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CALCULATION OF FREE-ENERGY DIFFERENCES FROM COMPUTER SIMULATIONS OF INITIAL AND FINAL STATES

机译:从初始状态和最终状态的计算机模拟计算自由能差异

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A class of simple expressions of increasing accuracy for the free-energy difference between two states is derived based on numerical thermodynamic integration. The implementation of these formulas requires simulations of the initial and fnal (and possibly a few intermediate) states. They involve higher free-energy derivatives at these states which are related to the moments of the probability distribution of the perturbation. Given a specified number of such derivatives, these integration formulas are optimal in the sense that they are exact to the highest possible order of free-energy perturbation theory. The utility of this approach is illustrated for the hydration free energy of water. This problem provides a quite stringent test because the free energy is a highly nonlinear function of the charge so that even fourth order perturbation theory gives a very poor estimate of the free-energy change. Our results should prove most useful for complex, computationally demanding problems where foe-energy differences arise primarily from changes in the electrostatic interactions (e.g., electron transfer, charging of ions, protonation of amino acids in proteins). (C) 1996 American Institute of Physics. [References: 45]
机译:基于数值热力学积分,得出一类简单的表达式,用于提高两种状态之间的自由能差的精度。这些公式的实现需要模拟初始状态和最终状态(可能还有一些中间状态)。它们在这些状态下涉及较高的自由能导数,这些自由能导数与扰动的概率分布的矩有关。在给定特定数量的此类导数的情况下,这些积分公式在精确于自由能扰动理论的最高可能阶数的意义上是最佳的。说明了该方法对水的水合自由能的实用性。这个问题提供了相当严格的测试,因为自由能是电荷的高度非线性函数,因此即使是四阶微扰理论也无法很好地估计自由能的变化。我们的结果应证明对复杂的,计算要求很高的问题最为有用,在这些问题中,敌对能差异主要是由静电相互作用的变化(例如,电子转移,离子的带电,蛋白质中氨基酸的质子化)引起的。 (C)1996年美国物理研究所。 [参考:45]

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