Melting Points of OPC and OPC3 Water Models

A recently introduced family of globally optimal water models, OPC, has shown promise in a variety of biomolecular simulations, but properties of these water models outside of the liquid phase remain mostly unexplored. Here, we contribute to filling the gap by reporting melting temperatures of ice Ih of OPC and OPC3 water models. Through the direct coexistence method, which we make available in the AMBER package, the melting points of OPC and OPC3 are estimated as 242 and 210 K, similar to TIP4P-Ew and SPC/E models, respectively, and appreciably below the experimental value of 273.15 K under 1 bar pressure. Water models of the OPC family were optimized to best reproduce water properties in the liquid phase where these models offer noteworthy accuracy advantages over many models of previous generations. It is not surprising that the accuracy of OPC models in describing the phase transition to the solid state does not appear to offer similar improvements. The new anisotropic barostat option implemented in AMBER may benefit system preparation and simulation outside of the direct coexistence applications, such as modeling of membranes or very long DNA strands.

近期提出的全局最优水模型系列OPC (OPC)已在多种生物分子模拟中展现出良好应用潜力，但这类水模型在液相以外的相态中的性质仍未得到充分探索。本研究通过报道OPC与OPC3水模型的Ih型冰熔点，填补了这一研究空白。我们借助已集成至AMBER软件包的直接共存法，测得OPC与OPC3水模型的熔点分别为242 K与210 K，其结果分别与TIP4P-Ew和SPC/E水模型相近，且显著低于1巴压力下的实验值273.15 K。OPC系列水模型的优化目标为最优复现液相水的各项性质，相较于诸多前代水模型，该系列在液相模拟中具备显著的精度优势。因此，OPC模型在描述固相相变时未展现出同等的精度提升，这一结果并不出人意料。AMBER中新增的各向异性恒压器模块，除直接共存法应用场景外，还可用于体系制备与其他模拟工作，例如生物膜建模或超长链DNA分子模拟。