In order to obtain molecular dynamics (MD) simulations trajectory for computing phonon dispersion relation at finite temperature, I performed NVT MD simulation using VASP for my target system.
Here is the temperature & total free energy profile I obtained (temperature in the unit of Kelvin, and total free energy in the unit of eV, the simulation timestep is 1 fs).
Clearly, there is something wrong with my simulation, the temperature keeps fluctuating over a wide range, while the total free energy is constantly decreasing. I have optimized my structure using the standard conjugate gradient method before MD simulation (under the same accuracy level).
What does this temperature & total free energy profile mean? Should I let it run for a bit longer until the total free energy converges?