Ab initio molecular dynamics to check material stability at finite temperature

I completed an ab initio molecular dynamic (AIMD) simulation in VASP for a hypothetical material. The simulation was done for 5ps with 1fs steps and the temperature was set to 300K using Nosé–Hoover thermostat. Now I've extracted the total energy variation w.r.t time and could not decide if the material is potentially stable or not from the plot.

Does this support that the material could be stable since the total energy converges around $$\ce{-800 eV/cell}$$ after 1ps? My concern is there is a huge variation in total energy during the 1st pico second, what does that mean? And what other tests should I do to investigate stability/instability of materials using AIMD simulations (e.g. variation of bond length over time)?

• +1. Interesting question, but what type of stability are you looking for? Are you looking for dynamical stability (the structure of the material stays the same), chemical stability (segregation into different compounds), or something else? – ProfM Jul 3 '20 at 7:16
• I am looking for both. Does the material maintain its structural integrity and does it not decompose to different compounds. What other tests should I do in addition to this energy curve to inspect this? – Achintha Ihalage Jul 3 '20 at 7:59
• Did you relax the structure first, before starting MD? If you didn't, then what you see in the MD is just the structure relaxation effect. If you did, then the MD appers to have found a close-lying lower minimum. – Susi Lehtola Jul 3 '20 at 10:53
• I did relax the structure first and used the optimised structure to start the MD simulation. By "close-lying lower minimum" do you mean the initial structure breaks at this temperature? – Achintha Ihalage Jul 3 '20 at 11:41
• @AchinthaIhalage your energy lowers by 600 eV in the simulation, which is huge. How big is the system, i.e. what is the energy change per atom? – Susi Lehtola Jul 4 '20 at 9:29