Ab Initio Molecular Dynamics Simulations on High-Temperature Reaction Rates of Reactions KO+CO==K+CO2, KO+C=K+CO, and K2O+CO2==K2CO3

2014 ◽  
Vol 875-877 ◽  
pp. 1037-1041
Author(s):  
Yan Hua Dong ◽  
Xiao Jia Li
Keyword(s):  
Molecular Dynamics ◽  
High Temperature ◽  
Ab Initio ◽  
Molecular Dynamics Simulations ◽  
Cross Sections ◽  
Reaction Rates ◽  
Molecular Collision ◽  
Collision Cross Sections ◽  
Reactive Trajectories ◽  
Dynamics Simulations

In this paper, we present a novel approach for calculating chemical reaction rates based on molecular collision theory, in which molecular collision cross sections are calculated by averaging over all reactive trajectories from ab initio molecular dynamics simulations. The molecular collision radius is determined by both reactive and non-reactive trajectories of molecular dynamics under constant temperature. Thus, both steric and temperature effects have been take into account for molecular collision cross sections. We have applied this approach to calculate reaction rates of reactions KO+CO==K+CO2, KO+C==K+CO, and K2O+CO2==K2CO3 under high temperature. It also shows that under higher temperature, the probabilities of a successful reaction resulting from particle collision are low, because the products are not stable.

Effects of boron defects on mechanical strengths of TiB2 at high temperature: ab initio molecular dynamics studies

2020 ◽  
Vol 22 (12) ◽  
pp. 6560-6571
Author(s):  
Shuchao Zhang ◽  
Hong Sun
Keyword(s):  
Molecular Dynamics ◽  
High Temperature ◽  
Mechanical Strength ◽  
Ab Initio ◽  
Molecular Dynamics Simulations ◽  
Elevated Temperatures ◽  
Ab Initio Molecular Dynamics ◽  
Dynamics Simulations ◽  
Mechanical Strengths

We report ab initio molecular dynamics simulations on diffusions of boron interstitials in TiB2 that cause deterioration of its mechanical strength by reducing interactions between deformed boron layers and nearby Ti-layers at elevated temperatures.

Active Learning Accelerates Ab Initio Molecular Dynamics on Pericyclic Reactive Energy Surfaces

2020 ◽  
Author(s):  
Shi Jun Ang ◽  
Wujie Wang ◽  
Daniel Schwalbe-Koda ◽  
Simon Axelrod ◽  
Rafael Gomez-Bombarelli
Keyword(s):  
Molecular Dynamics ◽  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Energy Surface ◽  
Computational Cost ◽  
Reactive Trajectories ◽  
Dynamics Simulations ◽  
Energy Surfaces

<div>Modeling dynamical effects in chemical reactions, such as post-transition state bifurcation, requires <i>ab initio</i> molecular dynamics simulations due to the breakdown of simpler static models like transition state theory. However, these simulations tend to be restricted to lower-accuracy electronic structure methods and scarce sampling because of their high computational cost. Here, we report the use of statistical learning to accelerate reactive molecular dynamics simulations by combining high-throughput ab initio calculations, graph-convolution interatomic potentials and active learning. This pipeline was demonstrated on an ambimodal trispericyclic reaction involving 8,8-dicyanoheptafulvene and 6,6-dimethylfulvene. With a dataset size of approximately</div><div>31,000 M062X/def2-SVP quantum mechanical calculations, the computational cost of exploring the reactive potential energy surface was reduced by an order of magnitude. Thousands of virtually costless picosecond-long reactive trajectories suggest that post-transition state bifurcation plays a minor role for the reaction in vacuum. Furthermore, a transfer-learning strategy effectively upgraded the potential energy surface to higher</div><div>levels of theory ((SMD-)M06-2X/def2-TZVPD in vacuum and three other solvents, as well as the more accurate DLPNO-DSD-PBEP86 D3BJ/def2-TZVPD) using about 10% additional calculations for each surface. Since the larger basis set and the dynamic correlation capture intramolecular non-covalent interactions more accurately, they uncover longer lifetimes for the charge-separated intermediate on the more accurate potential energy surfaces. The character of the intermediate switches from entropic to thermodynamic upon including implicit solvation effects, with lifetimes increasing with solvent polarity. Analysis of 2,000 reactive trajectories on the chloroform PES shows a qualitative agreement with the experimentally-reported periselectivity for this reaction. This overall approach is broadly applicable and opens a door to the study of dynamical effects in larger, previously-intractable reactive systems.</div>

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