<s>
In	O
molecular	O
dynamics	O
(	O
MD	O
)	O
simulations	O
,	O
the	O
flying	B-Algorithm
ice	I-Algorithm
cube	I-Algorithm
effect	O
is	O
an	O
artifact	O
in	O
which	O
the	O
energy	O
of	O
high-frequency	O
fundamental	O
modes	O
is	O
drained	O
into	O
low-frequency	O
modes	O
,	O
particularly	O
into	O
zero-frequency	O
motions	O
such	O
as	O
overall	O
translation	O
and	O
rotation	O
of	O
the	O
system	O
.	O
</s>
<s>
The	O
artifact	O
derives	O
its	O
name	O
from	O
a	O
particularly	O
noticeable	O
manifestation	O
that	O
arises	O
in	O
simulations	O
of	O
particles	O
in	O
vacuum	B-General_Concept
,	O
where	O
the	O
system	O
being	O
simulated	O
acquires	O
high	O
linear	O
momentum	B-Algorithm
and	O
experiences	O
extremely	O
damped	O
internal	O
motions	O
,	O
freezing	O
the	O
system	O
into	O
a	O
single	O
conformation	O
reminiscent	O
of	O
an	O
ice	O
cube	O
or	O
other	O
rigid	O
body	O
flying	O
through	O
space	O
.	O
</s>
<s>
The	O
flying	B-Algorithm
ice	I-Algorithm
cube	I-Algorithm
artifact	O
arises	O
from	O
repeated	O
rescalings	O
of	O
the	O
velocities	O
of	O
the	O
particles	O
in	O
the	O
simulation	O
system	O
.	O
</s>
<s>
Velocity	O
rescaling	O
is	O
a	O
means	O
of	O
imposing	O
a	O
thermostat	O
on	O
the	O
system	O
by	O
multiplying	O
the	O
velocities	O
of	O
a	O
system	O
's	O
particles	O
by	O
a	O
factor	O
after	O
an	O
integration	O
timestep	O
is	O
completed	O
,	O
as	O
is	O
done	O
by	O
the	O
Berendsen	B-Algorithm
thermostat	I-Algorithm
and	O
the	O
Bussi	O
–	O
Donadio	O
–	O
Parrinello	O
thermostat	O
.	O
</s>
<s>
These	O
schemes	O
fail	O
when	O
the	O
rescaling	O
is	O
done	O
to	O
a	O
kinetic	O
energy	O
distribution	O
of	O
an	O
ensemble	O
that	O
is	O
not	O
invariant	O
under	O
microcanonical	O
molecular	O
dynamics	O
;	O
thus	O
,	O
the	O
Berendsen	B-Algorithm
thermostat	I-Algorithm
(	O
which	O
rescales	O
to	O
the	O
isokinetic	O
ensemble	O
)	O
exhibits	O
the	O
artifact	O
,	O
while	O
the	O
Bussi	O
–	O
Donadio	O
–	O
Parrinello	O
thermostat	O
(	O
which	O
rescales	O
to	O
the	O
canonical	O
ensemble	O
)	O
does	O
not	O
exhibit	O
the	O
artifact	O
.	O
</s>
<s>
When	O
the	O
flying	B-Algorithm
ice	I-Algorithm
cube	I-Algorithm
problem	O
was	O
first	O
found	O
,	O
the	O
Bussi	O
–	O
Donadio	O
–	O
Parrinello	O
thermostat	O
had	O
not	O
yet	O
been	O
developed	O
,	O
and	O
it	O
was	O
desired	O
to	O
continue	O
using	O
the	O
Berendsen	B-Algorithm
thermostat	I-Algorithm
due	O
to	O
the	O
efficiency	O
with	O
which	O
velocity	O
rescaling	O
thermostats	O
relax	O
systems	O
to	O
desired	O
temperatures	O
.	O
</s>
<s>
Thus	O
,	O
suggestions	O
were	O
given	O
to	O
avoid	O
the	O
flying	B-Algorithm
ice	I-Algorithm
cube	I-Algorithm
effect	O
under	O
the	O
Berendsen	B-Algorithm
thermostat	I-Algorithm
,	O
such	O
as	O
periodically	O
removing	O
the	O
center-of-mass	O
motions	O
and	O
using	O
a	O
longer	O
temperature	O
coupling	O
time	O
.	O
</s>
<s>
However	O
,	O
more	O
recently	O
it	O
has	O
been	O
recommended	O
that	O
the	O
better	O
practice	O
is	O
to	O
discontinue	O
use	O
of	O
the	O
Berendsen	B-Algorithm
thermostat	I-Algorithm
entirely	O
in	O
favor	O
of	O
the	O
Bussi	O
–	O
Donadio	O
–	O
Parrinello	O
thermostat	O
,	O
as	O
it	O
has	O
been	O
shown	O
that	O
the	O
latter	O
thermostat	O
does	O
not	O
exhibit	O
the	O
flying	B-Algorithm
ice	I-Algorithm
cube	I-Algorithm
effect	O
.	O
</s>
