<s>
CASTEP	B-Application
is	O
a	O
shared-source	O
academic	O
and	O
commercial	B-Application
software	I-Application
package	O
which	O
uses	O
density	O
functional	O
theory	O
with	O
a	O
plane	O
wave	O
basis	O
set	O
to	O
calculate	O
the	O
electronic	O
properties	O
of	O
crystalline	O
solids	O
,	O
surfaces	O
,	O
molecules	O
,	O
liquids	O
and	O
amorphous	O
materials	O
from	O
first	O
principles	O
.	O
</s>
<s>
CASTEP	B-Application
permits	O
geometry	O
optimisation	O
and	O
finite	O
temperature	O
molecular	O
dynamics	O
with	O
implicit	O
symmetry	O
and	O
geometry	O
constraints	O
,	O
as	O
well	O
as	O
calculation	O
of	O
a	O
wide	O
variety	O
of	O
derived	O
properties	O
of	O
the	O
electronic	O
configuration	O
.	O
</s>
<s>
Although	O
CASTEP	B-Application
was	O
originally	O
a	O
serial	O
,	O
Fortran	B-Application
77-based	O
program	O
,	O
it	O
was	O
completely	O
redesigned	O
and	O
rewritten	O
from	O
1999	O
to	O
2001	O
using	O
Fortran	B-Application
95	O
and	O
MPI	O
for	O
use	O
on	O
parallel	O
computers	O
by	O
researchers	O
at	O
the	O
Universities	O
of	O
York	O
,	O
Durham	O
,	O
St.	O
Andrews	O
,	O
Cambridge	O
and	O
Rutherford	O
Labs	O
.	O
</s>
<s>
CASTEP	B-Application
was	O
created	O
in	O
the	O
late	O
1980s	O
and	O
early	O
1990s	O
in	O
the	O
TCM	O
Group	O
of	O
the	O
Cavendish	O
Laboratory	O
in	O
Cambridge	O
.	O
</s>
<s>
The	O
code	O
was	O
then	O
redesigned	O
and	O
completely	O
rewritten	O
from	O
1999	O
–	O
2001	O
to	O
make	O
use	O
of	O
the	O
features	O
of	O
modern	O
Fortran	B-Application
,	O
enable	O
parallelism	O
throughout	O
the	O
code	O
and	O
improve	O
its	O
software	O
sustainability	O
.	O
</s>
<s>
The	O
name	O
CASTEP	B-Application
was	O
adopted	O
by	O
the	O
new	O
codebase	O
,	O
but	O
without	O
the	O
implied	O
former	O
meaning	O
since	O
the	O
code	O
was	O
now	O
parallel	O
,	O
and	O
capable	O
of	O
computing	O
many	O
quantities	O
besides	O
the	O
total	O
energy	O
.	O
</s>
<s>
Despite	O
its	O
commercialisation	O
,	O
CASTEP	B-Application
and	O
its	O
source	O
code	O
remained	O
free	O
to	O
UK	O
academics	O
.	O
</s>
<s>
Commercial	B-Application
users	O
can	O
purchase	O
CASTEP	B-Application
as	O
part	O
of	O
Biovia	O
's	O
Materials	B-Application
Studio	I-Application
package	O
.	O
</s>
<s>
From	O
this	O
the	O
basis	O
functions	O
are	O
orthogonal	O
and	O
it	O
is	O
easy	O
to	O
perform	O
a	O
Fourier	B-Algorithm
transform	I-Algorithm
from	O
real	O
to	O
reciprocal	O
space	O
and	O
vice	O
versa	O
.	O
</s>
<s>
Fast	O
Fourier	B-Algorithm
Transforms	I-Algorithm
are	O
used	O
throughout	O
the	O
CASTEP	B-Application
code	O
,	O
as	O
is	O
the	O
Ewald	O
summation	O
method	O
for	O
Coulombic	O
energies	O
.	O
</s>
<s>
Along	O
with	O
plane	O
waves	O
and	O
iterative	O
diagonalisation	O
methods	O
(	O
via	O
conjugate	B-Algorithm
gradient	I-Algorithm
or	O
blocked	O
Davidson	O
algorithms	O
)	O
,	O
pseudopotentials	O
are	O
essential	O
to	O
the	O
CASTEP	B-Application
code	O
for	O
reducing	O
the	O
computational	O
expense	O
of	O
the	O
calculation	O
.	O
</s>
<s>
CASTEP	B-Application
is	O
capable	O
of	O
optimising	O
the	O
atomic	O
geometry	O
of	O
a	O
system	O
in	O
several	O
different	O
ways	O
.	O
</s>
<s>
The	O
default	O
is	O
BFGS	B-Algorithm
,	O
whereby	O
an	O
approximation	O
to	O
the	O
Hessian	O
matrix	O
is	O
built	O
up	O
over	O
successive	O
electronic	O
minimisation	O
steps	O
and	O
used	O
to	O
find	O
a	O
search	O
direction	O
at	O
each	O
.	O
</s>
<s>
Damped	O
molecular	O
dynamics	O
is	O
also	O
possible	O
and	O
often	O
quick	O
to	O
converge	O
,	O
sometimes	O
even	O
faster	O
than	O
BFGS	B-Algorithm
,	O
due	O
to	O
wavefunction	O
extrapolation	O
.	O
</s>
<s>
Damped	O
MD	O
is	O
most	O
often	O
chosen	O
over	O
BFGS	B-Algorithm
,	O
however	O
,	O
due	O
to	O
the	O
possibility	O
for	O
non-linear	O
ion	O
constraints	O
.	O
</s>
