Top panel: specific internal energy of AQUA as a function of pressure and temperature. Middle panel: relative difference between the internal energy of ANEOS vs. AQUA. Bottom panel: same comparison but between QEOS and AQUA. The internal energy potential of QEOS seems to be globally shifted compared to ANEOS and AQUA, probably due to a different choice of reference state. For the comparison we therefore subtracted 37.5 kJ g⁻¹ from u(T, P)_QEOS.