Department of Mathematics, University of California, San Diego, 9500 Gilman Drive, Mail code: 0112, La Jolla, California 92093-0112, USA.
J Chem Phys. 2013 Jul 14;139(2):024111. doi: 10.1063/1.4812839.
A phase-field variational implicit-solvent approach is developed for the solvation of charged molecules. The starting point of such an approach is the representation of a solute-solvent interface by a phase field that takes one value in the solute region and another in the solvent region, with a smooth transition from one to the other on a small transition layer. The minimization of an effective free-energy functional of all possible phase fields determines the equilibrium conformations and free energies of an underlying molecular system. All the surface energy, the solute-solvent van der Waals interaction, and the electrostatic interaction are coupled together self-consistently through a phase field. The surface energy results from the minimization of a double-well potential and the gradient of a field. The electrostatic interaction is described by the Coulomb-field approximation. Accurate and efficient methods are designed and implemented to numerically relax an underlying charged molecular system. Applications to single ions, a two-plate system, and a two-domain protein reveal that the new theory and methods can capture capillary evaporation in hydrophobic confinement and corresponding multiple equilibrium states as found in molecular dynamics simulations. Comparisons of the phase-field and the original sharp-interface variational approaches are discussed.
发展了一种用于带电分子溶剂化的相场变分隐溶剂方法。这种方法的出发点是通过一个相场来表示溶剂化界面，该相场在溶质区域取一个值，在溶剂区域取另一个值，在小的转变层上从一个值到另一个值的平滑转变。所有可能的相场的有效自由能泛函的最小化决定了基础分子系统的平衡构象和自由能。所有的表面能、溶质-溶剂范德华相互作用和静电相互作用都是通过相场自洽地耦合在一起的。表面能是通过最小化双势阱和场梯度来实现的。静电相互作用是通过库仑场近似来描述的。设计并实现了精确和有效的方法来数值松弛基础的带电分子系统。应用于单离子、两板系统和双域蛋白，揭示了新理论和方法可以捕捉疏水约束中的毛细蒸发和分子动力学模拟中发现的相应多个平衡状态。讨论了相场和原始锐利界面变分方法之间的比较。
