Johnson Margaret E, Head-Gordon Teresa, Louis Ard A
UCSF/UCB Joint Graduate Group in Bioengineering, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2007 Apr 14;126(14):144509. doi: 10.1063/1.2715953.
The use of an effective intermolecular potential often involves a compromise between more accurate, complex functional forms and more tractable simple representations. To study this choice in detail, we systematically derive coarse-grained isotropic pair potentials that accurately reproduce the oxygen-oxygen radial distribution function of the TIP4P-Ew water model at state points over density ranges from 0.88 to 1.30 g/cm3 and temperature ranges from 235 to 310 K. Although by construction these effective potentials correctly represent the isothermal compressibility of TIP4P-Ew water, they do not accurately resolve other thermodynamic properties such as the virial pressure, the internal energy, or thermodynamic anomalies. Because at a given state point the pair potential that reproduces the pair structure is unique, we have therefore explicitly demonstrated that it is impossible to simultaneously represent the pair structure and several key equilibrium thermodynamic properties of water with state-point dependent radially symmetric pair potentials. We argue that such representability problems are related to, but different from, more widely acknowledged transferability problems and discuss in detail the implications this has for the modeling of water and other liquids by coarse-grained potentials. Nevertheless, regardless of thermodynamic inconsistencies, the state-point dependent effective potentials for water do generate structural and dynamical anomalies.
使用有效的分子间势通常需要在更精确、复杂的函数形式与更易于处理的简单表示之间进行权衡。为了详细研究这种选择，我们系统地推导了粗粒度各向同性对势，该势在密度范围为0.88至1.30 g/cm³以及温度范围为235至310 K的状态点上准确再现了TIP4P-Ew水模型的氧-氧径向分布函数。尽管通过构建这些有效势正确地表示了TIP4P-Ew水的等温压缩性，但它们并未准确解析其他热力学性质，如维里压力、内能或热力学异常。由于在给定的状态点上，再现对结构的对势是唯一的，因此我们明确证明，不可能用与状态点相关的径向对称对势同时表示水的对结构和几个关键的平衡热力学性质。我们认为，这种可表示性问题与更广泛认可的可转移性问题相关，但又有所不同，并详细讨论了这对通过粗粒度势对水和其他液体进行建模的影响。然而，尽管存在热力学不一致性，与状态点相关的水的有效势确实会产生结构和动力学异常。
