ReaxFF: A Reactive Force Field for Hydrocarbons
22 Sep 2001-Journal of Physical Chemistry A (American Chemical Society)-Vol. 105, Iss: 41, pp 9396-9409
TL;DR: In this paper, a force field for large-scale reactive chemical systems (1000s of atoms) is proposed. But the force field does not have Coulomb and Morse potentials to describe nonbond interactions between all atoms.
Abstract: To make practical the molecular dynamics simulation of large scale reactive chemical systems (1000s of atoms), we developed ReaxFF, a force field for reactive systems. ReaxFF uses a general relationship between bond distance and bond order on one hand and between bond order and bond energy on the other hand that leads to proper dissociation of bonds to separated atoms. Other valence terms present in the force field (angle and torsion) are defined in terms of the same bond orders so that all these terms go to zero smoothly as bonds break. In addition, ReaxFF has Coulomb and Morse (van der Waals) potentials to describe nonbond interactions between all atoms (no exclusions). These nonbond interactions are shielded at short range so that the Coulomb and van der Waals interactions become constant as Rij → 0. We report here the ReaxFF for hydrocarbons. The parameters were derived from quantum chemical calculations on bond dissociation and reactions of small molecules plus heat of formation and geometry data for...
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TL;DR: The General Utility Lattice Program (GULP) as discussed by the authors has been extended to include the ability to simulate polymers and surfaces, as well as adding many other new features, and the current status of the program is fully documented.
Abstract: The General Utility Lattice Program (GULP) has been extended to include the ability to simulate polymers and surfaces, as well as adding many other new features, and the current status of the program is fully documented. Both the background theory is described, as well as providing a concise review of some of the previous applications in order to demonstrate the range of its use. Examples are presented of work performed using the new compatibilities of the software, including the calculation of Born effective charges, mechanical properties as a function of applied pressure, calculation of frequency-dependent dielectric data, surface reconstructions of calcite and the performance of a linear-scaling algorithm for bond-order potentials.
1,987 citations
Cites methods from "ReaxFF: A Reactive Force Field for ..."
...Here we propose a modified formulation from that of Rappe and Goddard that drastically simplifies the calculation of analytic derivatives: UH ¼ U0H þ x 0HqH þ 1 2 J0HH 1 þ 2qH 3z 0H ! q2H þ 1 2 qHVH: The reason for the simplification is based on the Hellmann – Feynman theorem and can be understood as follows....
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...The alternative, as used by Rappe and Goddard in their QEq method [41], is to use a damped Coulomb potential that allows for the fact that at short distances the interaction arises from the overlap of electron density, rather than from just simple point ions....
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...the ReaxFF model from the group of Goddard [203]....
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...There has already been significant progress in this area with the bond order potentials of Brenner and co-workers, and more recently with the ReaxFF model from the group of Goddard [203]....
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TL;DR: Several of the fundamental algorithms used in LAMMPS are described along with the design strategies which have made it flexible for both users and developers, and some capabilities recently added to the code which were enabled by this flexibility are highlighted.
1,956 citations
TL;DR: Atomistic modeling with ReaxFF provides a useful method for determining the initial events of oxidation of hydrocarbons under extreme conditions and can enhance existing combustion models.
Abstract: To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical reactivity of systems relevant to these reactions and optimized the force field parameters against a quantum mechanics (QM)-based training set. To validate the ReaxFF potential obtained after parameter optimization, we performed a range of NVT−MD simulations on various hydrocarbon/O2 systems. From simulations on methane/O2, o-xylene/O2, propene/O2, and benzene/O2 mixtures, we found that ReaxFF obtains the correct reactivity trend (propene > o-xylene > methane > benzene), following the trend in the C−H bond strength in these hydrocarbons. We also tracked in detail the reactions during a complete oxidation of isolated methane, propene, and o-xylene to a CO/CO2/H2O mixture and found that the pathways predicted by ReaxFF are in agreement with chemical intuition and our QM results. We o...
1,815 citations
1,800 citations
TL;DR: The chemical changes of oxygen-containing functional groups on the annealing of graphene oxide are elucidated and the simulations reveal the formation of highly stable carbonyl and ether groups that hinder its complete reduction to graphene.
Abstract: The excellent electrical, optical and mechanical properties of graphene have driven the search to find methods for its large-scale production, but established procedures (such as mechanical exfoliation or chemical vapour deposition) are not ideal for the manufacture of processable graphene sheets. An alternative method is the reduction of graphene oxide, a material that shares the same atomically thin structural framework as graphene, but bears oxygen-containing functional groups. Here we use molecular dynamics simulations to study the atomistic structure of progressively reduced graphene oxide. The chemical changes of oxygen-containing functional groups on the annealing of graphene oxide are elucidated and the simulations reveal the formation of highly stable carbonyl and ether groups that hinder its complete reduction to graphene. The calculations are supported by infrared and X-ray photoelectron spectroscopy measurements. Finally, more effective reduction treatments to improve the reduction of graphene oxide are proposed.
1,624 citations
Cites methods from "ReaxFF: A Reactive Force Field for ..."
...Methods Modelling MD simulations were performed using the reactive force-field ReaxFF, which is a general bond-order dependent potential that provides accurate descriptions of bond breaking and bond formation in hydrocarbon–oxygen system...
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References
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TL;DR: In this article, the Universal force field (UFF) is described, where the force field parameters are estimated using general rules based only on the element, its hybridization, and its connectivity.
Abstract: A new molecular mechanics force field, the Universal force field (UFF), is described wherein the force field parameters are estimated using general rules based only on the element, its hybridization, and its connectivity. The force field functional forms, parameters, and generating formulas for the full periodic table are presented
7,953 citations
TL;DR: In this paper, a new method for obtaining optimized parameters for semi-empirical methods has been developed and applied to the modified neglect of diatomic overlap (MNDO) method.
Abstract: A new method for obtaining optimized parameters for semiempirical methods has been developed and applied to the modified neglect of diatomic overlap (MNDO) method. The method uses derivatives of calculated values for properties with respect to adjustable parameters to obtain the optimized values of parameters. The large increase in speed is a result of using a simple series expression for calculated values of properties rather than employing full semiempirical calculations. With this optimization procedure, the rate-determining step for parameterizing elements changes from the mechanics of parameterization to the assembling of experimental reference data.
7,125 citations
TL;DR: The DREIDING force field as discussed by the authors uses general force constants and geometry parameters based on simple hybridization considerations rather than individual force constants or geometric parameters that depend on the particular combination of atoms involved in the bond, angle, or torsion terms.
Abstract: We report the parameters for a new generic force field, DREIDING, that we find useful for predicting structures and dynamics of organic, biological, and main-group inorganic molecules. The philosophy in DREIDING is to use general force constants and geometry parameters based on simple hybridization considerations rather than individual force constants and geometric parameters that depend on the particular combination of atoms involved in the bond, angle, or torsion terms. Thus all bond distances are derived from atomic radii, and there is only one force constant each for bonds, angles, and inversions and only six different values for torsional barriers. Parameters are defined for all possible combinations of atoms and new atoms can be added to the force field rather simply. This paper reports the parameters for the "nonmetallic" main-group elements (B, C, N, 0, F columns for the C, Si, Ge, and Sn rows) plus H and a few metals (Na, Ca, Zn, Fe). The accuracy of the DREIDING force field is tested by comparing with (i) 76 accurately determined crystal structures of organic compounds involving H, C, N, 0, F, P, S, CI, and Br, (ii) rotational barriers of a number of molecules, and (iii) relative conformational energies and barriers of a number of molecules. We find excellent results for these systems.
5,380 citations
TL;DR: An empirical many-body potential-energy expression is developed for hydrocarbons that can model intramolecular chemical bonding in a variety of small hydrocarbon molecules as well as graphite and diamond lattices based on Tersoff's covalent-bonding formalism with additional terms that correct for an inherent overbinding of radicals.
Abstract: An empirical many-body potential-energy expression is developed for hydrocarbons that can model intramolecular chemical bonding in a variety of small hydrocarbon molecules as well as graphite and diamond lattices. The potential function is based on Tersoff's covalent-bonding formalism with additional terms that correct for an inherent overbinding of radicals and that include nonlocal effects. Atomization energies for a wide range of hydrocarbon molecules predicted by the potential compare well to experimental values. The potential correctly predicts that the \ensuremath{\pi}-bonded chain reconstruction is the most stable reconstruction on the diamond {111} surface, and that hydrogen adsorption on a bulk-terminated surface is more stable than the reconstruction. Predicted energetics for the dimer reconstructed diamond {100} surface as well as hydrogen abstraction and chemisorption of small molecules on the diamond {111} surface are also given. The potential function is short ranged and quickly evaluated so it should be very useful for large-scale molecular-dynamics simulations of reacting hydrocarbon molecules.
3,588 citations
TL;DR: In this paper, an approach for predicting charge distributions in molecules for use in molecular dynamics simulations is presented, where an atomic chemical potential is constructed by using these quantities plus shielded electrostatic interactions between all charges.
Abstract: We report here an approach for predicting charge distributions in molecules for use in molecular dynamics simulations. The input data are experimental atomic ionization potentials, electron affinities, and atomic radii. An atomic chemical potential is constructed by using these quantities plus shielded electrostatic interactions between all charges. Requiring equal chemical potentials leads to equilibrium charges that depend upon geometry. This charge equilibration (QEq) approach leads to charges in excellent agreement with experimental dipole moments and with the atomic charges obtained from the electrostatic potentials of accurate ab initio calculations. QEq can be used to predict charges for any polymer, ceramic, semiconductor, or biological system, allowing extension of molecular dynamics studies to broad classes of new systems. The charges depend upon environment and change during molecular dynamics calculations. We indicate how this approach can also be used to predict infrared intensities, dielectric constants, and other charge-related properties.
2,820 citations