Condensed-phase Optimized Molecular Potentials For Atomistic Simulation Studies Research Articles

Anticorrosion mechanism of natural acidic amino acids on steel in chloride solution: Experimental, theoretical and machine learning approaches

This paper investigates the corrosion inhibition of steel by two natural acidic amino acids, glutamic acid and aspartic acid, in a 3.5 wt% NaCl solution. The anti-corrosion activity is evaluated using various electrochemical tests, such as potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV), in addition to quantum chemical calculation and molecular dynamic simulation. Results indicate that the natural compounds act as mixed-type inhibitors with a predominance of anodic inhibition and effectively increase charge transfer resistance and resistance to the solubility of Fe into Fe2+ as inhibitor concentration increases. At a concentration of 0.2 g/L, the inhibition efficiency reaches 57.84% for glutamic acid and 42.99% for aspartic acid. Moreover, the quantum chemistry calculations and molecular dynamics simulations, based on density functional theory (DFT) and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field methods respectively, demonstrate that glutamic acid shows superior corrosion inhibition performance as it has higher binding energy and more stable adsorption on the steel surface than aspartic acid. Additionally, machine learning (ML) methods, including regression analysis and Logic regression, are employed to analyze the data and confirm the better corrosion inhibition performance of glutamate compared to aspartate.

Study of elastic anisotropy for 1, 3, 5-trinitro-1, 3, 5-triazacyclohexane by supramolecular structural unit

The relation between elastic property and crystal structure provides a foundation for designing new materials with desired properties and understanding the chemical decomposition and explosion of energetic materials. The supramolecular structural unit is proposed as the smallest chemical unit to quantitatively characterize the elastic anisotropy of 1, 3, 5-trinitro-1, 3, 5-triazacyclohexane (RDX). The supramolecular structural unit refers to the nearest-neighbor coordination polyhedron of one molecule. The supramolecular structural unit of RDX is composed of 15 molecules, and analyzed by the total molecular number density and the density of intermolecular interactions. The elastic modulus model is established on the assumption that 1) the RDX molecule is of sphere and rigid-body; 2) the intermolecular interaction is regarded as a linear spring, i.e. it is described by a bond-spring model; 3) the molecules are close-packed in the series mode. The elastic modulus model based on the supramolecular structural unit demonstrates that the elastic modulus is intrinsically determined by the total molecular number, the equilibrium distance of the molecular pair, the intermolecular force constant, and the angle between the intermolecular non-bonding interaction and the normal to crystal face. The intermolecular force constant is calculated as the second derivative of the intermolecular interaction with respect to the equilibrium centroid distance. The intermolecular interaction is expressed as the summation of van der Waals and electrostatic interactions calculated by COMPASS (condensed-phase optimized molecular potentials for atomistic simulation studies) II forcefield. The calculated elastic moduli are 21.7, 17.1, 20.1, 19.1, and 15.3 GPa for RDX (100), (010), (001), (210), and (021) crystal faces, respectively. The calculation results are consistent with the theoretical values computed by the density functional theory. Excluding RDX(001), the calculated elastic moduli accord with the experimental results measured by the resonant ultrasound spectroscopy (RUS), impulsive stimulated thermal scattering, Brillouin spectroscopy, and nanoindentation methods. The theoretical value (20.1 GPa) of RDX(001) overestimates the experimental values in a range of 15.9–16.6 GPa. The reason can be attributed to the rigid-body approximation for flexible molecules, in which are ignored the motion and deformation of the ring and NO<sub>2</sub> groups when the external loads are applied to RDX(001). The results suggest that the supramolecular structural unit can be the smallest chemical unit to quantitatively characterize the elastic anisotropy of RDX and the elastic anisotropy is mainly due to the angle between the intermolecular interaction and the normal to crystal face.

Adhesive Strength of Hexadecane on Different Iron Compounds: an MD Approach

The lubricity of alkane is a research target for numerous tribological applications in either industrial area or fundamental scientific studies. In the current work, a comparative investigation using a classical molecular dynamics (MD) method is carried out to investigate the effect of pure iron and its oxide surfaces on structural properties, adsorption ability of hexadecane (C16H34). A reliable force field (FF) of condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) is employed to describe the intra- and intermolecular interactions for hexadecane and its interaction with iron oxide surfaces, while the interaction between hexadecane and pure iron is derived from an ab initio result. Regarding the surfaces, the pure iron surfaces are considered using embedded-atom method/Finnis-Sinclair potential (EAM/FS), while the iron oxide surfaces are constructed using the traditional Buckingham force field. The results reveal that hexadecane shows preferential adsorption on iron oxide surfaces compared to pure iron.

Anionic Tuning of Zeolite Crystallization

Zeolites are of great industrial relevance as catalysts, adsorbents, and ion-exchangers and typically synthesized under hydrothermal conditions. Rational regulation of their crystallization process...

Parameterization of a COMPASS force field for single layer blue phosphorene

We parameterize an accurate force field for single-layer blue phosphorene based on the framework of COMPASS (a nomenclature of condensed-phase optimized molecular potentials for atomistic simulation studies). During parameterization, the biaxial-strained samples and blue phosphorene nanotubes, as well as the phonon dispersion, are adopted as training sets. The combination of genetic algorithm and the simplex method finally leads to optimized parameters of the COMPASS force field whose accuracy is manifested by the excellent agreement between mechanical and vibrational properties predicted by our best-fitted COMPASS model and the ones by first-principles calculations. Such a high-accurate force field would be a good starting point for studying many physical properties of blue phosphorene based materials.

Evaluation of the intermolecular interactions and polymorphism of mefenamic acid crystals in N,N-dimethyl formamide solution: A molecular dynamics simulation and experimental study

Mefenamic acid [2-(2,3-dimethylphenyl)aminobenzoic acid] has been known to exist in different polymorphic forms. This study investigates the polymorphism of mefenamic acid in N , N -dimethyl formamide (DMF) through the combination of molecular dynamic simulations and experimental study. The molecular dynamic simulations were performed using the Material Studio 5.5 simulation package with a Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field. The simulation trajectory files were analyzed for radial distribution functions to investigate the intermolecular interactions. The experimental study was performed by the cooling crystallization method with DMF as the solvent. The saturated solution and crystals produced were analyzed by Fourier transform infrared spectroscopy, X-ray powder diffractometry, and scanning electron microscopy. The radial distribution function results showed the formation of a strong hydrogen bond between the solute–solute and solute–solvent interfaces, which were O1MA⋯H5MA and O F ⋯H15MA, respectively. The Fourier transform infrared results revealed the existence of O–H, N–H, and C O bonds, which contributed to the formation of a hydrogen motif in the mefenamic acid during crystallization with DMF as the solvent. The X-ray powder diffractometry and scanning electron microscopy results confirmed the formation of mefenamic acid form II crystals in cubic shape. Crystallization using different solvents may produce crystals with different polymorphic forms. The intermolecular solute–solute, solute–solvent, and solvent–solvent interactions existing in the solution control the self-assembly of mefenamic acid molecules and result in the formation of different polymorphs.

Impact sensitivity and moisture adsorption on the surface of CL-20/TNT cocrystal by molecular dynamics simulation

Water molecules in the air can be absorbed on the surface of the explosives in storage and transport process, which may lead to the transformation of sensitivity and storage safety. The interactions between cocrystal and water molecules are identified as a process of physical adsorption. To explore the effects of moisture sorption on the storage safety, this paper took the cocrystal composed of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 2,4,6-trinitrotoluene (TNT) in a 1:1 M ratio as the research object, and molecular dynamics simulation was conducted on the cocrystal for (0 0 1), (0 1 0), (1 0 0) crystal plane in COMPASS (condensed-phase optimized molecular potentials for atomistic simulation studies) force field. It turns out that there are hydrogen bonding interactions between the water molecules and the molecules in the cocrystal by analyzing the Radial distribution function diagrams. The length of trigger bond and the cohesive energy density of the cocrystal are adopted as theoretical criterion of sensitivity. The results indicate that it takes less energy for the NN bonds to rupture and the explosives would have higher sensitivity when water molecules are absorbed on the surface.

Development of a fused-sphere SAFT-γ Mie force field for poly(vinyl alcohol) and poly(ethylene)

SAFT-γ Mie, a group-contribution equation of state rooted in Statistical Associating Fluid Theory, provides an efficient framework for developing accurate, transferable coarse-grained force fields for molecular simulation. Building on the success of SAFT-γ Mie force fields for small molecules, we address two key issues in extending the SAFT-γ Mie coarse-graining methodology to polymers: (1) the treatment of polymer chain rigidity and (2) the disparity between the structure of linear chains of tangent spheres and the structure of the real polymers. We use Boltzmann inversion to derive effective bond-stretching and angle-bending potentials mapped from all-atom oligomer molecular dynamics (MD) simulations to the coarse-grained sites and a fused-sphere version of SAFT-γ Mie as the basis for non-bonded interactions. The introduction of an overlap parameter between Mie spheres leads to a degeneracy when fitting to monomer vapor-liquid equilibria (VLE) data, which we resolve by matching polymer density from coarse-grained MD simulation with that from all-atom simulation. The result is a chain of monomers rigorously parameterized to experimental VLE data and with structural detail consistent with all-atom simulations. We test our approach on atactic poly(vinyl alcohol) and polyethylene and compare the results for SAFT-γ Mie models with structural detail mapped from the Optimized Potentials for Liquid Simulations (OPLS) and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) all-atom force fields.

An Insight into molecular structure and properties of flexible amorphous polymers: A molecular dynamics simulation approach

ABSTRACTVisualization of polymer molecules by molecular dynamics simulation remains a challenging area in molecular modeling, as it involves a number of factors like type of force field, simulation time, simulation steps, and so forth. In our present study, we have used the condensed‐phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field, which is specific for polymers and organic molecules, in order to visualize the macromolecular chains of various flexible amorphous polymers: natural rubber, polybutadiene rubber, styrene–butadiene rubber, nitrile rubber, polychloroprene rubber, and fluoroelastomer. The study covered a wide range from nonpolar rubbers to polar rubbers, and the COMPASS force field was promising to understand the local structure and the packing of the chains inside the simulation box. The distance between different adjacent pairs of carbon atoms within the polymer chains was discussed in detail from intramolecular radial distribution function and represented pictorially in the polymer chains. Various bond angles were also examined for further details. In addition, interchain contacts, glass‐transition temperature, and solubility parameter were predicted and compared with the experimental values. The diffusive characteristic of the chains was assessed by mean square displacement which in turn described the polymer chain mobility. In essence, the present study is expected to aid in the vivid conceptualization of molecular orientation of various polymers and would help in predicting various physical properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47457

Vapor sensing and interface properties of reduced graphene oxide–poly(methyl methacrylate) nanocomposite

Synthesized reduced graphene oxide–poly(methyl methacrylate) (RGO–PMMA) nanocomposites were characterized by differential scanning calorimetry, thermogravimetric analysis, and probed for volatile organic compounds (VOC) sensing. A molecular dynamics simulation is performed to investigate the interaction between PMMA and a graphene surface. The condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS), polymer consistent force-field (PCFF) and consistent valence force-field (CVFF) are used to describe the interaction of the graphene–PMMA. None of the three simulated force fields COMPASS, PCFF, and CVFF exhibits a distinctive behaviour of interaction between graphene and PMMA, but CVFF predicts a higher interaction energy in comparison with the simulated force fields COMPASS and PCFF. Experimentally, the selective response for different VOC has been analysed and the highest response together with the fastest recovery is obtained for tetrahydrofuran. A model is introduced explaining observed features.

Rheological properties of super critical CO2 with CuO: Multi-scale computational modeling.

A multi-scale computational methodology based on the density functional theory and molecular dynamics has been used to investigate the rheological properties of super critical CO2 with CuO nano-particle (NP). Density functional theory which treats the electron density as the central variable has been used to explore the adsorption of CO2 molecules on the two most stable CuO surfaces [i.e., (111) and (011)] at absolute zero. The results of this theory would provide valuable information to make CuO NPs with the surface where the CO2 adsorption is maximum in order to have a stronger mono-layer of adsorbed CO2 molecules on the surface of the NP which is the most crucial factor in formation of a stable nanofluid. The results show that the CO2 molecule is adsorbed more strongly on the (011) surface with an adsorption energy of -99.06 kJ/mol compared to the (111) surface. A computational methodology based on molecular dynamics has been used to evaluate the enhancement of the rheological properties of the super-critical CO2 liquid based nanofluid at different temperatures and pressures. In this scale, first, the CO2 liquid has been modeled by employing the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field potential and the fluid properties computed are in excellent agreement with the literature and experiment values. Second, the nanofluid has been modeled in order to study the enhancement of the fluid properties with the CuO NPs. The charged optimized many-body force field potential has been employed to consider the effect of the charge transferring between the NPs and liquid molecules and breaking of existing bonds and the formation of new bonds. The COMPASS force field potential is also employed for the interactions between CO2 molecules. The combination of these potentials is quite a new approach for the study of the super-critical (SC)-CO2 based nanofluid. The results show that the viscosity of the SC-CO2 is enhanced between 1.3 and 2.5 times under the temperature and pressure conditions studied.

Comparison of Different Types of Carbamate Amine for Stripping Process

Amine absorption process is an approach for mitigation of carbon dioxide (CO2) from flue gas that was produced from the power plant. Modelling and simulation of amine absorption process for CO2 removal at macro-scale is well established. This study aims to investigate different carbamate molecules for the regerenation process using molecular dynamic (MD) simulation. MD simulation was installed in the HP240 workstation using the software of Material Studio (version 7.0). The MD simulation was carried out at mole, volume, energy (NVE) (200 ps) and mole, volume, temperature (NVT) (1 ns) ensemble. Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) and Ewald models were used for the force field and summation method calculation within the simulation box. The simulation results show that, the carbamate ions of monoethanolamine (MEA) were difficult to break compared to 2-amino-2-methyl-1- propanol (AMP) and piperazine (PZ) for inter- and intra-molecular interactions on the stripping process. The high tendency for inter- and intra-molecular interactions happened on AMP and PZ, making them good choices to be blended with other amine solvent to overcome the limitation of other less reactive amines. The simulation results obtained from this study gave the fundamental explanation on the experimental and simulations results reported in the literature. The application of MD simulation in amine absorption process is capable to improve the understanding and give insight about this process at molecular level.

Molecular Dynamics Calculation on Mechanical Properties and Binding Energy of JOB-9003 Explosive at Different Temperatures

To research the effect of temperature on mechanical properties and binding energy of JOB-9003 explosive, the crystal model of JOB-9003 explosive was established by Materials Studio (MS). Molecular dynamics simulation was applied to investigate the mechanical properties and binding energy of explosive by COMPASS (condensed-phase optimized molecular potentials for atomistic simulation studies) force field at different temperatures (195 K, 245 K, 295 K, 345 K, 395 K, 445 K). The results show that with the increasing of temperature, the mechanical properties (tensile modulus, shear modulus, bulk modulus and Cauchy pressure) of JOB-9003 explosive decrease gradually, which indicates that the rigidity and hardness of the explosive becomes worse, while the toughness and plastic property becomes better and it agrees with theoretical analysis result, thus illustrating that MD simulation can be used to predict the mechanical properties of JOB-9003 explosive. The results of binding energy show that the binding energy decreases with the increasing of temperature, thus indicating that the stability of explosive becomes worse. In other words, the increasing of temperature has a negative effect on mechanical properties and binding energy of JOB-9003 explosive. This paper could provide some theoretical references and technological support for the comprehensive assessment of mechanical properties and stability of explosives.

Computer simulations and analysis of structural and energetic features of crystalline cage energetic compound: 2, 4, 6, 8, 12-pentanitro-10-(3, 5, 6-trinitro (2-pyridyl))-2, 4, 6, 8, 12-hexaazatetracyclo [5.5.0.03,11 .05,9 ]dodecane

First principles molecular orbital and plane-wave ab initio calculations have been used to investigate the structural and energetic properties of a new cage compound 2, 4, 6, 8, 12-pentanitro-10-(3, 5, 6-trinitro (2-pyridyl))-2, 4, 6, 8, 12-hexaazatetracyclo [5.5.0.03,11.05,9]dodecane (PNTNPHATCD) in both the gas and solid phases. The molecular orbital calculations using the density functional theory methods at the B3LYP/6-31G(d,p) level indicate that both the heat of formation and strain energy of PNTNPHATCD are larger than those of 2, 4, 6, 8, 10, 12-hexanitro-2, 4, 6, 8, 10, 12-hexaazatetracyclo [5.5.0.0.0] dodecane (CL-20). The infrared spectra and the thermodynamic property in gas phase were predicted and discussed. The calculated detonation characteristics of PNTNPHATCD estimated using the Kamlet–Jacobs equation equally matched with those of CL-20. Bond-breaking results on the basis of natural bond orbital analysis imply that C–C bond in cage skeleton, C–N bond in pyridine, and N–NO2 bond in the side chain of cage may be the trigger bonds in the pyrolysis. The structural properties of PNTNPHATCD crystal have been studied by a plane-wave density functional theory method in the framework of the generalized gradient approximation. The crystal packing predicted using the Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force fields belongs to the Pbca space group, with the lattice parameters a = 20.87 A, b = 24.95 A, c = 7.48 A, and Z = 8, respectively. The results of the band gap and density of state suggest that the N–NO2 bond in PNTNPHATCD may be the initial breaking bond in the pyrolysis step. As the temperature increases, the heat capacity, enthalpy, and entropy of PNTNPHATCD crystal all increase, whereas the free energy decreases. Considering that the cage compound has the better detonation performances and stability, it may be a superior high energy density compound. Copyright © 2015 John Wiley & Sons, Ltd.

Predict the glass transition temperature and plasticization of β-cyclodextrin/water binary system by molecular dynamics simulation

The glass transition temperature, diffusion behavior and plasticization of β-cyclodextrin (β-CD), and three amorphous β-CD/water mixtures (3%, 5% and 10% [w/w] water, respectively) were investigated by molecular dynamics simulation, which were performed using Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field and isothermal–isobaric ensembles. The specific volumes of four amorphous cells were obtained as a function of temperature. The glass transition temperatures (Tg) were estimated to be 334.25K, 325.12K, 317.32K, and 305.41K for amorphous β-CD containing 0%, 3%, 5% and 10% w/w water, respectively, which compares well with the values observed in published literature. The radial distribution function was computed to elucidate the intermolecular interactions between amorphous β-CD and water, which acts as a plasticizer. These results indicate that the hydrogen bond interactions of oxygen in hydroxyl ions was higher than oxygen in acetal groups in β-CD amorphous mixtures with that in water, due to less accessibility of ring oxygens to the surrounding water molecules. The mobility of water molecules was investigated over various temperature ranges, including the rubbery and glassy phases of the β-CD/water mixtures, by calculating the diffusion coefficients and the fractional free volume. In β-CD amorphous models, the higher mobility of water molecules was observed at temperatures above Tg, and almost no change was observed at temperatures below Tg.

Molecular dynamics investigation of the adhesion mechanism acting between dopamine and the surface of dopamine-processed aramid fibers.

Dopamine, as a universal material for surface treatment, can effectively improve the surface performance of aramid fibers. However, directly processing the surface of aramid fibers using dopamine currently incurs a high cost. To seek dopamine substitutes, one must first explore the adhesion mechanism responsible for binding the dopamine to the surface of the fiber. In this study, we construct an all-atomic molecular dynamics model of an aramid fiber before and after surface modification using dopamine. A force field based on condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) is used. Using it, we analyze the surface adhesion mechanism of polydopamines aggregated by 21 kinds of molecular structures typically found on the surface of aramid fibers. The results show that a clear and smooth interface is formed between the polydopamine nanofilm layer and the surface of the aramid fiber. The high atomic density of the polydopamine in the small interface region is found to be conducive to noncovalent bonds of polydopamines with the surface of the aramid fiber. In addition, we investigate the works of adhesion of the 21 molecular structures typically found on the surface of aramid fibers. The results suggest that the work of adhesion of 5,6-indolequinone is the highest, followed by annular eumelanin molecules with annular planar structure. Straight-chain shaped dimers proved to be the molecules with the highest adhesion ability of the dihydroxyindole chain oligomers. Therefore, there is reason to suppose that more molecular structures (as above) can be formed by processing the surface of aramid fibers using dopamine by controlling the processing conditions. These molecular structures help improve the adhesion ability of the dopamine on the surface of the aramid fiber. Additionally, if these polydopamine molecules with high adhesion ability can be synthesized on a large scale, then new surface-processing materials are possible.

Molecular Simulation Study Conformation and Energy of Polyaniline/Graphite Composites

Under the COMPASS (condensed-phase optimized molecular potentials for atomistic simulation studies) force field, the MD (molecular dynamics) simulation was applied to Polyaniline/ Graphite Composites. In this paper, we briefly introduced the constructive process of the composite system by means of MD simulation. The stability and mechanism of five intercalation composites were studied with microcosmic figure and variational energy under the invariable NVT ensemble. The results indicate that the area of graphite sheets is particularly important in the intercalation bonding process. It is the key to control the final product. The area selection is based on the molecular weight and volume of the intercalated organic polymer.

Molecular-level computational studies of single wall carbon nanotube–polyethylene composites

Minimum energy structures of short (3,3) single wall carbon nanotube (SWCNT)–polyethylene (PE) structures, as well as the binding energy between the SWCNT and PE, were obtained from three commonly used molecular mechanics force fields and first principles methods. The molecular force fields were the Dreiding, Universal and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force fields and the first principles methods included the B3LYP density functional and MP2 post-Hartree Fock methods with, typically, 6-311G, 6-311G(d,p) and 6-311G(2d,2p) basis sets. These calculations show that the results obtained from all force fields are in qualitative agreement with the first principles results, and that PE prefers to be aligned with a non-zero angle along the SWCNT axis, where the angle depends on the force field or first principles method used. This indicates that longer PE chains may wrap around SWCNTs. This was studied using the COMPASS force field with longer (5,5) SWCNTs interacting with a PE chain and, in agreement with the minimum energy calculations, the PE wrapped around the SWCNT thereby increasing the radius of gyration of the PE. This force field was also used to assess the effect of (5,5) SWCNTs on the mechanical properties of PE nanocomposites. The calculated interfacial shear stress and interfacial bonding energy of SWCNT–PE structures was 141.09MPa and 0.14N/m. The simulations show that using short SWCNTs as reinforcement does not increase the Young’s modulus for the systems studied here, whereas longer, aligned SWCNTs increased the Young’s modulus in the SWCNT axial direction.

Molecular dynamics studies of the influence of single wall carbon nanotubes on the mechanical properties of Poly(vinylidene fluoride)

Molecular dynamics simulations and geometry optimizations based on the Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field were performed to understand the effect of Single Wall Carbon Nanotubes (SWCNTs) on the mechanical properties of Poly(vinylidene fluoride) (PVDF). In particular, the Young’s modulus, bulk and shear modulus, pullout energy, pullout force, interfacial shear stress and interfacial bonding energy were calculated. The presence of the SWCNTs can increase the Young’s modulus of the systems studied here by 1GPa in the direction of the SWCNT axis, although this depends on the distance between neighboring SWCNTs. The calculated interfacial shear stress was between 100 and 129MPa, which is in agreement with results obtained for other SWCNT-polymer systems. The results, and in particular those obtained for the bulk and shear modulus, show that SWCNTs do not have a significant effect on the bulk mechanical properties. Functionalizing the SWCNTs may yield stronger adhesion between the nanotube and the polymer, thereby achieving improved mechanical properties.

Stochastically driven vibrations of single-layered graphene sheets

Thermal vibration of single-layered graphene sheets (SLGSs) is investigated using plate model together with the law of equi-partition of energy and the molecular dynamics (MD) method based on the condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field. The in-plane stiffness and Poisson ratio of SLGSs are calculated by stretching SLGSs. The effective thickness of SLGSs is obtained by the MD simulations for the thermal vibration of SLGSs through the natural frequency. The root-mean-squared (RMS) amplitudes for SLGSs of differing temperatures and boundary conditions are calculated by the MD, and are compared with the results calculated by the thin plate model together with the law of equi-partition of energy. At the center of SLGSs, the thin plate theory can predict the MD results reasonably well. For the difference of bonding structure of the edge atoms, the deviation between the MD results and plate theory becomes more readily apparent near the edges of SLGSs.