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I’m trying to calculate the thermal conductivity of a crystal structure containing light atoms like lithium. I have a well-trained force field and plan to use it for large-scale simulations. Initially, I’d like to confirm—can I reliably obtain the correct thermal conductivity for such a system using this approach?
Also, I need the thermal conductivity in units of W/(m·K). Could someone clarify the units of the heat flux (in all three directions) provided in the ML_HEAT file?
Dear Paul Tanmoy,
The units of the flux in the ML_HEAT file are (eV A)/fs. I have updated the wiki page to reflect that.
Often, the convergence of Green-Kubo is slow with respect to simulation length, box size, etc. Some tips and tricks are shared in this forum post:
heat flow and thermal conductivity.
Light elements in your system will also make a small timestep (POTIM) necessary. For Hydrogen, that would be around 0.25 - 0.5, for Lithium, you have to do your own testing.
It might be better to use the Müller-Plathe method, which has been available in VASP since version 6.5.0. However, the Green-Kubo method should, in principle, work if your force field is accurate enough and you carefully converge.
I hope you understand that I cannot guarantee that you will achieve the "correct results", especially without knowing more about your material and simulation setup.
All the best, Michael
Respected Michael,
Thank you for your insightful response. I have figured out the unit conversion part for thermal conductivity calculation. Currently I am using Green-Kubo formalism and performing long NVE simulation with Noose-Hover thermostat of a snapshot picking randomly from NVT simulation of my structure. I have attached the plots of heat flux autocorrelation and thermal conductivity, from this thermal conductivity plot can I say that it's heading to a converged value? and to finalize the value of my system's thermal conductivity how many snapshots should I consider for NVE simulation?
Sincerely,
Tanmoy