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The Z method is a popular atomistic simulation method for determining themelting temperature where a sequence of molecular dynamics runs are carried outto target the lowest system energy where the solid always melts. Homogeneousmelting at the limit of critical superheating, Th, is accompanied by a drop intemperature as kinetic energy is converted to potential energy and theequilibrium melting temperature, Tm, can be calculated directly from the liquidstate. Implementation of the Z method interfaced with modern ab initioelectronic structure packages use Hellmann-Feynman forces to propagate the ionsin the microcanonical(NVE) ensemble where the Mermin free energy plus the ionickinetic energy is conserved. The electronic temperature, Tel, is kept fixedalong the trajectory which may introduce some spurious ion-electroninteractions in MD runs with large temperature changes such as often seen inhomogeneous melting and freezing processes in the NVE ensemble. We estimatesystematic errors in the calculated melting temperature to choice of Tel fortwo main mantle components, SiO2 and CaSiO3 at high pressure. Comparison of thecalculated melting temperature from runs where the Tel=Th and Tel=Tmrepresenting reasonable upper and lower boundaries respectively to choice ofTel shows that the difference in melting temperature is 200-300 K for our twotest systems. The melting temperature decreases with increasing Tel due to theincreasing entropic stabilisation of the liquid and the systems melts typicallyabout 3 times faster in MD runs with Tel = Th compared to runs where Tel = Tm.A careful choice of electron temperature in BOMD simulations where the ions arepropagated using Hellmann-Feynamn forces with the Mermin free energy + theionic kinetic energy being conserved is therefore essential for the criticalevaluation of the Z method and in particular at very high temperatures.

Influence of electronic entropy on Hellmann-Feynman forces in ab initio molecular dynamics with large temperature changes