Validation and application of orientational order-based TMD prediction

Through our recent examination of four famous water models, we hypothesized that there should be common features of orientational order universally at the temperature for maximum density (TMD) of 1 g/cm³ whatever reasonable water model used. However, it was derived empirically rather than theoretically and it demands more severe tests eagerly to be a common law. In the present work, we tested two additional water models, TIP4P-2005 and TIP5P-Ew models developed recently. From this, we found the consistent common features of orientational order around reported values of TMD again. To demonstrate simple yet effective predictability of an unknown TMD for a certain water model using the method derived from our hypothesis, simulations of our method were carried out at several temperatures with intervals of 20 °C for TIP4P-ice model. In spite of its much less computational cost and temperature range that was chosen arbitrarily, TMD was predicted correctly with resolution of 20 °C at least. We propose that our method offers a useful guideline for TMD by narrowing down the choice of TMD candidates without heavy computational efforts, at least for point-charge water models.