Hi, I want to calculate the phase change energy from solid to liquid, for example, water. For this, potential energy vs. temperature needs to be plotted, if I am not wrong. If yes, please correct me. What is the role of total energy (and kinetic energy) during the phase change? I want to use DFT (Quantum Espresso) or MD (Gromacs) simulations for the same.
With MD, can I do this with an energy minimization step? Or I have to follow the equilibration process for only temperature or for both temperature and pressure.
With DFT, how can I do this?
If possible, please share examples and script files.
Unless you are considering isochoric melting, you probably want to compare enthalpies (not energies!) of the liquid and the solid.
If you know the melting point of your substance, 2 single-phase MD simulations (one for the liquid, one for the solid) should be sufficient. Otherwise you need simulation techniques that gradually and reversibly transform a liquid into a solid by means of an artificial “crystal field“ (see the textbook of Frenkel and Smit), or the “entropy correlation method” (DOI: Article First-principles determination of the solid-liquid-vapor tri...
or 2-phase simulations in which liquid and solid phases coexist.
Thank you, Prof. Ulrich Deiters, I will try the "transform a liquid into a solid by means of an artificial “crystal field“.
If I also consider/vary the pressure, then the melting point will be changed, as I know. If I am wrong, please correct me. What significance does it have?
Usually, I convert pressure to energy units using E=P*V. But I don't think it is the correct way to state pressure and energy.
You may use Clapeyron's equation to assess the influence of pressure on the melting temperature, dp/dT = ∆H/(T ∆V). The deltas signify the differences of the enthalpy or volume, respectively, of the solid and the liquid.
If you do isobaric simulations, they will yield these properties.
I do not quite understand what you mean by “convert pressure to energy units”. You evidently need pressure units for the pressure.
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