic bath bi-linearly coupled to the relevant degrees of freedom

  19. Modeling and Bio molecular Self-assembly via Molecular Dynamics and Dissipative Particle Dynamics

    Science.gov (United States)

    Rakesh, L.

    2009-09-01

    Surfactants like materials can be used to increase the solubility of poorly soluble drugs in water and to increase drug bioavailability. A typical case study will be demonstrated using DPD simulation to model the distribution of anti-inflammatory drug molecules. Computer simulation is a convenient approach to understand drug distribution and solubility concepts without much wastage and costly experiments in the laboratory. Often in molecular dynamics (MD) the atoms are represented explicitly and the equation of motion as described by Newtonian dynamics is integrated explicitly. MD has been used to study spontaneous formation of micelles by hydrophobic molecules with amphiphilic head groups in bulk water, as well as stability of pre-configured micelles and membranes. DPD is a state-of the- art mesoscale simulation, it is a more recent molecular dynamics technique, originally developed for simulating complex fluids but lately also applied to membrane dynamics, hemodynamic in biomedical applications. Such fluids pervade industrial research from paints to pharmaceuticals and from cosmetics to the controlled release of drugs. Dissipative particle dynamics (DPD) can provide structural and dynamic properties of fluids in equilibrium, under shear or confined to narrow cavities, at length- and time-scales beyond the scope of traditional atomistic molecular dynamics simulation methods. Mesoscopic particles are used to represent clusters of molecules. The interaction conserves mass and momentum and as a consequence the dynamics is consistent with Navier-Stokes equations. In addition to the conservative forces, stochastic drive and dissipation is introduced to represent internal degrees of freedom in the mesoscopic particles. In this research, an initial study is being conducted using the aqueous solubilization of the nonsteroidal, anti-inflammatory drug is studied theoretically in micellar solution of nonionic (dodecyl hexa(ethylene oxide), C12E6) surfactants possessing the

  20. How Dynamic Visualization Technology Can Support Molecular Reasoning

    Science.gov (United States)

    Levy, Dalit

    2013-01-01

    This paper reports the results of a study aimed at exploring the advantages of dynamic visualization for the development of better understanding of molecular processes. We designed a technology-enhanced curriculum module in which high school chemistry students conduct virtual experiments with dynamic molecular visualizations of solid, liquid, and…

  1. Low-mass molecular dynamics simulation: A simple and generic technique to enhance configurational sampling

    International Nuclear Information System (INIS)

    Highlights: • Reducing atomic masses by 10-fold vastly improves sampling in MD simulations. • CLN025 folded in 4 of 10 × 0.5-μs MD simulations when masses were reduced by 10-fold. • CLN025 folded as early as 96.2 ns in 1 of the 4 simulations that captured folding. • CLN025 did not fold in 10 × 0.5-μs MD simulations when standard masses were used. • Low-mass MD simulation is a simple and generic sampling enhancement technique. - Abstract: CLN025 is one of the smallest fast-folding proteins. Until now it has not been reported that CLN025 can autonomously fold to its native conformation in a classical, all-atom, and isothermal–isobaric molecular dynamics (MD) simulation. This article reports the autonomous and repeated folding of CLN025 from a fully extended backbone conformation to its native conformation in explicit solvent in multiple 500-ns MD simulations at 277 K and 1 atm with the first folding event occurring as early as 66.1 ns. These simulations were accomplished by using AMBER forcefield derivatives with atomic masses reduced by 10-fold on Apple Mac Pros. By contrast, no folding event was observed when the simulations were repeated using the original AMBER forcefields of FF12SB and FF14SB. The results demonstrate that low-mass MD simulation is a simple and generic technique to enhance configurational sampling. This technique may propel autonomous folding of a wide range of miniature proteins in classical, all-atom, and isothermal–isobaric MD simulations performed on commodity computers—an important step forward in quantitative biology

  2. Low-mass molecular dynamics simulation: A simple and generic technique to enhance configurational sampling

    Energy Technology Data Exchange (ETDEWEB)

    Pang, Yuan-Ping, E-mail: pang@mayo.edu

    2014-09-26

    Highlights: • Reducing atomic masses by 10-fold vastly improves sampling in MD simulations. • CLN025 folded in 4 of 10 × 0.5-μs MD simulations when masses were reduced by 10-fold. • CLN025 folded as early as 96.2 ns in 1 of the 4 simulations that captured folding. • CLN025 did not fold in 10 × 0.5-μs MD simulations when standard masses were used. • Low-mass MD simulation is a simple and generic sampling enhancement technique. - Abstract: CLN025 is one of the smallest fast-folding proteins. Until now it has not been reported that CLN025 can autonomously fold to its native conformation in a classical, all-atom, and isothermal–isobaric molecular dynamics (MD) simulation. This article reports the autonomous and repeated folding of CLN025 from a fully extended backbone conformation to its native conformation in explicit solvent in multiple 500-ns MD simulations at 277 K and 1 atm with the first folding event occurring as early as 66.1 ns. These simulations were accomplished by using AMBER forcefield derivatives with atomic masses reduced by 10-fold on Apple Mac Pros. By contrast, no folding event was observed when the simulations were repeated using the original AMBER forcefields of FF12SB and FF14SB. The results demonstrate that low-mass MD simulation is a simple and generic technique to enhance configurational sampling. This technique may propel autonomous folding of a wide range of miniature proteins in classical, all-atom, and isothermal–isobaric MD simulations performed on commodity computers—an important step forward in quantitative biology.

  3. Accelerating all-atom MD simulations of lipids using a modified virtual-sites technique

    DEFF Research Database (Denmark)

    Loubet, Bastien; Kopec, Wojciech; Khandelia, Himanshu

    2014-01-01

    We present two new implementations of the virtual sites technique which completely suppresses the degrees of freedom of the hydrogen atoms in a lipid bilayer allowing for an increased time step of 5 fs in all-atom simulations of the CHARMM36 force field. One of our approaches uses the derivation of...

  4. Reparameterization of All-Atom Dipalmitoylphosphatidylcholine Lipid Parameters Enables Simulation of Fluid Bilayers at Zero Tension

    OpenAIRE

    Sonne, Jacob; Jensen, Morten Ø.; Hansen, Flemming Y.; Hemmingsen, Lars Bo Stegeager; Peters, Günther H.

    2007-01-01

    Molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using the CHARMM27 force field in the tensionless isothermal-isobaric (NPT) ensemble give highly ordered, gel-like bilayers with an area per lipid of ∼48 Å2. To obtain fluid (Lα) phase properties of DPPC bilayers represented by the CHARMM energy function in this ensemble, we reparameterized the atomic partial charges in the lipid headgroup and upper parts of the acyl chains. The new charges were determined ...

  5. Imaging the Breakdown of Molecular Frame Dynamics through Rotational Uncoupling

    CERN Document Server

    Zipp, Lucas J; Bucksbaum, Philip H

    2016-01-01

    We have observed directly in the time domain the uncoupling of electron motion from the molecular frame due to rotational-electronic coupling in a molecular Rydberg system. In contrast to Born- Oppenheimer dynamics, in which the electron is firmly fixed to the molecular frame, there exists a regime of molecular dynamics known as $l$-uncoupling where the motion of a non-penetrating Rydberg electron decouples from the instantaneous alignment of the molecular frame. We have imaged this unusual regime in time-dependent photoelectron angular distributions of a coherently prepared electron wave packet in the 4$f$ manifold of $N_2$.

  6. Multimillion atom molecular dynamics simulations of glasses and ceramic materials

    International Nuclear Information System (INIS)

    Molecular dynamics simulations are a powerful tool for studying physical and chemical phenomena in materials. In these lectures we shall review the molecular dynamics method and its implementation on parallel computer architectures. Using the molecular dynamics method we will study a number of materials in different ranges of density, temperature, and uniaxial strain. These include structural correlations in silica glass under pressure, crack propagation in silicon nitride films, sintering of silicon nitride nanoclusters, consolidation of nanophase materials, and dynamic fracture. Multimillion atom simulations of oxidation of aluminum nanoclusters and nanoindentation in silicon nitride will also be discussed. (c) 1999 American Institute of Physics

  7. A molecular dynamics simulation code ISIS

    International Nuclear Information System (INIS)

    Computer simulation based on the molecular dynamics (MD) method has become an important tool complementary to experiments and theoretical calculations in a wide range of scientific fields such as physics, chemistry, biology, and so on. In the MD method, the Newtonian equations-of-motion of classical particles are integrated numerically to reproduce a phase-space trajectory of the system. In the 1980's, several new techniques have been developed for simulation at constant-temperature and/or constant-pressure in convenient to compare result of computer simulation with experimental results. We first summarize the MD method for both microcanonical and canonical simulations. Then, we present and overview of a newly developed ISIS (Isokinetic Simulation of Soft-spheres) code and its performance on various computers including vector processors. The ISIS code has a capability to make a MD simulation under constant-temperature condition by using the isokinetic constraint method. The equations-of-motion is integrated by a very accurate fifth-order finite differential algorithm. The bookkeeping method is also utilized to reduce the computational time. Furthermore, the ISIS code is well adopted for vector processing: Speedup ratio ranged from 16 to 24 times is obtained on a VP2600/10 vector processor. (author)

  8. Quantum molecular dynamics simulations of dense matter

    Energy Technology Data Exchange (ETDEWEB)

    Collins, L.; Kress, J.; Troullier, N.; Lenosky, T.; Kwon, I. [Los Alamos National Lab., Albuquerque, NM (United States)

    1997-12-31

    The authors have developed a quantum molecular dynamics (QMD) simulation method for investigating the properties of dense matter in a variety of environments. The technique treats a periodically-replicated reference cell containing N atoms in which the nuclei move according to the classical equations-of-motion. The interatomic forces are generated from the quantum mechanical interactions of the (between?) electrons and nuclei. To generate these forces, the authors employ several methods of varying sophistication from the tight-binding (TB) to elaborate density functional (DF) schemes. In the latter case, lengthy simulations on the order of 200 atoms are routinely performed, while for the TB, which requires no self-consistency, upwards to 1000 atoms are systematically treated. The QMD method has been applied to a variety cases: (1) fluid/plasma Hydrogen from liquid density to 20 times volume-compressed for temperatures of a thousand to a million degrees Kelvin; (2) isotopic hydrogenic mixtures, (3) liquid metals (Li, Na, K); (4) impurities such as Argon in dense hydrogen plasmas; and (5) metal/insulator transitions in rare gas systems (Ar,Kr) under high compressions. The advent of parallel versions of the methods, especially for fast eigensolvers, presage LDA simulations in the range of 500--1000 atoms and TB runs for tens of thousands of particles. This leap should allow treatment of shock chemistry as well as large-scale mixtures of species in highly transient environments.

  9. Molecular dynamics in cytochrome c oxidase Moessbauer spectra deconvolution

    International Nuclear Information System (INIS)

    Research highlights: → Cytochrome c oxidase molecular dynamics serve to predict Moessbauer lineshape widths. → Half height widths are used in modeling of Lorentzian doublets. → Such spectral deconvolutions are useful in detecting the enzyme intermediates. -- Abstract: In this work low temperature molecular dynamics simulations of cytochrome c oxidase are used to predict an experimentally observable, namely Moessbauer spectra width. Predicted lineshapes are used to model Lorentzian doublets, with which published cytochrome c oxidase Moessbauer spectra were simulated. Molecular dynamics imposed constraints to spectral lineshapes permit to obtain useful information, like the presence of multiple chemical species in the binuclear center of cytochrome c oxidase. Moreover, a benchmark of quality for molecular dynamic simulations can be obtained. Despite the overwhelming importance of dynamics in electron-proton transfer systems, limited work has been devoted to unravel how much realistic are molecular dynamics simulations results. In this work, molecular dynamics based predictions are found to be in good agreement with published experimental spectra, showing that we can confidently rely on actual simulations. Molecular dynamics based deconvolution of Moessbauer spectra will lead to a renewed interest for application of this approach in bioenergetics.

  10. Molecular dynamics in cytochrome c oxidase Moessbauer spectra deconvolution

    Energy Technology Data Exchange (ETDEWEB)

    Bossis, Fabrizio [Department of Medical Biochemistry, Medical Biology and Medical Physics (DIBIFIM), University of Bari ' Aldo Moro' , Bari (Italy); Palese, Luigi L., E-mail: palese@biochem.uniba.it [Department of Medical Biochemistry, Medical Biology and Medical Physics (DIBIFIM), University of Bari ' Aldo Moro' , Bari (Italy)

    2011-01-07

    Research highlights: {yields} Cytochrome c oxidase molecular dynamics serve to predict Moessbauer lineshape widths. {yields} Half height widths are used in modeling of Lorentzian doublets. {yields} Such spectral deconvolutions are useful in detecting the enzyme intermediates. -- Abstract: In this work low temperature molecular dynamics simulations of cytochrome c oxidase are used to predict an experimentally observable, namely Moessbauer spectra width. Predicted lineshapes are used to model Lorentzian doublets, with which published cytochrome c oxidase Moessbauer spectra were simulated. Molecular dynamics imposed constraints to spectral lineshapes permit to obtain useful information, like the presence of multiple chemical species in the binuclear center of cytochrome c oxidase. Moreover, a benchmark of quality for molecular dynamic simulations can be obtained. Despite the overwhelming importance of dynamics in electron-proton transfer systems, limited work has been devoted to unravel how much realistic are molecular dynamics simulations results. In this work, molecular dynamics based predictions are found to be in good agreement with published experimental spectra, showing that we can confidently rely on actual simulations. Molecular dynamics based deconvolution of Moessbauer spectra will lead to a renewed interest for application of this approach in bioenergetics.

  11. Molecular Dynamics Simulation Study of the Selectivity of a Silica Polymer for Ibuprofen

    Science.gov (United States)

    Concu, Riccardo; Cordeiro, M. Natalia D. S.

    2016-01-01

    In the past few years, the sol-gel polycondensation technique has been increasingly employed with great success as an alternative approach to the preparation of molecularly imprinted materials (MIMs). The main aim of this study was to study, through a series of molecular dynamics (MD) simulations, the selectivity of an imprinted silica xerogel towards a new template—the (±)-2-(P-Isobutylphenyl) propionic acid (Ibuprofen, IBU). We have previously demonstrated the affinity of this silica xerogel toward a similar molecule. In the present study, we simulated the imprinting process occurring in a sol-gel mixture using the Optimized Potentials for Liquid Simulations-All Atom (OPLS-AA) force field, in order to evaluate the selectivity of this xerogel for a template molecule. In addition, for the first time, we have developed and verified a new parameterisation for the Ibuprofen® based on the OPLS-AA framework. To evaluate the selectivity of the polymer, we have employed both the radial distribution functions, interaction energies and cluster analyses. PMID:27399685

  12. Comparative study of local structure of two cyanobiphenyl liquid crystals by molecular dynamics method

    International Nuclear Information System (INIS)

    Fully-atomistic molecular dynamics simulations were carried out on two similar cyanobiphenyl nematogens, HO-6OCB and 7OCB, in order to study effects of hydrogen bonds on local structure of liquid crystals. Comparable length of these two molecules provides more evident results on the effects of hydrogen bonding. The analysis of radial and cylindrical distribution functions clearly shows the differences in local structure of two mesogens. The simulations showed that anti-parallel alignment is preferable for the HO-6OCB. Hydrogen bonds between OH-groups are observed for 51% of HO-6OCB molecules, while hydrogen bonding between CN- and OH-groups occurs only for 16% of molecules. The lifetimes of H-bonds differ due to different mobility of molecular fragments (50 ps for N⋅⋅⋅H–O and 41 ps for O⋅⋅⋅H–O). Although the standard Optimized Potentials for Liquid Simulations - All-Atom force field cannot reproduce some experimental parameters quantitatively (order parameters are overestimated, diffusion coefficients are not reproduced well), the comparison of relative simulated results for the pair of mesogens is nevertheless consistent with the same relative experimental parameters. Thus, the comparative study of simulated and experimental results for the pair of similar liquid crystals still can be assumed plausible

  13. Scaling of Multimillion-Atom Biological Molecular Dynamics Simulation on a Petascale Supercomputer.

    Science.gov (United States)

    Schulz, Roland; Lindner, Benjamin; Petridis, Loukas; Smith, Jeremy C

    2009-10-13

    A strategy is described for a fast all-atom molecular dynamics simulation of multimillion-atom biological systems on massively parallel supercomputers. The strategy is developed using benchmark systems of particular interest to bioenergy research, comprising models of cellulose and lignocellulosic biomass in an aqueous solution. The approach involves using the reaction field (RF) method for the computation of long-range electrostatic interactions, which permits efficient scaling on many thousands of cores. Although the range of applicability of the RF method for biomolecular systems remains to be demonstrated, for the benchmark systems the use of the RF produces molecular dipole moments, Kirkwood G factors, other structural properties, and mean-square fluctuations in excellent agreement with those obtained with the commonly used Particle Mesh Ewald method. With RF, three million- and five million-atom biological systems scale well up to ∼30k cores, producing ∼30 ns/day. Atomistic simulations of very large systems for time scales approaching the microsecond would, therefore, appear now to be within reach. PMID:26631792

  14. Combined Molecular Dynamics Simulations and Experimental Studies of the Structure and Dynamics of Poly-Amido-Saccharides.

    Science.gov (United States)

    Chin, Stacy L; Lu, Qing; Dane, Eric L; Dominguez, Laura; McKnight, Christopher J; Straub, John E; Grinstaff, Mark W

    2016-05-25

    Poly-amido-saccharides (PAS) are carbohydrate-based, enantiopure synthetic polymers in which sugar repeat units are joined by amide linkages. This unique and relatively rigid pyranose backbone contributes to their defined helical secondary structure and remarkable chemical properties. Glucose- (glc-) and galactose- (gal-) PAS 10-mer structures are synthesized and investigated with molecular dynamics (MD) simulations and experimental measurements. Quantum mechanical DFT energy minimization calculations, as well as experimental observables including circular dichroism, (1)H,(13)C-HSQC, and (1)H,(1)H-NOESY 2D-NMR studies, validated the all-atom simulation models produced using a modified CHARMM force field. Water radial distribution functions show distinct differences in the glc- and gal-PAS systems that correlate well with observed differences in solubility between gal-PASs and glc-PASs. The computational analysis and MD simulations are in good agreement with experimental results, validating the proposed models as reliable representations of novel glc- and gal-PASs. PMID:27119983

  15. Modeling shockwave deformation via molecular dynamics

    International Nuclear Information System (INIS)

    Molecular dynamics (MD), where the equations of motion of up to thousands of interacting atoms are solved on the computer, has proven to be a powerful tool for investigating a wide variety of nonequilibrium processes from the atomistic viewpoint. Simulations of shock waves in three-dimensional (3D) solids and fluids have shown conclusively that shear-stress relaxation is achieved through atomic rearrangement. In the case of fluids, the transverse motion is viscous, and the constitutive model of Navier-Stokes hydrodynamics has been shown to be accurate - even on the time and distance scales of MD experiments. For strong shocks in solids, the plastic flow that leads to shear-stress relaxation in MD is highly localized near the shock front, involving a slippage along close-packed planes. For shocks of intermediate strength, MD calculations exhibit an elastic precursor running out in front of the steady plastic wave, where slippage similar in character to that in the very strong shocks leads to shear-stress relaxation. An interesting correlation between the maximum shear stress and the Hugoniot pressure jump is observed for both 3D and fluid shockwave calculations, which may have some utility in modeling applications. At low shock strengths, the MD simulations show only elastic compression, with no permanent transverse atomic strains. The result for perfect 3D crystals is also seen in calculations for 1D chains. It is speculated that, if it were practical, a very large MD system containing dislocations could be expected to exhibit more realistic plastic flow for weak shock waves, too

  16. Analysis of the Time Reversible Born-Oppenheimer Molecular Dynamics

    CERN Document Server

    Lin, Lin; Shao, Sihong

    2013-01-01

    We analyze the time reversible Born-Oppenheimer molecular dynamics (TRBOMD) scheme, which preserves the time reversibility of the Born-Oppenheimer molecular dynamics even with non-convergent self-consistent field iteration. In the linear response regime, we derive the stability condition as well as the accuracy of TRBOMD for computing physical properties such as the phonon frequency obtained from the molecular dynamic simulation. We connect and compare TRBOMD with the Car-Parrinello molecular dynamics in terms of accuracy and stability. We further discuss the accuracy of TRBOMD beyond the linear response regime for non-equilibrium dynamics of nuclei. Our results are demonstrated through numerical experiments using a simplified one dimensional model for Kohn-Sham density functional theory.

  17. Analysis of Time Reversible Born-Oppenheimer Molecular Dynamics

    Directory of Open Access Journals (Sweden)

    Lin Lin

    2013-12-01

    Full Text Available We analyze the time reversible Born-Oppenheimer molecular dynamics (TRBOMD scheme, which preserves the time reversibility of the Born-Oppenheimer molecular dynamics even with non-convergent self-consistent field iteration. In the linear response regime, we derive the stability condition, as well as the accuracy of TRBOMD for computing physical properties, such as the phonon frequency obtained from the molecular dynamics simulation. We connect and compare TRBOMD with Car-Parrinello molecular dynamics in terms of accuracy and stability. We further discuss the accuracy of TRBOMD beyond the linear response regime for non-equilibrium dynamics of nuclei. Our results are demonstrated through numerical experiments using a simplified one-dimensional model for Kohn-Sham density functional theory.

  18. Visualization and orchestration of the dynamic molecular society in cells

    Institute of Scientific and Technical Information of China (English)

    Xuebiao Yao; Guowei Fang

    2009-01-01

    @@ Visualization of specific molecules and their interactions in real space and time is essential to delineate how cellular plasticity and dynamics are achieved and orchestrated as perturbation of cellular plasticity and dynamics is detrimental to health. Elucidation of cellular dynamics requires molecular imaging at nanometer scale at millisecond resolution. The 1st International Conference on Cellular Dynamics and Chemical Biology held in Hefei, China (from 12 September to 15 September,2008) launched the quest by bringing synergism among photonics, chemistry and biology.

  19. Las Palmeras Molecular Dynamics: A flexible and modular molecular dynamics code

    Science.gov (United States)

    Davis, Sergio; Loyola, Claudia; González, Felipe; Peralta, Joaquín

    2010-12-01

    Las Palmeras Molecular Dynamics (LPMD) is a highly modular and extensible molecular dynamics (MD) code using interatomic potential functions. LPMD is able to perform equilibrium MD simulations of bulk crystalline solids, amorphous solids and liquids, as well as non-equilibrium MD (NEMD) simulations such as shock wave propagation, projectile impacts, cluster collisions, shearing, deformation under load, heat conduction, heterogeneous melting, among others, which involve unusual MD features like non-moving atoms and walls, unstoppable atoms with constant-velocity, and external forces like electric fields. LPMD is written in C++ as a compromise between efficiency and clarity of design, and its architecture is based on separate components or plug-ins, implemented as modules which are loaded on demand at runtime. The advantage of this architecture is the ability to completely link together the desired components involved in the simulation in different ways at runtime, using a user-friendly control file language which describes the simulation work-flow. As an added bonus, the plug-in API (Application Programming Interface) makes it possible to use the LPMD components to analyze data coming from other simulation packages, convert between input file formats, apply different transformations to saved MD atomic trajectories, and visualize dynamical processes either in real-time or as a post-processing step. Individual components, such as a new potential function, a new integrator, a new file format, new properties to calculate, new real-time visualizers, and even a new algorithm for handling neighbor lists can be easily coded, compiled and tested within LPMD by virtue of its object-oriented API, without the need to modify the rest of the code. LPMD includes already several pair potential functions such as Lennard-Jones, Morse, Buckingham, MCY and the harmonic potential, as well as embedded-atom model (EAM) functions such as the Sutton-Chen and Gupta potentials. Integrators to

  20. Intramolecular interactions stabilizing compact conformations of the intrinsically disordered kinase-inhibitor domain of Sic1: a molecular dynamics investigation.

    Directory of Open Access Journals (Sweden)

    ElenaPapaleo

    2012-11-01

    The yeast CKI Sic1 is a 284-amino acid IDP that binds to Cdk1 in complex with the Clb5,6 cyclins, preventing phosphorylation of G1 substrates and, therefore, entrance to the S phase. Sic1 degradation, triggered by multiple phosphorylation events, promotes cell-cycle progression. Previous experimental studies pointed out a propensity of Sic1 and its isolated domains to populate both extended and compact conformations. The present contribution provides models of the compact conformations of the Sic1 kinase-inhibitory domain (KID by all-atom molecular-dynamics simulations in explicit solvent and in the absence of interactors. The results are integrated by spectroscopic and spectrometric data. Helical IFSUs are identified, along with networks of intramolecular interactions. The results identify a group of hub residues and electrostatic interactions which are likely to be involved in the stabilization of globular states.

  1. Molecular dynamics study of linear and comb-like polyelectrolytes in aqueous solution: effect of Ca2+ ions

    Science.gov (United States)

    Tong, Kefeng; Song, Xingfu; Sun, Shuying; Xu, Yanxia; Yu, Jianguo

    2014-08-01

    All-atom molecular dynamics simulations were employed to provide microscopic mechanism for the salt tolerance of polyelectrolytes dispersants. The conformational variation of polyelectrolytes and interactions between COO- groups and counterions/water molecules were also studied via radius of gyration and pair correlations functions. Sodium polyacrylate (NaPA) and sodium salts of poly(acrylic acid)-poly(ethylene oxide) (NaPA-PEO) were selected as the representative linear and comb-like polyelectrolyte, respectively. The results show that Ca2+ ions interact with COO- groups much stronger than Na+ ions and can bring ion-bridging interaction between intermolecular COO- groups in the NaPA systems. While in the NaPA-PEO systems, the introduced PEO side chains can prevent backbone chains from ion-bridging interactions and weaken the conformational changes. The present results can help in selecting and designing new-type efficient polyelectrolyte dispersants with good salt tolerance.

  2. Modelling of Spectroscopic and Structural Properties using Molecular Dynamics

    OpenAIRE

    Francesco Muniz Miranda

    2013-01-01

    The following dissertation is about the study that I performed at the Chemistry Department of the University of Florence and at the European Laboratory for Non- Linear Spectroscopy (LENS) to recover and elucidate structural, dynamical, and spectroscopic molecular features adopting computer simulations. In particular, here ab initio molecular dynamics simulations and time-frequency analysis are the most employed “tools”, in order to have a better understanding of the origins ...

  3. Multi CPU clusters and calculations by molecular dynamics method

    International Nuclear Information System (INIS)

    The technical characteristics of multi CPU (Central Processor Unit) clusters in Institute of Ion-Plasma and Laser Technologies AS RUz and Institute of Mathematics and Information Technologies AS RUz are described. There is detail information about cluster s architecture, installed programs and their productivity for decision of molecular dynamics tasks. Molecular dynamics program packages GROMACS, OPENMX and AutoDock-4.2.3 are described. The results of calculations using these program packages are presented. (author)

  4. Applications of Molecular Dynamics in Atmospheric and Solution Chemistry

    OpenAIRE

    Li, Xin

    2011-01-01

    This thesis focuses on the applications of molecular dynamics simulation techniques in the fields of solution chemistry and atmospheric chemistry. The work behind the thesis takes account of the fast development of computer hardware, which has made computationally intensive simulations become more and more popular in disciplines like pharmacy, biology and materials science. In molecular dynamics simulations using classical force fields, the atoms are represented by mass points with partial ch...

  5. Combining Optimal Control Theory and Molecular Dynamics for Protein Folding

    OpenAIRE

    Yaman Arkun; Mert Gur

    2012-01-01

    Combining Optimal Control Theory and Molecular Dynamics for Protein Folding Yaman Arkun1*, Mert Gur2¤ 1 Department of Chemical and Biological Engineering, Koc University, Istanbul, Turkey, 2 Center for Computational Biology and Bioinformatics, Koc University, Istanbul, Turkey Abstract A new method to develop low-energy folding routes for proteins is presented. The novel aspect of the proposed approach is the synergistic use of optimal control theory with Molecular Dynamic...

  6. HTMD: High-Throughput Molecular Dynamics for Molecular Discovery.

    Science.gov (United States)

    Doerr, S; Harvey, M J; Noé, Frank; De Fabritiis, G

    2016-04-12

    Recent advances in molecular simulations have allowed scientists to investigate slower biological processes than ever before. Together with these advances came an explosion of data that has transformed a traditionally computing-bound into a data-bound problem. Here, we present HTMD, a programmable, extensible platform written in Python that aims to solve the data generation and analysis problem as well as increase reproducibility by providing a complete workspace for simulation-based discovery. So far, HTMD includes system building for CHARMM and AMBER force fields, projection methods, clustering, molecular simulation production, adaptive sampling, an Amazon cloud interface, Markov state models, and visualization. As a result, a single, short HTMD script can lead from a PDB structure to useful quantities such as relaxation time scales, equilibrium populations, metastable conformations, and kinetic rates. In this paper, we focus on the adaptive sampling and Markov state modeling features. PMID:26949976

  7. Dynamical analysis of highly excited molecular spectra

    Energy Technology Data Exchange (ETDEWEB)

    Kellman, M.E. [Univ. of Oregon, Eugene (United States)

    1993-12-01

    The goal of this program is new methods for analysis of spectra and dynamics of highly excited vibrational states of molecules. In these systems, strong mode coupling and anharmonicity give rise to complicated classical dynamics, and make the simple normal modes analysis unsatisfactory. New methods of spectral analysis, pattern recognition, and assignment are sought using techniques of nonlinear dynamics including bifurcation theory, phase space classification, and quantization of phase space structures. The emphasis is chaotic systems and systems with many degrees of freedom.

  8. Development and application of all-atom structure-based models for studying the role of geometry in biomolecular folding and function

    OpenAIRE

    Noel, Jeffrey Kenneth

    2012-01-01

    Protein dynamics takes place on a rugged funnel-like energy landscape that is biased towards the native state. In naturally occurring proteins, this ruggedness caused by non-native interactions is sufficiently smooth (minimally frustrated) that the landscape is dominated by the native interactions. This provides the theoretical foundation for a class of minimalist protein models called structure- based models (SBMs). In the first half of the thesis we develop and characterize an all-atom SBM ...

  9. All-Atom Structural Models of the Transmembrane Domains of Insulin and Type 1 Insulin-Like Growth Factor Receptors

    Science.gov (United States)

    Mohammadiarani, Hossein; Vashisth, Harish

    2016-01-01

    The receptor tyrosine kinase superfamily comprises many cell-surface receptors including the insulin receptor (IR) and type 1 insulin-like growth factor receptor (IGF1R) that are constitutively homodimeric transmembrane glycoproteins. Therefore, these receptors require ligand-triggered domain rearrangements rather than receptor dimerization for activation. Specifically, binding of peptide ligands to receptor ectodomains transduces signals across the transmembrane domains for trans-autophosphorylation in cytoplasmic kinase domains. The molecular details of these processes are poorly understood in part due to the absence of structures of full-length receptors. Using MD simulations and enhanced conformational sampling algorithms, we present all-atom structural models of peptides containing 51 residues from the transmembrane and juxtamembrane regions of IR and IGF1R. In our models, the transmembrane regions of both receptors adopt helical conformations with kinks at Pro961 (IR) and Pro941 (IGF1R), but the C-terminal residues corresponding to the juxtamembrane region of each receptor adopt unfolded and flexible conformations in IR as opposed to a helix in IGF1R. We also observe that the N-terminal residues in IR form a kinked-helix sitting at the membrane–solvent interface, while homologous residues in IGF1R are unfolded and flexible. These conformational differences result in a larger tilt-angle of the membrane-embedded helix in IGF1R in comparison to IR to compensate for interactions with water molecules at the membrane–solvent interfaces. Our metastable/stable states for the transmembrane domain of IR, observed in a lipid bilayer, are consistent with a known NMR structure of this domain determined in detergent micelles, and similar states in IGF1R are consistent with a previously reported model of the dimerized transmembrane domains of IGF1R. Our all-atom structural models suggest potentially unique structural organization of kinase domains in each receptor. PMID

  10. Current-driven dynamics in molecular-scale devices

    International Nuclear Information System (INIS)

    We review recent theoretical work on current-triggered processes in molecular-scale devices - a field at the interface between solid state physics and chemical dynamics with potential applications in diverse areas, including artificial molecular machines, unimolecular transport, surface nanochemistry and nanolithography. The qualitative physics underlying current-triggered dynamics is first discussed and placed in context with several well-studied phenomena with which it shares aspects. A theory for modelling these dynamics is next formulated within a time-dependent scattering approach. Our end result provides useful insight into the system properties that determine the reaction outcome as well as a computationally convenient framework for numerical realization. The theory is applied to study single-molecule surface reactions induced by a scanning tunnelling microscope and current-triggered dynamics in single-molecule transistors. We close with a discussion of several potential applications of current-induced dynamics in molecular devices and several opportunities for future research. (topical review)

  11. A fermionic molecular dynamics technique to model nuclear matter

    International Nuclear Information System (INIS)

    Full text: At sub-nuclear densities of about 1014 g/cm3, nuclear matter arranges itself in a variety of complex shapes. This can be the case in the crust of neutron stars and in core-collapse supernovae. These slab like and rod like structures, designated as nuclear pasta, have been modelled with classical molecular dynamics techniques. We present a technique, based on fermionic molecular dynamics, to model nuclear matter at sub-nuclear densities in a semi classical framework. The dynamical evolution of an antisymmetric ground state is described making the assumption of periodic boundary conditions. Adding the concepts of antisymmetry, spin and probability distributions to classical molecular dynamics, brings the dynamical description of nuclear matter to a quantum mechanical level. Applications of this model vary from investigation of macroscopic observables and the equation of state to the study of fundamental interactions on the microscopic structure of the matter. (author)

  12. Unified rotational dynamics of molecular crystals with orientational phase transition

    NARCIS (Netherlands)

    Michel, K.H.; Raedt, H. De

    1976-01-01

    A unified theory for the rotational dynamics of molecular crystals with orientational phase transitions is given. As basic secular variables one takes symmetry adapted functions, which describe the molecular orientations, and the angular momenta of the molecules. Using Mori’s projection operator tec

  13. Elucidation of molecular dynamics of invasive species of rice

    Science.gov (United States)

    Cultivated rice fields are aggressively invaded by weedy rice in the U.S. and worldwide. Weedy rice results in loss of yield and seed contamination. The molecular dynamics of the evolutionary adaptive traits of weedy rice are not fully understood. To understand the molecular basis and identify the i...

  14. Shapiro like steps reveals molecular nanomagnets' spin dynamics

    OpenAIRE

    Babak Abdollahipour; Jahanfar Abouie; Navid Ebrahimi

    2015-01-01

    We present an accurate way to detect spin dynamics of a nutating molecular nanomagnet by inserting it in a tunnel Josephson junction and studying the current voltage (I-V) characteristic. The spin nutation of the molecular nanomagnet is generated by applying two circularly polarized magnetic fields. We demonstrate that modulation of the Josephson current by the nutation of the molecular nanomagnet’s spin appears as a stepwise structure like Shapiro steps in the I-V characteristic of the junct...

  15. Molecular Dynamics of Channelrhodopsin at the Early Stages of Channel Opening.

    Directory of Open Access Journals (Sweden)

    Mizuki Takemoto

    Full Text Available Channelrhodopsin (ChR is a light-gated cation channel that responds to blue light. Since ChR can be readily expressed in specific neurons to precisely control their activities by light, it has become a powerful tool in neuroscience. Although the recently solved crystal structure of a chimeric ChR, C1C2, provided the structural basis for ChR, our understanding of the molecular mechanism of ChR still remains limited. Here we performed electrophysiological analyses and all-atom molecular dynamics (MD simulations, to investigate the importance of the intracellular and central constrictions of the ion conducting pore observed in the crystal structure of C1C2. Our electrophysiological analysis revealed that two glutamate residues, Glu122 and Glu129, in the intracellular and central constrictions, respectively, should be deprotonated in the photocycle. The simulation results suggested that the deprotonation of Glu129 in the central constriction leads to ion leakage in the ground state, and implied that the protonation of Glu129 is important for preventing ion leakage in the ground state. Moreover, we modeled the 13-cis retinal bound; i.e., activated C1C2, and performed MD simulations to investigate the conformational changes in the early stage of the photocycle. Our simulations suggested that retinal photoisomerization induces the conformational change toward channel opening, including the movements of TM6, TM7 and TM2. These insights into the dynamics of the ground states and the early photocycle stages enhance our understanding of the channel function of ChR.

  16. Coarse-graining to the meso and continuum scales with molecular-dynamics-like models

    Science.gov (United States)

    Plimpton, Steve

    Many engineering-scale problems that industry or the national labs try to address with particle-based simulations occur at length and time scales well beyond the most optimistic hopes of traditional coarse-graining methods for molecular dynamics (MD), which typically start at the atomic scale and build upward. However classical MD can be viewed as an engine for simulating particles at literally any length or time scale, depending on the models used for individual particles and their interactions. To illustrate I'll highlight several coarse-grained (CG) materials models, some of which are likely familiar to molecular-scale modelers, but others probably not. These include models for water droplet freezing on surfaces, dissipative particle dynamics (DPD) models of explosives where particles have internal state, CG models of nano or colloidal particles in solution, models for aspherical particles, Peridynamics models for fracture, and models of granular materials at the scale of industrial processing. All of these can be implemented as MD-style models for either soft or hard materials; in fact they are all part of our LAMMPS MD package, added either by our group or contributed by collaborators. Unlike most all-atom MD simulations, CG simulations at these scales often involve highly non-uniform particle densities. So I'll also discuss a load-balancing method we've implemented for these kinds of models, which can improve parallel efficiencies. From the physics point-of-view, these models may be viewed as non-traditional or ad hoc. But because they are MD-style simulations, there's an opportunity for physicists to add statistical mechanics rigor to individual models. Or, in keeping with a theme of this session, to devise methods that more accurately bridge models from one scale to the next.

  17. Tunable Interfacial Thermal Conductance by Molecular Dynamics

    Science.gov (United States)

    Shen, Meng

    We study the mechanism of tunable heat transfer through interfaces between solids using a combination of non-equilibrium molecular dynamics simulation (NEMD), vibrational mode analysis and wave packet simulation. We investigate how heat transfer through interfaces is affected by factors including pressure, interfacial modulus, contact area and interfacial layer thickness, with an overreaching goal of developing fundamental knowledge that will allow one to tailor thermal properties of interfacial materials. The role of pressure and interfacial stiffness is unraveled by our studies on an epitaxial interface between two Lennard-Jones (LJ) crystals. The interfacial stiffness is varied by two different methods: (i) indirectly by applying pressure which due to anharmonic nature of bonding, increases interfacial stiffness, and (ii) directly by changing the interfacial bonding strength by varying the depth of the potential well of the LJ potential. When the interfacial bonding strength is low, quantitatively similar behavior to pressure tuning is observed when the interfacial thermal conductance is increased by directly varying the potential-well depth parameter of the LJ potential. By contrast, when the interfacial bonding strength is high, thermal conductance is almost pressure independent, and even slightly decreases with increasing pressure. This decrease can be explained by the change in overlap between the vibrational densities of states of the two crystalline materials. The role of contact area is studied by modeling structures comprised of Van der Waals junctions between single-walled nanotubes (SWCNT). Interfacial thermal conductance between SWCNTs is obtained from NEMD simulation as a function of crossing angle. In this case the junction conductance per unit area is essentially a constant. By contrast, interfacial thermal conductance between multiwalled carbon nanotubes (MWCNTs) is shown to increase with diameter of the nanotubes by recent experimental studies [1

  18. Energy conservation in molecular dynamics simulations of classical systems

    DEFF Research Database (Denmark)

    Toxværd, Søren; Heilmann, Ole; Dyre, J. C.

    2012-01-01

    Classical Newtonian dynamics is analytic and the energy of an isolated system is conserved. The energy of such a system, obtained by the discrete “Verlet” algorithm commonly used in molecular dynamics simulations, fluctuates but is conserved in the mean. This is explained by the existence...

  19. The Computer Simulation of Liquids by Molecular Dynamics.

    Science.gov (United States)

    Smith, W.

    1987-01-01

    Proposes a mathematical computer model for the behavior of liquids using the classical dynamic principles of Sir Isaac Newton and the molecular dynamics method invented by other scientists. Concludes that other applications will be successful using supercomputers to go beyond simple Newtonian physics. (CW)

  20. Automatic identification of mobile and rigid substructures in molecular dynamics simulations and fractional structural fluctuation analysis.

    Directory of Open Access Journals (Sweden)

    Leandro Martínez

    Full Text Available The analysis of structural mobility in molecular dynamics plays a key role in data interpretation, particularly in the simulation of biomolecules. The most common mobility measures computed from simulations are the Root Mean Square Deviation (RMSD and Root Mean Square Fluctuations (RMSF of the structures. These are computed after the alignment of atomic coordinates in each trajectory step to a reference structure. This rigid-body alignment is not robust, in the sense that if a small portion of the structure is highly mobile, the RMSD and RMSF increase for all atoms, resulting possibly in poor quantification of the structural fluctuations and, often, to overlooking important fluctuations associated to biological function. The motivation of this work is to provide a robust measure of structural mobility that is practical, and easy to interpret. We propose a Low-Order-Value-Optimization (LOVO strategy for the robust alignment of the least mobile substructures in a simulation. These substructures are automatically identified by the method. The algorithm consists of the iterative superposition of the fraction of structure displaying the smallest displacements. Therefore, the least mobile substructures are identified, providing a clearer picture of the overall structural fluctuations. Examples are given to illustrate the interpretative advantages of this strategy. The software for performing the alignments was named MDLovoFit and it is available as free-software at: http://leandro.iqm.unicamp.br/mdlovofit.

  1. Molecular dynamics simulation on adsorption of pyrene-polyethylene onto ultrathin single-walled carbon nanotube

    Science.gov (United States)

    Cai, Lu; Lv, Wenzhen; Zhu, Hong; Xu, Qun

    2016-07-01

    The mechanism of the adsorption of pyrene-polyethylene (Py-PE) onto ultrathin single-walled carbon nanotube (SWNT) was studied by using all-atom molecular dynamics (MD) simulations. We found that solvent polarity and pyrene group are two critical factors in the Py-PE decoration on ultrathin SWNT. Combined MD simulations with free energy calculations, our results indicate that larger solvent polarity can decrease the contribution of conformation entropy, but contributes little to the interaction energy, moreover, larger SWNT diameter can decrease the contribution of conformation entropy but lead to the increasing of the interaction energy. In polar organic solvent (N, N-Dimethylacetamide), the pyrene group plays a key role in the adsorption of Py-PE onto ultrathin SWNT, not only facilitates the spontaneous adsorption of Py-PE onto ultrathin SWNT, but also helps to form compact structure between themselves in the final adsorption states. While in aqueous solution, pyrene group no longer works as an anchor, but still affects a lot to the final adsorption conformation. Our present work provides detailed theoretical clue to understand the noncovalent interaction between aromatic segment appended polymer and ultrathin SWNT, and helps to explore the potential application of ultrathin SWNT in the fields of hybrid material, biomedical and electronic materials.

  2. Electrostatic unfolding and interactions of albumin driven by pH changes: a molecular dynamics study.

    Science.gov (United States)

    Baler, K; Martin, O A; Carignano, M A; Ameer, G A; Vila, J A; Szleifer, I

    2014-01-30

    A better understanding of protein aggregation is bound to translate into critical advances in several areas, including the treatment of misfolded protein disorders and the development of self-assembling biomaterials for novel commercial applications. Because of its ubiquity and clinical potential, albumin is one of the best-characterized models in protein aggregation research; but its properties in different conditions are not completely understood. Here, we carried out all-atom molecular dynamics simulations of albumin to understand how electrostatics can affect the conformation of a single albumin molecule just prior to self-assembly. We then analyzed the tertiary structure and solvent accessible surface area of albumin after electrostatically triggered partial denaturation. The data obtained from these single protein simulations allowed us to investigate the effect of electrostatic interactions between two proteins. The results of these simulations suggested that hydrophobic attractions and counterion binding may be strong enough to effectively overcome the electrostatic repulsions between the highly charged monomers. This work contributes to our general understanding of protein aggregation mechanisms, the importance of explicit consideration of free ions in protein solutions, provides critical new insights about the equilibrium conformation of albumin in its partially denatured state at low pH, and may spur significant progress in our efforts to develop biocompatible protein hydrogels driven by electrostatic partial denaturation. PMID:24393011

  3. Molecular dynamics study of the shock response in hydroxyl-terminated polybutadiene melts

    Science.gov (United States)

    Froehlich, Markus G.; Sewell, Thomas D.; Thompson, Donald L.

    2013-03-01

    All-atom molecular dynamics (MD) simulations using the non-reactive OPLS-AA force field were performed to study the detailed structural, mechanical, and spectroscopic response of hydroxyl-terminated polybutadiene (HTPB) melts subjected to supported shock waves. A combination of Monte Carlo and MD techniques was used to generate thoroughly equilibrated initial configurations, for monodisperse systems with chain lengths ranging from 64 to 256 backbone carbons per chain. Properties characterizing the size, shape and orientation of single chains, as well as the vibrational density of states, were evaluated prior to and following shock passage for four impact velocities between 1.0 and 2.5 km/s. The structural properties and global scaling behaviors of the unshocked systems are in excellent agreement with literature data. Results for the shocked systems, obtained using a geometric binning approach that provides spatio-temporal resolution in the reference frame centered on the shock front, indicate a transition to a glass-like state with a concomitant increase by several orders of magnitude of structural relaxation times in the shocked material. Supported by the Defense Threat Reduction Agency, grant number HDTRA1-10-1-0078.

  4. Molecular Dynamics Simulation for the Binary Mixtures of High Pressure Carbon Dioxide and Ionic Liquids

    Institute of Scientific and Technical Information of China (English)

    徐君臣; 王松; 喻文; 徐琴琴; 王伟彬; 银建中

    2014-01-01

    Molecular dynamics simulation with an all-atom force field has been carried out on the two binary sys-tems of [bmim][PF6]-CO2 and [bmim][NO3]-CO2 to study the transport properties, volume expansion and micro-structures. It was found that addition of CO2 in the liquid phase can greatly decrease the viscosity of ionic liquids (ILs) and increase their diffusion coefficient obviously. Furthermore, the volume expansion of ionic liquids was found to increase with the increase of the mole fraction of CO2 in the liquid phase but less than 35%for the two simulated systems, which had a significant difference with CO2 expanded organic solvents. The main reason was that there were some void spaces inter and intra the molecules of ionic liquids. Finally, site to site radial distribution functions and corresponding number integrals were investigated and it was found that the change of microstructures of ILs by addition CO2 had a great influence on the properties of ILs.

  5. The ABCs of molecular dynamics simulations on B-DNA, circa 2012

    Indian Academy of Sciences (India)

    David L Beveridge; Thomas E Cheatham III; Mihaly Mezei

    2012-07-01

    This article provides a retrospective on the ABC initiative in the area of all-atom molecular dynamics (MD) simulations including explicit solvent on all tetranucleotide steps of duplex B-form DNA duplex, ca. 2012. The ABC consortium has completed two phases of simulations, the most current being a set of 50–100 trajectories based on the AMBER ff99 force field together with the parmbsc0 modification. Some general perspectives on the field of MD on DNA and sequence effects on DNA structure are provided, followed by an overview our MD results, including a detailed comparison of the ff99/parmbsc0 results with crystal and NMR structures available for d(CGCGAATTCGCG). Some projects inspired by or related to the ABC initiative and database are also reviewed, including methods for the trajectory analyses, informatics of dealing with the large database of results, compressions of trajectories for efficacy of distribution, DNA solvation by water and ions, parameterization of coarse-grained models with applications and gene finding and genome annotation

  6. Temperature dependence of protein hydration hydrodynamics by molecular dynamics simulations.

    Energy Technology Data Exchange (ETDEWEB)

    Lau, E Y; Krishnan, V V

    2007-07-18

    The dynamics of water molecules near the protein surface are different from those of bulk water and influence the structure and dynamics of the protein itself. To elucidate the temperature dependence hydration dynamics of water molecules, we present results from the molecular dynamic simulation of the water molecules surrounding two proteins (Carboxypeptidase inhibitor and Ovomucoid) at seven different temperatures (T=273 to 303 K, in increments of 5 K). Translational diffusion coefficients of the surface water and bulk water molecules were estimated from 2 ns molecular dynamics simulation trajectories. Temperature dependence of the estimated bulk water diffusion closely reflects the experimental values, while hydration water diffusion is retarded significantly due to the protein. Protein surface induced scaling of translational dynamics of the hydration waters is uniform over the temperature range studied, suggesting the importance protein-water interactions.

  7. Refined OPLS All-Atom Force Field for Saturated Phosphatidylcholine Bilayers at Full Hydration

    DEFF Research Database (Denmark)

    Maciejewski, A.; Pasenkiewicz-Gierula, M.; Cramariuc, O.; Vattulainen, I.; Rog, T.

    2014-01-01

    validation, and it is also one of the highly important and abundant lipid types, e.g., in lung surfactant. Overall, PCs have not been previously parametrized in the OPLS-AA force field; thus, there is a need to derive its bonding and nonbonding parameters for both the polar and nonpolar parts of the molecule......We report parametrization of dipalmitoyl-phosphatidylcholine (DPPC) in the framework of the Optimized Parameters for Liquid Simulations all-atom (OPLS-AA) force field. We chose DPPC as it is one of the most studied phospholipid species and thus has plenty of experimental data necessary for model...

  8. Interfacial Molecular Searching Using Forager Dynamics

    Science.gov (United States)

    Monserud, Jon H.; Schwartz, Daniel K.

    2016-03-01

    Many biological and technological systems employ efficient non-Brownian intermittent search strategies where localized searches alternate with long flights. Coincidentally, molecular species exhibit intermittent behavior at the solid-liquid interface, where periods of slow motion are punctuated by fast flights through the liquid phase. Single-molecule tracking was used here to observe the interfacial search process of DNA for complementary DNA. Measured search times were qualitatively consistent with an intermittent-flight model, and ˜10 times faster than equivalent Brownian searches, suggesting that molecular searches for reactive sites benefit from similar efficiencies as biological organisms.

  9. Molecular dynamics with deterministic and stochastic numerical methods

    CERN Document Server

    Leimkuhler, Ben

    2015-01-01

    This book describes the mathematical underpinnings of algorithms used for molecular dynamics simulation, including both deterministic and stochastic numerical methods. Molecular dynamics is one of the most versatile and powerful methods of modern computational science and engineering and is used widely in chemistry, physics, materials science and biology. Understanding the foundations of numerical methods means knowing how to select the best one for a given problem (from the wide range of techniques on offer) and how to create new, efficient methods to address particular challenges as they arise in complex applications.  Aimed at a broad audience, this book presents the basic theory of Hamiltonian mechanics and stochastic differential equations, as well as topics including symplectic numerical methods, the handling of constraints and rigid bodies, the efficient treatment of Langevin dynamics, thermostats to control the molecular ensemble, multiple time-stepping, and the dissipative particle dynamics method...

  10. Dynamics Studies on Molecular Diffusion in Zeolites

    Institute of Scientific and Technical Information of China (English)

    王秋霞; 樊建芬; 肖鹤鸣

    2003-01-01

    A review about the applications of molecular dynamics(MD)simulation in zeolites is presented. MD simulation has been proved to be a useful tool due to its applications in this field for the recent two decades. The fundamental theory of MD is introduced and the hydrocarbon diffusion in zeolites is mainly focused on in this paper.

  11. A comparative molecular dynamics study on BACE1 and BACE2 flap flexibility.

    Science.gov (United States)

    Kumalo, H M; Soliman, Mahmoud E

    2016-10-01

    Beta-amyloid precursor protein cleavage enzyme1 (BACE1) and beta-amyloid precursor protein cleavage enzyme2 (BACE2), members of aspartyl protease family, are close homologs and have high similarity in their protein crystal structures. However, their enzymatic properties are different, which leads to different clinical outcomes. In this study, we performed sequence analysis and all-atom molecular dynamic (MD) simulations for both enzymes in their ligand-free states in order to compare their dynamical flap behaviors. This is to enhance our understanding of the relationship between sequence, structure and the dynamics of this protein family. Sequence analysis shows that in BACE1 and BACE2, most of the ligand-binding sites are conserved, indicative of their enzymatic property as aspartyl protease members. The other conserved residues are more or less unsystematically localized throughout the structure. Herein, we proposed and applied different combined parameters to define the asymmetric flap motion; the distance, d1, between the flap tip and the flexible region; the dihedral angle, φ, to account for the twisting motion and the TriCα angle, θ2 and θ1. All four combined parameters were found to appropriately define the observed "twisting" motion during the flaps different conformational states. Additional analysis of the parameters indicated that the flaps can exist in an ensemble of conformations, i.e. closed, semi-open and open conformations for both systems. However, the behavior of the flap tips during simulations is different between BACE1 and BACE2. The BACE1 active site cavity is more spacious as compared to that of BACE2. The analysis of 10S loop and 113S loop showed a similar trend to that of flaps, with the BACE1 loops being more flexible and less stable than those of BACE2. We believe that the results, methods and perspectives highlighted in this report would assist researchers in the discovery of BACE inhibitors as potential Alzheimer's disease therapies

  12. Interaction of I50V Mutant and I50L/A71V Double Mutant HIV-protease with Inhibitor TMC114 (Darunavir): Molecular Dynamics Simulation and Binding Free Energy Studies

    OpenAIRE

    Meher, Biswa Ranjan; Wang, Yixuan

    2012-01-01

    In the present work the binding of inhibitor TMC114 (darunavir) to wild type (WT), single (I50V) as well as double (I50L/A71V) mutant HIV-proteases (HIV-pr) was investigated with all-atom molecular dynamics (MD) simulations as well as molecular mechanic-Poisson Boltzmann surface area (MM-PBSA) calculation. For both the apo and complexed HIV-pr, many intriguing effects due to double mutant, I50L/A71V, are observed. For example, the flap-flap distance and the distance from the active site to th...

  13. Reparameterization of all-atom dipalmitoylphosphatidylcholine lipid parameters enables simulation of fluid bilayers at zero tension

    DEFF Research Database (Denmark)

    Sonne, Jacob; Jensen, Morten Ø.; Hansen, Flemming Y.; Hemmingsen, Lars Bo Stegeager; Peters, Günther H.

    2007-01-01

    Molecular dynamics (MD) simulations of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using the CHARMM27 force field in the tensionless isothermal-isobaric (N PT) ensemble give highly ordered, gel-like bilayers (20) with an area per lipid of ~48 Å2 (31). To obtain fluid (L ) phase properties...... of DPPC bilayers represented by the CHARMM energy function in this ensemble, we reparameterized the atomic partial charges in the lipid head group and upper parts of the acyl chains. The new charges were determined from the electron structure using both the Mulliken method and the restricted...... electrostatic potential (RESP) fitting method (5). We tested the derived charges in MD simulations of a fully hydrated DPPC bilayer. Only the simulation with the new RESP charges shows significant improvements compared with simulations using the original CHARMM27 force field resulting in an area per lipid of 60...

  14. Reparameterization of all-atom dipalmitoylphosphatidylcholine lipid parameters enables simulation of fluid bilayers at zero tension

    DEFF Research Database (Denmark)

    Sonne, Jacob; Jensen, M.Ø.; Hansen, Flemming Yssing; Hemmingsen, L.; Peters, Günther H.j.

    2007-01-01

    lipid of 60.4 ± 0.1 Å2. Compared to the 48 Å2, the new value of 60.4 Å2 is in fair agreement with the experimental value of 64 Å2. In addition, the simulated order parameter profile and electron density profile are in satisfactory agreement with experimental data. Thus, the biologically more interesting......Molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using the CHARMM27 force field in the tensionless isothermal-isobaric (NPT) ensemble give highly ordered, gel-like bilayers with an area per lipid of ∼48 Å2. To obtain fluid (Lα) phase properties of DPPC bilayers...... represented by the CHARMM energy function in this ensemble, we reparameterized the atomic partial charges in the lipid headgroup and upper parts of the acyl chains. The new charges were determined from the electron structure using both the Mulliken method and the restricted electrostatic potential fitting...

  15. Accelerating All-Atom Normal Mode Analysis with Graphics Processing Unit.

    Science.gov (United States)

    Liu, Li; Liu, Xiaofeng; Gong, Jiayu; Jiang, Hualiang; Li, Honglin

    2011-06-14

    All-atom normal mode analysis (NMA) is an efficient way to predict the collective motions in a given macromolecule, which is essential for the understanding of protein biological function and drug design. However, the calculations are limited in time scale mainly because the required diagonalization of the Hessian matrix by Householder-QR transformation is a computationally exhausting task. In this paper, we demonstrate the parallel computing power of the graphics processing unit (GPU) in NMA by mapping Householder-QR transformation onto GPU using Compute Unified Device Architecture (CUDA). The results revealed that the GPU-accelerated all-atom NMA could reduce the runtime of diagonalization significantly and achieved over 20× speedup over CPU-based NMA. In addition, we analyzed the influence of precision on both the performance and the accuracy of GPU. Although the performance of GPU with double precision is weaker than that with single precision in theory, more accurate results and an acceptable speedup of double precision were obtained in our approach by reducing the data transfer time to a minimum. Finally, the inherent drawbacks of GPU and the corresponding solution to deal with the limitation in computational scale are also discussed in this study. PMID:26596427

  16. Electrostatic Unfolding and Interactions of Albumin Driven by pH Changes: A Molecular Dynamics Study

    OpenAIRE

    Baler, K.; Martin, O. A.; Carignano, M. A.; Ameer, G.A.; Vila, J. A.; Szleifer, I.

    2014-01-01

    A better understanding of protein aggregation is bound to translate into critical advances in several areas, including the treatment of misfolded protein disorders and the development of self-assembling biomaterials for novel commercial applications. Because of its ubiquity and clinical potential, albumin is one of the best-characterized models in protein aggregation research; but its properties in different conditions are not completely understood. Here, we carried out all-atom molecular dyn...

  17. Dynamic strength of molecular adhesion bonds.

    OpenAIRE

    Evans, E; Ritchie, K

    1997-01-01

    In biology, molecular linkages at, within, and beneath cell interfaces arise mainly from weak noncovalent interactions. These bonds will fail under any level of pulling force if held for sufficient time. Thus, when tested with ultrasensitive force probes, we expect cohesive material strength and strength of adhesion at interfaces to be time- and loading rate-dependent properties. To examine what can be learned from measurements of bond strength, we have extended Kramers' theory for reaction k...

  18. Tunneling Dynamics Between Atomic and Molecular Bose-Einstein Condensates

    Institute of Scientific and Technical Information of China (English)

    CHEN Chang-Yong

    2004-01-01

    Tunneling dynamics of multi-atomic molecules between atomic and multi-atomic molecular Bose-Einstein condensates with Feshbach resonance is investigated.It is indicated that the tunneling in the two Bose-Einstein condensates depends on not only the inter-atomic-molecular nonlinear interactions and the initial number of atoms in these condensates,but also the tunneling coupling between the atomic condensate and the multi-atomic molecular condensate.It is discovered that besides oscillating tunneling current between the atomic condensate and the multi-atomic molecular condensate,the nonlinear multi-atomic molecular tunneling dynamics sustains a self-locked population imbalance:a macroscopic quantum self-trapping effect.The influence of de-coherence caused by non-condensate atoms on the tunneling dynamics is studied.It is shown that de-coherence suppresses the multi-atomic molecular tunneling.Moreover,the conception of the molecular Bose-Einstein condensate,which is different from the conventional single-atomic Bose-Einstein condensate,is specially emphasized in this paper.

  19. Passage from quantum to classical molecular dynamics in the presence of Coulomb interactions

    OpenAIRE

    Ambrosio, Luigi; Friesecke, Gero; Giannoulis, Jannis

    2009-01-01

    We present a rigorous derivation of classical molecular dynamics (MD) from quantum molecular dynamics (QMD) that applies to the standard Hamiltonians of molecular physics with Coulomb interactions. The derivation is valid away from possible electronic eigenvalue crossings.

  20. Molecular Mechanotransduction: how forces trigger cytoskeletal dynamics

    Science.gov (United States)

    Ehrlicher, Allen

    2012-02-01

    Mechanical stresses elicit cellular reactions mediated by chemical signals. Defective responses to forces underlie human medical disorders, such as cardiac failure and pulmonary injury. Despite detailed knowledge of the cytoskeleton's structure, the specific molecular switches that convert mechanical stimuli into chemical signals have remained elusive. Here we identify the actin-binding protein, filamin A (FLNa) as a central mechanotransduction element of the cytoskeleton by using Fluorescence Loss After photoConversion (FLAC), a novel high-speed alternative to FRAP. We reconstituted a minimal system consisting of actin filaments, FLNa and two FLNa-binding partners: the cytoplasmic tail of ß-integrin, and FilGAP. Integrins form an essential mechanical linkage between extracellular and intracellular environments, with ß integrin tails connecting to the actin cytoskeleton by binding directly to filamin. FilGAP is a FLNa-binding GTPase-activating protein specific for Rac, which in vivo regulates cell spreading and bleb formation. We demonstrate that both externally-imposed bulk shear and myosin II driven forces differentially regulate the binding of integrin and FilGAP to FLNa. Consistent with structural predictions, strain increases ß-integrin binding to FLNa, whereas it causes FilGAP to dissociate from FLNa, providing a direct and specific molecular basis for cellular mechanotransduction. These results identify the first molecular mechanotransduction element within the actin cytoskeleton, revealing that mechanical strain of key proteins regulates the binding of signaling molecules. Moreover, GAP activity has been shown to switch cell movement from mesenchymal to amoeboid motility, suggesting that mechanical forces directly impact the invasiveness of cancer.

  1. Real time quantum dynamics preaveraged over imaginary time path integral: A formal basis for both Centroid Molecular Dynamics and Ring Polymer Molecular Dynamics

    OpenAIRE

    Jang, Seogjoo

    2013-01-01

    An exact real time quantum dynamics preaveraged over imaginary time path integral is formulated for general condensed phase equilibrium ensemble. This formulation results in the well-known centroid dynamics approach upon filtering of centroid constraint, and provides a rigorous framework to understand and analyze a related quantum dynamics approximation method called ring polymer molecular dynamics. The formulation also serves as the basis for developing new kinds of quantum dynamics that uti...

  2. Nonlocalized cluster dynamics and nuclear molecular structure

    OpenAIRE

    Zhou, Bo; Funaki, Yasuro; Horiuchi, Hisashi; Ren, Zhongzhou; Röpke, Gerd; Schuck, Peter; Tohsaki, Akihiro; Xu, Chang; Yamada, Taiichi

    2013-01-01

    A container picture is proposed for understanding cluster dynamics where the clusters make nonlocalized motion occupying the lowest orbit of the cluster mean-field potential characterized by the size parameter $``B"$ in the THSR (Tohsaki-Horiuchi-Schuck-R\\"{o}pke) wave function. The nonlocalized cluster aspects of the inversion-doublet bands in $^{20}$Ne which have been considered as a typical manifestation of localized clustering are discussed. So far unexplained puzzling features of the THS...

  3. EXCITON DYNAMICS IN ORGANIC MOLECULAR CRYSTALS

    OpenAIRE

    A. Matsui; Mizuno, K.; Kobayashi, M.

    1985-01-01

    Dynamical behavior of Frenkel excitons in aromatic hydrocarbon crystals, pyrene, α-perylene, β-perylene, and tetracene are overviewed based on the published references and in terms of the self-trap depth. Then pressure-induced instability in exciton states (the change in the self-trap depth) in α-perylene and anthracene is demonstrated and discussed. Finally a quasi-free exciton state is suggested to be the origin of the luminescence in anthracene at room temperature.

  4. On the stochastic dynamics of molecular conformation

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    An important functioning mechanism of biological macromolecules is the transition between different conformed states due to thermal fluctuation. In the present paper, a biological macromolecule is modeled as two strands with side chains facing each other, and its stochastic dynamics including the statistics of stationary motion and the statistics of conformational transition is studied by using the stochastic averaging method for quasi Hamiltonian systems. The theoretical results are confirmed with the results from Monte Carlo simulation.

  5. Theoretical analysis of dynamic processes for interacting molecular motors

    International Nuclear Information System (INIS)

    Biological transport is supported by the collective dynamics of enzymatic molecules that are called motor proteins or molecular motors. Experiments suggest that motor proteins interact locally via short-range potentials. We investigate the fundamental role of these interactions by carrying out an analysis of a new class of totally asymmetric exclusion processes, in which interactions are accounted for in a thermodynamically consistent fashion. This allows us to explicitly connect microscopic features of motor proteins with their collective dynamic properties. A theoretical analysis that combines various mean-field calculations and computer simulations suggests that the dynamic properties of molecular motors strongly depend on the interactions, and that the correlations are stronger for interacting motor proteins. Surprisingly, it is found that there is an optimal strength of interactions (weak repulsion) that leads to a maximal particle flux. It is also argued that molecular motor transport is more sensitive to attractive interactions. Applications of these results for kinesin motor proteins are discussed. (paper)

  6. Molecular dynamics insights into human aquaporin 2 water channel.

    Science.gov (United States)

    Binesh, A R; Kamali, R

    2015-12-01

    In this study, the first molecular dynamics simulation of the human aquaporin 2 is performed and for a better understanding of the aquaporin 2 permeability performance, the characteristics of water transport in this protein channel and key biophysical parameters of AQP2 tetramer including osmotic and diffusive permeability constants and the pore radius are investigated. For this purpose, recently recovered high resolution X-ray crystal structure of` the human aquaporin 2 is used to perform twenty nanosecond molecular dynamics simulation of fully hydrated tetramer of this protein embedded in a lipid bilayer. The resulting water permeability characteristics of this protein channel showed that the water permeability of the human AQP2 is in a mean range in comparison with other human aquaporins family. Finally, the results reported in this research demonstrate that molecular dynamics simulation of human AQP2 provided useful insights into the mechanisms of water permeation and urine concentration in the human kidney. PMID:26489820

  7. Trapping dynamics of diindenoperylene (DIP) in self-assembled monolayers using molecular simulation

    KAUST Repository

    Kaushik, Ananth P.

    2011-07-01

    All-atom Molecular Dynamics simulation methods employing a well-tested intermolecular potential model, MM3 (Molecular Mechanics 3), demonstrate the propensity for diindenoperylene (DIP) molecules to insert between molecules of a self-assembled monolayer (SAM) during a deposition process intended to grow a thin film of this organic semiconductor molecule onto the surface of self-assembled monolayers. The tendency to insert between SAM molecules is fairly prevalent at normal growth temperatures and conditions, but is most strongly dependent on the density and the nature of the SAM. We posit the existence of an optimal density to favor surface adsorption over insertion for this system. DIP is less likely to insert in fluorinated SAMs, like FOTS (fluorooctatrichlorosilane), than its unfluorinated analog, OTS (octatrichlorosilane). It is also less likely to insert between shorter SAMs (e.g., less insertion in OTS than ODTS (octadecyltrichlorosilane)). Very short length, surface-coating molecules, like HDMS (hexamethyldisilazane), are more likely to scatter energetic incoming DIP molecules with little insertion on first impact (depending on the incident energy of the DIP molecule). Grazing angles of incidence of the depositing molecules generally favor surface adsorption, at least in the limit of low coverage, but are shown to be dependent on the nature of the SAM. The validity of these predictions is confirmed by comparison of the predicted sticking coefficients of DIP at a variety of incident energies on OTS, ODTS, and FOTS SAMs with results obtained experimentally by Desai et al. (2010) [23]. The simulation predictions of the tendency of DIP to insert can be explained, in large part, in terms of binding energies between SAM and DIP molecules. However, we note that entropic and stochastic events play a role in the deposition outcomes. Preliminary studies of multiple deposition events, emulating growth, show an unexpected diffusion of DIP molecules inserted within the

  8. Molecular phenomena in dynamic wetting: superspreading and precursors

    OpenAIRE

    Isele-Holder, Rolf Erwin

    2015-01-01

    Wetting is a multiscale process that can be controlled simultaneously by complex flow patterns on the macroscale and contact line phenomena at the Ångstrom scale. While resolving the latter scale is often circumvented by usage of boundary conditions, there are molecular wetting phenomena in which this approach is infeasible. The focus of this study is to use molecular dynamics simulations to examine two of these phenomena: superspreading, the ultra-rapid wetting of aqueous solutions facilitat...

  9. Polarizable Molecular Dynamics in a Polarizable Continuum Solvent

    OpenAIRE

    Lipparini, Filippo; Lagardère, Louis; Raynaud, Christophe; Stamm, Benjamin; Cancès, Eric; Mennucci, Benedetta; Schnieders, Michael; Ren, Pengyu; Maday, Yvon; Piquemal, Jean-Philip

    2015-01-01

    We present for the first time scalable polarizable molecular dynamics (MD) simulations within a polarizable continuum solvent with molecular shape cavities and exact solution of the mutual polarization. The key ingredients are a very efficient algorithm for solving the equations associated with the polarizable continuum, in particular, the domain decomposition Conductor-like Screening Model (ddCOSMO), a rigorous coupling of the continuum with the polarizable force field achieved through a rob...

  10. Molecular Dynamics Computer Simulations of Multidrug RND Efflux Pumps

    OpenAIRE

    Paolo Ruggerone; Vargiu, Attilio V.; Francesca Collu; Nadine Fischer; Christian Kandt

    2013-01-01

    Over-expression of multidrug efflux pumps of the Resistance Nodulation Division (RND) protein super family counts among the main causes for microbial resistance against pharmaceuticals. Understanding the molecular basis of this process is one of the major challenges of modern biomedical research, involving a broad range of experimental and computational techniques. Here we review the current state of RND transporter investigation employing molecular dynamics simulations providing conformation...

  11. Driving ordering processes in molecular-dynamics simulations.

    Science.gov (United States)

    Dittmar, Harro; Kusalik, Peter G

    2014-05-16

    Self-organized criticality describes the emergence of complexity in dynamical nonequilibrium systems. In this paper we introduce a unique approach whereby a driven energy conversion is utilized as a sampling bias for ordered arrangements in molecular dynamics simulations of atomic and molecular fluids. This approach gives rise to dramatically accelerated nucleation rates, by as much as 30 orders of magnitude, without the need of predefined order parameters, which commonly employed rare-event sampling methods rely on. The measured heat fluxes suggest how the approach can be generalized. PMID:24877946

  12. Finite Temperature Infrared Spectra from Polarizable Molecular Dynamics Simulations.

    Science.gov (United States)

    Semrouni, David; Sharma, Ashwani; Dognon, Jean-Pierre; Ohanessian, Gilles; Clavaguéra, Carine

    2014-08-12

    Infrared spectra of biomolecules are obtained from molecular dynamics simulations at finite temperature using the AMOEBA force field. Diverse examples are presented such as N-methylacetamide and its derivatives and a helical peptide. The computed spectra from polarizable molecular dynamics are compared in each case to experimental ones at various temperatures. The role of high-level electrostatic treatment and explicit polarization, including parameters improvements, is highlighted for obtaining spectral sensitivity to the environment including hydrogen bonds and water molecules and a better understanding of the observed experimental bands. PMID:26588289

  13. The application of molecular dynamics in the uracil

    International Nuclear Information System (INIS)

    Under the (N, V, T) system, the position, speed, strength and direction of under stress and the changes of bond distance and bond angle of the evolution of each atom in uracil molecule are calculated by using the semiempirical molecular dynamics. The calculations come to the conclusions which are difficult or failed to be obtained on the microcosmic information of particles during the experiment be- cause of the limit of today's technology. It is to provide the theoretical basis that will go a step further to know molecular inner dynamics. (authors)

  14. State-to-state dynamics of molecular energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Gentry, W.R.; Giese, C.F. [Univ. of Minnesota, Minneapolis (United States)

    1993-12-01

    The goal of this research program is to elucidate the elementary dynamical mechanisms of vibrational and rotational energy transfer between molecules, at a quantum-state resolved level of detail. Molecular beam techniques are used to isolate individual molecular collisions, and to control the kinetic energy of collision. Lasers are used both to prepare specific quantum states prior to collision by stimulated-emission pumping (SEP), and to measure the distribution of quantum states in the collision products by laser-induced fluorescence (LIF). The results are interpreted in terms of dynamical models, which may be cast in a classical, semiclassical or quantum mechanical framework, as appropriate.

  15. Femtochemistry and femtobiology ultrafast dynamics in molecular science

    CERN Document Server

    Douhal, Abderrazzak

    2002-01-01

    This book contains important contributions from top international scientists on the-state-of-the-art of femtochemistry and femtobiology at the beginning of the new millennium. It consists of reviews and papers on ultrafast dynamics in molecular science.The coverage of topics highlights several important features of molecular science from the viewpoint of structure (space domain) and dynamics (time domain). First of all, the book presents the latest developments, such as experimental techniques for understanding ultrafast processes in gas, condensed and complex systems, including biological mol

  16. Detachment of semiflexible polymer chains from a substrate: A molecular dynamics investigation

    Energy Technology Data Exchange (ETDEWEB)

    Paturej, J. [Leibniz-Institut of Poslymer Research Dresden, 01069 Dresden (Germany); Institute of Physics, University of Szczecin, Wielkopolska 15, 70451 Szczecin (Poland); Erbas, A. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States); Milchev, A. [Institute for Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Rostiashvili, V. G. [Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany)

    2014-12-07

    Using Molecular Dynamics simulations, we study the force-induced detachment of a coarse-grained model polymer chain from an adhesive substrate. One of the chain ends is thereby pulled at constant speed off the attractive substrate and the resulting saw-tooth profile of the measured mean force 〈f〉 vs height D of the end-segment over the plane is analyzed for a broad variety of parameters. It is shown that the observed characteristic oscillations in the 〈f〉-D profile depend on the bending and not on the torsional stiffness of the detached chains. Allowing for the presence of hydrodynamic interactions (HI) in a setup with explicit solvent and dissipative particle dynamics-thermostat, rather than the case of Langevin thermostat, one finds that HI have little effect on the 〈f〉-D profile. Also the change of substrate affinity with respect to the solvent from solvophilic to solvophobic is found to play negligible role in the desorption process. In contrast, a changing ratio ε{sub s}{sup B}/ε{sub s}{sup A} of the binding energies of A- and B-segments in the detachment of an AB-copolymer from adhesive surface strongly changes the 〈f〉-D profile whereby the B-spikes vanish when ε{sub s}{sup B}/ε{sub s}{sup A}<0.15. Eventually, performing an atomistic simulation of (bio)-polymers, we demonstrate that the simulation results, derived from our coarse-grained model, comply favorably with those from the all-atom simulation.

  17. Electron-phonon interaction within classical molecular dynamics

    Science.gov (United States)

    Tamm, A.; Samolyuk, G.; Correa, A. A.; Klintenberg, M.; Aabloo, A.; Caro, A.

    2016-07-01

    We present a model for nonadiabatic classical molecular dynamics simulations that captures with high accuracy the wave-vector q dependence of the phonon lifetimes, in agreement with quantum mechanics calculations. It is based on a local view of the e -ph interaction where individual atom dynamics couples to electrons via a damping term that is obtained as the low-velocity limit of the stopping power of a moving ion in a host. The model is parameter free, as its components are derived from ab initio-type calculations, is readily extended to the case of alloys, and is adequate for large-scale molecular dynamics computer simulations. We also show how this model removes some oversimplifications of the traditional ionic damped dynamics commonly used to describe situations beyond the Born-Oppenheimer approximation.

  18. Shapiro like steps reveals molecular nanomagnets' spin dynamics

    Science.gov (United States)

    Abdollahipour, Babak; Abouie, Jahanfar; Ebrahimi, Navid

    2015-09-01

    We present an accurate way to detect spin dynamics of a nutating molecular nanomagnet by inserting it in a tunnel Josephson junction and studying the current voltage (I-V) characteristic. The spin nutation of the molecular nanomagnet is generated by applying two circularly polarized magnetic fields. We demonstrate that modulation of the Josephson current by the nutation of the molecular nanomagnet's spin appears as a stepwise structure like Shapiro steps in the I-V characteristic of the junction. Width and heights of these Shapiro-like steps are determined by two parameters of the spin nutation, frequency and amplitude of the nutation, which are simply tuned by the applied magnetic fields.

  19. A Coupling Tool for Parallel Molecular Dynamics-Continuum Simulations

    KAUST Repository

    Neumann, Philipp

    2012-06-01

    We present a tool for coupling Molecular Dynamics and continuum solvers. It is written in C++ and is meant to support the developers of hybrid molecular - continuum simulations in terms of both realisation of the respective coupling algorithm as well as parallel execution of the hybrid simulation. We describe the implementational concept of the tool and its parallel extensions. We particularly focus on the parallel execution of particle insertions into dense molecular systems and propose a respective parallel algorithm. Our implementations are validated for serial and parallel setups in two and three dimensions. © 2012 IEEE.

  20. Imaging the molecular dynamics of dissociative electron attachment to water

    Energy Technology Data Exchange (ETDEWEB)

    Adaniya, Hidihito; Rudek, B.; Osipov, Timur; Haxton, Dan; Weber, Thorsten; Rescigno, Thomas N.; McCurdy, C.W.; Belkacem, Ali

    2009-10-19

    Momentum imaging experiments on dissociative electron attachment to the water molecule are combined with ab initio theoretical calculations of the angular dependence of the quantum mechanical amplitude for electron attachment to provide a detailed picture of the molecular dynamics of dissociation attachment via the two lowest energy Feshbach resonances. The combination of momentum imaging experiments and theory can reveal dissociation dynamics for which the axial recoil approximation breaks down and thus provides a powerful reaction microscope for DEA to polyatomics.

  1. Molecular Dynamics Simulations of Poly(dimethylsiloxane) Properties

    Czech Academy of Sciences Publication Activity Database

    Fojtíková, J.; Kalvoda, L.; Sedlák, Petr

    2015-01-01

    Roč. 128, č. 4 (2015), s. 637-639. ISSN 0587-4246 R&D Projects: GA ČR GB14-36566G Institutional support: RVO:61388998 Keywords : molecular dynamics * poly(dimethylsiloxane) * dissipative particle dynamics Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.530, year: 2014 http://przyrbwn.icm.edu.pl/APP/PDF/128/a128z4p40.pdf

  2. Molecular Dynamics Simulation of Nitrobenzene Dioxygenase Using AMBER Force Field

    OpenAIRE

    Pabis, Anna; Geronimo, Inacrist; York, Darrin M.; Paneth, Piotr

    2014-01-01

    Molecular dynamics simulation of the oxygenase component of nitrobenzene dioxygenase (NBDO) system, a member of the naphthalene family of Rieske nonheme iron dioxygenases, has been carried out using the AMBER force field combined with a new set of parameters for the description of the mononuclear nonheme iron center and iron–sulfur Rieske cluster. Simulation results provide information on the structure and dynamics of nitrobenzene dioxygenase in an aqueous environment and shed light on specif...

  3. Molecular Dynamics Study of Iron-Nickel Alloys

    OpenAIRE

    Meyer, R.; Entel, P.

    1995-01-01

    We present results of molecular dynamics simulations of disordered iron-nickel alloys. In particular we discuss the α-γ transition and associated anharmonic properties by making use of semiempirical potentials. Our results show that the structural transformation in these alloys is driven by local disorder. From data of specific heat and thermal expansion we conclude that the lattice dynamics at elevated temperatures (above the Curie temperature) can be described correctly without considering ...

  4. ProtoMD: A Prototyping Toolkit for Multiscale Molecular Dynamics

    OpenAIRE

    Somogyi, Endre; Mansour, Andrew Abi; Ortoleva, Peter J.

    2013-01-01

    ProtoMD is a toolkit that facilitates the development of algorithms for multiscale molecular dynamics (MD) simulations. It is designed for multiscale methods which capture the dynamic transfer of information across multiple spatial scales, such as the atomic to the mesoscopic scale, via coevolving microscopic and coarse-grained (CG) variables. ProtoMD can be also be used to calibrate parameters needed in traditional CG-MD methods. The toolkit integrates `GROMACS wrapper' to initiate MD simula...

  5. RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    OpenAIRE

    Allen, Joshua W.; Green, William H; Suleimanov, Yu. V.

    2013-01-01

    We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett–Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any ...

  6. Micellar Crystals in Solution from Molecular Dynamics Simulations

    OpenAIRE

    Anderson, J A; Lorenz, C. D.; Travesset, A.

    2008-01-01

    Polymers with both soluble and insoluble blocks typically self-assemble into micelles, aggregates of a finite number of polymers where the soluble blocks shield the insoluble ones from contact with the solvent. Upon increasing concentration, these micelles often form gels that exhibit crystalline order in many systems. In this paper, we present a study of both the dynamics and the equilibrium properties of micellar crystals of triblock polymers using molecular dynamics simulations. Our result...

  7. Dynamics of excess electrons in atomic and molecular clusters

    OpenAIRE

    Young, Ryan Michael

    2011-01-01

    Femtosecond time-resolved photoelectron imaging (TRPEI) is applied to the study of excess electrons in clusters as well as to microsolvated anion species. This technique can be used to perform explicit time-resolved as well as one-color (single- or multiphoton) studies on gas phase species. The first part of this dissertation details time-resolved studies done on atomic clusters with an excess electron, the excited-state dynamics of solvated molecular anions, and charge-transfer dynamics to...

  8. Investigation of nuclear multifragmentation using molecular dynamics and restructured aggregation

    International Nuclear Information System (INIS)

    We study the stability of excited 197 Au nuclei with respect to multifragmentation. For that we use a dynamical simulation based on molecular dynamics and restructured aggregation. A particular attention is paid to check the stability of the ground state nuclei generated by the simulation. Four kinds of excitations are considered: heat, compression, rotation and a geometrical instability created when a projectile drills a hole in a 197 Au nucleus

  9. Deposition of Small Clusters on Surface: a Molecular Dynamics Simulation

    Institute of Scientific and Technical Information of China (English)

    DUAN Xiang-Mei; GONG Xin-Gao

    2000-01-01

    By using the molecular dynamics simulation, we have studied the dynamic behaviors of small energetic clusters deposited on the surface. We find that, at incident energy as low as 1.0eV/atom, the structure of the cluster is destroyed and cluster atoms form an epitaxial layer above the surface. At high energy incidence, the site exchange between cluster atom and surface atom is observed. The effects of the cluster size and orientation are discussed.

  10. The origin of chiral discrimination: supersonic molecular beam experiments and molecular dynamics simulations of collisional mechanisms

    International Nuclear Information System (INIS)

    The target of the present paper is the study of chirality effects in molecular dynamics from both a theoretical and an experimental point of view under the hypothesis of a molecular dynamics mechanism as the origin of chiral discrimination. This is a fundamental problem per se, and of possible relevance for the problem of the intriguing homochirality in Nature, so far lacking satisfactory explanations. We outline the steps that have been taken so far toward this direction, motivated by various experimental studies of supersonic molecular beams carried out in this laboratory, such as the detection of aligned oxygen in gaseous streams and further evidence on nitrogen, benzene and various hydrocarbons, showing the insurgence of molecular orientation in the dynamics of molecules in flows and in molecular collisions. Chiral effects are theoretically demonstrated to show up in the differential scattering of oriented molecules, also when impinging on surfaces. Focus on possible mechanisms for chiral bio-stereochemistry of oriented reactants may be of pre-biotical interest, for example when flowing in atmospheres of rotating bodies, specifically the planet Earth, as well as in vortex motions of celestial objects. Molecular dynamics simulations and experimental verifications of the hypothesis are reviewed and objectives of future research activity proposed.

  11. The origin of chiral discrimination: supersonic molecular beam experiments and molecular dynamics simulations of collisional mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Aquilanti, Vincenzo; Grossi, Gaia; Lombardi, Andrea; Maciel, Glauciete S; Palazzetti, Federico [Dipartimento di Chimica, Universita di Perugia, Via Elce di Sotto 8, 06123 Perugia (Italy)], E-mail: abulafia@dyn.unipg.it

    2008-10-15

    The target of the present paper is the study of chirality effects in molecular dynamics from both a theoretical and an experimental point of view under the hypothesis of a molecular dynamics mechanism as the origin of chiral discrimination. This is a fundamental problem per se, and of possible relevance for the problem of the intriguing homochirality in Nature, so far lacking satisfactory explanations. We outline the steps that have been taken so far toward this direction, motivated by various experimental studies of supersonic molecular beams carried out in this laboratory, such as the detection of aligned oxygen in gaseous streams and further evidence on nitrogen, benzene and various hydrocarbons, showing the insurgence of molecular orientation in the dynamics of molecules in flows and in molecular collisions. Chiral effects are theoretically demonstrated to show up in the differential scattering of oriented molecules, also when impinging on surfaces. Focus on possible mechanisms for chiral bio-stereochemistry of oriented reactants may be of pre-biotical interest, for example when flowing in atmospheres of rotating bodies, specifically the planet Earth, as well as in vortex motions of celestial objects. Molecular dynamics simulations and experimental verifications of the hypothesis are reviewed and objectives of future research activity proposed.

  12. Simplistic Coulomb Forces in Molecular Dynamics

    DEFF Research Database (Denmark)

    Hansen, Jesper Schmidt; Schrøder, Thomas; Dyre, J. C.

    2012-01-01

    salt model the SF approximation overall reproduces the structural and dynamical properties as accurately as does the Wolf method. It is shown that the optimal Wolf damping parameter depends on the property in focus and that neither the potential energy nor the radial distribution function are useful...... measures for the convergence of the Wolf method to the Ewald summation method. The SF approximation is also tested for the SPC/Fw model of liquid water at room temperature, showing good agreement with both the Wolf and the particle mesh Ewald methods; this confirms previous findings [Fennell, C. J......In this paper we compare the Wolf method to the shifted forces (SF) method for efficient computer simulation of bulk systems with Coulomb forces, taking results from the Ewald summation and particle mesh Ewald methods as representing the true behavior. We find that for the Hansen–McDonald molten...

  13. Superspreading: molecular dynamics simulations and experimental results

    Science.gov (United States)

    Theodorakis, Panagiotis; Kovalchuk, Nina; Starov, Victor; Muller, Erich; Craster, Richard; Matar, Omar

    2015-11-01

    The intriguing ability of certain surfactant molecules to drive the superspreading of liquids to complete wetting on hydrophobic substrates is central to numerous applications that range from coating flow technology to enhanced oil recovery. Recently, we have observed that for superspreading to occur, two key conditions must be simultaneously satisfied: the adsorption of surfactants from the liquid-vapor surface onto the three-phase contact line augmented by local bilayer formation. Crucially, this must be coordinated with the rapid replenishment of liquid-vapor and solid-liquid interfaces with surfactants from the interior of the droplet. Here, we present the structural characteristics and kinetics of the droplet spreading during the different stages of this process, and we compare our results with experimental data for trisiloxane and poly oxy ethylene surfactants. In this way, we highlight and explore the differences between surfactants, paving the way for the design of molecular architectures tailored specifically for applications that rely on the control of wetting. EPSRC Platform Grant MACIPh (EP/L020564/).

  14. Molecular circuits for dynamic noise filtering.

    Science.gov (United States)

    Zechner, Christoph; Seelig, Georg; Rullan, Marc; Khammash, Mustafa

    2016-04-26

    The invention of the Kalman filter is a crowning achievement of filtering theory-one that has revolutionized technology in countless ways. By dealing effectively with noise, the Kalman filter has enabled various applications in positioning, navigation, control, and telecommunications. In the emerging field of synthetic biology, noise and context dependency are among the key challenges facing the successful implementation of reliable, complex, and scalable synthetic circuits. Although substantial further advancement in the field may very well rely on effectively addressing these issues, a principled protocol to deal with noise-as provided by the Kalman filter-remains completely missing. Here we develop an optimal filtering theory that is suitable for noisy biochemical networks. We show how the resulting filters can be implemented at the molecular level and provide various simulations related to estimation, system identification, and noise cancellation problems. We demonstrate our approach in vitro using DNA strand displacement cascades as well as in vivo using flow cytometry measurements of a light-inducible circuit in Escherichia coli. PMID:27078094

  15. Thermostatted molecular dynamics: How to avoid the Toda demon hidden in Nose-Hoover dynamics

    International Nuclear Information System (INIS)

    The Nose-Hoover thermostat, which is often used in the hope of modifying molecular dynamics trajectories in order to achieve canonical-ensemble averages, has hidden in it a Toda ''demon,'' which can give rise to unwanted, noncanonical undulations in the instantaneous kinetic temperature. We show how these long-lived oscillations arise from insufficient coupling of the thermostat to the atoms, and give straightforward, practical procedures for avoiding this weak-coupling pathology in isothermal molecular dynamics simulations

  16. Stability of molecular dynamics simulations of classical systems

    DEFF Research Database (Denmark)

    Toxværd, Søren

    2012-01-01

    The existence of a shadow Hamiltonian for discrete classical dynamics, obtained by an asymptotic expansion for a discrete symplectic algorithm, is employed to determine the limit of stability for molecular dynamics (MD) simulations with respect to the time-increment h of the discrete dynamics....... The method is also used to investigate higher-order central difference algorithms, which are symplectic and also have shadow Hamiltonians, and for which one can also determine the exact criteria for the limit of stability of a single harmonic mode. A fourth-order central difference algorithm gives...

  17. Probing Molecular Dynamics by Laser-Induced Backscattering Holography

    Science.gov (United States)

    Haertelt, Marko; Bian, Xue-Bin; Spanner, Michael; Staudte, André; Corkum, Paul B.

    2016-04-01

    We use differential holography to overcome the forward scattering problem in strong-field photoelectron holography. Our differential holograms of H2 and D2 molecules exhibit a fishbonelike structure, which arises from the backscattered part of the recolliding photoelectron wave packet. We demonstrate that the backscattering hologram can resolve the different nuclear dynamics between H2 and D2 with subangstrom spatial and subcycle temporal resolution. In addition, we show that attosecond electron dynamics can be resolved. These results open a new avenue for ultrafast studies of molecular dynamics in small molecules.

  18. C60 molecular dynamics studied by muon spin relaxation

    International Nuclear Information System (INIS)

    In muonium-substituted organic radicals, the muon spin can serve as a probe of molecular dynamics. The motional perturbation induces transitions between the coupled spin states of muon and unpaired electron. Studies of the resultant muon spin relaxation in C60Mu, the species formed by muon implantation in solid C60, yield the correlation time characteristic of the reorientational motion

  19. THE REFINEMENT OF NMR STRUCTURES BY MOLECULAR-DYNAMICS SIMULATION

    NARCIS (Netherlands)

    TORDA, AE; VANGUNSTEREN, WF

    1991-01-01

    We discuss the use of molecular dynamics simulations as a tool for the refinement of structures based on NMR data. The procedure always involves the construction of a pseudo-energy term to model the experimental data and we consider the various approaches to this problem. We detail recent work where

  20. Active site modeling in copper azurin molecular dynamics simulations

    NARCIS (Netherlands)

    Rizzuti, B; Swart, M; Sportelli, L; Guzzi, R

    2004-01-01

    Active site modeling in molecular dynamics simulations is investigated for the reduced state of copper azurin. Five simulation runs (5 ns each) were performed at room temperature to study the consequences of a mixed electrostatic/constrained modeling for the coordination between the metal and the po

  1. Reasoning with Atomic-Scale Molecular Dynamic Models

    Science.gov (United States)

    Pallant, Amy; Tinker, Robert F.

    2004-01-01

    The studies reported in this paper are an initial effort to explore the applicability of computational models in introductory science learning. Two instructional interventions are described that use a molecular dynamics model embedded in a set of online learning activities with middle and high school students in 10 classrooms. The studies indicate…

  2. Quantum Molecular Dynamics Simulations of Nanotube Tip Assisted Reactions

    Science.gov (United States)

    Menon, Madhu

    1998-01-01

    In this report we detail the development and application of an efficient quantum molecular dynamics computational algorithm and its application to the nanotube-tip assisted reactions on silicon and diamond surfaces. The calculations shed interesting insights into the microscopic picture of tip surface interactions.

  3. Clustering Molecular Dynamics Trajectories for Optimizing Docking Experiments

    Directory of Open Access Journals (Sweden)

    Renata De Paris

    2015-01-01

    Full Text Available Molecular dynamics simulations of protein receptors have become an attractive tool for rational drug discovery. However, the high computational cost of employing molecular dynamics trajectories in virtual screening of large repositories threats the feasibility of this task. Computational intelligence techniques have been applied in this context, with the ultimate goal of reducing the overall computational cost so the task can become feasible. Particularly, clustering algorithms have been widely used as a means to reduce the dimensionality of molecular dynamics trajectories. In this paper, we develop a novel methodology for clustering entire trajectories using structural features from the substrate-binding cavity of the receptor in order to optimize docking experiments on a cloud-based environment. The resulting partition was selected based on three clustering validity criteria, and it was further validated by analyzing the interactions between 20 ligands and a fully flexible receptor (FFR model containing a 20 ns molecular dynamics simulation trajectory. Our proposed methodology shows that taking into account features of the substrate-binding cavity as input for the k-means algorithm is a promising technique for accurately selecting ensembles of representative structures tailored to a specific ligand.

  4. Molecular Dynamics ofa Coulomb System with Deformable Periodic Boundary Conditions

    OpenAIRE

    Totsuji, Hiroo; Shirokoshi, Hideki; Nara, Shigetoshi

    1991-01-01

    Variable shape molecular dynamics is formulated for the one-component plasma and the structural transition from the fcc lattice to the bcc lattice has been observed. It is emphasized that the condition of constant volume should be imposed when deformations of periodic boundary conditions are taken into account.

  5. Molecular Dynamics Simulations Study on Chiral Room -Temperature Ionic Liquids

    Czech Academy of Sciences Publication Activity Database

    Lísal, Martin; Chvál, Z.; Storch, Jan; Izák, Pavel; Aim, Karel

    Frankfurt : DECHEMA, 2012, P2-35. ISBN N. [European Symposium on Applied Thermodynamics - ESAT 2012 /26./. Potsdam (DE), 07.10.2012-10.10.2012] Institutional support: RVO:67985858 Keywords : ionic liquids * molecular dynamics simulations * thermodynamics properties Subject RIV: CF - Physical ; Theoretical Chemistry http://events.dechema.de/events/en/esat2012.html

  6. Open boundary molecular dynamics of sheared star-polymer melts.

    Science.gov (United States)

    Sablić, Jurij; Praprotnik, Matej; Delgado-Buscalioni, Rafael

    2016-02-28

    Open boundary molecular dynamics (OBMD) simulations of a sheared star polymer melt under isothermal conditions are performed to study the rheology and molecular structure of the melt under a fixed normal load. Comparison is made with the standard molecular dynamics (MD) in periodic (closed) boxes at a fixed shear rate (using the SLLOD dynamics). The OBMD system exchanges mass and momentum with adjacent reservoirs (buffers) where the external pressure tensor is imposed. Insertion of molecules in the buffers is made feasible by implementing there a low resolution model (blob-molecules with soft effective interactions) and then using the adaptive resolution scheme (AdResS) to connect with the bulk MD. Straining with increasing shear stress induces melt expansion and a significantly different redistribution of pressure compared with the closed case. In the open sample, the shear viscosity is also a bit lowered but more stable against the viscous heating. At a given Weissenberg number, molecular deformations and material properties (recoverable shear strain and normal stress ratio) are found to be similar in both setups. We also study the modelling effect of normal and tangential friction between monomers implemented in a dissipative particle dynamics (DPD) thermostat. Interestingly, the tangential friction substantially enhances the elastic response of the melt due to a reduction of the kinetic stress viscous contribution. PMID:26820315

  7. Molecular dynamics simulations on PGLa using NMR orientational constraints

    International Nuclear Information System (INIS)

    NMR data obtained by solid state NMR from anisotropic samples are used as orientational constraints in molecular dynamics simulations for determining the structure and dynamics of the PGLa peptide within a membrane environment. For the simulation the recently developed molecular dynamics with orientational constraints technique (MDOC) is used. This method introduces orientation dependent pseudo-forces into the COSMOS-NMR force field. Acting during a molecular dynamics simulation these forces drive molecular rotations, re-orientations and folding in such a way that the motional time-averages of the tensorial NMR properties are consistent with the experimentally measured NMR parameters. This MDOC strategy does not depend on the initial choice of atomic coordinates, and is in principle suitable for any flexible and mobile kind of molecule; and it is of course possible to account for flexible parts of peptides or their side-chains. MDOC has been applied to the antimicrobial peptide PGLa and a related dimer model. With these simulations it was possible to reproduce most NMR parameters within the experimental error bounds. The alignment, conformation and order parameters of the membrane-bound molecule and its dimer were directly derived with MDOC from the NMR data. Furthermore, this new approach yielded for the first time the distribution of segmental orientations with respect to the membrane and the order parameter tensors of the dimer systems. It was demonstrated the deuterium splittings measured at the peptide to lipid ratio of 1/50 are consistent with a membrane spanning orientation of the peptide

  8. Molecular dynamics simulations on PGLa using NMR orientational constraints

    Energy Technology Data Exchange (ETDEWEB)

    Sternberg, Ulrich, E-mail: ulrich.sternberg@partner.kit.edu; Witter, Raiker [Tallinn University of Technology, Technomedicum (Estonia)

    2015-11-15

    NMR data obtained by solid state NMR from anisotropic samples are used as orientational constraints in molecular dynamics simulations for determining the structure and dynamics of the PGLa peptide within a membrane environment. For the simulation the recently developed molecular dynamics with orientational constraints technique (MDOC) is used. This method introduces orientation dependent pseudo-forces into the COSMOS-NMR force field. Acting during a molecular dynamics simulation these forces drive molecular rotations, re-orientations and folding in such a way that the motional time-averages of the tensorial NMR properties are consistent with the experimentally measured NMR parameters. This MDOC strategy does not depend on the initial choice of atomic coordinates, and is in principle suitable for any flexible and mobile kind of molecule; and it is of course possible to account for flexible parts of peptides or their side-chains. MDOC has been applied to the antimicrobial peptide PGLa and a related dimer model. With these simulations it was possible to reproduce most NMR parameters within the experimental error bounds. The alignment, conformation and order parameters of the membrane-bound molecule and its dimer were directly derived with MDOC from the NMR data. Furthermore, this new approach yielded for the first time the distribution of segmental orientations with respect to the membrane and the order parameter tensors of the dimer systems. It was demonstrated the deuterium splittings measured at the peptide to lipid ratio of 1/50 are consistent with a membrane spanning orientation of the peptide.

  9. Molecular dynamics of flows in the Knudsen regime

    OpenAIRE

    Cieplak, Marek; Koplik, Joel; Banavar, Jayanth R.

    2000-01-01

    Novel technological applications often involve fluid flows in the Knudsen regime in which the mean free path is comparable to the system size. We use molecular dynamics simulations to study the transition between the dilute gas and the dense fluid regimes as the fluid density is increased.

  10. Optimizing legacy molecular dynamics software with directive-based offload

    Science.gov (United States)

    Michael Brown, W.; Carrillo, Jan-Michael Y.; Gavhane, Nitin; Thakkar, Foram M.; Plimpton, Steven J.

    2015-10-01

    Directive-based programming models are one solution for exploiting many-core coprocessors to increase simulation rates in molecular dynamics. They offer the potential to reduce code complexity with offload models that can selectively target computations to run on the CPU, the coprocessor, or both. In this paper, we describe modifications to the LAMMPS molecular dynamics code to enable concurrent calculations on a CPU and coprocessor. We demonstrate that standard molecular dynamics algorithms can run efficiently on both the CPU and an x86-based coprocessor using the same subroutines. As a consequence, we demonstrate that code optimizations for the coprocessor also result in speedups on the CPU; in extreme cases up to 4.7X. We provide results for LAMMPS benchmarks and for production molecular dynamics simulations using the Stampede hybrid supercomputer with both Intel®  Xeon Phi™ coprocessors and NVIDIA GPUs. The optimizations presented have increased simulation rates by over 2X for organic molecules and over 7X for liquid crystals on Stampede. The optimizations are available as part of the "Intel package" supplied with LAMMPS.

  11. Molecular dynamics simulation of the Ni(001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Chirita, V.; Pailthorpe, B.A. (School of Physics, Univ. of Sydney, New South Wales (Australia))

    1992-02-10

    A Lennard-Jones two-body interatomic potential is used in a molecular dynamics simulation of bulk nickel and of the Ni(001) surface stabilized using a Dion-Barker-Merrill substrate interaction. It is found that the bulk and surface Debye temperatures and surface atomic displacements compare well with previous theoretical and experimental studies. (orig.).

  12. Enhanced molecular dynamics performance with a programmable graphics processor

    CERN Document Server

    Rapaport, D C

    2009-01-01

    Design considerations for molecular dynamics algorithms capable of taking advantage of the computational power of a graphics processing unit (GPU) are described. Accommodating the constraints of multistream processor hardware necessitates a reformulation of the underlying algorithm. Performance measurements demonstrate the considerable benefit and cost-effectiveness of such an approach.

  13. A Molecular Dynamics Approach to Grain Boundary Structure and Migration

    DEFF Research Database (Denmark)

    Cotterill, R. M. J.; Leffers, Torben; Lilholt, Hans

    1974-01-01

    It has been demonstrated that grain boundary formation from the melt can be simulated by the molecular dynamics method. The space between two mutually-misoriented crystal slabs was filled with atoms in a random manner and this liquid was then cooled until crystallization occurred. The general...

  14. Molecular dynamics simulation of a charged biological membrane

    NARCIS (Netherlands)

    López Cascales, J.J.; García de la Torre, J.; Marrink, S.J.; Berendsen, H.J.C.

    1996-01-01

    A molecular dynamics simulation of a membrane with net charge in its liquid-crystalline state was carried out. It was modeled by dipalmitoylphosphatidylserine lipids with net charge, sodium ions as counterions and water molecules. The behavior of this membrane differs from that was shown by other me

  15. Molecular dynamics simulations of n-hexane at 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide interface

    International Nuclear Information System (INIS)

    Molecular dynamics simulations of n-hexane adsorbed onto the interface of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([bmim][Tf2N]) are performed at three n-hexane surface densities, ranged from 0.7 to 2.3 μmol/m2 at 300 K. For [bmim][Tf2N] room-temperature ionic liquid, we use a non-polarizable all-atom force field with the partial atomic charges based on ab initio calculations for the isolated ion pair. The net charges of the ions are ±0.89e, which mimics the anion to cation charge transfer and polarization effects. The OPLS-AA force field is employed for modeling of n-hexane. The surface tension is computed using the mechanical route and its value decreases with increase of the n-hexane surface density. The [bmim][Tf2N]/n-hexane interface is analyzed using the intrinsic method, and the structural and dynamic properties of the interfacial, sub-interfacial, and central layers are computed. We determine the surface roughness, global and intrinsic density profiles, and orientation ordering of the molecules to describe the structure of the interface. We further compute the survival probability, normal and lateral self-diffusion coefficients, and re-orientation correlation functions to elucidate the effects of n-hexane on dynamics of the cations and anions in the layers

  16. pH dependence of ligand-induced human epidermal growth factor receptor activation investigated by molecular dynamics simulations.

    Science.gov (United States)

    Dong, Jun; Zhang, Yonghui; Zhang, Zhiyong

    2016-06-01

    The activation of human epidermal growth factor receptor (hEGFR) involves a large conformational change in its soluble extracellular domains (sECD, residues 1-620), from a tethered to an extended conformation upon binding of ligands, such as EGF. It has been reported that this dynamic process is pH-dependent, that is, hEGFR can be activated by EGF at high pH to form an extended dimer but remains as an inactive monomer at low pH. In this paper, we perform all-atom molecular dynamics (MD) simulations starting from the tethered conformation of sECD:EGF complex, at pH 5.0 and 8.5, respectively. Simulation results indicate that sECD:EGF shows different dynamic properties between the two pHs, and the complex may have a higher tendency of activation at pH 8.5. Twenty residues, including 13 histidines, in sECD:EGF have different protonation states between the two pHs (calculated by the H++ server). The charge distribution at pH 8.5 is more favorable for forming an extended conformation toward the active state of sECD than that at pH 5.0. Our study may shed light on the mechanism of pH dependence of hEGFR activation. Graphical abstract pH dependence of ligand-induced human epidermal growth factor receptor activation. PMID:27179806

  17. Watching coherent molecular structural dynamics during photoreaction: beyond kinetic description

    CERN Document Server

    Lemke, Henrik T; Hartsock, Robert; van Driel, Tim Brandt; Chollet, Matthieu; Glownia, J M; Song, Sanghoon; Zhu, Diling; Pace, Elisabetta; Nielsen, Martin M; Benfatto, Maurizio; Gaffney, Kelly J; Collet, Eric; Cammarata, Marco

    2015-01-01

    A deep understanding of molecular photo-transformations occurring is challenging because of the complex interaction between electronic and nuclear structure. The initially excited electronic energy dissipates into electronic and structural reconfigurations often in less than a billionth of a second. Molecular dynamics induced by photoexcitation have been very successfully studied with femtosecond optical spectroscopies, but electronic and nuclear dynamics are often very difficult to disentangle. X-ray based spectroscopies can reduce the ambiguity between theoretical models and experimental data, but it is only with the recent development of bright ultrafast X-ray sources, that key information during transient molecular processes can be obtained on their intrinsic timescale. We use Free Electron Laser (FEL) based time-resolved X-ray Absorption Near Edge Structure (XANES) measurements around the Iron K-edge of a spin crossover prototypical compound. We reveal its transformation from the ligand-located electroni...

  18. Collisional dynamics in a gas of molecular super-rotors

    Science.gov (United States)

    Khodorkovsky, Yuri; Steinitz, Uri; Hartmann, Jean-Michel; Averbukh, Ilya Sh.

    2015-07-01

    Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable `gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational-translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the `gyroscopic stage' is abruptly terminated by an explosive rotational-translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules.

  19. Influence of conformational molecular dynamics on matter wave interferometry

    CERN Document Server

    Gring, Michael; Eibenberger, Sandra; Nimmrichter, Stefan; Berrada, Tarik; Arndt, Markus; Ulbricht, Hendrik; Hornberger, Klaus; Müri, Marcel; Mayor, Marcel; Böckmann, Marcus; Doltsinis, Nikos

    2014-01-01

    We investigate the influence of thermally activated internal molecular dynamics on the phase shifts of matter waves inside a molecule interferometer. While de Broglie physics generally describes only the center-of-mass motion of a quantum object, our experiment demonstrates that the translational quantum phase is sensitive to dynamic conformational state changes inside the diffracted molecules. The structural flexibility of tailor-made hot organic particles is sufficient to admit a mixture of strongly fluctuating dipole moments. These modify the electric susceptibility and through this the quantum interference pattern in the presence of an external electric field. Detailed molecular dynamics simulations combined with density functional theory allow us to quantify the time-dependent structural reconfigurations and to predict the ensemble-averaged square of the dipole moment which is found to be in good agreement with the interferometric result. The experiment thus opens a new perspective on matter wave interfe...

  20. Molecular dynamics computer simulation of permeation in solids

    Energy Technology Data Exchange (ETDEWEB)

    Pohl, P.I.; Heffelfinger, G.S.; Fisler, D.K.; Ford, D.M. [Sandia National Labs., Albuquerque, NM (United States)

    1997-12-31

    In this work the authors simulate permeation of gases and cations in solid models using molecular mechanics and a dual control volume grand canonical molecular dynamics technique. The molecular sieving nature of microporous zeolites are discussed and compared with that for amorphous silica made by sol-gel methods. One mesoporous and one microporous membrane model are tested with Lennard-Jones gases corresponding to He, H{sub 2}, Ar and CH{sub 4}. The mesoporous membrane model clearly follows a Knudsen diffusion mechanism, while the microporous model having a hard-sphere cutoff pore diameter of {approximately}3.4 {angstrom} demonstrates molecular sieving of the methane ({sigma} = 3.8 {angstrom}) but anomalous behavior for Ar ({sigma} = 3.4 {angstrom}). Preliminary results of Ca{sup +} diffusion in calcite and He/H{sub 2} diffusion in polyisobutylene are also presented.

  1. Laser-enhanced dynamics in molecular rate processes

    Science.gov (United States)

    George, T. F.; Zimmerman, I. H.; Devries, P. L.; Yuan, J.-M.; Lam, K.-S.; Bellum, J. C.; Lee, H.-W.; Slutsky, M. S.

    1978-01-01

    The present discussion deals with some theoretical aspects associated with the description of molecular rate processes in the presence of intense laser radiation, where the radiation actually interacts with the molecular dynamics. Whereas for weak and even moderately intense radiation, the absorption and stimulated emission of photons by a molecular system can be described by perturbative methods, for intense radiation, perturbation theory is usually not adequate. Limiting the analysis to the gas phase, an attempt is made to describe nonperturbative approaches applicable to the description of such processes (in the presence of intense laser radiation) as electronic energy transfer in molecular (in particular atom-atom) collisions; collision-induced ionization and emission; and unimolecular dissociation.

  2. Molecular dynamics simulations of silicate and borate glasses and melts : structure, diffusion dynamics and vibrational properties

    OpenAIRE

    Scherer, Christoph

    2015-01-01

    Molecular dynamics simulations of silicate and borate glasses and melts: Structure, diffusion dynamics and vibrational properties. In this work computer simulations of the model glass formers SiO2 and B2O3 are presented, using the techniques of classical molecular dynamics (MD) simulations and quantum mechanical calculations, based on density functional theory (DFT). The latter limits the system size to about 100−200 atoms. SiO2 and B2O3 are the two most important network formers for industri...

  3. A stochastic phase-field model determined from molecular dynamics

    KAUST Repository

    von Schwerin, Erik

    2010-03-17

    The dynamics of dendritic growth of a crystal in an undercooled melt is determined by macroscopic diffusion-convection of heat and by capillary forces acting on the nanometer scale of the solid-liquid interface width. Its modelling is useful for instance in processing techniques based on casting. The phase-field method is widely used to study evolution of such microstructural phase transformations on a continuum level; it couples the energy equation to a phenomenological Allen-Cahn/Ginzburg-Landau equation modelling the dynamics of an order parameter determining the solid and liquid phases, including also stochastic fluctuations to obtain the qualitatively correct result of dendritic side branching. This work presents a method to determine stochastic phase-field models from atomistic formulations by coarse-graining molecular dynamics. It has three steps: (1) a precise quantitative atomistic definition of the phase-field variable, based on the local potential energy; (2) derivation of its coarse-grained dynamics model, from microscopic Smoluchowski molecular dynamics (that is Brownian or over damped Langevin dynamics); and (3) numerical computation of the coarse-grained model functions. The coarse-grained model approximates Gibbs ensemble averages of the atomistic phase-field, by choosing coarse-grained drift and diffusion functions that minimize the approximation error of observables in this ensemble average. © EDP Sciences, SMAI, 2010.

  4. Molecular dynamics analysis on impact behavior of carbon nanotubes

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • We present an analytical solution of impact based on two degree of freedom model. • The accuracy is verified by Molecular dynamics simulations. • The effects of the small-size effects on the dynamic deflections are investigated. • The relative motion is also accounted that is due to local indentation. - Abstract: Dynamic analysis of impact of a nanoparticle on carbon nanotubes is investigated based on two degree of freedom model. The accuracy and stability of the present methods are verified by molecular dynamics (MD) simulations. The effect of different types of boundary condition on the maximum dynamic deflections is studied for zigzag and armchair SWCNTs with various aspect ratios (length/diameter). Besides, the influences of velocity of impactor on the dynamic deflections are studied. It is shown that the dynamic behavior on the armchair and zigzag single-walled carbon nanotubes are almost similar. Finally, by making use of the above MD simulation and theoretical results some insight has been obtained about the dynamic characteristics of the impact problems of nanobeam structures. Nonlocal Timoshenko beam models TBT2 should be employed for an accurate prediction of the dynamic deflection rather than nonlocal Euler–Bernoulli beam models EBT2 which ignores the effects of transverse shear deformation and rotary inertia that is especially significant for short beams. The results from nonlocal EBT2 and TBT2 models demonstrated good agreement with MD simulation. The EBT2 and TBT2 models also account for the relative motion between the nanoparticle and the nanobeam that is due to local indentation as can be seen in MD simulation

  5. Molecular dynamics analysis on impact behavior of carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Seifoori, Sajjad, E-mail: sajjad.seifoori@vru.ac.ir

    2015-01-30

    Graphical abstract: - Highlights: • We present an analytical solution of impact based on two degree of freedom model. • The accuracy is verified by Molecular dynamics simulations. • The effects of the small-size effects on the dynamic deflections are investigated. • The relative motion is also accounted that is due to local indentation. - Abstract: Dynamic analysis of impact of a nanoparticle on carbon nanotubes is investigated based on two degree of freedom model. The accuracy and stability of the present methods are verified by molecular dynamics (MD) simulations. The effect of different types of boundary condition on the maximum dynamic deflections is studied for zigzag and armchair SWCNTs with various aspect ratios (length/diameter). Besides, the influences of velocity of impactor on the dynamic deflections are studied. It is shown that the dynamic behavior on the armchair and zigzag single-walled carbon nanotubes are almost similar. Finally, by making use of the above MD simulation and theoretical results some insight has been obtained about the dynamic characteristics of the impact problems of nanobeam structures. Nonlocal Timoshenko beam models TBT2 should be employed for an accurate prediction of the dynamic deflection rather than nonlocal Euler–Bernoulli beam models EBT2 which ignores the effects of transverse shear deformation and rotary inertia that is especially significant for short beams. The results from nonlocal EBT2 and TBT2 models demonstrated good agreement with MD simulation. The EBT2 and TBT2 models also account for the relative motion between the nanoparticle and the nanobeam that is due to local indentation as can be seen in MD simulation.

  6. Molecular Dynamics Simulation of DNA Capture and Transport in Heated Nanopores.

    Science.gov (United States)

    Belkin, Maxim; Aksimentiev, Aleksei

    2016-05-25

    The integration of local heat sources with solid-state nanopores offers new means for controlling the transmembrane transport of charged biomacromolecules. In the case of electrophoretic transport of DNA, recent experimental studies revealed unexpected temperature dependences of the DNA capture rate, the DNA translocation velocity, and the ionic current blockades produced by the presence of DNA in the nanopore. Here, we report the results of all-atom molecular dynamics simulations that elucidated the effect of temperature on the key microscopic processes governing electric field-driven transport of DNA through nanopores. Mimicking the experimental setup, we simulated the capture and subsequent translocation of short DNA duplexes through a locally heated nanopore at several temperatures and electrolyte conditions. The temperature dependence of ion mobility at the DNA surface was found to cause the dependence of the relative conductance blockades on temperature. To the first order, the effective force on DNA in the nanopore was found to be independent of temperature, despite a considerable reduction of solution viscosity. The temperature dependence of the solution viscosity was found to make DNA translocations faster for a uniformly heated system but not in the case of local heating that does not affect viscosity of solution surrounding the untranslocated part of the molecule. Increasing solution temperature was also found to reduce the lifetime of bonds formed between cations and DNA. Using a flow suppression algorithm, we were able to separate the effects of electro-osmotic flow and direct ion binding, finding the reduced durations of DNA-ion bonds to increase, albeit weakly, the effective force experienced by DNA in an electric field. Unexpectedly, our simulations revealed a considerable temperature dependence of solvent velocity at the DNA surface-slip velocity, an effect that can alter hydrodynamic coupling between the motion of DNA and the surrounding fluid

  7. Molecular Dynamics simulations of liquid isoquinoline as a function of temperature

    Science.gov (United States)

    Ahmad, Norariza; Adnan, Rohana; Soetens, Jean-Christophe; Millot, Claude

    2012-10-01

    Molecular Dynamics simulations of isoquinoline in liquid phase have been conducted in the temperature range 300-365 K corresponding to the normal liquid phase in order to investigate the evolution of translational and rotational diffusion with temperature. Molecules are supposed to be rigid and interact through an all-atom potential composed of Coulombic and Lennard-Jones terms. Translational diffusion coefficients are computed from velocity autocorrelation functions and mean square displacement. Anisotropic rotational diffusion coefficients are computed from angular velocity autocorrelation functions. The evolution of the 13C spin-lattice relaxation time with temperature has been obtained from the simulations and compared with experimental results. A small non-Arrhenius behavior, more pronounced than what was observed experimentally, has been found for this property. The structure has been analyzed in terms of populations of different kinds of first-neighbor dimers. A continuous evolution of the structure with temperature has been observed. The general trend is thus a continuous smooth evolution of the structure at dimer level and a slight non-Arrhenius evolution for diffusion coefficients and reorientational correlation times. These results are compared with those obtained for liquid quinoline where a clear non-Arrhenius break around 290 K was observed for the 13C spin-lattice relaxation time from experiments [D. Jalabert, J.-B. Robert, H. Roux-Buisson, J.-P. Kintzinger, J.-M. Lehn, R. Zinzius, D. Canet, P. Tekely, Europhys. Lett. 15 (1991) 435] and from simulations [C. Millot, J.-C. Soetens, N. Ahmad, R. Adnan, Europhys. Lett. 96 (2011) 43002]. Moreover, the identification of break temperatures for liquid isoquinoline appears to be less clear than for quinoline.

  8. Linearly scaling and almost Hamiltonian dielectric continuum molecular dynamics simulations through fast multipole expansions

    Science.gov (United States)

    Lorenzen, Konstantin; Mathias, Gerald; Tavan, Paul

    2015-11-01

    Hamiltonian Dielectric Solvent (HADES) is a recent method [S. Bauer et al., J. Chem. Phys. 140, 104103 (2014)] which enables atomistic Hamiltonian molecular dynamics (MD) simulations of peptides and proteins in dielectric solvent continua. Such simulations become rapidly impractical for large proteins, because the computational effort of HADES scales quadratically with the number N of atoms. If one tries to achieve linear scaling by applying a fast multipole method (FMM) to the computation of the HADES electrostatics, the Hamiltonian character (conservation of total energy, linear, and angular momenta) may get lost. Here, we show that the Hamiltonian character of HADES can be almost completely preserved, if the structure-adapted fast multipole method (SAMM) as recently redesigned by Lorenzen et al. [J. Chem. Theory Comput. 10, 3244-3259 (2014)] is suitably extended and is chosen as the FMM module. By this extension, the HADES/SAMM forces become exact gradients of the HADES/SAMM energy. Their translational and rotational invariance then guarantees (within the limits of numerical accuracy) the exact conservation of the linear and angular momenta. Also, the total energy is essentially conserved—up to residual algorithmic noise, which is caused by the periodically repeated SAMM interaction list updates. These updates entail very small temporal discontinuities of the force description, because the employed SAMM approximations represent deliberately balanced compromises between accuracy and efficiency. The energy-gradient corrected version of SAMM can also be applied, of course, to MD simulations of all-atom solvent-solute systems enclosed by periodic boundary conditions. However, as we demonstrate in passing, this choice does not offer any serious advantages.

  9. Linearly scaling and almost Hamiltonian dielectric continuum molecular dynamics simulations through fast multipole expansions

    International Nuclear Information System (INIS)

    Hamiltonian Dielectric Solvent (HADES) is a recent method [S. Bauer et al., J. Chem. Phys. 140, 104103 (2014)] which enables atomistic Hamiltonian molecular dynamics (MD) simulations of peptides and proteins in dielectric solvent continua. Such simulations become rapidly impractical for large proteins, because the computational effort of HADES scales quadratically with the number N of atoms. If one tries to achieve linear scaling by applying a fast multipole method (FMM) to the computation of the HADES electrostatics, the Hamiltonian character (conservation of total energy, linear, and angular momenta) may get lost. Here, we show that the Hamiltonian character of HADES can be almost completely preserved, if the structure-adapted fast multipole method (SAMM) as recently redesigned by Lorenzen et al. [J. Chem. Theory Comput. 10, 3244-3259 (2014)] is suitably extended and is chosen as the FMM module. By this extension, the HADES/SAMM forces become exact gradients of the HADES/SAMM energy. Their translational and rotational invariance then guarantees (within the limits of numerical accuracy) the exact conservation of the linear and angular momenta. Also, the total energy is essentially conserved—up to residual algorithmic noise, which is caused by the periodically repeated SAMM interaction list updates. These updates entail very small temporal discontinuities of the force description, because the employed SAMM approximations represent deliberately balanced compromises between accuracy and efficiency. The energy-gradient corrected version of SAMM can also be applied, of course, to MD simulations of all-atom solvent-solute systems enclosed by periodic boundary conditions. However, as we demonstrate in passing, this choice does not offer any serious advantages

  10. Folding simulations of gramicidin A into the β-helix conformations: Simulated annealing molecular dynamics study

    Science.gov (United States)

    Mori, Takaharu; Okamoto, Yuko

    2009-10-01

    Gramicidin A is a linear hydrophobic 15-residue peptide which consists of alternating D- and L-amino acids and forms a unique tertiary structure, called the β6.3-helix, to act as a cation-selective ion channel in the natural conditions. In order to investigate the intrinsic ability of the gramicidin A monomer to form secondary structures, we performed the folding simulation of gramicidin A using a simulated annealing molecular dynamics (MD) method in vacuum mimicking the low-dielectric, homogeneous membrane environment. The initial conformation was a fully extended one. From the 200 different MD runs, we obtained a right-handed β4.4-helix as the lowest-potential-energy structure, and left-handed β4.4-helix, right-handed and left-handed β6.3-helix as local-minimum energy states. These results are in accord with those of the experiments of gramicidin A in homogeneous organic solvent. Our simulations showed a slight right-hand sense in the lower-energy conformations and a quite β-sheet-forming tendency throughout almost the entire sequence. In order to examine the stability of the obtained right-handed β6.3-helix and β4.4-helix structures in more realistic membrane environment, we have also performed all-atom MD simulations in explicit water, ion, and lipid molecules, starting from these β-helix structures. The results suggested that β6.3-helix is more stable than β4.4-helix in the inhomogeneous, explicit membrane environment, where the pore water and the hydrogen bonds between Trp side-chains and lipid-head groups have a role to further stabilize the β6.3-helix conformation.

  11. Nature of protein-CO2 interactions as elucidated via molecular dynamics.

    Science.gov (United States)

    Drummond, Michael L; Wilson, Angela K; Cundari, Thomas R

    2012-09-27

    Rising global temperatures require innovative measures to reduce atmospheric concentrations of CO(2). The most successful carbon capture technology on Earth is the enzymatic capture of CO(2) and its sequestration in the form of glucose. Efforts to improve upon or mimic this naturally occurring process will require a rich understanding of protein-CO(2) interactions. Toward that end, extensive all-atom molecular dynamics (MD) simulations were performed on the CO(2)-utilizing enzyme phosphoenolpyruvate carboxykinase (PEPCK). Preliminary simulations were performed using implicit and explicit solvent models, which yielded similar results: arginine, lysine, tyrosine, and asparagine enhance the ability of a protein to bind carbon dioxide. Extensive explicit solvent simulations were performed for both wild-type PEPCK and five single-point PEPCK mutants, revealing three prevalent channels by which CO(2) enters (or exits) the active site cleft, as well as a fourth channel (observed only once), the existence of which can be rationalized in terms of the position of a key Arg residue. The strongest CO(2) binding sites in these simulations consist of appropriately positioned hydrogen bond donors and acceptors. Interactions between CO(2) and both Mn(2+) and Mg(2+) present in PEPCK are minimal due to the stable protein- and solvent-based coordination environments of these cations. His 232, suggested by X-ray crystallography as being a potential important CO(2) binding site, is indeed found to be particularly "CO(2)-philic" in these simulations. Finally, a recent mechanism, proposed on the basis of X-ray crystallography, for PEPCK active site lid closure is discussed in light of the MD trajectories. Overall, the results of this work will prove useful not only to scientists investigating PEPCK, but also to groups seeking to develop an environmentally benign, protein-based carbon capture, sequestration, and utilization system. PMID:22882078

  12. Amino acids and proteins at ZnO-water interfaces in molecular dynamics simulations.

    Science.gov (United States)

    Nawrocki, Grzegorz; Cieplak, Marek

    2013-08-28

    We determine potentials of the mean force for interactions of amino acids with four common surfaces of ZnO in aqueous solutions. The method involves all-atom molecular dynamics simulations combined with the umbrella sampling technique. The profiled nature of the density of water with the strongly adsorbed first layer affects the approach of amino acids to the surface and generates either repulsion or weak binding. The largest binding energy is found for tyrosine interacting with the surface in which the Zn ions are at the top. It is equal to 7 kJ mol(-1) which is comparable to that of the hydrogen bonds in a protein. This makes the adsorption of amino acids onto the ZnO surface much weaker than onto the well studied surface of gold. Under vacuum, binding energies are more than 40 times stronger (for one of the surfaces). The precise manner in which water molecules interact with a given surface influences the binding energies in a way that depends on the surface. Among the four considered surfaces the one with Zn at the top is recognized as binding almost all amino acids with an average binding energy of 2.60 kJ mol(-1). Another (O at the top) is non-binding for most amino acids. For binding situations the average energy is 0.66 kJ mol(-1). The remaining two surfaces bind nearly as many amino acids as they do not and the average binding energies are 1.46 and 1.22 kJ mol(-1). For all of the surfaces the binding energies vary between amino acids significantly: the dispersion in the range of 68-154% of the mean. A small protein is shown to adsorb onto ZnO only intermittently and with only a small deformation. Various adsorption events lead to different patterns in mobilities of amino acids within the protein. PMID:23836065

  13. Molecular dynamics simulation of rotational relaxation in nitrogen: Implications for rotational collision number models

    Science.gov (United States)

    Valentini, Paolo; Zhang, Chonglin; Schwartzentruber, Thomas E.

    2012-10-01

    We study the rotational relaxation process in nitrogen using all-atom molecular dynamics (MD) simulations and direct simulation Monte Carlo (DSMC). The intermolecular model used in the MD simulations is shown to (i) reproduce very well the shear viscosity of nitrogen over a wide range of temperatures, (ii) predict the near-equilibrium rotational collision number in good agreement with published trajectory calculations done on ab initio potential energy surfaces, and (iii) produce shock wave profiles in excellent accordance with the experimental measurements. We find that the rotational relaxation process is dependent not only on the near-equilibrium temperature (i.e., when systems relax to equilibrium after a small perturbation), but more importantly on both the magnitude and direction of the initial deviation from the equilibrium state. The comparison between MD and DSMC, based on the Borgnakke-Larsen model, for shock waves (both at low and high temperatures) and one-dimensional expansions shows that a judicious choice of a constant Zrot can produce DSMC results which are in relatively good agreement with MD. However, the selection of the rotational collision number is case-specific, depending not only on the temperature range, but more importantly on the type of flow (compression or expansion), with significant limitations for more complex simulations characterized both by expansion and compression zones. Parker's model, parametrized for nitrogen, overpredicts Zrot for temperatures above about 300 K. It is also unable to describe the dependence of the relaxation process on the direction to equilibrium. Finally, we present a demonstrative cell-based formulation of a rotational relaxation model to illustrate how, by including the key physics obtained from the MD data (dependence of the relaxation process on both the rotational and the translational state of the gas), the agreement between MD and DSMC solutions is drastically improved.

  14. Linearly scaling and almost Hamiltonian dielectric continuum molecular dynamics simulations through fast multipole expansions

    Energy Technology Data Exchange (ETDEWEB)

    Lorenzen, Konstantin; Mathias, Gerald; Tavan, Paul, E-mail: tavan@physik.uni-muenchen.de [Lehrstuhl für BioMolekulare Optik, Ludig–Maximilians Universität München, Oettingenstr. 67, 80538 München (Germany)

    2015-11-14

    Hamiltonian Dielectric Solvent (HADES) is a recent method [S. Bauer et al., J. Chem. Phys. 140, 104103 (2014)] which enables atomistic Hamiltonian molecular dynamics (MD) simulations of peptides and proteins in dielectric solvent continua. Such simulations become rapidly impractical for large proteins, because the computational effort of HADES scales quadratically with the number N of atoms. If one tries to achieve linear scaling by applying a fast multipole method (FMM) to the computation of the HADES electrostatics, the Hamiltonian character (conservation of total energy, linear, and angular momenta) may get lost. Here, we show that the Hamiltonian character of HADES can be almost completely preserved, if the structure-adapted fast multipole method (SAMM) as recently redesigned by Lorenzen et al. [J. Chem. Theory Comput. 10, 3244-3259 (2014)] is suitably extended and is chosen as the FMM module. By this extension, the HADES/SAMM forces become exact gradients of the HADES/SAMM energy. Their translational and rotational invariance then guarantees (within the limits of numerical accuracy) the exact conservation of the linear and angular momenta. Also, the total energy is essentially conserved—up to residual algorithmic noise, which is caused by the periodically repeated SAMM interaction list updates. These updates entail very small temporal discontinuities of the force description, because the employed SAMM approximations represent deliberately balanced compromises between accuracy and efficiency. The energy-gradient corrected version of SAMM can also be applied, of course, to MD simulations of all-atom solvent-solute systems enclosed by periodic boundary conditions. However, as we demonstrate in passing, this choice does not offer any serious advantages.

  15. Orbital free molecular dynamics; Approche sans orbitale des plasmas denses

    Energy Technology Data Exchange (ETDEWEB)

    Lambert, F

    2007-08-15

    The microscopic properties of hot and dense plasmas stay a field essentially studied thanks to classical theories like the One Component Plasma, models which rely on free parameters, particularly ionization. In order to investigate these systems, we have used, in this PhD work, a semi-classical model, without free parameters, that is based on coupling consistently classical molecular dynamics for the nuclei and orbital free density functional theory for the electrons. The electronic fluid is represented by a free energy entirely determined by the local density. This approximation was validated by a comparison with an ab initio technique, quantum molecular dynamics. This one is identical to the previous except for the description of the free energy that depends on a quantum-independent-particle model. Orbital free molecular dynamics was then used to compute equation of state of boron and iron plasmas in the hot and dense regime. Furthermore, comparisons with classical theories were performed on structural and dynamical properties. Finally, equation of state and transport coefficients mixing laws were studied by direct simulation of a plasma composed of deuterium and copper. (author)

  16. Imaging molecular structure and dynamics using laser driven recollisions

    International Nuclear Information System (INIS)

    Complete test of publication follows. Laser driven electron recollision provides a unique tool for measuring the structure and dynamics of matter. We illustrate this with experiments that use HHG to measure molecular structure with sub-Angstrom spatial and sub-femtosecond temporal resolution. Our recent work has looked in particular at the signal from high order harmonic generation which contains rich information about the structure and intra-molecular dynamics of small molecules. This we will illustrate by two types of experiment; (a) measurements of HHG from aligned molecular samples to observe two-centre recombination interference and electronic structure dependence of the angle dependent yield, (b) reconstruction of intra-molecular proton dynamics from the spectral dependence of the HHG using the intrinsic chirp of recolliding electrons. We experimentally investigate the process of intramolecular quantum interference in high-order harmonic generation in impulsively aligned CO2 molecules. The recombination interference effect is clearly seen through the order dependence of the harmonic yield in an aligned sample. This confirms that the effective de Broglie wavelength of the returning electron wave is not significantly altered by acceleration in the Coulomb field of the molecular ion. For the first time, to our knowledge, we demonstrate that such interference effects can be effectively controlled by changing the ellipticity of the driving laser field. Here we also report the results of angular dependence measurements of high order harmonics (17tth - 27th) from impulsively aligned organic molecules: Acetylene, Ethylene, and Allene. Since these molecules have a relatively low Ip an appropriately short pulse is required to produce as many harmonic orders as possible. This was provided by the ∼ 10 fs beam line of the ASTRA laser at Rutherford Appleton Laboratory whilst a somewhat longer pulse, properly forwarded with respect to the driving pulse, induced the

  17. Rarefied Gas Flow in Rough Microchannels by Molecular Dynamics Simulation

    Institute of Scientific and Technical Information of China (English)

    曹炳阳; 陈民; 过增元

    2004-01-01

    The molecular dynamics simulation method is applied to investigate the rarefied gas flow in a submicron channel with surface roughness which is modelled by an array of triangle modules. The boundary conditions are found to be determined not only by the Knudsen number but also the roughness, which implies that the breakdown of the Maxwell slip model under the conditions that the surface roughness is comparable to the molecular mean free path. The effects of the rarefaction and the surface roughness on the boundary conditions and the flow characteristics are strongly coupled. The flow friction increases with increasing roughness and with decreasing Knudsen number.

  18. Spectra modelling combining molecular dynamics and quantum mechanics

    Czech Academy of Sciences Publication Activity Database

    Novák, Vít; Bouř, Petr

    2015-01-01

    Roč. 22, č. 1 (2015), s. 48. ISSN 1211-5894. [Discussions in Structural Molecular Biology. Annual Meeting of the Czech Society for Structural Biology /13./. 19.03.2015-21.03.2015, Nové Hrady] R&D Projects: GA ČR GAP208/11/0105; GA ČR GA15-09072S Grant ostatní: GA MŠk(CZ) LM2010005; GA MŠk(CZ) ED3.2.00/08.0144 Institutional support: RVO:61388963 Keywords : Raman scattering * molecular dynamics * autocorrelation function Subject RIV: CF - Physical ; Theoretical Chemistry

  19. Accelerating convergence of molecular dynamics-based structural relaxation

    DEFF Research Database (Denmark)

    Christensen, Asbjørn

    2005-01-01

    We describe strategies to accelerate the terminal stage of molecular dynamics (MD)based relaxation algorithms, where a large fraction of the computational resources are used. First, we analyze the qualitative and quantitative behavior of the QuickMin family of MD relaxation algorithms and explore...... the influence of spectral properties and dimensionality of the molecular system on the algorithm efficiency. We test two algorithms, the MinMax and Lanczos, for spectral estimation from an MD trajectory, and use this to derive a practical scheme of time step adaptation in MD relaxation algorithms to...

  20. Chemical Dynamics, Molecular Energetics, and Kinetics at the Synchrotron

    Energy Technology Data Exchange (ETDEWEB)

    Leone, Stephen R.; Ahmed, Musahid; Wilson, Kevin R.

    2010-03-14

    Scientists at the Chemical Dynamics Beamline of the Advanced Light Source in Berkeley are continuously reinventing synchrotron investigations of physical chemistry and chemical physics with vacuum ultraviolet light. One of the unique aspects of a synchrotron for chemical physics research is the widely tunable vacuum ultraviolet light that permits threshold ionization of large molecules with minimal fragmentation. This provides novel opportunities to assess molecular energetics and reaction mechanisms, even beyond simple gas phase molecules. In this perspective, significant new directions utilizing the capabilities at the Chemical Dynamics Beamline are presented, along with an outlook for future synchrotron and free electron laser science in chemical dynamics. Among the established and emerging fields of investigations are cluster and biological molecule spectroscopy and structure, combustion flame chemistry mechanisms, radical kinetics and product isomer dynamics, aerosol heterogeneous chemistry, planetary and interstellar chemistry, and secondary neutral ion-beam desorption imaging of biological matter and materials chemistry.

  1. Molecular-Level Organization of the Tear Film Lipid Layer: A Molecular Dynamics Simulation Study

    Czech Academy of Sciences Publication Activity Database

    Wizert, A.; Iskander, D. R.; Jungwirth, Pavel; Cwiklik, Lukasz

    Elsevier. Roč. 106, č. 2 (2014), 710A. ISSN 0006-3495. [Annual Meeting of the Biophysical Society /58./. 15.02.2014-19.02.2014, San Francisco] Institutional support: RVO:61388963 ; RVO:61388955 Keywords : tear film * lipid layer * molecular dynamics simulations Subject RIV: BO - Biophysics

  2. A Series of Molecular Dynamics and Homology Modeling Computer Labs for an Undergraduate Molecular Modeling Course

    Science.gov (United States)

    Elmore, Donald E.; Guayasamin, Ryann C.; Kieffer, Madeleine E.

    2010-01-01

    As computational modeling plays an increasingly central role in biochemical research, it is important to provide students with exposure to common modeling methods in their undergraduate curriculum. This article describes a series of computer labs designed to introduce undergraduate students to energy minimization, molecular dynamics simulations,…

  3. Development and application of a free energy force field for all atom protein folding

    International Nuclear Information System (INIS)

    Proteins are the workhorses of all cellular life. They constitute the building blocks and the machinery of all cells and typically function in specific three-dimensional conformations into which each protein folds. Currently over one million protein sequences are known, compared to about 40,000 structures deposited in the Protein Data Bank (the world-wide database of protein structures). Reliable theoretical methods for protein structure prediction could help to reduce the gap between sequence and structural databases and elucidate the biological information in structurally unresolved sequences. In this thesis we explore an approach for protein structure prediction and folding that is based on the Anfinsen's hypothesis that most proteins in their native state are in thermodynamic equilibrium with their environment. We have developed a free energy forcefield (PFF02) that locates the native conformation of many proteins from all structural classes at the global minimum of the free-energy model. We have validated the forcefield against a large decoy set (Rosetta). The average root mean square deviation (RMSD) for the lowest energy structure for the 32 proteins of the decoy set was only 2.14 Aa from the experimental conformation. We have successfully implemented and used stochastic optimization methods, such as the basin hopping technique and evolutionary algorithms for all atom protein structure prediction. The evolutionary algorithm performs exceptionally well on large supercomputational architectures, such as BlueGene and MareNostrum. Using the PFF02 forcefield, we were able to fold 13 proteins (12-56 amino acids), which include helix, sheet and mixed secondary structure. On average the predicted structure of these proteins deviated from their experimental conformation by only 2.89 Aa RMSD. (orig.)

  4. Molecular Dynamics simulations of liquid isoquinoline as a function of temperature

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, Norariza [Universiti Sains Malaysia, School of Chemical Sciences, Minden, Penang 11800 (Malaysia); Adnan, Rohana, E-mail: r_adnan@usm.my [Universiti Sains Malaysia, School of Chemical Sciences, Minden, Penang 11800 (Malaysia); Soetens, Jean-Christophe [Universite de Bordeaux 1, ISM, UMR 5255, 351, Cours de la Liberation, Talence F-33405 (France); CNRS, ISM, UMR 5255, 351, Cours de la Liberation, Talence F-33405 (France); Millot, Claude, E-mail: Claude.Millot@univ-lorraine.fr [Universite de Lorraine, SRSMC, UMR 7565, Boulevard des Aiguillettes, BP 70239, Vandoeuvre-les-Nancy F-54506 (France); CNRS, SRSMC, UMR 7565, Boulevard des Aiguillettes, BP 70239, Vandoeuvre-les-Nancy F-54506 (France)

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer Molecular Dynamics simulations of liquid isoquinoline between 300 and 365 K are done. Black-Right-Pointing-Pointer Dependence on temperature of {sup 13}C T{sub 1} NMR relaxation time is calculated. Black-Right-Pointing-Pointer A small non-Arrhenius behavior is found for translational and rotational diffusion. Black-Right-Pointing-Pointer Comparison with liquid quinoline shows similarities but no clear break temperature. -- Abstract: Molecular Dynamics simulations of isoquinoline in liquid phase have been conducted in the temperature range 300-365 K corresponding to the normal liquid phase in order to investigate the evolution of translational and rotational diffusion with temperature. Molecules are supposed to be rigid and interact through an all-atom potential composed of Coulombic and Lennard-Jones terms. Translational diffusion coefficients are computed from velocity autocorrelation functions and mean square displacement. Anisotropic rotational diffusion coefficients are computed from angular velocity autocorrelation functions. The evolution of the {sup 13}C spin-lattice relaxation time with temperature has been obtained from the simulations and compared with experimental results. A small non-Arrhenius behavior, more pronounced than what was observed experimentally, has been found for this property. The structure has been analyzed in terms of populations of different kinds of first-neighbor dimers. A continuous evolution of the structure with temperature has been observed. The general trend is thus a continuous smooth evolution of the structure at dimer level and a slight non-Arrhenius evolution for diffusion coefficients and reorientational correlation times. These results are compared with those obtained for liquid quinoline where a clear non-Arrhenius break around 290 K was observed for the {sup 13}C spin-lattice relaxation time from experiments [D. Jalabert, J.-B. Robert, H. Roux-Buisson, J.-P. Kintzinger, J.-M. Lehn

  5. Balancing an accurate representation of the molecular surface in generalized Born formalisms with integrator stability in molecular dynamics simulations

    Czech Academy of Sciences Publication Activity Database

    Chocholoušová, Jana; Feig, M.

    2006-01-01

    Roč. 27, č. 6 (2006), s. 719-729. ISSN 0192-8651 Keywords : molecular surface * generalized Born formalisms * molecular dynamic simulations Subject RIV: CC - Organic Chemistry Impact factor: 4.893, year: 2006

  6. Microscopic study of nuclear 'pasta' by quantum molecular dynamics

    International Nuclear Information System (INIS)

    Structure of cold dense matter at subnuclear densities is investigated by quantum molecular dynamics (QMD) simulations. We succeeded in showing that the phases with slab-like and rod-like nuclei etc. and be formed dynamically from hot uniform nuclear matter without any assumptions on nuclear shape. We also observe intermediate phases, which has complicated nuclear shapes. Geometrical structures of matter are analyzed with Minkowski functionals, and it is found out that intermediate phases can be characterized as ones with negative Euler characteristic. Our result suggests the existence of these kinds of phases in addition to the simple 'pasta' phases in neutron star crusts. (author)

  7. Ab initio molecular dynamics study of liquid methanol

    CERN Document Server

    Handgraaf, J W; Meijer, E J; Handgraaf, Jan-Willem; Erp, Titus S. van; Meijer, Evert Jan

    2003-01-01

    We present a density-functional theory based molecular-dynamics study of the structural, dynamical, and electronic properties of liquid methanol under ambient conditions. The calculated radial distribution functions involving the oxygen and hydroxyl hydrogen show a pronounced hydrogen bonding and compare well with recent neutron diffraction data, except for an underestimate of the oxygen-oxygen correlation. We observe that, in line with infrared spectroscopic data, the hydroxyl stretching mode is significantly red-shifted in the liquid. A substantial enhancement of the dipole moment is accompanied by significant fluctuations due to thermal motion. Our results provide valuable data for improvement of empirical potentials.

  8. Molecular Dynamics Simulations of Laser Powered Carbon Nanotube Gears

    Science.gov (United States)

    Srivastava, Deepak; Globus, Al; Han, Jie; Chancellor, Marisa K. (Technical Monitor)

    1997-01-01

    Dynamics of laser powered carbon nanotube gears is investigated by molecular dynamics simulations with Brenner's hydrocarbon potential. We find that when the frequency of the laser electric field is much less than the intrinsic frequency of the carbon nanotube, the tube exhibits an oscillatory pendulam behavior. However, a unidirectional rotation of the gear with oscillating frequency is observed under conditions of resonance between the laser field and intrinsic gear frequencies. The operating conditions for stable rotations of the nanotube gears, powered by laser electric fields are explored, in these simulations.

  9. Finite Temperature Quasicontinuum: Molecular Dynamics without all the Atoms

    Energy Technology Data Exchange (ETDEWEB)

    Dupuy, L; Tadmor, E B; Miller, R E; Phillips, R

    2005-02-02

    Using a combination of statistical mechanics and finite-element interpolation, the authors develop a coarse-grained (CG) alternative to molecular dynamics (MD) for crystalline solids at constant temperature. The new approach is significantly more efficient than MD and generalizes earlier work on the quasi-continuum method. The method is validated by recovering equilibrium properties of single crystal Ni as a function of temperature. CG dynamical simulations of nanoindentation reveal a strong dependence on temperature of the critical stress to nucleate dislocations under the indenter.

  10. Coalescence of silver unidimensional structures by molecular dynamics simulation

    International Nuclear Information System (INIS)

    The study of nanoparticles coalescence and silver nano rods phenomena by means of molecular dynamics simulation under the thermodynamic laws is reported. In this work we focus ourselves to see the conditions under which the one can be given one dimension growth of silver nano rods for the coalescence phenomenon among two nano rods or one nano rod and one particle; what allows us to study those structural, dynamic and morphological properties of the silver nano rods to different thermodynamic conditions. The simulations are carried out using the Sutton-Chen potentials of interaction of many bodies that allow to obtain appropriate results with the real physical systems. (Author)

  11. Molecular dynamical simulations of melting behaviors of metal clusters

    International Nuclear Information System (INIS)

    The melting behaviors of metal clusters are studied in a wide range by molecular dynamics simulations. The calculated results show that there are fluctuations in the heat capacity curves of some metal clusters due to the strong structural competition; For the 13-, 55- and 147-atom clusters, variations of the melting points with atomic number are almost the same; It is found that for different metal clusters the dynamical stabilities of the octahedral structures can be inferred in general by a criterion proposed earlier by F. Baletto et al. [J. Chem. Phys. 116 3856 (2002)] for the statically stable structures

  12. The chaos and order in nuclear molecular dynamics

    International Nuclear Information System (INIS)

    The subject of the presented report is role of chaos in scattering processes in the frame of molecular dynamics. In this model, it is assumed that scattering particles (nuclei) consist of not-interacted components as alpha particles or 12C, 16O and 20Ne clusters. The results show such effects as dynamical in stabilities and fractal structure as well as compound nuclei decay and heavy-ion fusion. The goal of the report is to make the reader more familiar with the chaos model and its application to nuclear phenomena. 157 refs, 40 figs

  13. Counter-ion binding and mobility in the presence of hydrophobic polyions – combining molecular dynamics simulations and NMR

    Science.gov (United States)

    Druchok, Maksym; Malikova, Natalie; Rollet, Anne-Laure; Vlachy, Vojko

    2016-06-01

    Counter-ion binding and mobility in aqueous solutions of partially hydrophobic ionene oligoions is studied here by a combination of all-atomic molecular dynamics (MD) simulations and NMR (19F and 81Br nuclei) measurements. We present results for 12, 12-ionenes in the presence of different halide ions (F-, Cl-, Br- and I-), as well as their mixtures; the latter allowing us to probe counter-ion selectivity of these oligoions. We consolidate both structural and dynamic information, in particular simulated radial distribution functions and average residence times of counter-ions in the vicinity of ionenes and NMR data in the form of counter-ion chemical shift and self-diffusion coefficients. On one hand, previously reported enthalpy of dilution and mixing measurements show a reverse counter-ion sequence for 12, 12-ionenes with respect to their less hydrophobic 3, 3- and 6, 6- analogues. On the other hand, the current MD and NMR data, reflecting the counter-ion binding tendencies to the ionene chain, give evidence for the same ordering as that observed by MD for 3, 3-ionenes. This is not seen as a contradiction and can be rationalized on the basis of increasing chain hydrophobicity, which has different consequences for enthalpy and ion-binding. The latter is reflecting free energy changes and as such includes both enthalpic and entropic contributions.

  14. Excitation Dynamics and Relaxation in a Molecular Heterodimer

    CERN Document Server

    Balevicius, V; Abramavicius, D; Mancal, T; Valkunas, L

    2011-01-01

    The exciton dynamics in a molecular heterodimer is studied as a function of differences in excitation and reorganization energies, asymmetry in transition dipole moments and excited state lifetimes. The heterodimer is composed of two molecules modeled as two-level systems coupled by the resonance interaction. The system-bath coupling is taken into account as a modulating factor of the energy gap of the molecular excitation, while the relaxation to the ground state is treated phenomenologically. Comparison of the description of the excitation dynamics modeled using either the Redfield equations (secular and full forms) or the Hierarchical quantum master equation (HQME) is demonstrated and discussed. Possible role of the dimer as an excitation quenching center in photosynthesis self-regulation is discussed. It is concluded that the system-bath interaction rather than the excitonic effect determines the excitation quenching ability of such a dimer.

  15. Coherent Amplification of Ultrafast Molecular Dynamics in an Optical Oscillator

    Science.gov (United States)

    Aharonovich, Igal; Pe'er, Avi

    2016-02-01

    Optical oscillators present a powerful optimization mechanism. The inherent competition for the gain resources between possible modes of oscillation entails the prevalence of the most efficient single mode. We harness this "ultrafast" coherent feedback to optimize an optical field in time, and show that, when an optical oscillator based on a molecular gain medium is synchronously pumped by ultrashort pulses, a temporally coherent multimode field can develop that optimally dumps a general, dynamically evolving vibrational wave packet, into a single vibrational target state. Measuring the emitted field opens a new window to visualization and control of fast molecular dynamics. The realization of such a coherent oscillator with hot alkali dimers appears within experimental reach.

  16. Fermionic molecular dynamics for ground states and collisions of nuclei

    International Nuclear Information System (INIS)

    The antisymmetric many-body trial state which describes a system of interacting fermions is parametrized in terms of localized wave packets. The equations of motion are derived from the time-dependent quantum variational principle. The resulting Fermionic Molecular Dynamics (FMD) equations include a wide range of semi-quantal to classical physics extending from deformed Hartree-Fock theory to Newtonian molecular dynamics. Conservation laws are discussed in connection with the choice of the trial state. The model is applied to heavy-ion collisions with which its basic features are illustrated. The results show a great variety of phenomena including deeply inelastic collisions, fusion, incomplete fusion, fragmentation, neck emission, promptly emitted nucleons and evaporation. (orig.)

  17. Kinetic distance and kinetic maps from molecular dynamics simulation

    CERN Document Server

    Noe, Frank

    2015-01-01

    Characterizing macromolecular kinetics from molecular dynamics (MD) simulations requires a distance metric that can distinguish slowly-interconverting states. Here we build upon diffusion map theory and define a kinetic distance for irreducible Markov processes that quantifies how slowly molecular conformations interconvert. The kinetic distance can be computed given a model that approximates the eigenvalues and eigenvectors (reaction coordinates) of the MD Markov operator. Here we employ the time-lagged independent component analysis (TICA). The TICA components can be scaled to provide a kinetic map in which the Euclidean distance corresponds to the kinetic distance. As a result, the question of how many TICA dimensions should be kept in a dimensionality reduction approach becomes obsolete, and one parameter less needs to be specified in the kinetic model construction. We demonstrate the approach using TICA and Markov state model (MSM) analyses for illustrative models, protein conformation dynamics in bovine...

  18. Serine Proteases an Ab Initio Molecular Dynamics Study

    CERN Document Server

    De Santis, L

    1999-01-01

    In serine proteases (SP's), the H-bond between His-57 and Asp-102, and that between Gly-193 and the transition state intermediate play a crucial role for enzymatic function. To shed light on the nature of these interactions, we have carried out ab initio molecular dynamics simulations on complexes representing adducts between the reaction intermediate and elastase (one protein belonging to the SP family). Our calculations indicate the presence of a low--barrier H-bond between His-57 and Asp-102, in complete agreement with NMR experiments on enzyme--transition state analog complexes. Comparison with an ab initio molecular dynamics simulation on a model of the substrate--enzyme adduct indicates that the Gly-193--induced strong stabilization of the intermediate is accomplished by charge/dipole interactions and not by H-bonding as previously suggested. Inclusion of the protein electric field in the calculations does not affect significantly the charge distribution.

  19. Tensor-optimized antisymmetrized molecular dynamics in nuclear physics

    CERN Document Server

    Myo, Takayuki; Ikeda, Kiyomi; Horiuchi, Hisashi; Suhara, Tadahiro

    2015-01-01

    We develop a new formalism to treat nuclear many-body systems using bare nucleon-nucleon interaction. It has become evident that the tensor interaction plays important role in nuclear many-body systems due to the role of the pion in strongly interacting system. We take the antisymmetrized molecular dynamics (AMD) as a basic framework and add a tensor correlation operator acting on the AMD wave function using the concept of the tensor-optimized shell model (TOSM). We demonstrate a systematical and straightforward formulation utilizing the Gaussian integration and differentiation method and the antisymmetrization technique to calculate all the matrix elements of the many-body Hamiltonian. We can include the three-body interaction naturally and calculate the matrix elements systematically in the progressive order of the tensor correlation operator. We call the new formalism "tensor-optimized antisymmetrized molecular dynamics".

  20. Optical spectra and lattice dynamics of molecular crystals

    CERN Document Server

    Zhizhin, GN

    1995-01-01

    The current volume is a single topic volume on the optical spectra and lattice dynamics of molecular crystals. The book is divided into two parts. Part I covers both the theoretical and experimental investigations of organic crystals. Part II deals with the investigation of the structure, phase transitions and reorientational motion of molecules in organic crystals. In addition appendices are given which provide the parameters for the calculation of the lattice dynamics of molecular crystals, procedures for the calculation of frequency eigenvectors of utilizing computers, and the frequencies and eigenvectors of lattice modes for several organic crystals. Quite a large amount of Russian literature is cited, some of which has previously not been available to scientists in the West.

  1. Surface hopping methodology in laser-driven molecular dynamics

    CERN Document Server

    Fiedlschuster, T; Gross, E K U; Schmidt, R

    2016-01-01

    A theoretical justification of the empirical surface hopping method for the laser-driven molecular dynamics is given utilizing the formalism of the exact factorization of the molecular wavefunction [Abedi et al., PRL $\\textbf{105}$, 123002 (2010)] in its quantum-classical limit. Employing an exactly solvable $\\textrm H_2^{\\;+}$-like model system, it is shown that the deterministic classical nuclear motion on a single time-dependent surface in this approach describes the same physics as stochastic (hopping-induced) motion on several surfaces, provided Floquet surfaces are applied. Both quantum-classical methods do describe reasonably well the exact nuclear wavepacket dynamics for extremely different dissociation scenarios. Hopping schemes using Born-Oppenheimer surfaces or instantaneous Born-Oppenheimer surfaces fail completely.

  2. Reaction dynamics of molecular hydrogen on silicon surfaces

    DEFF Research Database (Denmark)

    Bratu, P.; Brenig, W.; Gross, A.; Hartmann, M.; Höfer, U.; Kratzer, Peter; Russ, R.

    1996-01-01

    Experimental and theoretical results on the dynamics of dissociative adsorption and recombinative desorption of hydrogen on silicon are presented. Using optical second-harmonic generation, extremely small sticking probabilities in the range 10(-9)-10(-5) could be measured for H-2 and D-2 on Si(111...... between the two surfaces. These results indicate that tunneling, molecular vibrations, and the structural details of the surface play only a minor role for the adsorption dynamics. Instead, they appear to be governed by the localized H-Si bonding and Si-Si lattice vibrations. Theoretically, an effective...... five-dimensional model is presented taking lattice distortion, corrugation, and molecular vibrations into account within the framework of coupled-channel calculations. While the temperature dependence of the sticking is dominated by lattice distortion, the main effect of corrugation is a reduction of...

  3. An implicit divalent counterion force field for RNA molecular dynamics

    Science.gov (United States)

    Henke, Paul S.; Mak, Chi H.

    2016-03-01

    How to properly account for polyvalent counterions in a molecular dynamics simulation of polyelectrolytes such as nucleic acids remains an open question. Not only do counterions such as Mg2+ screen electrostatic interactions, they also produce attractive intrachain interactions that stabilize secondary and tertiary structures. Here, we show how a simple force field derived from a recently reported implicit counterion model can be integrated into a molecular dynamics simulation for RNAs to realistically reproduce key structural details of both single-stranded and base-paired RNA constructs. This divalent counterion model is computationally efficient. It works with existing atomistic force fields, or coarse-grained models may be tuned to work with it. We provide optimized parameters for a coarse-grained RNA model that takes advantage of this new counterion force field. Using the new model, we illustrate how the structural flexibility of RNA two-way junctions is modified under different salt conditions.

  4. Shock induced phase transition of water: Molecular dynamics investigation

    Energy Technology Data Exchange (ETDEWEB)

    Neogi, Anupam, E-mail: anupamneogi@atdc.iitkgp.ernet.in [Advanced Technology Development Center, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Mitra, Nilanjan, E-mail: nilanjan@civil.iitkgp.ernet.in [Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India)

    2016-02-15

    Molecular dynamics simulations were carried out using numerous force potentials to investigate the shock induced phenomenon of pure bulk liquid water. Partial phase transition was observed at single shock velocity of 4.0 km/s without requirement of any external nucleators. Change in thermodynamic variables along with radial distribution function plots and spectral analysis revealed for the first time in the literature, within the context of molecular dynamic simulations, the thermodynamic pathway leading to formation of ice VII from liquid water on shock loading. The study also revealed information for the first time in the literature about the statistical time-frame after passage of shock in which ice VII formation can be observed and variations in degree of crystallinity of the sample over the entire simulation time of 100 ns.

  5. Shock induced phase transition of water: Molecular dynamics investigation

    International Nuclear Information System (INIS)

    Molecular dynamics simulations were carried out using numerous force potentials to investigate the shock induced phenomenon of pure bulk liquid water. Partial phase transition was observed at single shock velocity of 4.0 km/s without requirement of any external nucleators. Change in thermodynamic variables along with radial distribution function plots and spectral analysis revealed for the first time in the literature, within the context of molecular dynamic simulations, the thermodynamic pathway leading to formation of ice VII from liquid water on shock loading. The study also revealed information for the first time in the literature about the statistical time-frame after passage of shock in which ice VII formation can be observed and variations in degree of crystallinity of the sample over the entire simulation time of 100 ns

  6. Tensor-optimized antisymmetrized molecular dynamics in nuclear physics

    Science.gov (United States)

    Myo, Takayuki; Toki, Hiroshi; Ikeda, Kiyomi; Horiuchi, Hisashi; Suhara, Tadahiro

    2015-07-01

    We develop a new formalism to treat nuclear many-body systems using the bare nucleon-nucleon interaction. It has become evident that the tensor interaction plays an important role in nuclear many-body systems due to the role of the pion in strongly interacting systems. We take the antisymmetrized molecular dynamics (AMD) as a basic framework and add a tensor correlation operator acting on the AMD wave function using the concept of the tensor-optimized shell model. We demonstrate a systematical and straightforward formulation utilizing the Gaussian integration and differentiation method and the antisymmetrization technique to calculate all the matrix elements of the many-body Hamiltonian. We can include the three-body interaction naturally and calculate the matrix elements systematically in the progressive order of the tensor correlation operator. We call the new formalism "tensor-optimized antisymmetrized molecular dynamics".

  7. Ab initio molecular dynamics on the electronic Boltzmann equilibrium distribution

    Energy Technology Data Exchange (ETDEWEB)

    Alonso, J L; Echenique, P [Departamento de Fisica Teorica, Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza (Spain); Castro, A; Polo, V [Institute for Biocomputation and Physics of Complex Systems (BIFI), University of Zaragoza, Mariano Esquillor s/n, E-50018 Zaragoza (Spain); Rubio, A [Nano-Bio Spectroscopy group and ETSF Scientific Development Centre, Departamento de Fisica de Materiales, Universidad del PaIs Vasco, Centro de Fisica de Materiales, CSIC-UPV/EHU-MPC and DIPC, E-20018 San Sebastian (Spain); Zueco, D, E-mail: dzueco@unizar.e [Instituto de Ciencia de Materiales de Aragon and Departamento de Fisica de la Materia Condensada, CSIC-Universidad de Zaragoza, E-50009 Zaragoza (Spain)

    2010-08-15

    We prove that for a combined system of classical and quantum particles, it is possible to describe a dynamics for the classical particles that incorporates in a natural way the Boltzmann equilibrium population for the quantum subsystem. In addition, these molecular dynamics (MD) do not need to assume that the electrons immediately follow the nuclear motion (in contrast to any adiabatic approach) and do not present problems in the presence of crossing points between different potential energy surfaces (conical intersections or spin-crossings). A practical application of this MD to the study of the effect of temperature on molecular systems presenting (nearly) degenerate states-such as the avoided crossing in the ring-closure process of ozone-is presented.

  8. Nonequilibrium Molecular Dynamics Simulation of the Thermocapillary Effect

    OpenAIRE

    Maier, Holger Andreas

    2011-01-01

    A natural convection occurs at lateral spatially variable solid-fluid or liquid-fluid interfaces [probstein1994]. It can play an important role in the transport of heat or mass across such interfaces, e.g. in evaporation or solvent extraction as they are often employed in chemical engineering [sherwood1975]. Model systems of such interfacial systems have been studied by different methods [colinet2001]. A very fundamental method is the usage of so-called molecular dynamics (MD) simulation...

  9. Molecular Dynamics Study of the Primary Ferrofluid Aggregate Formation

    OpenAIRE

    Tanygin, B. M.; Kovalenko, V. F.; Petrychuk, M.V.; Dzyan, S. A.

    2011-01-01

    Investigations of the phase transitions and self-organization in the magnetic aggregates are of the fundamental and applied interest. The long-range ordering structures described in the Tom\\'anek's systematization (M. Yoon, and D. Tom\\'anek, 2010 [1]) are not yet obtained in the direct molecular dynamics simulations. The resulted structures usually are the linear chains or circles, or, else, amorphous (liquid) formations. In the present work, it was shown, that the thermodynamically equilibri...

  10. Molecular dynamics simulation of melittin in a dimyristoylphosphatidylcholine bilayer membrane.

    OpenAIRE

    Bernèche, S; Nina, M; Roux, B

    1998-01-01

    Molecular dynamics trajectories of melittin in an explicit dimyristoyl phosphatidylcholine (DMPC) bilayer are generated to study the details of lipid-protein interactions at the microscopic level. Melittin, a small amphipathic peptide found in bee venom, is known to have a pronounced effect on the lysis of membranes. The peptide is initially set parallel to the membrane-solution interfacial region in an alpha-helical conformation with unprotonated N-terminus. Solid-state nuclear magnetic reso...

  11. Nonlinear dynamics of zigzag molecular chains (in Russian)

    DEFF Research Database (Denmark)

    Savin, A. V.; Manevitsch, L. I.; Christiansen, Peter Leth;

    1999-01-01

    Nonlinear, collective, soliton type excitations in zigzag molecular chains are analyzed. It is shown that the nonlinear dynamics of a chain dramatically changes in passing from the one-dimensional linear chain to the more realistic planar zigzag model-due, in particular, to the geometry...... types (such as extension and compression varieties) develop simultaneously in the chain. Accordingly, the inclusion of chain geometry is necessary if physical phenomena are to be described in terms of solitary waves...

  12. Ab initio molecular dynamics simulation of laser melting of silicon

    OpenAIRE

    Silvestrelli, P.-L.; Alavi, A; Parrinello, M.; Frenkel, D

    1996-01-01

    The method of ab initio molecular dynamics, based on finite temperature density functional theory, is used to simulate laser heating of crystal silicon. We have found that a high concentration of excited electrons dramatically weakens the covalent bond. As a result, the system undergoes a melting transition to a metallic state. In contrast to ordinary liquid silicon, the new liquid is characterized by a high coordination number and a strong reduction of covalent bonding effects.

  13. Understanding disordered and membrane protein recognition by molecular dynamics

    OpenAIRE

    Stanley, Nathaniel H., 1983-

    2015-01-01

    This thesis has been about the use of a simulation technique, known as molecular dynamics simulations, to study biophysics in proteins that have historically been difficult to study with other methods. We have studied numerous systems, namely binding to the membrane proteins Fatty acid amide hydrolase (FAAH) and the sphingosine-1-phosphate receptor 1 (S1P1R), and folding in the disordered protein kinase inducible domain (KID). In each case we have been able to analyze processes and uncover be...

  14. Automated processing of data generated by molecular dynamics

    International Nuclear Information System (INIS)

    A new integrated tool for automated processing of data generated by molecular dynamics packages and programs have been developed. The program allows to calculate important quantities such as pair correlation function, the analysis of common neighbors, counting nanoparticles and their size distribution, conversion of output files between different formats. The work explains in detail the modules of the tool, the interface between them. The uses of program are illustrated in application examples in the calculation of various properties of silver nanoparticles. (author)

  15. Efficient stochastic thermostatting of path integral molecular dynamics

    OpenAIRE

    Ceriotti, Michele; Parrinello, Michele; Markland, Thomas E.; Manolopoulos, David E.

    2010-01-01

    The path integral molecular dynamics (PIMD) method provides a convenient way to compute the quantum mechanical structural and thermodynamic properties of condensed phase systems at the expense of introducing an additional set of high-frequency normal modes on top of the physical vibrations of the system. Efficiently sampling such a wide range of frequencies provides a considerable thermostatting challenge. Here we introduce a simple stochastic path integral Langevin equation (PILE) thermostat...

  16. Quantum tunneling splittings from path-integral molecular dynamics.

    Science.gov (United States)

    Mátyus, Edit; Wales, David J; Althorpe, Stuart C

    2016-03-21

    We illustrate how path-integral molecular dynamics can be used to calculate ground-state tunnelling splittings in molecules or clusters. The method obtains the splittings from ratios of density matrix elements between the degenerate wells connected by the tunnelling. We propose a simple thermodynamic integration scheme for evaluating these elements. Numerical tests on fully dimensional malonaldehyde yield tunnelling splittings in good overall agreement with the results of diffusion Monte Carlo calculations. PMID:27004863

  17. Viscosity in molecular dynamics with periodic boundary conditions

    OpenAIRE

    Viscardy, S.; Gaspard, P.

    2003-01-01

    We report a study of viscosity by the method of Helfand moment in systems with periodic boundary conditions. We propose a new definition of Helfand moment which takes into account the minimum image convention used in molecular dynamics with periodic boundary conditions. Our Helfand-moment method is equivalent to the method based on the Green-Kubo formula and is not affected by ambiguities due to the periodic boundary conditions. Moreover, in hard-ball systems, our method is equivalent to the ...

  18. Coupling Lattice Boltzmann and Molecular Dynamics models for dense fluids

    OpenAIRE

    Dupuis, A.; Kotsalis, E. M.; Koumoutsakos, P.

    2006-01-01

    We propose a hybrid model, coupling Lattice Boltzmann and Molecular Dynamics models, for the simulation of dense fluids. Time and length scales are decoupled by using an iterative Schwarz domain decomposition algorithm. The MD and LB formulations communicate via the exchange of velocities and velocity gradients at the interface. We validate the present LB-MD model in simulations of flows of liquid argon past and through a carbon nanotube. Comparisons with existing hybrid algorithms and with r...

  19. Simulational nanoengineering: Molecular dynamics implementation of an atomistic Stirling engine.

    Science.gov (United States)

    Rapaport, D C

    2009-04-01

    A nanoscale-sized Stirling engine with an atomistic working fluid has been modeled using molecular dynamics simulation. The design includes heat exchangers based on thermostats, pistons attached to a flywheel under load, and a regenerator. Key aspects of the behavior, including the time-dependent flows, are described. The model is shown to be capable of stable operation while producing net work at a moderate level of efficiency. PMID:19518394

  20. Simulational nanoengineering: Molecular dynamics implementation of an atomistic Stirling engine

    CERN Document Server

    Rapaport, D C

    2009-01-01

    A nanoscale-sized Stirling engine with an atomistic working fluid has been modeled using molecular dynamics simulation. The design includes heat exchangers based on thermostats, pistons attached to a flywheel under load, and a regenerator. Key aspects of the behavior, including the time-dependent flows, are described. The model is shown to be capable of stable operation while producing net work at a moderate level of efficiency.

  1. Molecular dynamics simulations of HIV-1 protease complexed with saquinavir

    OpenAIRE

    Watson, S. J.

    2009-01-01

    Inhibition of the Human Immunode�ficiency virus type-1 (HIV-1) protease enzyme blocks HIV-1 replication. Protease inhibitor drugs have successfully been used as a therapy for HIV-infected individuals to reduce their viral loads and slow the progression to Acquired Immune Defi�ciency Syndrome (AIDS). However, mutations readily and rapidly accrue in the protease gene resulting in a reduced sensitivity of the protein to the inhibitor. In this thesis, molecular dynamics simulations (MDS)...

  2. Molecular dynamics simulation of nanoindentation on nanocomposite pearlite

    OpenAIRE

    Ghaffarian, Hadi; Taheri, Ali Karimi; Ryu, Seunghwa; Kang, Keonwook

    2016-01-01

    We carry out molecular dynamics simulations of nanoindentation to investigate the effect of cementite size and temperature on the deformation behavior of nanocomposite pearlite composed of alternating ferrite and cementite layers. We find that, instead of the coherent transmission, dislocation propagates by forming a widespread plastic deformation in cementite layer. We also show that increasing temperature enhances the distribution of plastic strain in the ferrite layer, which reduces the st...

  3. Molecular Dynamics for Low Temperature Plasma-Surface Interaction Studies

    OpenAIRE

    Graves, David B.; Brault, Pascal

    2009-01-01

    The mechanisms of physical and chemical interactions of low temperature plasmas with surfaces can be fruitfully explored using molecular dynamics (MD) simulations. MD simulations follow the detailed motion of sets of interacting atoms through integration of atomic equations of motion, using inter-atomic potentials that can account for bond breaking and formation that result when energetic species from the plasma impact surfaces. This article summarizes the current status of the technique for ...

  4. Simulational nanoengineering: Molecular dynamics implementation of an atomistic Stirling engine

    Science.gov (United States)

    Rapaport, D. C.

    2009-04-01

    A nanoscale-sized Stirling engine with an atomistic working fluid has been modeled using molecular dynamics simulation. The design includes heat exchangers based on thermostats, pistons attached to a flywheel under load, and a regenerator. Key aspects of the behavior, including the time-dependent flows, are described. The model is shown to be capable of stable operation while producing net work at a moderate level of efficiency.

  5. DNA basepair step deformability inferred from molecular dynamics simulations

    Czech Academy of Sciences Publication Activity Database

    Lankaš, Filip; Šponer, Jiří; Langowski, J.; Cheatham III, T. E.

    2003-01-01

    Roč. 85, č. 5 (2003), s. 2872-2883. ISSN 0006-3495 R&D Projects: GA MŠk LN00A032 Grant ostatní: National Science Foundation(US) CHE-0218739; Wellcome Trust(GB) GR067507MF Institutional research plan: CEZ:AV0Z5004920; CEZ:AV0Z4040901 Keywords : molecular dynamics simulations * DNA basepair step deformability Subject RIV: BO - Biophysics Impact factor: 4.463, year: 2003

  6. Spin dynamics of an ultra-small nanoscale molecular magnet

    Directory of Open Access Journals (Sweden)

    Ciftja Orion

    2007-01-01

    Full Text Available AbstractWe present mathematical transformations which allow us to calculate the spin dynamics of an ultra-small nanoscale molecular magnet consisting of a dimer system of classical (high Heisenberg spins. We derive exact analytic expressions (in integral form for the time-dependent spin autocorrelation function and several other quantities. The properties of the time-dependent spin autocorrelation function in terms of various coupling parameters and temperature are discussed in detail.

  7. Molecular Dynamics Simulation of Myoglobin Collision with Low Energy Ions

    Institute of Scientific and Technical Information of China (English)

    CHENG Wei; ZHANG Feng-Shou; ZHOU Hong-Yu

    2007-01-01

    Collisions of a low energy heavy ion with a myoglobin in water are simulated by molecular dynamics model. The increase of total energy is very small. The mean squared fluctuation decreases at 300 K and increases at 250K.This is an important novel cooling effect that protects the protein from ion damage. The possible collision side effect is the change of tertiary structure that blocks the normal functions of the myogiobin.

  8. Molecular dynamics simulation of nanocrystalline nickel: structure and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Swygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Caro, A. [Comision Nacional de Energia Atomica, San Carlos de Bariloche (Argentina). Centro Atomico Bariloche

    1997-09-01

    Molecular dynamics computer simulations of low temperature elastic and plastic deformation of Ni nanophase samples (3-7 nm) are performed. The samples are polycrystals nucleated from different seeds, with random locations and orientations. Bulk and Young`s modulus, onset of plastic deformation and mechanism responsible for the plastic behaviour are studied and compared with the behaviour of coarse grained samples. (author) 1 fig., 3 refs.

  9. Thermal conductivity of ZnTe investigated by molecular dynamics

    International Nuclear Information System (INIS)

    The thermal conductivity of ZnTe with zinc-blende structure has been computed by equilibrium molecular dynamics method based on Green-Kubo formalism. A Tersoff's potential is adopted in the simulation to model the atomic interactions. The calculations are performed as a function of temperature up to 800 K. The calculated thermal conductivities are in agreement with the experimental values between 150 K and 300 K, while the results above the room temperature are comparable with the Slack's equation.

  10. Chemical Dynamics, Molecular Energetics, and Kinetics at the Synchrotron

    OpenAIRE

    Leone, Stephen R.

    2010-01-01

    Scientists at the Chemical Dynamics Beamline of the Advanced Light Source in Berkeley are continuously reinventing synchrotron investigations of physical chemistry and chemical physics with vacuum ultraviolet light. One of the unique aspects of a synchrotron for chemical physics research is the widely tunable vacuum ultraviolet light that permits threshold ionization of large molecules with minimal fragmentation. This provides novel opportunities to assess molecular energetics and reaction me...

  11. Molecular dynamics in electrospun amorphous plasticized polylactide fibers

    OpenAIRE

    MONNIER, X; DELPOUVE, N; BASSON, N; GUINAULT, A; DOMENEK, S; Saiter, A; MALLON, P.E; Dargent, E

    2015-01-01

    The molecular dynamics in the amorphous phase of electrospun fibers of polylactide (PLA) has been investigated using the cooperative rearranging region concept. An unusual and significant increase of the cooperativity length at the glass transition induced by the electrospinning has been observed. This behavior is attributed to the singularity of the amorphous phase organization. Electrospun PLA fibers rearrange in a pre-ordered metastable state which is characterized by highly oriented but n...

  12. Enhanced molecular dynamics performance with a programmable graphics processor

    OpenAIRE

    Rapaport, D. C.

    2009-01-01

    Design considerations for molecular dynamics algorithms capable of taking advantage of the computational power of a graphics processing unit (GPU) are described. Accommodating the constraints of scalable streaming-multiprocessor hardware necessitates a reformulation of the underlying algorithm. Performance measurements demonstrate the considerable benefit and cost-effectiveness of such an approach, which produces a factor of 2.5 speed improvement over previous work for the case of the soft-sp...

  13. Molecular Dynamics Simulation of Macromolecules Using Graphics Processing Unit

    OpenAIRE

    Xu, Ji; Ren, Ying; Ge, Wei; Yu, Xiang; Yang, Xiaozhen; Li, Jinghai

    2010-01-01

    Molecular dynamics (MD) simulation is a powerful computational tool to study the behavior of macromolecular systems. But many simulations of this field are limited in spatial or temporal scale by the available computational resource. In recent years, graphics processing unit (GPU) provides unprecedented computational power for scientific applications. Many MD algorithms suit with the multithread nature of GPU. In this paper, MD algorithms for macromolecular systems that run entirely on GPU ar...

  14. Molecular dynamics simulations of complex shaped particles using Minkowski operators

    OpenAIRE

    Galindo-Torres, Sergio-Andres; Alonso-Marroquin, Fernando

    2008-01-01

    The Minkowski operators (addition and substraction of sets in vectorial spaces) has been extensively used for Computer Graphics and Image Processing to represent complex shapes. Here we propose to apply those mathematical concepts to extend the Molecular Dynamics (MD) Methods for simulations with complex-shaped particles. A new concept of Voronoi-Minkowski diagrams is introduced to generate random packings of complex-shaped particles with tunable particle roundness. By extending the classical...

  15. Molecular Dynamics study of Pb overlayer on Cu(100)

    Science.gov (United States)

    Karimi, M.; Tibbits, P.; Ila, D.; Dalins, I.; Vidali, G.

    1991-01-01

    Isothermal-isobaric Molecular Dynamics (MD) simulation of a submonolayer Pb film in c(2x2) ordered structure adsorbed on a Cu(100) substrate showed retention of order to high T. The Embedded Atom Method (EAM) calculated the energy of atoms of overlayer and substrate. The time-averaged squared modulus of the two dimensional structure factor for the Pb overlayer measured the order of the overlayer. The results are for increasing T only, and require verification by simulated cooling.

  16. Protocol for MM/PBSA Molecular Dynamics Simulations of Proteins

    OpenAIRE

    Fogolari, Federico; Brigo, Alessandro; Molinari, Henriette

    2003-01-01

    Continuum solvent models have been employed in past years for understanding processes such as protein folding or biomolecular association. In the last decade, several attempts have been made to merge atomic detail molecular dynamics simulations with solvent continuum models. Among continuum models, the Poisson-Boltzmann solvent accessible surface area model is one of the oldest and most fundamental. Notwithstanding its wide usage for simulation of biomolecular electrostatic potential, the Poi...

  17. Molecular dynamics investigation of radiation damage in semiconductors

    Science.gov (United States)

    Good, Brian S.

    1991-01-01

    Results of a molecular dynamics investigation of the effects of radiation damage on the crystallographic structure of semiconductors are reported. Particular cosiderastion is given to the formation of point defects and small defect complexes in silicon at the end of a radiation-damage cascade. The calculations described make use of the equivalent crystal theory of Smith and Banerjea (1988). Results on the existence of an atomic displacement threshold, the defect formation energy, and some crystallographic information on the defects observed are reported.

  18. Molecular dynamics simulation study of polyelectrolyte adsorption on cellulose surfaces

    OpenAIRE

    Biermann, Oliver

    2002-01-01

    The adsorption of two polyelectrolyte ((carboxy methyl) cellulose and poly(acrylate) in water on crystalline cellulose is studied in this work. The multi-component problem has been splitted up into simulations of solutions of the polyelectrolyte (polyanions including sodium counterions) in water, into simulations of the interface of crystalline cellulose towards water. Finally polyelectrolyte-cellulose systems were studied. Molecular dynamics simulations of diluted (_ 2:5 weight percent) aque...

  19. Hydration of polyelectrolytes studied by molecular dynamics simulation

    OpenAIRE

    Biermann, Oliver; Haedicke, Erich; Koltzenburg, Sebastian; Seufert, Michael; Mueller-Plathe, Florian

    2001-01-01

    Molecular dynamics simulations of diluted (~2.5 weight percent) aqueous solutions of two polyelectrolytes, namely sodium carboxy methyl cellulose (CMC) and sodium poly(acrylate) (PAA) have been performed. Water and counterions were taken into account explicitly. For CMC the substitution pattern and starting conformation is all-important. Two simulations of CMC oligomers resulted in different structures: One molecule takes a stretched conformation, while the second one keeps a globule-like, to...

  20. Incorporation of quantum statistical features in molecular dynamics

    International Nuclear Information System (INIS)

    We formulate a method for incorporating quantum fluctuations into molecular-dynamics simulations of many-body systems, such as those employed for energetic nuclear collision processes. Based on Fermi's Golden Rule, we allow spontaneous transitions to occur between the wave packets which are not energy eigenstates. The ensuing diffusive evolution in the space of the wave packet parameters exhibits appealing physical properties, including relaxation towards quantum-statistical equilibrium. (author)

  1. Molecular packing in 1-hexanol-DMPC bilayers studied by molecular dynamics simulation

    DEFF Research Database (Denmark)

    Pedersen, U.R.; Peters, Günther H.j.; Westh, P.

    2007-01-01

    on comparable systems. The local density or molecular packing in DMPC–hexanol was elucidated through the average Voronoi volumes of all heavy (non-hydrogen) atoms. Analogous analysis was conducted on trajectories from simulations of pure 1-hexanol and pure (hydrated) DMPC bilayers. The results......The structure and molecular packing density of a “mismatched” solute, 1-hexanol, in lipid membranes of dimyristoyl phosphatidylcholine (DMPC) was studied by molecular dynamics simulations. We found that the average location and orientation of the hexanol molecules matched earlier experimental data...... of the alcohol upon partitioning and an even stronger loosening in the packing of the lipid. Furthermore, analysis of Voronoi volumes along the membrane normal identifies a distinctive depth dependence of the changes in molecular packing. The outer (interfacial) part of the lipid acyl chains (up to C...

  2. Shapiro like steps reveals molecular nanomagnets’ spin dynamics

    International Nuclear Information System (INIS)

    We present an accurate way to detect spin dynamics of a nutating molecular nanomagnet by inserting it in a tunnel Josephson junction and studying the current voltage (I-V) characteristic. The spin nutation of the molecular nanomagnet is generated by applying two circularly polarized magnetic fields. We demonstrate that modulation of the Josephson current by the nutation of the molecular nanomagnet’s spin appears as a stepwise structure like Shapiro steps in the I-V characteristic of the junction. Width and heights of these Shapiro-like steps are determined by two parameters of the spin nutation, frequency and amplitude of the nutation, which are simply tuned by the applied magnetic fields

  3. Shapiro like steps reveals molecular nanomagnets’ spin dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Abdollahipour, Babak, E-mail: b-abdollahi@tabrizu.ac.ir [Faculty of Physics, University of Tabriz, Tabriz 51666-16471 (Iran, Islamic Republic of); Abouie, Jahanfar, E-mail: jahan@iasbs.ac.ir; Ebrahimi, Navid [Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731 (Iran, Islamic Republic of)

    2015-09-15

    We present an accurate way to detect spin dynamics of a nutating molecular nanomagnet by inserting it in a tunnel Josephson junction and studying the current voltage (I-V) characteristic. The spin nutation of the molecular nanomagnet is generated by applying two circularly polarized magnetic fields. We demonstrate that modulation of the Josephson current by the nutation of the molecular nanomagnet’s spin appears as a stepwise structure like Shapiro steps in the I-V characteristic of the junction. Width and heights of these Shapiro-like steps are determined by two parameters of the spin nutation, frequency and amplitude of the nutation, which are simply tuned by the applied magnetic fields.

  4. Shapiro like steps reveals molecular nanomagnets’ spin dynamics

    Directory of Open Access Journals (Sweden)

    Babak Abdollahipour

    2015-09-01

    Full Text Available We present an accurate way to detect spin dynamics of a nutating molecular nanomagnet by inserting it in a tunnel Josephson junction and studying the current voltage (I-V characteristic. The spin nutation of the molecular nanomagnet is generated by applying two circularly polarized magnetic fields. We demonstrate that modulation of the Josephson current by the nutation of the molecular nanomagnet’s spin appears as a stepwise structure like Shapiro steps in the I-V characteristic of the junction. Width and heights of these Shapiro-like steps are determined by two parameters of the spin nutation, frequency and amplitude of the nutation, which are simply tuned by the applied magnetic fields.

  5. Molecular dynamics of a water jet from a carbon nanotube.

    Science.gov (United States)

    Hanasaki, Itsuo; Yonebayashi, Toru; Kawano, Satoyuki

    2009-04-01

    A carbon nanotube (CNT) can be viewed as a molecular nozzle. It has a cylindrical shape of atomistic regularity, and the diameter can be even less than 1 nm. We have conducted molecular-dynamics simulations of water jet from a (6,6) CNT that confines water in a form of single-file molecular chain. The results show that the water forms nanoscale clusters at the outlet and they are released intermittently. The jet breakup is dominated by the thermal fluctuations, which leads to the strong dependence on the temperature. The cluster size n decreases and the release frequency f increases at higher temperatures. The f roughly follows the reaction kinetics by the transition state theory. The speed of a cluster is proportional to the 1/sqrt[n] because of the central limit theorem. These properties make great contrast with the macroscopic liquid jets. PMID:19518333

  6. Molecular Dynamics Studies on the Buffalo Prion Protein

    CERN Document Server

    Zhang, Jiapu

    2015-01-01

    It was reported that buffalo is a low susceptibility species resisting to TSEs (Transmissible Spongiform Encephalopathies) (same as rabbits, horses and dogs). TSEs, also called prion diseases, are invariably fatal and highly infectious neurodegenerative diseases that affect a wide variety of species (in humans prion diseases are (v)CJDs, GSS, FFI, and kulu etc). It was reported that buffalo is a low susceptibility species resisting to prion diseases (as rabbits, dogs, horses). In molecular structures, these neurodegenerative diseases are caused by the conversion from a soluble normal cellular prion protein, predominantly with alpha-helices, into insoluble abnormally folded infectious prions, rich in beta-sheets. This paper studies the molecular structure and structural dynamics of buffalo prion protein, in order to find out the reason why buffaloes are resistant to prion diseases. We first did molecular modeling a homology structure constructed by one mutation at residue 143 from the Nuclear Magnetic Resonanc...

  7. Applications of the molecular dynamics flexible fitting method.

    Science.gov (United States)

    Trabuco, Leonardo G; Schreiner, Eduard; Gumbart, James; Hsin, Jen; Villa, Elizabeth; Schulten, Klaus

    2011-03-01

    In recent years, cryo-electron microscopy (cryo-EM) has established itself as a key method in structural biology, permitting the structural characterization of large biomolecular complexes in various functional states. The data obtained through single-particle cryo-EM has recently seen a leap in resolution thanks to landmark advances in experimental and computational techniques, resulting in sub-nanometer resolution structures being obtained routinely. The remaining gap between these data and revealing the mechanisms of molecular function can be closed through hybrid modeling tools that incorporate known atomic structures into the cryo-EM data. One such tool, molecular dynamics flexible fitting (MDFF), uses molecular dynamics simulations to combine structures from X-ray crystallography with cryo-EM density maps to derive atomic models of large biomolecular complexes. The structures furnished by MDFF can be used subsequently in computational investigations aimed at revealing the dynamics of the complexes under study. In the present work, recent applications of MDFF are presented, including the interpretation of cryo-EM data of the ribosome at different stages of translation and the structure of a membrane-curvature-inducing photosynthetic complex. PMID:20932910

  8. Exploiting molecular dynamics in Nested Sampling simulations of small peptides

    Science.gov (United States)

    Burkoff, Nikolas S.; Baldock, Robert J. N.; Várnai, Csilla; Wild, David L.; Csányi, Gábor

    2016-04-01

    Nested Sampling (NS) is a parameter space sampling algorithm which can be used for sampling the equilibrium thermodynamics of atomistic systems. NS has previously been used to explore the potential energy surface of a coarse-grained protein model and has significantly outperformed parallel tempering when calculating heat capacity curves of Lennard-Jones clusters. The original NS algorithm uses Monte Carlo (MC) moves; however, a variant, Galilean NS, has recently been introduced which allows NS to be incorporated into a molecular dynamics framework, so NS can be used for systems which lack efficient prescribed MC moves. In this work we demonstrate the applicability of Galilean NS to atomistic systems. We present an implementation of Galilean NS using the Amber molecular dynamics package and demonstrate its viability by sampling alanine dipeptide, both in vacuo and implicit solvent. Unlike previous studies of this system, we present the heat capacity curves of alanine dipeptide, whose calculation provides a stringent test for sampling algorithms. We also compare our results with those calculated using replica exchange molecular dynamics (REMD) and find good agreement. We show the computational effort required for accurate heat capacity estimation for small peptides. We also calculate the alanine dipeptide Ramachandran free energy surface for a range of temperatures and use it to compare the results using the latest Amber force field with previous theoretical and experimental results.

  9. Dynamical correlation between quantum entanglement and intramolecular energy in molecular vibrations: An algebraic approach

    International Nuclear Information System (INIS)

    The dynamical correlation between quantum entanglement and intramolecular energy in realistic molecular vibrations is explored using the Lie algebraic approach. The explicit expression of entanglement measurement can be achieved using algebraic operations. The common and different characteristics of dynamical entanglement in different molecular vibrations are also provided. The dynamical study of quantum entanglement and intramolecular energy in small molecular vibrations can be helpful for controlling the entanglement and further understanding the intramolecular dynamics. (atomic and molecular physics)

  10. Molecular structure and elastic properties of thermotropic liquid crystals: integrated molecular dynamics--statistical mechanical theory vs molecular field approach.

    Science.gov (United States)

    Ilk Capar, M; Nar, A; Ferrarini, A; Frezza, E; Greco, C; Zakharov, A V; Vakulenko, A A

    2013-03-21

    The connection between the molecular structure of liquid crystals and their elastic properties, which control the director deformations relevant for electro-optic applications, remains a challenging objective for theories and computations. Here, we compare two methods that have been proposed to this purpose, both characterized by a detailed molecular level description. One is an integrated molecular dynamics-statistical mechanical approach, where the bulk elastic constants of nematics are calculated from the direct correlation function (DCFs) and the single molecule orientational distribution function [D. A. McQuarrie, Statistical Mechanics (Harper & Row, New York, 1973)]. The latter is obtained from atomistic molecular dynamics trajectories, together with the radial distribution function, from which the DCF is then determined by solving the Ornstein-Zernike equation. The other approach is based on a molecular field theory, where the potential of mean torque experienced by a mesogen in the liquid crystal phase is parameterized according to its molecular surface. In this case, the calculation of elastic constants is combined with the Monte Carlo sampling of single molecule conformations. Using these different approaches, but the same description, at the level of molecular geometry and torsional potentials, we have investigated the elastic properties of the nematic phase of two typical mesogens, 4'-n-pentyloxy-4-cyanobiphenyl and 4'-n-heptyloxy-4-cyanobiphenyl. Both methods yield K3(bend) >K1 (splay) >K2 (twist), although there are some discrepancies in the average elastic constants and in their anisotropy. These are interpreted in terms of the different approximations and the different ways of accounting for the structural properties of molecules in the two approaches. In general, the results point to the role of the molecular shape, which is modulated by the conformational freedom and cannot be fully accounted for by a single descriptor such as the aspect ratio

  11. A flexible, grid-enabled web portal for GROMACS molecular dynamics simulations

    NARCIS (Netherlands)

    van Dijk, M.; Wassenaar, T.A.; Bonvin, A.M.J.J.

    2012-01-01

    Molecular dynamics simulations are becoming a standard part of workflows in structural biology. They are used for tasks as diverse as assessing molecular flexibility, probing conformational changes, assessing the impact of mutations, or gaining information about molecular interactions. However, perf

  12. A Flexible, Grid-Enabled Web Portal for GROMACS Molecular Dynamics Simulations

    NARCIS (Netherlands)

    van Dijk, Marc; Wassenaar, Tsjerk A.; Bonvin, Alexandre M. J. J.

    2012-01-01

    Molecular dynamics simulations are becoming a standard part of workflows in structural biology. They are used for tasks as diverse as assessing molecular flexibility, probing conformational changes, assessing the impact of mutations, or gaining information about molecular interactions. However, perf

  13. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    Energy Technology Data Exchange (ETDEWEB)

    Hall, G.E.

    2011-05-31

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  14. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    Energy Technology Data Exchange (ETDEWEB)

    Hall G. E.; Goncharov, V.

    2012-05-29

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  15. Classical molecular dynamics simulation on the dynamical properties of H2 on silicene layer

    OpenAIRE

    Casuyac Miqueas; Bantaculo Rolando

    2016-01-01

    This study investigates the diffusion of hydrogen molecule physisorbed on the surface of silicene nanoribbon (SiNR)using the classical molecular dynamic (MD) simulation in LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). The interactions between silicon atoms are modeled using the modified Tersoff potential, the Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential for hydrogen – hydrogen interaction and the Lennard – Jones potential for the physisorbed H...

  16. A Hierarchical Coarse-Grained (All-Atom-to-All-Residue) Computer Simulation Approach: Self-Assembly of Peptides

    OpenAIRE

    Pandey, Ras B.; Kuang, Zhifeng; Farmer, Barry L.

    2013-01-01

    A hierarchical computational approach (all-atom residue to all-residue peptide) is introduced to study self-organizing structures of peptides as a function of temperature. A simulated residue-residue interaction involving all-atom description, analogous to knowledge-based analysis (with different input), is used as an input to a phenomenological coarse-grained interaction for large scales computer simulations. A set of short peptides P1 (1H 2S 3S 4Y 5W 6Y 7A 8F 9N 10N 11K 12T) is considered a...

  17. The classical and quantum dynamics of molecular spins on graphene.

    Science.gov (United States)

    Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo

    2016-02-01

    Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic and quantum computing devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics and electrical spin manipulation. However, the influence of the graphene environment on the spin systems has yet to be unravelled. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets on graphene. Whereas the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly developed model. Coupling to Dirac electrons introduces a dominant quantum relaxation channel that, by driving the spins over Villain's threshold, gives rise to fully coherent, resonant spin tunnelling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin manipulation in graphene nanodevices. PMID:26641019

  18. Molecular dynamics investigation of tracer diffusion in a simple liquid

    International Nuclear Information System (INIS)

    Extensive Molecular-Dynamics (MD) simulations have been carried out for a model trace-solvent system made up of 100 solvent molecules and 8 tracer molecules interacting through truncated Lennard-Jones potentials. The influence of the size ratio between solute and solvent, of their mass ratio and of the solvent viscosity on the diffusivity of a small tracer were investigated. Positive deviations from a Stokes-Einstein behaviour are observed, in qualitative agreement with experimental observations. It was also observed that as tracer and solvent become increasingly dissimilar, their respective dynamics becomes decoupled. We suggest that such decouplings can be interpreted by writing their mobility of the tracer as the sum of two terms, the first one arising from a coupling between tracer dynamics and hydrodynamics modes of the solvent, and the second one describing jump motion in a locally nearly frozen environment. (author). 17 refs, 4 figs, 6 tabs

  19. Wave packet dynamics in molecular excited electronic states

    International Nuclear Information System (INIS)

    We theoretically explore the use of UV pump – UV probe schemes to resolve in time the dynamics of nuclear wave packets in excited electronic states of the hydrogen molecule. The pump pulse ignites the dynamics in singly excited states, that will be probed after a given time delay by a second identical pulse that will ionize the molecule. The field-free molecular dynamics is first explored by analyizing the autocorrelation function for the pumped wave packet and the excitation probabilities. We investigate both energy and angle differential ionization probabilities and demonstrate that the asymmetry induced in the electron angular distributions gives a direct map of the time evolution of the pumped wave packet

  20. Molecular dynamics of coalescence and collisions of silver nanoparticles

    International Nuclear Information System (INIS)

    We study how different relative orientations and impact velocity on the collision of two silver nanoparticles affect the first stages of the formation of a new, larger nanoparticle. In order to do this, we implemented a set of molecular dynamics simulations on the NVE ensemble on pairs of silver icosahedral nanoparticles at several relative orientations, that allowed us to follow the dynamics of the first nanoseconds of the coalescence processes. Using bond angle analysis, we found that the initial relative orientation of the twin planes has a critical role on the final stability of the resulting particle, and on the details of the dynamics itself. When the original particles have their closest twins aligned to each other, the formed nanoparticle will likely stabilize its structure onto a particle with a defined center and a low surface-to-volume ratio, while nanoparticles with misaligned twins will promote the formation of highly defective particles with a high inner energy

  1. Steered molecular dynamics simulations of protein-ligand interactions

    Institute of Scientific and Technical Information of China (English)

    XU Yechun; SHEN Jianhua; LUO Xiaomin; SHEN Xu; CHEN Kaixian; JIANG Hualiang

    2004-01-01

    Studies of protein-ligand interactions are helpful to elucidating the mechanisms of ligands, providing clues for rational drug design. The currently developed steered molecular dynamics (SMD) is a complementary approach to experimental techniques in investigating the biochemical processes occurring at microsecond or second time scale, thus SMD may provide dynamical and kinetic processes of ligand-receptor binding and unbinding, which cannot be accessed by the experimental methods. In this article, the methodology of SMD is described, and the applications of SMD simulations for obtaining dynamic insights into protein-ligand interactions are illustrated through two of our own examples. One is associated with the simulations of binding and unbinding processes between huperzine A and acetylcholinesterase, and the other is concerned with the unbinding process of α-APA from HIV-1 reverse transcriptase.

  2. Molecular dynamics of coalescence and collisions of silver nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Guevara-Chapa, Enrique, E-mail: enrique_guevara@hotmail.com [Universidad Autónoma de Nuevo León, Facultad de Ciencias Físico Matemáticas (Mexico); Mejía-Rosales, Sergio [Universidad Autónoma de Nuevo León, Center for Innovation, Research and Development in Engineering and Technology (CIIDIT), and CICFIM-Facultad de Ciencias Físico Matemáticas (Mexico)

    2014-12-15

    We study how different relative orientations and impact velocity on the collision of two silver nanoparticles affect the first stages of the formation of a new, larger nanoparticle. In order to do this, we implemented a set of molecular dynamics simulations on the NVE ensemble on pairs of silver icosahedral nanoparticles at several relative orientations, that allowed us to follow the dynamics of the first nanoseconds of the coalescence processes. Using bond angle analysis, we found that the initial relative orientation of the twin planes has a critical role on the final stability of the resulting particle, and on the details of the dynamics itself. When the original particles have their closest twins aligned to each other, the formed nanoparticle will likely stabilize its structure onto a particle with a defined center and a low surface-to-volume ratio, while nanoparticles with misaligned twins will promote the formation of highly defective particles with a high inner energy.

  3. Two methods for molecular dynamics on curved surfaces

    CERN Document Server

    Paquay, Stefan

    2014-01-01

    Lateral diffusion along membranes is an important transport mechanism in biology. Dynamical simulations of this transport can greatly aid in understanding biological processes where this diffusion plays a role. Brownian dynamics simulations in local coordinates are one possibility, but we show here that it is also possible to combine constraint algorithms with a velocity Verlet scheme to perform molecular dynamics simulations of particles confined on arbitrary time-independent curved surfaces. The main advantage is that this method is based on Cartesian coordinates instead of local coordinates, allowing the reuse of many other standard tools, including parallelisation through domain decomposition, without adapting those to local coordinates. Of the two constraint algorithms we considered, RATTLE is more computationally efficient and easier to implement, while the symmetric projection method has slightly better energy conservation. By applying the schemes to the Langevin equation, Brownian motion on various cu...

  4. The classical and quantum dynamics of molecular spins on graphene

    Science.gov (United States)

    Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo

    2016-02-01

    Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic and quantum computing devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics and electrical spin manipulation. However, the influence of the graphene environment on the spin systems has yet to be unravelled. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets on graphene. Whereas the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly developed model. Coupling to Dirac electrons introduces a dominant quantum relaxation channel that, by driving the spins over Villain’s threshold, gives rise to fully coherent, resonant spin tunnelling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin manipulation in graphene nanodevices.

  5. Molecular dynamics-based refinement of nanodiamond size measurements obtained with dynamic light scattering

    CERN Document Server

    Koniakhin, S V; Terterov, I N; Shvidchenko, A V; Eidelman, E D; Dubina, M V

    2016-01-01

    The determination of particle size by dynamic light scattering uses the Stokes-Einstein relation, which can break down for nanoscale objects. Here we employ a molecular dynamics simulation of fully solvated 1-5 nm carbon nanoparticles for the refinement of the experimental data obtained for nanodiamonds in water by using dynamic light scattering. We performed molecular dynamics simulations in differently sized boxes and calculated nanoparticles diffusion coefficients using the velocity autocorrelation function and mean-square displacement. We found that the predictions of the Stokes-Einstein relation are accurate for nanoparticles larger than 3 nm while for smaller nanoparticles the diffusion coefficient should be corrected and different boundary conditions should be taken into account.

  6. Molecular imaging with dynamic contrast-enhanced computed tomography

    International Nuclear Information System (INIS)

    Dynamic contrast-enhanced computed tomography (DCE-CT) is a quantitative technique that employs rapid sequences of CT images after bolus administration of intravenous contrast material to measure a range of physiological processes related to the microvasculature of tissues. By combining knowledge of the molecular processes underlying changes in vascular physiology with an understanding of the relationship between vascular physiology and CT contrast enhancement, DCE-CT can be redefined as a molecular imaging technique. Some DCE-CT derived parameters reflect tissue hypoxia and can, therefore, provide information about the cellular microenvironment. DCE-CT can also depict physiological processes, such as vasodilatation, that represent the physiological consequences of molecular responses to tissue hypoxia. To date the main applications have been in stroke and oncology. Unlike some other molecular imaging approaches, DCE-CT benefits from wide availability and ease of application along with the use of contrast materials and software packages that have achieved full regulatory approval. Hence, DCE-CT represents a molecular imaging technique that is applicable in clinical practice today.

  7. Molecular-dynamics analysis of the diffusion of molecular hydrogen in all-silica sodalite

    OpenAIRE

    Van den Berg, A.W.C.; Bromley, S.T.; Flikkema, E.; Wojdel, J.; Maschmeyer, T; Jansen, J C

    2004-01-01

    In order to investigate the technical feasibility of crystalline porous silicates as hydrogen storage materials, the self-diffusion of molecular hydrogen in all-silica sodalite is modeled using large-scale classical molecular-dynamics simulations employing full lattice flexibility. In the temperature range of 700–1200 K, the diffusion coefficient is found to range from 1.6⋅10−10 to 1.8⋅10−9 m2/s. The energy barrier for hydrogen diffusion is determined from the simulations allowing the applica...

  8. Dynamical properties of liquid Al near melting. An orbital-free molecular dynamics study

    OpenAIRE

    Gonzalez, David J; Gonzalez, Luis Enrique; Lopez, Jose Manuel; Stott, Malcolm J.

    2001-01-01

    The static and dynamic structure of liquid Al is studied using the orbital free ab-initio molecular dynamics method. Two thermodynamic states along the coexistence line are considered, namely T = 943 K and 1323 K for which X-ray and neutron scattering data are available. A new kinetic energy functional, which fulfills a number of physically relevant conditions is employed, along with a local first principles pseudopotential. In addition to a comparison with experiment, we also compare our ab-...

  9. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    Energy Technology Data Exchange (ETDEWEB)

    Hall,G.E.; Sears, T.J.

    2009-04-03

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.

  10. Anomalous Molecular Weight Dependence of Chain Dynamics in Unentangled Polymer Blends with Strong Dynamic Asymmetry

    OpenAIRE

    Arrese-Igor, Silvia; Alegría, Ángel; Moreno Segurado, Ángel J.; Colmenero de León, Juan

    2011-01-01

    We address the general question of how the molecular weight dependence of chain dynamics in unentangled polymers is modified by blending. By dielectric spectroscopy we measure the normal mode relaxation of polyisoprene in blends with a slower component of poly(ter-butylstyrene). Unentangled polyisoprene in the blend exhibits strong deviations from Rouse scaling, approaching 'entangled-like' behavior at low temperatures in concomitance with the increase of the dynamic asymmetry in the blend. T...

  11. Molecular dynamics study of the formation mechanisms of ionic SDS and nonionic C12E8 micelles and n-dodecane droplets

    Science.gov (United States)

    Kawada, Shinji; Komori, Mika; Fujimoto, Kazushi; Yoshii, Noriyuki; Okazaki, Susumu

    2016-02-01

    In order to clarify the early-stage kinetics of micelle formation in concentrated surfactant solutions, all-atom molecular dynamics (MD) calculations of the aggregation of surfactant molecules dispersed in water were performed for ionic sodium dodecyl sulfate (SDS), nonionic octaethyleneglycol monododecyl ether (C12E8), and n-dodecane. The relationship between aggregate domain length and elapsed time from the beginning of the MD calculation obeyed the well-known Lifshitz-Slyozov (LS) law for C12E8 and n-dodecane. In contrast, the aggregation rate of SDS did not obey the LS law. This difference is likely due to the differences in strength of the electrostatic interactions between the aggregates.

  12. Molecular dynamics study of MspA arginine mutants predicts slow DNA translocations and ion current blockades indicative of DNA sequence.

    Science.gov (United States)

    Bhattacharya, Swati; Derrington, Ian M; Pavlenok, Mikhail; Niederweis, Michael; Gundlach, Jens H; Aksimentiev, Aleksei

    2012-08-28

    The protein nanopore Mycobacteria smegmatis porin A (MspA), can be used to sense individual nucleotides within DNA, potentially enabling a technique known as nanopore sequencing. In this technique, single-stranded DNA electrophoretically moves through the nanopore and results in an ionic current that is nucleotide-specific. However, with a high transport velocity of the DNA within the nanopore, the ionic current cannot be used to distinguish signals within noise. Through extensive (~100 μs in total) all-atom molecular dynamics simulations, we examine the effect of positively charged residues on DNA translocation rate and the ionic current blockades in MspA. Simulation of several arginine mutations show a ~10-30 fold reduction of DNA translocation speed without eliminating the nucleotide induced current blockages. Comparison of our results with similar engineering efforts on a different nanopore (α-hemolysin) reveals a nontrivial effect of nanopore geometry on the ionic current blockades in mutant nanopores. PMID:22747101

  13. Accelerated molecular dynamics methods: introduction and recent developments

    Energy Technology Data Exchange (ETDEWEB)

    Uberuaga, Blas Pedro [Los Alamos National Laboratory; Voter, Arthur F [Los Alamos National Laboratory; Perez, Danny [Los Alamos National Laboratory; Shim, Y [UNIV OF TOLEDO; Amar, J G [UNIV OF TOLEDO

    2009-01-01

    A long-standing limitation in the use of molecular dynamics (MD) simulation is that it can only be applied directly to processes that take place on very short timescales: nanoseconds if empirical potentials are employed, or picoseconds if we rely on electronic structure methods. Many processes of interest in chemistry, biochemistry, and materials science require study over microseconds and beyond, due either to the natural timescale for the evolution or to the duration of the experiment of interest. Ignoring the case of liquids xxx, the dynamics on these time scales is typically characterized by infrequent-event transitions, from state to state, usually involving an energy barrier. There is a long and venerable tradition in chemistry of using transition state theory (TST) [10, 19, 23] to directly compute rate constants for these kinds of activated processes. If needed dynamical corrections to the TST rate, and even quantum corrections, can be computed to achieve an accuracy suitable for the problem at hand. These rate constants then allow them to understand the system behavior on longer time scales than we can directly reach with MD. For complex systems with many reaction paths, the TST rates can be fed into a stochastic simulation procedure such as kinetic Monte Carlo xxx, and a direct simulation of the advance of the system through its possible states can be obtained in a probabilistically exact way. A problem that has become more evident in recent years, however, is that for many systems of interest there is a complexity that makes it difficult, if not impossible, to determine all the relevant reaction paths to which TST should be applied. This is a serious issue, as omitted transition pathways can have uncontrollable consequences on the simulated long-time kinetics. Over the last decade or so, we have been developing a new class of methods for treating the long-time dynamics in these complex, infrequent-event systems. Rather than trying to guess in advance what

  14. Computational Studies on the Anharmonic Dynamics of Molecular Clusters

    Science.gov (United States)

    Mancini, John S.

    Molecular nanoclusters present ideal systems to probe the physical forces and dynamics that drive the behavior of larger bulk systems. At the nanocluster limit the first instances of several phenomena can be observed including the breaking of hydrogen and molecular bonds. Advancements in experimental and theoretical techniques have made it possible to explore these phenomena in great detail. The most fruitful of these studies have involved the use of both experimental and theoretical techniques to leverage to strengths of the two approaches. This dissertation seeks to explore several important phenomena of molecular clusters using new and existing theoretical methodologies. Three specific systems are considered, hydrogen chloride clusters, mixed water and hydrogen chloride clusters and the first cluster where hydrogen chloride autoionization occurs. The focus of these studies remain as close as possible to experimentally observable phenomena with the intention of validating, simulating and expanding on experimental work. Specifically, the properties of interested are those related to the vibrational ground and excited state dynamics of these systems. Studies are performed using full and reduced dimensional potential energy surface alongside advanced quantum mechanical methods including diffusion Monte Carlo, vibrational configuration interaction theory and quasi-classical molecular dynamics. The insight gained from these studies are great and varied. A new on-they-fly ab initio method for studying molecular clusters is validated for (HCl)1--6. A landmark study of the dissociation energy and predissociation mechanism of (HCl)3 is reported. The ground states of mixed (HCl)n(H2O)m are found to be highly delocalized across multiple stationary point configurations. Furthermore, it is identified that the consideration of this delocalization is required in vibrational excited state calculations to achieve agreement with experimental measurements. Finally, the theoretical

  15. Molecular Dynamics Simulation of Carbon Nanotube Based Gears

    Science.gov (United States)

    Han, Jie; Globus, Al; Jaffe, Richard; Deardorff, Glenn; Chancellor, Marisa K. (Technical Monitor)

    1996-01-01

    We used molecular dynamics to investigate the properties and design space of molecular gears fashioned from carbon nanotubes with teeth added via a benzyne reaction known to occur with C60. A modified, parallelized version of Brenner's potential was used to model interatomic forces within each molecule. A Leonard-Jones 6-12 potential was used for forces between molecules. One gear was powered by forcing the atoms near the end of the buckytube to rotate, and a second gear was allowed.to rotate by keeping the atoms near the end of its buckytube on a cylinder. The meshing aromatic gear teeth transfer angular momentum from the powered gear to the driven gear. A number of gear and gear/shaft configurations were simulated. Cases in vacuum and with an inert atmosphere were examined. In an extension to molecular dynamics technology, some simulations used a thermostat on the atmosphere while the hydrocarbon gear's temperature was allowed to fluctuate. This models cooling the gears with an atmosphere. Results suggest that these gears can operate at up to 50-100 gigahertz in a vacuum or inert atmosphere at room temperature. The failure mode involves tooth slip, not bond breaking, so failed gears can be returned to operation by lowering temperature and/or rotation rate. Videos and atomic trajectory files in xyz format are presented.

  16. A molecular understanding of the dynamic mechanism of aquaporin osmosis

    CERN Document Server

    Shua, Liangsuo; Qian, Xin; Wanga, Xiyun; Lin, Yixin; Tan, Kai; Shu, Chaohui; Jin, Shiping

    2014-01-01

    AQPs (aquaporins), the rapid water channels of cells, play a key role in maintaining osmotic equilibrium of cells. In this paper, we reported the dynamic mechanism of AQP osmosis at the molecular level. A theoretical model based on molecular dynamics was carried out and verified by the published experimental data. The reflection coefficients ({\\sigma}) of neutral molecules are mainly decided by their relative size with AQPs, and increase with a third power up to a constant value 1. This model also indicated that the reflection coefficient of a complete impermeable solute can be smaller than 1. The H+ concentration of solution can influence the driving force of the AQPs by changing the equivalent diameters of vestibules surrounded by loops with abundant polar amino acids. In this way, pH of solution can regulate water permeability of AQPs. Therefore, an AQP may not only work as a switch to open or close, but as a rapid response molecular valve to control its water flow. The vestibules can prevent the channel b...

  17. Accurate modeling of molecular optical properties by a combination of molecular dynamics and quantum chemistry

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, Valery; Bouř, Petr

    Katowice : University of Silesia, 2014. O6. [Chemistry towards Biology. Central Europe Conference /7./. 09.09.2014-12.09.2014, Katowice] R&D Projects: GA ČR(CZ) GA14-03564S Grant ostatní: AV ČR(CZ) M200550902 Institutional support: RVO:61388963 Keywords : molecular dynamics * quantum chemistry * multi-scale spectra Subject RIV: CF - Physical ; Theoretical Chemistry

  18. Structural and Dynamic Properties of Amorphous Silicon:Tight-Binding Molecular Dynamics Simulation

    Institute of Scientific and Technical Information of China (English)

    HUANG Shi-Ping; WANG Wen-Chuan

    2004-01-01

    @@ The tight-binding molecular dynamics simulation has been performed to study structural and dynamical properties of amorphous silicon. It is found that the radial distribution function and static structure factor are in good agreement with the experimental measurements. The bond order parameters Ql are sensitive to the structure change at different quenching rates. For the dynamical properties, we have calculated the vibration and electronic density of states. The simulation results show that the transverse acoustic is in good agreement with the experimental data, and the high frequency transverse optical (TO) peak shifts to the right of the experimental TO peak.

  19. Study of critical dynamics in fluids via molecular dynamics in canonical ensemble.

    Science.gov (United States)

    Roy, Sutapa; Das, Subir K

    2015-12-01

    With the objective of understanding the usefulness of thermostats in the study of dynamic critical phenomena in fluids, we present results for transport properties in a binary Lennard-Jones fluid that exhibits liquid-liquid phase transition. Various collective transport properties, calculated from the molecular dynamics (MD) simulations in canonical ensemble, with different thermostats, are compared with those obtained from MD simulations in microcanonical ensemble. It is observed that the Nosé-Hoover and dissipative particle dynamics thermostats are useful for the calculations of mutual diffusivity and shear viscosity. The Nosé-Hoover thermostat, however, as opposed to the latter, appears inadequate for the study of bulk viscosity. PMID:26687057

  20. Gas-Phase Molecular Dynamics: Theoretical Studies In Spectroscopy and Chemical Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Yu H. G.; Muckerman, J.T.

    2012-05-29

    The main goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods, and extends them to understand some important properties of materials in condensed phases and interstellar medium as well as in combustion environments.

  1. Visualization of Early Events in Acetic Acid Denaturation of HIV-1 Protease: A Molecular Dynamics Study

    OpenAIRE

    Borkar, Aditi Narendra; Rout, Manoj Kumar; Hosur, Ramakrishna V.

    2011-01-01

    Protein denaturation plays a crucial role in cellular processes. In this study, denaturation of HIV-1 Protease (PR) was investigated by all-atom MD simulations in explicit solvent. The PR dimer and monomer were simulated separately in 9 M acetic acid (9 M AcOH) solution and water to study the denaturation process of PR in acetic acid environment. Direct visualization of the denaturation dynamics that is readily available from such simulations has been presented. Our simulations in 9 M AcOH re...

  2. DYNAMIC SURFACE BOUNDARY-CONDITIONS - A SIMPLE BOUNDARY MODEL FOR MOLECULAR-DYNAMICS SIMULATIONS

    NARCIS (Netherlands)

    JUFFER, AH; BERENDSEN, HJC

    1993-01-01

    A simple model for the treatment of boundaries in molecular dynamics simulations is presented. The method involves the positioning of boundary atoms on a surface that surrounds a system of interest. The boundary atoms interact with the inner region and represent the effect of atoms outside the surfa

  3. Molecular dynamics simulations of Pd-Ni transition metal alloys

    International Nuclear Information System (INIS)

    Molecular Dynamics simulations are performed to study bulk properties of fcc metals and metal alloys by using the quantum Sutton-Chen many-body potentials within the context of the tight-binding approach. The Molecular Dynamics algorithms we used in the simulations of Pd-Ni alloys are based on an extended Hamiltonian formalism arising from the works of Andersen (1980), Parinello and Rahman (1980), Nose (1984), Hoover (1985) and Cagin (1988). In these simulations, the effect of temperature and concentration on the solid and liquid properties are studied. Elastic constants and phonon dispersion relation are the solid properties we simulated in this work. Dynamic and static properties of liquid Pd-Ni are also computed by examining the behavior of density, enthalpy, pair distribution function and structure factor. The melting temperatures of Pd-Ni alloys are investigated. The diffusion coefficients are calculated from the mean square displacement using Einstein relation and from velocity auto-correlation function using Green-Kubo relations. The simulation results are in good agreement with the experiments

  4. Non-adiabatic molecular dynamics by accelerated semiclassical Monte Carlo

    International Nuclear Information System (INIS)

    Non-adiabatic dynamics, where systems non-radiatively transition between electronic states, plays a crucial role in many photo-physical processes, such as fluorescence, phosphorescence, and photoisomerization. Methods for the simulation of non-adiabatic dynamics are typically either numerically impractical, highly complex, or based on approximations which can result in failure for even simple systems. Recently, the Semiclassical Monte Carlo (SCMC) approach was developed in an attempt to combine the accuracy of rigorous semiclassical methods with the efficiency and simplicity of widely used surface hopping methods. However, while SCMC was found to be more efficient than other semiclassical methods, it is not yet as efficient as is needed to be used for large molecular systems. Here, we have developed two new methods: the accelerated-SCMC and the accelerated-SCMC with re-Gaussianization, which reduce the cost of the SCMC algorithm up to two orders of magnitude for certain systems. In most cases shown here, the new procedures are nearly as efficient as the commonly used surface hopping schemes, with little to no loss of accuracy. This implies that these modified SCMC algorithms will be of practical numerical solutions for simulating non-adiabatic dynamics in realistic molecular systems

  5. Non-adiabatic molecular dynamics by accelerated semiclassical Monte Carlo

    International Nuclear Information System (INIS)

    Non-adiabatic dynamics, where systems non-radiatively transition between electronic states, plays a crucial role in many photo-physical processes, such as fluorescence, phosphorescence, and photoisomerization. Methods for the simulation of non-adiabatic dynamics are typically either numerically impractical, highly complex, or based on approximations which can result in failure for even simple systems. Recently, the Semiclassical Monte Carlo (SCMC) approach was developed in an attempt to combine the accuracy of rigorous semiclassical methods with the efficiency and simplicity of widely used surface hopping methods. However, while SCMC was found to be more efficient than other semiclassical methods, it is not yet as efficient as is needed to be used for large molecular systems. Here, we have developed two new methods: the accelerated-SCMC and the accelerated-SCMC with re-Gaussianization, which reduce the cost of the SCMC algorithm up to two orders of magnitude for certain systems. In many cases shown here, the new procedures are nearly as efficient as the commonly used surface hopping schemes, with little to no loss of accuracy. This implies that these modified SCMC algorithms will be of practical numerical solutions for simulating non-adiabatic dynamics in realistic molecular systems

  6. Modeling and Computer Simulation: Molecular Dynamics and Kinetic Monte Carlo

    Energy Technology Data Exchange (ETDEWEB)

    Wirth, B.D.; Caturla, M.J.; Diaz de la Rubia, T.

    2000-10-10

    Recent years have witnessed tremendous advances in the realistic multiscale simulation of complex physical phenomena, such as irradiation and aging effects of materials, made possible by the enormous progress achieved in computational physics for calculating reliable, yet tractable interatomic potentials and the vast improvements in computational power and parallel computing. As a result, computational materials science is emerging as an important complement to theory and experiment to provide fundamental materials science insight. This article describes the atomistic modeling techniques of molecular dynamics (MD) and kinetic Monte Carlo (KMC), and an example of their application to radiation damage production and accumulation in metals. It is important to note at the outset that the primary objective of atomistic computer simulation should be obtaining physical insight into atomic-level processes. Classical molecular dynamics is a powerful method for obtaining insight about the dynamics of physical processes that occur on relatively short time scales. Current computational capability allows treatment of atomic systems containing as many as 10{sup 9} atoms for times on the order of 100 ns (10{sup -7}s). The main limitation of classical MD simulation is the relatively short times accessible. Kinetic Monte Carlo provides the ability to reach macroscopic times by modeling diffusional processes and time-scales rather than individual atomic vibrations. Coupling MD and KMC has developed into a powerful, multiscale tool for the simulation of radiation damage in metals.

  7. Molecular dynamics simulations of peptide adsorption on self-assembled monolayers

    Science.gov (United States)

    Xie, Yun; Liu, Meifeng; Zhou, Jian

    2012-08-01

    All-atom molecular dynamics simulations are performed to investigate the neuromedin-B peptide adsorption on the self-assembled monolayers (SAMs) of SH(CH2)10N+(CH3)2CH2CH(OH)CH2SO3- (SBT), SH(CH2)10OH and SH(CH2)10CH3. The force-distance profiles show that the surface resistance to peptide adsorption is mainly generated by the water molecules tightly bound to surfaces via hydrogen bonds (hydration water molecules); but surfaces themselves may also set an energy barrier for the approaching peptide. For the SBT-SAM, the surface first exerts a relatively high repulsive force and then a rather week attractive force on the approaching peptide; meanwhile the hydration water molecules exert a strong repulsive force on the peptide. Therefore, SBT-SAM has an excellent performance on resisting protein adsorption. For the OH-SAM and CH3-SAM, surfaces show low or little energy barrier but strong affinity to the peptide; and the hydration water molecules apply merely a repulsive force within a much narrower range and with lower intensity compared with the case for the SBT-SAM. The analysis of structural and dynamical properties of the peptide, surface and water indicates that possible factors contributing to surface resistance include the hydrogen-bond formation capability of surfaces, mobility of water molecules near surfaces, surface packing density and chain flexibility of SAMs. There are a large number of hydrogen bonds formed between the hydration water molecules and the functional groups of the SBT-SAM, which greatly lowers the mobility of water molecules near the surface. This tightly-bound water layer effectively reduces the direct contact between the surface and the peptide. Furthermore, the SBT-SAM also has a high flexibility and a low surface packing density, which allows water molecules to penetrate into the surface to form tightly-bound networks and therefore reduces the affinity between the peptide and the surface. The results show that the protein

  8. Molecular dynamics simulations of peptide adsorption on self-assembled monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Xie Yun; Liu Meifeng [School of Chemistry and Chemical Engineering, Guangdong Provincial Key Lab for Green Chemical Product Technology, South China University of Technology, Guangzhou, Guangdong Province, 510640 (China); Zhou Jian, E-mail: jianzhou@scut.edu.cn [School of Chemistry and Chemical Engineering, Guangdong Provincial Key Lab for Green Chemical Product Technology, South China University of Technology, Guangzhou, Guangdong Province, 510640 (China)

    2012-08-01

    All-atom molecular dynamics simulations are performed to investigate the neuromedin-B peptide adsorption on the self-assembled monolayers (SAMs) of SH(CH{sub 2}){sub 10}N{sup +}(CH{sub 3}){sub 2}CH{sub 2}CH(OH)CH{sub 2}SO{sub 3}{sup -} (SBT), SH(CH{sub 2}){sub 10}OH and SH(CH{sub 2}){sub 10}CH{sub 3}. The force-distance profiles show that the surface resistance to peptide adsorption is mainly generated by the water molecules tightly bound to surfaces via hydrogen bonds (hydration water molecules); but surfaces themselves may also set an energy barrier for the approaching peptide. For the SBT-SAM, the surface first exerts a relatively high repulsive force and then a rather week attractive force on the approaching peptide; meanwhile the hydration water molecules exert a strong repulsive force on the peptide. Therefore, SBT-SAM has an excellent performance on resisting protein adsorption. For the OH-SAM and CH{sub 3}-SAM, surfaces show low or little energy barrier but strong affinity to the peptide; and the hydration water molecules apply merely a repulsive force within a much narrower range and with lower intensity compared with the case for the SBT-SAM. The analysis of structural and dynamical properties of the peptide, surface and water indicates that possible factors contributing to surface resistance include the hydrogen-bond formation capability of surfaces, mobility of water molecules near surfaces, surface packing density and chain flexibility of SAMs. There are a large number of hydrogen bonds formed between the hydration water molecules and the functional groups of the SBT-SAM, which greatly lowers the mobility of water molecules near the surface. This tightly-bound water layer effectively reduces the direct contact between the surface and the peptide. Furthermore, the SBT-SAM also has a high flexibility and a low surface packing density, which allows water molecules to penetrate into the surface to form tightly-bound networks and therefore reduces the

  9. Kinetic theory molecular dynamics and hot dense matter: Theoretical foundations

    Science.gov (United States)

    Graziani, F. R.; Bauer, J. D.; Murillo, M. S.

    2014-09-01

    Electrons are weakly coupled in hot, dense matter that is created in high-energy-density experiments. They are also mildly quantum mechanical and the ions associated with them are classical and may be strongly coupled. In addition, the dynamical evolution of plasmas under these hot, dense matter conditions involve a variety of transport and energy exchange processes. Quantum kinetic theory is an ideal tool for treating the electrons but it is not adequate for treating the ions. Molecular dynamics is perfectly suited to describe the classical, strongly coupled ions but not the electrons. We develop a method that combines a Wigner kinetic treatment of the electrons with classical molecular dynamics for the ions. We refer to this hybrid method as "kinetic theory molecular dynamics," or KTMD. The purpose of this paper is to derive KTMD from first principles and place it on a firm theoretical foundation. The framework that KTMD provides for simulating plasmas in the hot, dense regime is particularly useful since current computational methods are generally limited by their inability to treat the dynamical quantum evolution of the electronic component. Using the N-body von Neumann equation for the electron-proton plasma, three variations of KTMD are obtained. Each variant is determined by the physical state of the plasma (e.g., collisional versus collisionless). The first variant of KTMD yields a closed set of equations consisting of a mean-field quantum kinetic equation for the electron one-particle distribution function coupled to a classical Liouville equation for the protons. The latter equation includes both proton-proton Coulombic interactions and an effective electron-proton interaction that involves the convolution of the electron density with the electron-proton Coulomb potential. The mean-field approach is then extended to incorporate equilibrium electron-proton correlations through the Singwi-Tosi-Land-Sjolander (STLS) ansatz. This is the second variant of KTMD

  10. Dynamics of water and solute transport in polymeric reverse osmosis membranes via molecular dynamics simulations

    CERN Document Server

    Shen, Meng; Lueptow, Richard M

    2016-01-01

    The Angstrom-scale transport characteristics of water and six different solutes, methanol, ethanol, 2-propanol, urea, Na+, and Cl-, were studied for a polyamide reverse osmosis (RO) membrane, FT-30, using non-equilibrium molecular dynamics (NEMD) simulations. Results indicate that water transport increases with an increasing fraction of connected percolated free volume, or water-accessible open space, in the membrane polymer structure. This free volume is enhanced by the dynamic structure of the membrane at the molecular level as it swells when hydrated and vibrates due to molecular collisions allowing a continuous path connecting the opposite membrane surfaces. The tortuous paths available for transport of solutes result in Brownian motion of solute molecules and hopping from pore to pore as they pass through the polymer network structure of the membrane. The transport of alcohol solutes decreases for solutes with larger Van der Waals volume, which corresponds to less available percolated free volume, or sol...

  11. Nanochannel flow past permeable walls via molecular dynamics

    Science.gov (United States)

    Xie, Jian-Fei; Cao, Bing-Yang

    2016-07-01

    The nanochannel flow past permeable walls with nanopores is investigated by molecular dynamics (MD) simulations, including the density distribution, velocity field, molecular penetration mechanism and surface friction coefficient. A low density distribution has been found at the gas-wall interface demonstrating the low pressure region. In addition, there exists a jump of the gas density on the permeable surface, which indicates the discontinuity of the density distribution across the permeable surface. On the other hand, the nanoscale vortices are observed in nanopores of the permeable wall, and the reduced mass flux of the flow in nanopores results in a shifted hydrodynamic boundary above the permeable surface. Particularly the slip length of the gas flow on the permeable surface is pronounced a non-linear function of the molecular mean free path, which produces a large value of the tangential momentum accommodation coefficient (TMAC) and a big portion of the diffusive refection. Moreover, the gas-gas interaction and multi-collision among gas molecules may take place in nanopores, which contribute to large values of TMAC. Consequently the boundary friction coefficient on the permeable surface is increased because of the energy dissipation consumed by the nanoscale vortices in nanopores. The molecular boundary condition provides us with a new picture of the nanochannel flow past the permeable wall with nanopores.

  12. Generalized master equations for exciton dynamics in molecular systems

    Science.gov (United States)

    Schreiber, Michael; May, V.

    1995-02-01

    The paper demonstrates the applicability of a special type of density matrix theory for the derivation of generalized Master equations. The density matrix theory has been formulated for the description of the dissipative electron transfer dynamics in molecular complexes. The theoretical approach is based on a representation of the density matrix in appropriately taken diabatic electron-vibrational states. Dissipative effects are taken into account by a coupling of these states to further vibrational modes of the molecular complex as well as to environmental degrees of freedom. The approach is applied to a two-center system as well as to a molecular chain. Memory kernels are derived in second order with respect to the inter-center coupling. The kernels are discussed under the assumption of a quick intra-center relaxation for a part of the vibrational modes as well as for all vibrational modes. Standard expressions for the transition rates between different sites are extended to include finite life times of the vibrational levels. Results which have been obtained in the study of the so-called spin boson model can be simply reproduced. The application of the derived generalized Master equations to the investigation of the motion of Frenkel excitons in molecular chains is also presented.

  13. Dynamics of Nanoscale Grain-Boundary Decohesion in Aluminum by Molecular-Dynamics Simulation

    Science.gov (United States)

    Yamakov, V.; Saether, E.; Phillips, D. R.; Glaessegen, E. H.

    2007-01-01

    The dynamics and energetics of intergranular crack growth along a flat grain boundary in aluminum is studied by a molecular-dynamics simulation model for crack propagation under steady-state conditions. Using the ability of the molecular-dynamics simulation to identify atoms involved in different atomistic mechanisms, it was possible to identify the energy contribution of different processes taking place during crack growth. The energy contributions were divided as: elastic energy, defined as the potential energy of the atoms in fcc crystallographic state; and plastically stored energy, the energy of stacking faults and twin boundaries; grain-boundary and surface energy. In addition, monitoring the amount of heat exchange with the molecular-dynamics thermostat gives the energy dissipated as heat in the system. The energetic analysis indicates that the majority of energy in a fast growing crack is dissipated as heat. This dissipation increases linearly at low speed, and faster than linear at speeds approaching 1/3 the Rayleigh wave speed when the crack tip becomes dynamically unstable producing periodic dislocation bursts until the crack is blunted.

  14. Molecular Dynamics Simulations of Solutions at Constant Chemical Potential

    CERN Document Server

    Perego, Claudio; Parrinello, Michele

    2015-01-01

    Molecular Dynamics studies of chemical processes in solution are of great value in a wide spectrum of applications, that range from nano-technology to pharmaceutical chemistry. However, these calculations are affected by severe finite-size effects, such as the solution being depleted as the chemical process proceeds, that influence the outcome of the simulations. To overcome these limitations, one must allow the system to exchange molecules with a macroscopic reservoir, thus sampling a Grand-Canonical ensemble. Despite the fact that different remedies have been proposed, this still represents a key challenge in molecular simulations. In the present work we propose the C$\\mu$MD method, which introduces an external force that controls the environment of the chemical process of interest. This external force, drawing molecules from a finite reservoir, maintains the chemical potential constant in the region where the process takes place. We have applied the C$\\mu$MD method to the paradigmatic case of urea crystall...

  15. Molecular dynamics study of the water/n-alkane interface

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Molecular dynamics simulations on the interface between liquid water and liquid n-alkane (including octane, nonane, decane, undecane and dodecane) have been performed with the purpose to study the interfacial properties: (Ⅰ) density profile; (Ⅱ) molecular orientation; (Ⅲ) interfacial tension and the temperature effect on the interfacial tension. Simulation results show that at the interface the structures of both water and n-alkane are different from those in the bulk. Water has an orientational preference due to the number of hydrogen bonds per molecule maximized. N-alkane has a more lateral orientation with respect to the interface in order to be in close contact with water. The calculated individual phase bulk density and interfacial tension of water/n-alkane systems are in good agreement with the corresponding experimental ones.

  16. Sugar transport across lactose permease probed by steered molecular dynamics

    DEFF Research Database (Denmark)

    Jensen, Morten Østergaard; Yin, Ying; Tajkhorshid, Emad;

    2007-01-01

    Escherichia coli lactose permease (LacY) transports sugar across the inner membrane of the bacterium using the proton motive force to accumulate sugar in the cytosol. We have probed lactose conduction across LacY using steered molecular dynamics, permitting us to follow molecular and energetic......, forcing it to interact with channel lining residues. Lactose forms a multitude of direct sugar-channel hydrogen bonds, predominantly with residues of the flexible N-domain, which is known to contribute a major part of LacY's affinity for lactose. In the periplasmic half-channel lactose predominantly......-sugar interaction maximal. Upon unbinding from the binding pocket, lactose undergoes a rotation to permeate either half-channel with its long axis aligned parallel to the channel axis. The results hint at the possibility of a transport mechanism, in which lactose permeates LacY through a narrow periplasmic half...

  17. Molecular Dynamics Simulations of Homogeneous Crystallization in Polymer Melt

    Science.gov (United States)

    Kong, Bin

    2015-03-01

    Molecular mechanisms of homogeneous nucleation and crystal growth from the melt of polyethylene-like polymer were investigated by molecular dynamics simulations. The crystallinity was determined by using the site order parameter method (SOP), which described local order degree around an atom. Snapshots of the simulations showed evolution of the nucleation and the crystal growth through SOP images clearly. The isothermal crystallization kinetics was determined at different temperatures. The rate of crystallization, Kc, and the Avrami exponents, n, were determined as a function of temperature. The forming of nucleis was traced to reveal that the nucleis were formed with more ordered cores and less ordered shells. A detailed statistical analysis of the MD snapshots and trajectories suggested conformations of the polymer chains changed smoothly from random coil to chain folded lamella in the crystallization processes.

  18. Molecular Modeling of Enzyme Dynamics Towards Understanding Solvent Effects

    DEFF Research Database (Denmark)

    Wedberg, Nils Hejle Rasmus Ingemar

    This thesis describes the development of a molecular simulation methodology to study properties of enzymes in non-aqueous media at fixed thermodynamic water activities. The methodology is applied in a molecular dynamics study of the industrially important enzyme Candida antarctica lipase B (CALB...... of enzyme kinetics in non-aqueous media, it has been a fruitful approach to fix the enzyme hydration level by controlling the water activity of the medium. In this work, a protocol is therefore developed for determining the water activity in non-aqueous protein simulations. The method relies on determining...... the system size of the simulation box generally used in simulation. Therefore, a method is developed for extending the RDFs to arbitrary distances so that the integrals can be evaluated. The method, which was first used in the classical study of the Lennard-Jones fluid by Verlet (Verlet (1968), Phys. Rev...

  19. Classical molecular dynamics investigations of biphenyl-based carbon nanomembranes

    Directory of Open Access Journals (Sweden)

    Andreas Mrugalla

    2014-06-01

    Full Text Available Background: Free-standing carbon nanomembranes (CNM with molecular thickness and macroscopic size are fascinating objects both for fundamental reasons and for applications in nanotechnology. Although being made from simple and identical precursors their internal structure is not fully known and hard to simulate due to the large system size that is necessary to draw definite conclusions.Results: We performed large-scale classical molecular dynamics investigations of biphenyl-based carbon nanomembranes. We show that one-dimensional graphene-like stripes constitute a highly symmetric quasi one-dimensional energetically favorable ground state. This state does not cross-link. Instead cross-linked structures are formed from highly excited precursors with a sufficient amount of broken phenyls.Conclusion: The internal structure of the CNM is very likely described by a disordered metastable state which is formed in the energetic initial process of electron irradiation and depends on the process of relaxation into the sheet phase.

  20. Dynamical Transition of Myoglobin and Cu/Zn Superoxide Dismutase Revealed by Molecular Dynamics Simulation

    Institute of Scientific and Technical Information of China (English)

    张莉莉; 张建华; 周林祥

    2002-01-01

    We have carried out parallel molecular dynamics simulations of solvated and non-solvated myoglobin and solvated Cu/Zn superoxide dismutase at different temperatures. By analysis of several methods, the simulations reproduce the quasielastic neutron scattering experimental results. Below 200 K these two proteins behave as harmonic solids with essentially only vibrational motion, while above this temperature, there is a striking dynamic transition into anharmonic motion. Moreover, the simulations further show that water molecules play an important role for this dynamical transition. There is no such sharp dynamical transition in non-solvated proteins and the higher the solvate density is, the steeper at transition point the curve of mean square displacement versus temperature will be. The simulations also display that the dynamical transition is a general property for globular protein and this transition temperature is a demarcation of enzyme activity.