<s>
The	O
Bethe	B-General_Concept
–	I-General_Concept
Slater	I-General_Concept
curve	I-General_Concept
is	O
a	O
heuristic	B-Algorithm
explanation	O
for	O
why	O
certain	O
metals	O
are	O
ferromagnetic	O
and	O
others	O
are	O
antiferromagnetic	O
.	O
</s>
<s>
It	O
assumes	O
a	O
Heisenberg	O
model	O
of	O
magnetism	O
,	O
and	O
explains	O
the	O
differences	O
in	O
exchange	B-General_Concept
energy	I-General_Concept
of	O
transition	O
metals	O
as	O
due	O
to	O
the	O
ratio	O
of	O
the	O
interatomic	O
distance	O
a	O
to	O
the	O
radius	O
r	O
of	O
the	O
3d	O
electron	O
shell	O
.	O
</s>
<s>
When	O
the	O
magnetically	O
important	O
3d	O
electrons	O
of	O
adjacent	O
atoms	O
are	O
relatively	O
close	O
to	O
each	O
other	O
,	O
the	O
exchange	B-General_Concept
interaction	I-General_Concept
,	O
,	O
is	O
negative	O
,	O
but	O
when	O
they	O
are	O
further	O
away	O
,	O
the	O
exchange	B-General_Concept
interaction	I-General_Concept
becomes	O
positive	O
,	O
before	O
slowly	O
dropping	O
off	O
.	O
</s>
<s>
The	O
idea	O
of	O
relating	O
exchange	B-General_Concept
energy	I-General_Concept
to	O
inter-atomic	O
distance	O
was	O
first	O
proposed	O
by	O
John	O
C	O
.	O
Slater	O
in	O
1930	O
,	O
and	O
illustrated	O
as	O
a	O
curve	O
on	O
a	O
graph	O
in	O
a	O
review	O
by	O
Sommerfeld	O
and	O
Bethe	O
in	O
1933	O
.	O
</s>
<s>
For	O
a	O
pair	O
of	O
atoms	O
,	O
the	O
exchange	B-General_Concept
interaction	I-General_Concept
wij	O
(	O
responsible	O
for	O
the	O
energy	O
E	O
)	O
is	O
calculated	O
as	O
:	O
</s>
<s>
However	O
,	O
more	O
recent	O
evaluations	O
with	O
realistic	O
calculations	O
of	O
the	O
exchange	B-General_Concept
interactions	I-General_Concept
show	O
significantly	O
more	O
complex	O
physics	O
when	O
treating	O
the	O
interactions	O
of	O
different	O
atomic	O
orbitals	O
in	O
an	O
atom	O
separately	O
,	O
rather	O
than	O
as	O
a	O
single	O
unit	O
.	O
</s>
