The paper discusses the problem of internal pressure PINT of liquid water, a fundamental parameter whose molecular nature remains a subject of debate within the framework of modern understandings of water structure. Using the van der Waals gas–liquid equation (vdW), the temperature dependence PINT(T) of the internal pressure is calculated over the range from the triple point to the critical point (273–647 K). The graph of PINT(T) qualitatively differs from that known from thermodynamics by a high value of PINT ~ 450 MPa at the triple point of 273 K and by a decrease toward the intersection with the liquid–vapor saturation curve PS(T) at the critical point. The problem of discrepancy between PINT(T) calculated within the van der Waals model and thermodynamic PINT(T) is fundamental and requires further investigation.
Чучупал et al. (Sun,) studied this question.