Environmental Engineering Reference
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Figure 1.7 Normalized velocity autocorrelation function with different
number of layers (NL) of Nose-Hover and Langevin heat bath applied.
Exceptforthesolidline,theotherthreelinesalmostoverlapwitheachother.
velocity-scaling type heat bath, withthe scaling factor [38]
1
T 0
T
1 1 / 2
+
t
τ T
γ =
,
(1.35)
where t is the time step, τ T is the relaxation time, T 0 and
T are the aimed temperature and instantaneous temperature,
respectively. The relaxation time τ T should be properly chosen to
avoidunrealisticallylow-temperaturefluctuationswithsmall τ T ,and
the inactive sampling with large τ T (e.g., τ T →∞ ) [39]. Based on
such considerations, we set τ T = t × 10 4 (8 ps) in our study.
As shown in Fig. 1.8, with Berendsen heat bath, the NW fails to
reach the aimed temperature (310 K and 290 K) at two ends.
More seriously, large TJ persists regardless of the number of heat
bath layers applied. This even poorer performance of Berendsen
heat bath is a consequence of its inability to reproduce canonical
ensemble, because of the artificial velocity-scaling scheme [39],
which has been reported to cause artifacts in various studies
 
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