Rogers David M, Beck Thomas L
Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221-0172, USA.
J Chem Phys. 2008 Oct 7;129(13):134505. doi: 10.1063/1.2985613.
A recently developed statistical mechanical quasichemical theory (QCT) has led to significant insights into solvation phenomena for both hydrophilic and hydrophobic solutes. The QCT exactly partitions solvation free energies into three components: (1) Inner-shell chemical, (2) outer-shell packing, and (3) outer-shell long-ranged contributions. In this paper, we discuss efficient methods for computing each of the three parts of the free energy. A Bayesian estimation approach is developed to compute the inner-shell chemical and outer-shell packing contributions. We derive upper and lower bounds on the outer-shell long-ranged portion of the free energy by expressing this component in two equivalent ways. Local, high-energy contacts between the solute and solvent are eliminated by spatial conditioning in this free energy piece, leading to near-Gaussian distributions of solute-solvent interaction energies. Thus, the average of the two mean-field bounds yields an accurate and efficient free energy estimate. Aqueous solvation free energy results are presented for several solutes, including methane, perfluoromethane, water, and sodium and chloride ions. The results demonstrate the accuracy and efficiency of the methods. The approach should prove useful in computing solvation free energies in inhomogeneous, restricted environments.
最近发展起来的统计力学准化学理论（QCT）为亲水性和疏水性溶质的溶剂化现象带来了重要见解。QCT将溶剂化自由能精确地划分为三个部分：（1）内壳层化学作用，（2）外壳层堆积作用，以及（3）外壳层长程作用贡献。在本文中，我们讨论了计算自由能这三个部分的有效方法。开发了一种贝叶斯估计方法来计算内壳层化学作用和外壳层堆积作用的贡献。我们通过以两种等效方式表示自由能的外壳层长程部分，推导出了该部分的上下界。在这部分自由能中，通过空间条件设定消除了溶质与溶剂之间的局部高能接触，从而得到溶质 - 溶剂相互作用能的近似高斯分布。因此，两个平均场界的平均值给出了准确且高效的自由能估计。给出了几种溶质（包括甲烷、全氟甲烷、水以及钠离子和氯离子）的水合溶剂化自由能结果。结果证明了这些方法的准确性和效率。该方法在计算非均匀受限环境中的溶剂化自由能时应会很有用。
