<s>
Q-Chem	B-Language
is	O
a	O
general-purpose	O
electronic	O
structure	O
package	O
featuring	O
a	O
variety	O
of	O
established	O
and	O
new	O
methods	O
implemented	O
using	O
innovative	O
algorithms	O
that	O
enable	O
fast	O
calculations	O
of	O
large	O
systems	O
on	O
various	O
computer	O
architectures	O
,	O
from	O
laptops	O
and	O
regular	O
lab	O
workstations	O
to	O
midsize	O
clusters	O
and	O
HPCC	O
,	O
using	O
density	O
functional	O
and	O
wave-function	O
based	O
approaches	O
.	O
</s>
<s>
In	O
addition	O
to	O
serving	O
the	O
computational	O
chemistry	O
community	O
,	O
Q-Chem	B-Language
also	O
provides	O
a	O
versatile	O
code	O
development	O
platform	O
.	O
</s>
<s>
Q-Chem	B-Language
software	O
is	O
maintained	O
and	O
distributed	O
by	O
Q-Chem	B-Language
,	O
Inc.	O
,	O
located	O
in	O
Pleasanton	O
,	O
California	O
,	O
USA	O
.	O
</s>
<s>
It	O
was	O
founded	O
in	O
1993	O
as	O
a	O
result	O
of	O
disagreements	O
within	O
the	O
Gaussian	B-Application
company	O
that	O
led	O
to	O
the	O
departure	O
(	O
and	O
subsequent	O
"	O
banning	O
"	O
)	O
of	O
John	O
Pople	O
and	O
a	O
number	O
of	O
his	O
students	O
and	O
postdocs	O
(	O
see	O
Gaussian	B-Application
License	O
Controversy	O
)	O
.	O
</s>
<s>
The	O
first	O
lines	O
of	O
the	O
Q-Chem	B-Language
code	O
were	O
written	O
by	O
Peter	O
Gill	O
,	O
at	O
that	O
time	O
a	O
postdoc	O
of	O
Pople	O
,	O
during	O
a	O
winter	O
vacation	O
(	O
December	O
1992	O
)	O
in	O
Australia	O
.	O
</s>
<s>
In	O
preparation	O
for	O
the	O
first	O
commercial	O
release	O
,	O
the	O
company	O
hired	O
Eugene	O
Fleischmann	O
as	O
marketing	O
director	O
and	O
acquired	O
its	O
URL	O
www.q-chem.com	O
in	O
January	O
1997	O
.	O
</s>
<s>
The	O
first	O
commercial	O
product	O
,	O
Q-Chem	B-Language
1.0	O
,	O
was	O
released	O
in	O
March	O
1997	O
.	O
</s>
<s>
However	O
,	O
vigorous	O
code	O
development	O
continued	O
,	O
and	O
by	O
the	O
following	O
year	O
Q-Chem	B-Language
1.1	O
was	O
able	O
to	O
offer	O
most	O
of	O
the	O
basic	O
quantum	O
chemical	O
functionality	O
as	O
well	O
as	O
a	O
growing	O
list	O
of	O
features	O
(	O
the	O
continuous	B-Algorithm
fast	I-Algorithm
multipole	I-Algorithm
method	I-Algorithm
,	O
J-matrix	O
engine	O
,	O
COLD	O
PRISM	O
for	O
integrals	O
,	O
and	O
G96	O
density	O
functional	O
,	O
for	O
example	O
)	O
that	O
were	O
not	O
available	O
in	O
any	O
other	O
package	O
.	O
</s>
<s>
In	O
1998	O
,	O
Fritz	O
Schaefer	O
accepted	O
an	O
invitation	O
to	O
join	O
the	O
Board	O
of	O
Directors	O
and	O
,	O
early	O
in	O
1999	O
,	O
as	O
soon	O
as	O
his	O
non-compete	O
agreement	O
with	O
Gaussian	B-Application
had	O
expired	O
,	O
John	O
Pople	O
joined	O
as	O
both	O
a	O
Director	O
and	O
code	O
developer	O
.	O
</s>
<s>
In	O
2000	O
,	O
Q-Chem	B-Language
established	O
a	O
collaboration	O
with	O
Wavefunction	O
Inc.	O
,	O
which	O
led	O
to	O
the	O
incorporation	O
of	O
Q-Chem	B-Language
as	O
the	O
ab	O
initio	O
engine	O
in	O
all	O
subsequent	O
versions	O
of	O
the	O
Spartan	B-Application
package	O
.	O
</s>
<s>
The	O
Q-Chem	B-Language
Board	O
was	O
expanded	O
in	O
March	O
2003	O
with	O
the	O
addition	O
of	O
Anna	O
Krylov	O
and	O
Jing	O
Kong	O
.	O
</s>
<s>
The	O
following	O
year	O
,	O
Shirin	O
Faraji	O
joined	O
the	O
Board	O
;	O
Peter	O
Gill	O
,	O
who	O
had	O
been	O
President	O
of	O
Q-Chem	B-Language
since	O
1988	O
,	O
stepped	O
down	O
;	O
and	O
Anna	O
Krylov	O
became	O
the	O
new	O
president	O
.	O
</s>
<s>
Currently	O
,	O
there	O
are	O
thousands	O
of	O
Q-Chem	B-Language
licenses	O
in	O
use	O
,	O
and	O
Q-Chem	B-Language
'	O
s	O
user	O
base	O
is	O
expanding	O
,	O
as	O
illustrated	O
by	O
citation	O
records	O
for	O
releases	O
2.0	O
,	O
3.0	O
,	O
and	O
4.0	O
,	O
which	O
reached	O
400	O
per	O
year	O
in	O
2016	O
(	O
see	O
Figure	O
2	O
)	O
.	O
</s>
<s>
Q-Chem	B-Language
has	O
been	O
used	O
as	O
an	O
engine	O
in	O
high-throughput	O
studies	O
,	O
such	O
as	O
the	O
Harvard	O
Clean	B-Operating_System
Energy	I-Operating_System
Project	I-Operating_System
,	O
in	O
which	O
about	O
350,000	O
calculations	O
were	O
performed	O
daily	O
on	O
the	O
IBM	O
World	B-Operating_System
Community	I-Operating_System
Grid	I-Operating_System
.	O
</s>
<s>
This	O
transition	O
,	O
from	O
in-house	O
code	O
to	O
major	O
electronic	O
structure	O
engine	O
,	O
has	O
become	O
possible	O
due	O
to	O
contributions	O
from	O
numerous	O
scientific	O
collaborators	O
;	O
the	O
Q-Chem	B-Language
business	O
model	O
encourages	O
broad	O
developer	O
participation	O
.	O
</s>
<s>
Q-Chem	B-Language
defines	O
its	O
genre	O
as	O
open-teamware	O
:	O
its	O
source	O
code	O
is	O
open	O
to	O
a	O
large	O
group	O
of	O
developers	O
.	O
</s>
<s>
In	O
addition	O
,	O
some	O
Q-Chem	B-Language
modules	O
are	O
distributed	O
as	O
open	O
source	O
.	O
</s>
<s>
Q-Chem	B-Language
5.2.2	O
,	O
released	O
in	O
December	O
2019	O
,	O
consists	O
of	O
7.5	O
million	O
lines	O
of	O
code	O
,	O
which	O
includes	O
contributions	O
by	O
more	O
than	O
300	O
active	O
developers	O
(	O
current	O
estimate	O
is	O
312	O
)	O
.	O
</s>
<s>
Q-Chem	B-Language
can	O
perform	O
a	O
number	O
of	O
general	O
quantum	O
chemistry	O
calculations	O
,	O
such	O
as	O
Hartree	O
–	O
Fock	O
,	O
density	O
functional	O
theory	O
(	O
DFT	O
)	O
including	O
time-dependent	O
DFT	O
(	O
TDDFT	O
)	O
,	O
Møller	O
–	O
Plesset	O
perturbation	O
theory	O
(	O
MP2	O
)	O
,	O
coupled	O
cluster	O
(	O
CC	O
)	O
,	O
equation-of-motion	O
coupled-cluster	O
(	O
EOM-CC	O
)	O
,	O
configuration	O
interaction	O
(	O
CI	O
)	O
,	O
algebraic	O
diagrammatic	O
construction	O
(	O
ADC	O
)	O
,	O
and	O
other	O
advanced	O
electronic	O
structure	O
methods	O
.	O
</s>
<s>
Q-Chem	B-Language
also	O
includes	O
QM/MM	B-Algorithm
functionality	O
.	O
</s>
<s>
Q-Chem	B-Language
4.0	O
and	O
higher	O
releases	O
come	O
with	O
the	O
graphical	O
user	O
interface	O
,	O
IQMol	O
,	O
which	O
includes	O
a	O
hierarchical	O
input	O
generator	O
,	O
a	O
molecular	O
builder	O
,	O
and	O
general	O
visualization	O
capabilities	O
(	O
MOs	O
,	O
densities	O
,	O
molecular	O
vibrations	O
,	O
reaction	O
pathways	O
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
IQMol	O
is	O
developed	O
by	O
Andrew	O
Gilbert	O
(	O
in	O
coordination	O
with	O
Q-Chem	B-Language
)	O
and	O
is	O
distributed	O
as	O
free	O
open-source	O
software	O
.	O
</s>
<s>
IQmol	O
is	O
written	O
using	O
the	O
Qt	O
libraries	O
,	O
enabling	O
it	O
to	O
run	O
on	O
a	O
range	O
of	O
platforms	O
,	O
including	O
OS	B-Operating_System
X	I-Operating_System
,	O
Widows	O
,	O
and	O
Linux	B-Application
.	O
</s>
<s>
It	O
provides	O
an	O
intuitive	O
environment	O
to	O
set	O
up	O
,	O
run	O
,	O
and	O
analyze	O
Q-Chem	B-Language
calculations	O
.	O
</s>
<s>
A	O
complete	O
,	O
up-to-date	O
list	O
of	O
features	O
is	O
published	O
on	O
the	O
Q-Chem	B-Language
website	O
and	O
in	O
the	O
user	O
manual	O
.	O
</s>
<s>
In	O
addition	O
,	O
Q-Chem	B-Language
is	O
interfaced	O
with	O
WebMO	O
and	O
is	O
used	O
as	O
the	O
computing	O
engine	O
in	O
Spartan	B-Application
,	O
or	O
as	O
a	O
back-end	O
to	O
CHARMM	B-Application
,	O
GROMACS	B-Application
,	O
NAMD	B-Application
,	O
and	O
ChemShell	O
.	O
</s>
<s>
Other	O
popular	O
visualization	O
programs	O
such	O
as	O
Jmol	B-Language
and	O
Molden	B-Application
can	O
also	O
be	O
used	O
.	O
</s>
<s>
In	O
2018	O
,	O
Q-Chem	B-Language
established	O
a	O
partnership	O
with	O
BrianQC	O
,	O
produced	O
by	O
StreamNovation	O
,	O
Ltd.	O
,	O
a	O
new	O
integral	O
engine	O
exploiting	O
the	O
computational	O
power	O
of	O
GPUs	O
.	O
</s>
<s>
The	O
BrianQC	O
plug-in	O
speeds	O
up	O
Q-Chem	B-Language
calculations	O
by	O
taking	O
advantage	O
of	O
GPUs	O
on	O
mixed	O
architectures	O
,	O
which	O
is	O
highly	O
efficient	O
for	O
simulating	O
large	O
molecules	O
and	O
extended	O
systems	O
.	O
</s>
<s>
Beginning	O
with	O
Q-Chem	B-Language
2.0	O
only	O
major	O
releases	O
versions	O
are	O
shown	O
.	O
</s>
