<s>
Quantum	B-Application
ESPRESSO	I-Application
is	O
a	O
suite	O
for	O
first-principles	O
electronic-structure	O
calculations	O
and	O
materials	O
modeling	O
,	O
distributed	O
for	O
free	O
and	O
as	O
free	B-Application
software	I-Application
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
The	O
core	O
plane	O
wave	O
DFT	O
functions	O
of	O
QE	O
are	O
provided	O
by	O
the	O
PWscf	B-Application
component	O
(	O
PWscf	B-Application
previously	O
existed	O
as	O
an	O
independent	O
project	O
)	O
.	O
</s>
<s>
PWscf	B-Application
(	O
Plane-Wave	O
Self-Consistent	O
Field	O
)	O
is	O
a	O
set	O
of	O
programs	O
for	O
electronic	O
structure	O
calculations	O
within	O
density	O
functional	O
theory	O
and	O
density	O
functional	O
perturbation	O
theory	O
,	O
using	O
plane	O
wave	O
basis	O
sets	O
and	O
pseudopotentials	O
.	O
</s>
<s>
The	O
software	O
is	O
released	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
Quantum	B-Application
ESPRESSO	I-Application
is	O
an	O
open	O
initiative	O
of	O
the	O
CNR-IOM	O
DEMOCRITOS	O
National	O
Simulation	O
Center	O
in	O
Trieste	O
(	O
Italy	O
)	O
and	O
its	O
partners	O
,	O
in	O
collaboration	O
with	O
different	O
centers	O
worldwide	O
such	O
as	O
MIT	O
,	O
Princeton	O
University	O
,	O
the	O
University	O
of	O
Minnesota	O
and	O
the	O
École	O
Polytechnique	O
Fédérale	O
de	O
Lausanne	O
.	O
</s>
<s>
The	O
project	O
is	O
coordinated	O
by	O
the	O
QUANTUM	B-Application
ESPRESSO	I-Application
foundation	O
,	O
which	O
was	O
formed	O
by	O
many	O
research	O
centers	O
and	O
groups	O
all	O
over	O
the	O
world	O
.	O
</s>
<s>
The	O
program	O
,	O
written	O
mainly	O
in	O
Fortran-90	O
with	O
some	O
parts	O
in	O
C	B-Language
or	O
in	O
Fortran-77	O
,	O
was	O
built	O
out	O
of	O
the	O
merging	O
and	O
re-engineering	O
of	O
different	O
independently	O
developed	O
core	O
packages	O
,	O
plus	O
a	O
set	O
of	O
packages	O
,	O
designed	O
to	O
be	O
inter-operable	O
with	O
the	O
core	O
components	O
,	O
which	O
allow	O
more	O
advanced	O
tasks	O
to	O
be	O
performed	O
.	O
</s>
<s>
The	O
basic	O
packages	O
include	O
Pwscf	B-Application
,	O
which	O
solves	O
the	O
self-consistent	O
Kohn-Sham	O
equations	O
,	O
obtained	O
for	O
a	O
periodic	O
solid	O
,	O
CP	O
to	O
carry	O
out	O
Car-Parrinello	B-Application
molecular	I-Application
dynamics	I-Application
,	O
and	O
PostProc	O
,	O
which	O
allows	O
data	O
analysis	O
and	O
plotting	O
.	O
</s>
<s>
The	O
main	O
components	O
of	O
the	O
Quantum	B-Application
ESPRESSO	I-Application
distribution	O
are	O
designed	O
to	O
exploit	O
the	O
architecture	O
of	O
today	O
's	O
supercomputers	O
characterized	O
by	O
multiple	O
levels	O
and	O
layers	O
of	O
inter-processor	O
communication	O
.	O
</s>
<s>
The	O
parallelization	O
is	O
achieved	O
using	O
both	O
MPI	B-Application
and	O
OpenMP	B-Application
parallelization	O
,	O
allowing	O
the	O
main	O
codes	O
of	O
the	O
distribution	O
to	O
run	O
in	O
parallel	O
on	O
most	O
or	O
all	O
parallel	O
machines	O
with	O
very	O
good	O
performance	O
.	O
</s>
