Constant for different types of lattices

[LagrangeEuler]

$C=\frac{1}{N}\sum_{\vec{k}} \frac{J(0)}{J(0)-J(\vec{k})}$
$J(\vec{k})$ is exchange integral in $\vec{k}$ space. What is the name of this constant and where I can find more about it?

For simple cubic lattice
$C_{SC}=1.516$

 

[M Quack]

Can you provide a bit more context?

Exchange integrals usually depend on details of the band structure, so I am surprised that you can get a universal constant for all simple cubic lattices irrespective of lattice constant, atomic flavor etc.

J(0) would favor ferromagnetism

J(k) with k != 0 would favor antiferromagnetism with a modulation wave vector k.

 

[LagrangeEuler]

See this paper.

 

[LagrangeEuler]

Or here.