Many-body reactive force field development for carbon condensation in C/O systems under extreme conditions

Abstract

We describe the development of a reactive force field for C/O systems under extreme temperatures and pressures, based on the many-body Chebyshev Interaction Model for Efficient Simulation (ChIMES). The resulting model, which targets carbon condensation under thermodynamic conditions of 6500 K and 2.5 g cm−3, affords a balance between model accuracy, complexity, and training set generation expense. We show that the model recovers much of the accuracy of density functional theory for the prediction of structure, dynamics, and chemistry when applied to dissociative condensed phase systems at 1:1 and 1:2 C:O ratios, as well as molten carbon. Our C/O modeling approach exhibits a 104 increase in efficiency for the same system size (i.e., 128 atoms) and a linear system size scalability over standard quantum molecular dynamics methods, allowing the simulation of significantly larger systems than previously possible. We find that the model captures the condensed-phase reaction-coupled formation of carbon clusters implied by recent experiments, and that this process is susceptible to strong finite size effects. Overall, we find the present ChIMES model to be well suited for studying 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 broader high pressure–high temperature force-field for condensed phase chemistry in organic materials.

Calculation of the Detonation State of HN3 with Quantum Accuracy

“…Similar to previous ChIMES studies 28,30,31 , we found that ChIMES force field stability is improved with the use of an iterative fitting scheme. The initial model is generated by fitting directly to configurations from DFT-MD simulations.…”

“…The ChIMES model is parameterized by matching to reference data for selected configurations which are taken from short DFT-MD trajectories. It has been shown that ChIMES models yield good agreement with DFT results for the structural, dynamical properties and/or the chemistry of molten carbon 28 , liquid water at ambient conditions 30 , and carbon monoxide at extreme conditions 31 .…”

Using DFTB to Model Photocatalytic Anatase–Rutile TiO2 Nanocrystalline Interfaces and Their Band Alignment

“…Specifically, the two-body interactions are expressed as a linear combination of Chebyshev polynomials of the first kind In this case, T n ( s ij ) is the Chebyshev polynomial of the first kind of n th order, e i and e j are the element types of atoms i and j , and s ij is a transformation of the interatomic distance r ij over the Chebyshev interval of [−1,1] using a Morse-like function. In addition, Θ 2 corresponds to the two-body polynomial order, f C ij ( r ij ) is the cutoff function that ensures the potential and its derivative vary smoothly to zero beyond a specified distance, and f P ij ( r ij ) is a penalty function 13 , 17 that helps to prevent sampling of interatomic distances below those seen in the training set (see ref ( 18 ) for further details). is a set of permutationally invariant coefficients of linear combination for a given atom pair type that are determined via a linear least-squares method.…”

First principles reactive simulation for equation of state prediction

“…Modern machine learning (ML) force fields are providing additional options for computationally tractable chemically reactive simulations. [27][28][29][30][31][32][33][34][35][36][37][38][39][40] . ChiMES is one such approach that has been applied to chemically reactive fluids.…”