Comparison of adiabatic gradient obtained from models with phase separation with values used by Stixrude et al. (2021) and James & Stixrude (2024). (a) Interior P–T profiles for Neptune for different T_{1 bar} temperatures. The metallicity Z₁ = Z_atm is varied with T_{1 bar} according to the Berg24 phase diagram, while Z₂ essentially stays at ∼0.7. (b) Bulk volume-weighted-adiabatic gradient over temperature since the start of demixing (right side of the x-axis) to the present temperature. Blue bands show the range of values for ∇_ad found by Stixrude et al. (2021) for Uranus and James & Stixrude (2024) for Neptune to match the cooling times, amongst their range of tested values between 0.24 and 0.29 (dashed lines).