Horn Hans W, Swope William C, Pitera Jed W
International Business Machines Corporation (IBM) Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA.
J Chem Phys. 2005 Nov 15;123(19):194504. doi: 10.1063/1.2085031.
The liquid-vapor-phase equilibrium properties of the previously developed TIP4P-Ew water model have been studied using thermodynamic integration free-energy simulation techniques in the temperature range of 274-400 K. We stress that free-energy results from simulations need to be corrected in order to be compared to the experiment. This is due to the fact that the thermodynamic end states accessible through simulations correspond to fictitious substances (classical rigid liquids and classical rigid ideal gases) while experiments operate on real substances (liquids and real gases, with quantum effects). After applying analytical corrections the vapor pressure curve obtained from simulated free-energy changes is in excellent agreement with the experimental vapor pressure curve. The boiling point of TIP4P-Ew water under ambient pressure is found to be at 370.3+/-1.9 K, about 7 K higher than the boiling point of TIP4P water (363.7+/-5.1 K; from simulations that employ finite range treatment of electrostatic and Lennard-Jones interactions). This is in contrast to the approximately +15 K by which the temperature of the density maximum and the melting temperature of TIP4P-Ew are shifted relative to TIP4P, indicating that the temperature range over which the liquid phase of TIP4P-Ew is stable is narrower than that of TIP4P and resembles more that of real water. The quality of the vapor pressure results highlights the success of TIP4P-Ew in describing the energetic and entropic aspects of intermolecular interactions in liquid water.
利用热力学积分自由能模拟技术，在274 - 400 K的温度范围内研究了先前开发的TIP4P - Ew水模型的液 - 气平衡性质。我们强调，为了与实验结果进行比较，模拟得到的自由能结果需要进行校正。这是因为通过模拟可达到的热力学终态对应于虚拟物质（经典刚性液体和经典刚性理想气体），而实验是针对真实物质（液体和真实气体，存在量子效应）进行的。应用解析校正后，从模拟自由能变化得到的蒸气压曲线与实验蒸气压曲线高度吻合。发现TIP4P - Ew水在环境压力下的沸点为370.3±1.9 K，比TIP4P水的沸点（363.7±5.1 K；来自采用静电和 Lennard - Jones 相互作用有限范围处理的模拟）高约7 K。这与TIP4P - Ew的密度最大值温度和熔化温度相对于TIP4P大约 +15 K的偏移形成对比，表明TIP4P - Ew液相稳定的温度范围比TIP4P窄，更类似于真实水的情况。蒸气压结果的质量突出了TIP4P - Ew在描述液态水中分子间相互作用的能量和熵方面的成功。
