Application of the ChIMES Force Field to Nonreactive Molecular Systems: Water at Ambient Conditions

Lindsey, Rebecca; Fried, Laurence E.; Goldman, Nir

doi:10.1021/acs.jctc.8b00831

Cited by 34 publications

(44 citation statements)

References 82 publications

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“…Since then, the method has been applied to systems including transition metal complexes, 33,34 anions, 35 ionic liquids, 36 and microporous materials. 37 Recently, the force-matching technique has also been employed to develop FFs for water, 38,39 water on graphene surface, 40 and explicit three-body interactions for molten carbon. 41 In this work, we extend the adaptive force matching technique to rapidly parameterize FFs for complex conjugated systems.…”

Section: Introductionmentioning

confidence: 99%

Force Fields for Macromolecular Assemblies Containing Diketopyrrolopyrrole and Thiophene

Jiang

Rogers

Hirst

et al. 2020

J. Chem. Theory Comput.

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Utilising a force matching procedure, we parameterise new force fields systematically for large conjugated systems. We model both conjugated polymers and molecular crystals that contain diketopyrrolopyrrole, thiophene, and thieno[3,2-b]thiophene units. These systems have recently been found to have low band gaps, which exhibit high efficiency for photovoltaic devices. The equilibrium structures, forces and energies of the building block chromophores: diketopyrrolopyrrole thiophene, and thieno[3,2b]thiophene computed using our parameters are comparable to those computed using the reference electronic structure method. We assess the suitability of this new force field for electronic property calculations by comparing the electronic excitation properties computed along classical and ab initio molecular dynamics trajectories. For both trajectories, we find similar distributions of TDDFT calculated excitation energies and oscillator strengths for the building block chromophore diketopyrrolopyrrole-thieno[3,2b]thiophene. The structural, dynamical, and electronic properties of the macromolecular assemblies built upon these chromophores are characterised. For both polymers and molecular crystals, pronounced peaks around 0 o or 180 o are observed for the torsions between chromophores under ambient conditions. The high planarity in these systems can promote local ordering and π-π stacking, thereby potentially facilitating charge transport across these materials. For the model conducting polymers, we found that the fluctuations in the density of states per chain per monomer is neglegibly small and does not vary significantly with chains comprising 20 to 40 monomers. Analysis of the electron-hole distributions and the transition density matrices indicates that the delocalised length is approximately four to six monomers, which is in good agreement with other theoretical and experimental studies of different conducting polymers. For the molecular crystals, our investigation of the characteristic timescale of the fluctuation in the excitonic couplings shows that low frequency vibration below 10 cm −1 is observed for the nearest neighbors. These observations are in line with previous studies on other molecular crystals, in which low frequency vibrations are believed to be responsible for the large modulation of the excitonic coupling. Thus, our approach and the new force fields provide a direct route for studying the structure-property relations and the molecular level origins of the high-efficiency of these classes of materials.

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Section: Introductionmentioning

confidence: 99%

Force Fields for Macromolecular Assemblies Containing Diketopyrrolopyrrole and Thiophene

Jiang

Rogers

Hirst

et al. 2020

J. Chem. Theory Comput.

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“…As will be described in greater detail below, ChIMES force fields are fit to forces (and optionally energies and stresses) arising from Kohn-Sham density functional theory (DFT) simulations of 2-20 ps and have typically leveraged 2+3-body interaction terms and an iterative refinement scheme, where frames from molecular dynamics (MD) simulations with the i th ChIMES force field are occasionally sent back to DFT for single point calculation and combined with the training repository, from which an i + 1 th ChIMES model is generated; the cycle is repeated until desired model performance is achieved. This iterative approach has worked well for molten carbon 22 , ambient water 25 , and dissociative carbon monoxide 26 , where in all cases species were small and chemistry was rapid when present. However, upon application to systems in which larger and more complex species form, shortcomings arising from use of a 2+3-body ChIMES many-body truncation have been identified 26 .…”

Section: A the Chimes Force Fieldmentioning

confidence: 99%

“…In this work, we will consider the following objective function, which contains terms for per-atom forces and per-system-configuration energies, though we note additional terms for the system stress tensor can also easily be included 14,22,25,26 :…”

Section: The Generalized Chimes Potential Energy Equation Is Given Bymentioning

confidence: 99%

Active Learning for Robust, High-Complexity Reactive Atomistic Simulations

Lindsey

Fried²,

Goldman³

et al. 2020

Preprint

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Machine learned reactive force fields based on polynomial expansions have been shown to be highly effective for describing simulations involving reactive materials. Nevertheless, the highly flexible nature of these models can give rise to a large number of candidate parameters for complicated systems. In these cases, reliable parameterization requires a well-formed training set, which can be difficult to achieve through standard iterative fitting methods. Here we present an active learning approach based on cluster analysis and Shannon information theory to enable semi-automated generation of informative training sets and robust machine learned force fields. Use of this tool is demonstrated for development of a model based on linear combinations of Chebyshev polynomials explicitly describing up to four-body interactions, for a chemically and structurally diverse system of C/O under extreme conditions. We show that this flexible training repository management approach enables development of models exhibiting excellent agreement with Kohn–Sham density functional theory (DFT) in terms of structure, dynamics, and speciation.

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“…Recently, the Chebyshev Interaction Model for Efficient Simulation (ChIMES) was developed which, in its current state, describes explicit two- 31 and three-body interactions 32 through linear combinations of Chebyshev polynomials. ChIMES models are parameterized by force matching 33 to short DFT MD trajectories, circumventing the issue of scant experimental training data at high T and p. To date, this model has been proven highly suitable for extending DFT forces to molten metallic carbon at extreme conditions 32 , as well as liquid water under moderate T and p 34 . Here, we apply ChIMES to a problem of higher complexity, namely that of reactive carbon condensation in carbon monoxide under extreme conditions.…”

Section: Introductionmentioning

confidence: 99%

“…In this framework, one begins by inputting a training trajectory from DFT MD. The cycle then begins, by (a) fitting a model, FF i to the in-2B , r c,out,2B , r c,out,3B , λ, O 2B , O 3B , A p , and d p ) were set using protocols established in previous work32,34 . All ChIMES force fields discussed here use polynomial orders of O 2B = 12 and O 3B = 4, resulting in a total of 228 fitting parameters.…”

mentioning

confidence: 99%

Development of the ChIMES Force Field for Reactive Molecular Systems: Carbon Monoxide at Extreme Conditions

Lindsey

Goldman²,

Fried³

et al. 2019

Preprint

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<p>We have developed a transferable reactive force field for C/O systems under extreme temperature and pressure conditions based on the many-body Chebyshev Interaction Model for Efficient Simulation (ChIMES). The resulting model is shown to recover much of the accuracy of DFT for prediction of structure, dynamics and chemistry when applied to dissociative systems at 1:1 and 1:2 C:O ratios, as well as molten carbon. Our C/O modeling approach exhibits a 10<sup>4</sup> increase in efficiency and linear system size scalability over standard quantum molecular dynamics methods, allowing simulation of significantly larger systems than previously possible. Furthermore, we show that system sizes of at least 500 atoms are required to observe the formation of experimentally predicted molten carbon condensates under oxygen-deficient conditions, indicative of possible system size effects in quantum simulations of these types of systems. Overall, we find the present ChIMES model to be well suited for modeling chemical processes and cluster formation at pressures and temperatures typical of shock waves. We expect that the present C/O modeling paradigm can serve as a template for the development of a high pressure --high temperature organic chemistry force-field. </p>

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Application of the ChIMES Force Field to Nonreactive Molecular Systems: Water at Ambient Conditions

Cited by 34 publications

References 82 publications

Force Fields for Macromolecular Assemblies Containing Diketopyrrolopyrrole and Thiophene

Force Fields for Macromolecular Assemblies Containing Diketopyrrolopyrrole and Thiophene

Active Learning for Robust, High-Complexity Reactive Atomistic Simulations

Development of the ChIMES Force Field for Reactive Molecular Systems: Carbon Monoxide at Extreme Conditions

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