Convergence of single-step free energy perturbation
Convergence of single-step free energy perturbation
复制标题
DOI：
10.1080/00268976.2016.1269960
复制
发表时间：
2017-01-01
影响因子：
1.7
通讯作者：
Woodcock, H. Lee
中科院分区：
文献类型：
--
作者：
Boresch, Stefan;Woodcock, H. Lee
本文从实用的角度研究了自由能扰动（Zwanzig 方程）的收敛性及其非平衡扩展（Jarzynski 方程）。我们重点关注中间步骤和双边方法（Bennett、Crooks）都不能用于计算感兴趣的自由能差的情况。使用从多个概率密度采样的模型数据，以及将实际自由能模拟结果与参考值进行比较，我们发现，与现有理论工作一致，系统误差与能量差/非平衡功值分布的方差密切相关。 Wu 和 Kofke 引入的偏差度量（J. Chem. Phys. 121, 8742 (2004)）被发现是对偏差（即结果中的系统误差）是否存在的有用测试。相比之下，使用二阶累积量近似来近似完整的 Zwanzig 或 Jarzynski 方程在几乎所有情况下都会导致较差的结果。[图形]。
The convergence of free energy perturbation (Zwanzig's equation) and its non-equilibrium extension (Jarzynski's equation) is herein investigated from a practical point of view. We focus on cases where neither intermediate steps nor two-sided methods (Bennett, Crooks) can be used to compute the free energy difference of interest. Using model data sampled from several probability densities, as well as comparing results of actual free energy simulations with reference values, we find, in agreement with existing theoretical work, that systematic errors are strongly correlated with the variance in the distribution of energy differences / non-equilibrium work values. The bias metric introduced by Wu and Kofke (J. Chem. Phys. 121, 8742 (2004)) is found to be a useful test for the presence of bias, i.e. systematic error in the results. By contrast, use of the second-order cumulant approximation to approximate the full Zwanzig or Jarzynski equation leads to poorer results in almost all cases.[GRAPHICS].