论文标题

跳跃蒙特卡洛:一种有效克服损坏的恐怖性的方法

Funnel Hopping Monte Carlo: An efficient method to overcome broken ergodicity

论文作者

Finkler, Jonas A., Goedecker, Stefan

论文摘要

蒙特卡洛模拟是研究原子系统热力学特性的强大工具。然而,在实践中,整个配置空间的采样通常受到配置空间不同区域之间的高能屏障的阻碍,这可以使厄尔及性采样在可访问的模拟时间内完全不可行。尽管已经开发了传统的蒙特卡洛方案的几个扩展,这使得能够处理此类系统,但这些扩展通常需要大量的计算成本或依赖谐波近似。在这项工作中,我们提出了一种称为漏斗蒙特卡洛(FHMC)的精确方法,该方法受到智能飞镖思想的启发,但效率更高。高斯混合物用于近似于局部能量极小周围的玻尔兹曼分布,然后将其用于提出高质量的蒙特卡洛移动,使蒙特卡洛模拟能够直接在不同的漏斗之间跳跃。为了适应高斯混合物,我们开发了期望最大化算法的扩展版,该算法能够利用许多低能配置中存在的高对称性。我们在38个示例以及75个原子Lennard-Jones群集中演示了方法性能,这些群集以其双漏斗能量景观而闻名,这些景观可以防止使用常规的Monte Carlo Simulations进行奇异采样。通过将FHMC整合到并行的回火方案中,我们能够减少所需的步骤数,直到显着收敛。

Monte Carlo simulations are a powerful tool to investigate the thermodynamic properties of atomic systems. In practice however, sampling of the complete configuration space is often hindered by high energy barriers between different regions of configuration space which can make ergodic sampling completely infeasible within accessible simulation times. Although several extensions to the conventional Monte Carlo scheme have been developed, that enable the treatment of such systems, these extensions often entail substantial computational cost or rely on the harmonic approximation. In this work we propose an exact method called Funnel Hopping Monte Carlo (FHMC) that is inspired by the the ideas of smart darting but is more efficient. Gaussian mixtures are used to approximate the Boltzmann distribution around local energy minima which are then used to propose high quality Monte Carlo moves that enable the Monte Carlo simulation to directly jump between different funnels. To fit the Gaussian mixtures we developed an extended version of the expectation-maximization algorithm that is able to take advantage of the high symmetry present in many low energy configurations. We demonstrate the methods performance on the example of the 38 as well as the 75 atom Lennard-Jones clusters which are well known for their double funnel energy landscapes that prevent ergodic sampling with conventional Monte Carlo simulations. By integrating FHMC into the parallel tempering scheme we were able to reduce the number of steps required until convergence of the simulation significantly.

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