Wang Ke, Yu Yang-Xin, Gao Guang-Hua
Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China.
J Chem Phys. 2008 May 14;128(18):185101. doi: 10.1063/1.2918342.
A density functional theory (DFT) in the framework of cell model is proposed to calculate the structural and thermodynamic properties of aqueous DNA-electrolyte solution with finite DNA concentrations. The hard-sphere contribution to the excess Helmholtz energy functional is derived from the modified fundamental measure theory, and the electrostatic interaction is evaluated through a quadratic functional Taylor expansion around a uniform fluid. The electroneutrality in the cell leads to a variational equation with a constraint. Since the reference fluid is selected to be a bulk phase, the Lagrange multiplier proves to be the potential drop across the cell boundary (Donnan potential). The ion profiles and electrostatic potential profiles in the cell are calculated from the present DFT-cell model. Our DFT-cell model gives better prediction of ion profiles than the Poisson-Boltzmann (PB)- or modified PB-cell models when compared to the molecular simulation data. The effects of polyelectrolyte concentration, ion size, and added-salt concentration on the electrostatic potential difference between the DNA surface and the cell boundary are investigated. The expression of osmotic coefficient is derived from the general formula of grand potential. The osmotic coefficients predicted by the DFT are lower than the PB results and are closer to the simulation results and experimental data.
提出了一种基于元胞模型框架的密度泛函理论（DFT），用于计算有限DNA浓度下的DNA - 电解质水溶液的结构和热力学性质。硬球对过量亥姆霍兹自由能泛函的贡献源自修正的基本度量理论，静电相互作用通过围绕均匀流体的二次泛函泰勒展开来评估。元胞中的电中性导致了一个带有约束的变分方程。由于参考流体被选为体相，拉格朗日乘子被证明是跨元胞边界的电势降（唐南电势）。元胞中的离子分布和静电势分布由当前的DFT - 元胞模型计算得出。与分子模拟数据相比，我们的DFT - 元胞模型在离子分布预测方面比泊松 - 玻尔兹曼（PB）或修正PB - 元胞模型表现更好。研究了聚电解质浓度、离子大小和加盐浓度对DNA表面与元胞边界之间静电势差的影响。渗透系数的表达式由巨势的一般公式推导得出。DFT预测的渗透系数低于PB结果，且更接近模拟结果和实验数据。
