I have tried to do the calculation for MoS2 applying NPT system by choosing MDALGO=3 and ISIF=3 for NSW=10000. But the temperature fluctuation is very large; for example, if I choose TEBEG=TEEND=300, the temperature varies from almost 57 to 500 K. So free energy of the system also fluctuates. I want to know how to choose SMASS and POTIM or anyother parameter to reduce temperature fluctuation and get the exact value of free energy for a particular temperature.