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Volume 30, Issue 3
Examining Saddle Point Searches in the Context of Off-Lattice Kinetic Monte Carlo

Jonathan Hicks & Timothy P. Schulze

Commun. Comput. Phys., 30 (2021), pp. 749-770.

Published online: 2021-07

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  • Abstract

In calculating the time evolution of an atomic system on diffusive timescales, off-lattice kinetic Monte Carlo (OLKMC) can sometimes be used to overcome the limitations of Molecular Dynamics. OLKMC relies on the harmonic approximation to Transition State Theory, in which the rate of rare transitions from one energy minimum to a neighboring minimum scales exponentially with an energy barrier on the potential energy surface. This requires locating the index-1 saddle point, commonly referred to as a transition state, that separates two neighboring energy minima. In modeling the evolution of an atomic system, it is desirable to find all the relevant transitions surrounding the current minimum. Due to the large number of minima on the potential energy surface, exhaustively searching the landscape for these saddle points is a challenging task. In examining the particular case of isolated Lennard-Jones clusters of around 50 particles, we observe very slow convergence of the total number of saddle points found as a function of successful searches. We seek to understand this behavior by modeling the distribution of successful searches and sampling this distribution to create a stochastic process that mimics this behavior. Finally, we will discuss an improvement to a rejection scheme for OLKMC where we terminate searches that appear to be failing early in the search process.

  • AMS Subject Headings

65C05

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COPYRIGHT: © Global Science Press

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@Article{CiCP-30-749, author = {Hicks , Jonathan and P. Schulze , Timothy}, title = {Examining Saddle Point Searches in the Context of Off-Lattice Kinetic Monte Carlo}, journal = {Communications in Computational Physics}, year = {2021}, volume = {30}, number = {3}, pages = {749--770}, abstract = {

In calculating the time evolution of an atomic system on diffusive timescales, off-lattice kinetic Monte Carlo (OLKMC) can sometimes be used to overcome the limitations of Molecular Dynamics. OLKMC relies on the harmonic approximation to Transition State Theory, in which the rate of rare transitions from one energy minimum to a neighboring minimum scales exponentially with an energy barrier on the potential energy surface. This requires locating the index-1 saddle point, commonly referred to as a transition state, that separates two neighboring energy minima. In modeling the evolution of an atomic system, it is desirable to find all the relevant transitions surrounding the current minimum. Due to the large number of minima on the potential energy surface, exhaustively searching the landscape for these saddle points is a challenging task. In examining the particular case of isolated Lennard-Jones clusters of around 50 particles, we observe very slow convergence of the total number of saddle points found as a function of successful searches. We seek to understand this behavior by modeling the distribution of successful searches and sampling this distribution to create a stochastic process that mimics this behavior. Finally, we will discuss an improvement to a rejection scheme for OLKMC where we terminate searches that appear to be failing early in the search process.

}, issn = {1991-7120}, doi = {https://doi.org/10.4208/cicp.OA-2020-0211}, url = {http://global-sci.org/intro/article_detail/cicp/19309.html} }
TY - JOUR T1 - Examining Saddle Point Searches in the Context of Off-Lattice Kinetic Monte Carlo AU - Hicks , Jonathan AU - P. Schulze , Timothy JO - Communications in Computational Physics VL - 3 SP - 749 EP - 770 PY - 2021 DA - 2021/07 SN - 30 DO - http://doi.org/10.4208/cicp.OA-2020-0211 UR - https://global-sci.org/intro/article_detail/cicp/19309.html KW - Off-lattice kinetic Monte Carlo, energy landscape, saddle point search, dimer method, Lennard-Jones clusters. AB -

In calculating the time evolution of an atomic system on diffusive timescales, off-lattice kinetic Monte Carlo (OLKMC) can sometimes be used to overcome the limitations of Molecular Dynamics. OLKMC relies on the harmonic approximation to Transition State Theory, in which the rate of rare transitions from one energy minimum to a neighboring minimum scales exponentially with an energy barrier on the potential energy surface. This requires locating the index-1 saddle point, commonly referred to as a transition state, that separates two neighboring energy minima. In modeling the evolution of an atomic system, it is desirable to find all the relevant transitions surrounding the current minimum. Due to the large number of minima on the potential energy surface, exhaustively searching the landscape for these saddle points is a challenging task. In examining the particular case of isolated Lennard-Jones clusters of around 50 particles, we observe very slow convergence of the total number of saddle points found as a function of successful searches. We seek to understand this behavior by modeling the distribution of successful searches and sampling this distribution to create a stochastic process that mimics this behavior. Finally, we will discuss an improvement to a rejection scheme for OLKMC where we terminate searches that appear to be failing early in the search process.

Jonathan Hicks & Timothy P. Schulze. (2021). Examining Saddle Point Searches in the Context of Off-Lattice Kinetic Monte Carlo. Communications in Computational Physics. 30 (3). 749-770. doi:10.4208/cicp.OA-2020-0211
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