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Portlandite dissolution: Part 1. Mechanistic insight by Molecular Dynamics (MD)
Published in Günther Meschke, Bernhard Pichler, Jan G. Rots, Computational Modelling of Concrete and Concrete Structures, 2022
K.M. Salah Uddin, Bernhard Middendorf, Mohammadreza Izadifar, Neven Ukrainczyk, Eduardus Koenders
ReaxFF has been developed to investigate the reaction mechanism at the material interface. It has already been implemented successfully in many materials, i.e. hydrocarbons (Chenoweth et al. 2008), polymer chemistry (Senftle et al. 2016), metal oxides (Si/SiO2) (Fogarty et al. 2010), metal hydrides (Cheung et al. 2005). ReaxFF usually calculates molecular dynamics in femtosecond (i.e. 10−15 seconds) time steps. Therefore, it could be computationally expensive especially during the Transition state calculation despite its efficiencies compared to classical force field theory. Metadynamics (metaD) is integrated into ReaxFF to solve these timescale issues. Metadynamics is an efficient algorithm to accelerate observing the rare events by adding biased potential on a selected number of collective variables (CVs) (Barducci et al. 2011). During the MD simulation, the bias potential is applied as a sum of Gaussian acting directly on the microscopic coordinates of the system (Aktulga et al. 2012).
Molecular Dynamics Simulation of Advanced Machining Processes
Published in V. K. Jain, Advanced Machining Science, 2023
Xichun Luo, Xiaoguang Guo, Jian Gao, Saurav Goel, Saeed Zare Chavoshi
The high calculation cost of quantum mechanics (QM) limits the time and scale, and classical MD lacks the description for chemical reactions. The reactive force field (ReaxFF) can be considered as a good remedy to study the chemical reactions and mechanical effects occurring during processes like CMP. This section discusses the CMP processes from the point of view of the micromechanical and chemical effects under the synergy of velocity, pressure, and polishing slurry as well as the influence of process parameters on the material removal and wear debris.
Modeling of Mechanical Properties in Nanoparticle Reinforced Polymers Using Atomistic Simulations
Published in Frank Abdi, Mohit Garg, Characterization of Nanocomposites, 2017
Samit Roy, Avinash Reddy Akepati
Work is currently underway to quantify and verify the difference due to the entropic contribution at even higher temperatures. All the simulations till now have been done using optimized potentials for liquid simulations (OPLS) force field. Work is currently underway to use ReaxFF force field (van Duin, 2001) for MD simulations. ReaxFF is a bond order–based force field which can model chemical reactions including formation and breaking of chemical bonds. This force field is useful for fracture simulation because it can model crack propagation by breaking chemical bonds, which is a more accurate representation of the physical phenomenon occurring at atomic scale. This would give a better understanding of the effect of nanographene on fracture properties of EPON 862. As mentioned earlier, our ultimate goal is to be able to use MD simulations to compute parameters such as the partition function, free energy density, bond density function (for bonded as well as nonbonded interactions), Piola–Kirchoff stress, etc., in order to quantify the influence of nanofillers such as graphene nanoplatelets on macroscale phenomenon such as delamination crack propagation in a nanoreinforced laminated polymer composite. As mentioned in an earlier section, the local harmonic (LH) approximation is not valid for an amorphous (disordered) crosslinked polymer network. A methodology for the derivation of a proper partition function (Z) for a flexible polymer crosslinked network through the use of statistical mechanics of phantom networks is described in (Weiner, 1983) and will be adapted for evaluating J-integral for polymers at finite temperatures. In the event, the partition function computation proves to be computationally intractable for a large amorphous polymeric system, an alternate approach using a cohesive zone–based technique will be employed for computation of J-integral at the nanoscale, as outlined by Klein and Gao (1998). Atomistic J-integral evaluation scheme discussed earlier can then be applied to polymeric systems to evaluate performance metrics such as work of separation at the polymer–nanoparticle interface. These data can subsequently be incorporated in a multiscale model for simulating failure at the macroscale. The multiscale analysis will be performed using a concurrent coupling scheme as discussed in by Roy and Nair (2011). A major advantage of the coupled simulation over pure MD simulation of crack propagation is that the spurious effect of stress waves reflected from the boundaries of the MD domain impinging on the moving crack tip is mitigated. The nanoscale fracture toughness data obtained will subsequently be hierarchically incorporated at the microscale to predict fuzzy fiber/matrix debonding or at the macroscale to predict inter-ply delamination in a composite laminate reinforced with interlaced layers of CNT forest.
Insights at the neutron irradiation-induced structural homogenization effect of calcium silicate hydrates and degradation mechanism of mechanical properties: a molecular dynamics study
Published in Journal of Sustainable Cement-Based Materials, 2023
Yang Zhou, Yuan Chen, Ming Jin, Jiaping Liu, Changwen Miao
In this work, the reactive force field (ReaxFF) was used in the construction of the C-S-H model, irradiation simulations, and mechanical performance testing process. ReaxFF force field is a reactive force field designed based on the bond order–bond length scheme, which can be used to simulate processes involving chemical reactions and capture reactivity characteristics. Previous studies have shown that the ReaxFF force field can be applied into both organic and inorganic systems [35]. Besides, it has good compatibility in the simulations of the C-S-H system [34, 36, 37], and can accurately characterize the structural information and mechanical response under stress conditions. The Ca/Si/H/O parameters of the ReaxFF force field adopted in this paper are obtained according to Ref. [38, 39].
Influence of curing agent ratio, asphalt content and crosslinking degree on the compatibility and component distribution of epoxy asphalt in compound curing agent system
Published in International Journal of Pavement Engineering, 2022
Mingyue Li, Zhaohui Min, Qichang Wang, Wei Huang, Zhiyong Shi
In this study, molecular dynamics simulations were carried out based on Materials studio software. To describe the potential energy of the molecular system accurately, the consistent force field COMPASSII was employed. COMPASSII is suitable for covalent molecular systems, where the valence parameters and atomic point charges are obtained by fitting the ab initio data, and the van der Waals parameters are obtained by fitting the measured cohesive energy density and equilibrium density data (Sun 1995, 1998). Several researchers’ studies have verified that COMPASSII could predict the structure, conformation, frequency, and thermophysical properties of the system accurately and rapidly (Du et al. 2021). ReaxFF is a reaction force field based on the bond order, atoms are set as the basic unit of the simulation, and the interatomic potential is used to describe the reaction in the form of bond order, where the bond order is empirically calculated from the distance between atoms (Shishehbor et al. 2018, 2019). The ReaXFF force field serves the Lammps simulation software. Therefore, due to the limitation of the simulation software, the COMPASSII was used in this paper instead of the ReaXFF.
A study on the reaction mechanism of microwave pyrolysis of oily sludge by products analysis and ReaxFF MD simulation
Published in Environmental Technology, 2022
Yanjun Wen, Wenxuan Li, Yingshen Xie, Zhiwen Qin, Meixia Gu, Tianli Wang, Yingfei Hou
ReaxFF (Reactive force field) is a bond order based response field proposed by Van Duin and Goddard et al. in 2001 [24]. When ReaxFF is combined with molecular dynamics (MD) simulation, the cleavage and formation of chemical bonds in complex systems can be described [25]. The ReaxFF MD is intermediate between quantum chemical reaction computation and traditional molecular simulation computation and performs well in relatively complex molecular systems. ReaxFF MD is widely used in the pyrolysis and combustion of coal, biomass, and hydrocarbons [25–28]. Zheng et al. used the ReaxFF MD simulation to study product changes during coal pyrolysis. Zhang et al. used ReaxFF MD to investigate the lignin pyrolysis mechanism and revealed the reaction scheme for major pyrolyzates [29]. Jin et al. simulated the catalytic hydrogen production of biomass in supercritical water by ReaxFF MD [30]. Rismiller et al. simulated the water assisted liquefaction of cellulose and lignin by ReaxFF MD, and reproduced the experimental results of lignin char formation [31]. Si et al. revealed the effect of CaO on cellulose pyrolysis, and mechanisms were obtained by ReaxFF MD [32]. Therefore, ReaxFF is also applicable to the pyrolysis of biomaterials.