<s>
In	O
statistical	O
mechanics	O
the	O
Ornstein	O
–	O
Zernike	O
(	O
OZ	O
)	O
equation	O
is	O
an	O
integral	B-Algorithm
equation	I-Algorithm
introduced	O
by	O
Leonard	O
Ornstein	O
and	O
Frits	O
Zernike	O
that	O
relates	O
different	O
correlation	O
functions	O
with	O
each	O
other	O
.	O
</s>
<s>
The	O
pair	O
correlation	O
function	O
is	O
related	O
via	O
Fourier	B-Algorithm
transform	I-Algorithm
to	O
the	O
static	O
structure	O
factor	O
,	O
which	O
can	O
be	O
determined	O
experimentally	O
using	O
X-ray	O
diffraction	O
or	O
neutron	O
diffraction	O
.	O
</s>
<s>
The	O
OZ	B-Algorithm
equation	I-Algorithm
relates	O
the	O
pair	O
correlation	O
function	O
to	O
the	O
direct	B-Algorithm
correlation	I-Algorithm
function	I-Algorithm
.	O
</s>
<s>
The	O
direct	B-Algorithm
correlation	I-Algorithm
function	I-Algorithm
is	O
only	O
used	O
in	O
connection	O
with	O
the	O
OZ	B-Algorithm
equation	I-Algorithm
,	O
which	O
can	O
actually	O
be	O
seen	O
as	O
its	O
definition	O
.	O
</s>
<s>
Besides	O
the	O
OZ	B-Algorithm
equation	I-Algorithm
,	O
other	O
methods	O
for	O
the	O
computation	O
of	O
the	O
pair	O
correlation	O
function	O
include	O
the	O
virial	O
expansion	O
at	O
low	O
densities	O
,	O
and	O
the	O
Bogoliubov	O
–	O
Born	O
–	O
Green	O
–	O
Kirkwood	O
–	O
Yvon	O
(	O
BBGKY	O
)	O
hierarchy	O
.	O
</s>
<s>
It	O
is	O
convenient	O
to	O
define	O
the	O
total	B-Algorithm
correlation	I-Algorithm
function	I-Algorithm
as	O
:	O
</s>
<s>
The	O
direct	O
contribution	O
defines	O
the	O
direct	B-Algorithm
correlation	I-Algorithm
function	I-Algorithm
,	O
The	O
indirect	O
part	O
is	O
due	O
to	O
the	O
influence	O
of	O
molecule1	O
on	O
a	O
third	O
,	O
labeled	O
molecule3	O
,	O
which	O
in	O
turn	O
affects	O
molecule2	O
,	O
directly	O
and	O
indirectly	O
.	O
</s>
<s>
The	O
integral	O
in	O
the	O
OZ	B-Algorithm
equation	I-Algorithm
is	O
a	O
convolution	B-Language
.	O
</s>
<s>
Therefore	O
,	O
the	O
OZ	B-Algorithm
equation	I-Algorithm
can	O
be	O
resolved	O
by	O
Fourier	B-Algorithm
transform	I-Algorithm
.	O
</s>
<s>
While	O
the	O
OZ	B-Algorithm
equation	I-Algorithm
is	O
purely	O
formal	O
,	O
the	O
closure	O
must	O
introduce	O
some	O
physically	O
motivated	O
approximation	O
.	O
</s>
