I looked at the T(t) data and computed its power spectrum using a maximum entropy method. There is a peak near 1100 cm-1 which would correspond to a vibrational mode at about 550 cm-1 (the frequency of oscillations in the temperature are twice the frequency of the atomic motions). There are also several other peaks at higher frequencies. My interpretation of these peaks would be as follows: the peak at 550 cm-1 may be related to the Raman peak near 520 cm-1 observed in amorphous-Si, possibly shifted in frequency due to pressure. The other peaks are probably spurious and result from the use of the thermostat. Using a high collision frequency (th_time=30) causes many discontinuous changes in the kinetic energy on a short time scale, which likely results in a large spectral content at high frequency.
I would suggest that you try the new Bussi-Donadio-Parrinello thermostat that has been implemented since version 1.52.0. The keyword for that thermostat is BDP. This thermostat yields smooth trajectories, as opposed to the LOEWE and ANDERSEN thermostats. This should result in a better power spectrum of T(t), i.e. without high-frequency noise.
I have the following questions regarding this simulation:
- Did you verify that the system is liquid? Using a Loewe thermostat with very high collision frequency can lead to a large increase in viscosity. This may affect your simulation.