NVE ensemble Temp instability in tersoff SiO2

Hi everyone,

I’m using Tersoff potential to simulate both amorphous Sio2 and β-cristobalite crystal structure using the pair coefficients from SiO.tersoff file which is given by LAMMPS. I’m having a temperature increasing issue in nve ensemble roughly as follows with a time step of 0.5fs.

40K/ns in amorphous SiO2 started at 300K
80K/ns in β-cristobalite started at 1800K

I was able to solve the issue by reducing the time step to 0.1fs but as I read, it should be possible to maintain energy conservation with 0.5fs.
I wish to have your opinion on this to solve my issue. Have attached the input script(for β-cristobalite), log file and SiO.tersoff files

Thank you. Regards
Chamara Somarathna

SiO2.in (2.31 KB)

SiO.tersoff (1.85 KB)

log.lammps (281 KB)