Ari:
Indeed! You are right on spot. The too small size unit cell that leads to
inaccurate structure and energy is responsible for large temperature
fluctuation here.
I am trying to increase the size of the supercell now.
Thanks!
On Sat, Apr 14, 2018 at 6:06 AM, Ari P Seitsonen
Dear Jie Peng,
suppose you were running a model harmonic system in 1 dimension.
M a = - K x
at fixed energy E.
The kinetic energy would fluctuate harmonically between 0 (at
maximum/minimum elongation) and E at the equilibrium distance .
On average the Kinetic energy would be E/2 and
Dear Jie,
I do not know about the other options, but
1) simulating a periodic system of only three atoms with only the Gamma
point cannot lead to an accurate description of the electronic structure,
and thus the forces on the ionic cores,
2) the standard deviation in the fluctuations
