<s>
General	O
Atomic	O
and	O
Molecular	O
Electronic	O
Structure	O
System	O
(	O
GAMESS	B-Application
(	O
US	O
)	O
)	O
is	O
computer	O
software	O
for	O
computational	O
chemistry	O
program	O
.	O
</s>
<s>
In	O
1981	O
,	O
the	O
code	O
base	O
split	O
into	O
GAMESS	B-Application
(	O
US	O
)	O
and	O
GAMESS	B-Application
(	O
UK	O
)	O
variants	O
,	O
which	O
now	O
differ	O
significantly	O
.	O
</s>
<s>
GAMESS	B-Application
(	O
US	O
)	O
is	O
maintained	O
by	O
the	O
members	O
of	O
the	O
Gordon	O
Research	O
Group	O
at	O
Iowa	O
State	O
University	O
.	O
</s>
<s>
GAMESS	B-Application
(	O
US	O
)	O
source	O
code	O
is	O
available	O
as	O
source-available	O
freeware	B-License
,	O
but	O
is	O
not	O
open-source	B-Application
software	I-Application
,	O
due	O
to	O
license	O
restrictions	O
.	O
</s>
<s>
GAMESS	B-Application
(	O
US	O
)	O
can	O
perform	O
several	O
general	O
computational	O
chemistry	O
calculations	O
,	O
including	O
Hartree	O
–	O
Fock	O
method	O
,	O
density	O
functional	O
theory	O
(	O
DFT	O
)	O
,	O
generalized	O
valence	O
bond	O
(	O
GVB	O
)	O
,	O
and	O
multi-configurational	O
self-consistent	O
field	O
(	O
MCSCF	O
)	O
.	O
</s>
<s>
The	O
GAMESS	B-Application
(	O
US	O
)	O
program	O
possesses	O
Resolution-of-the-Identity	O
(	O
RI	O
)	O
approximated	O
methods	O
,	O
which	O
decrease	O
the	O
overall	O
cost	O
of	O
a	O
method	O
by	O
projecting	O
the	O
ERI	O
tensor	O
into	O
three	O
center	O
matrices	O
.	O
</s>
<s>
GAMESS	B-Application
(	O
US	O
)	O
also	O
has	O
a	O
series	O
of	O
fragmentation	O
methods	O
that	O
allow	O
the	O
user	O
to	O
target	O
larger	O
molecular	O
systems	O
by	O
partitioning	O
a	O
large	O
molecule	O
into	O
smaller	O
,	O
more	O
feasible	O
fragments	O
.	O
</s>
<s>
The	O
GAMESS	B-Application
(	O
US	O
)	O
software	O
also	O
provides	O
a	O
comprehensive	O
bonding	O
analysis	O
technique	O
based	O
on	O
the	O
Quasi-Atomic	O
Orbital	O
(	O
QUAO	O
)	O
analysis	O
proposed	O
by	O
professor	O
Klaus	O
Ruedenberg	O
.	O
</s>
<s>
While	O
the	O
program	O
does	O
not	O
directly	O
perform	O
molecular	O
mechanics	O
,	O
it	O
can	O
do	O
mixed	O
quantum	O
mechanics	O
and	O
molecular	O
mechanics	O
calculations	O
through	O
effective	O
fragment	O
potentials	O
or	O
through	O
an	O
interface	O
with	O
the	O
Tinker	B-Application
code	O
.	O
</s>
<s>
It	O
can	O
also	O
be	O
interfaced	O
with	O
the	O
valence	O
bond	O
VB2000	B-Application
and	I-Application
XMVB	I-Application
programs	I-Application
and	O
the	O
Natural	O
Bond	O
Orbital	O
(	O
NBO	O
)	O
population	O
analysis	O
program	O
.	O
</s>
