text: λx Hperturbation, x = λx[Sj1 
  
  Sk1 + sgn(Jx) 
  Sj2 + Sk1  (Sj2 
  · 
  Sk2). 
  
  Sk2)] 
  ·  · 
  Jx(Sj1 
  
  − 
  Jx| · 
  
  ·  · 
  
  where λx = 
  of Jx. 
  
  12  Jcluster, sgn(Jx) =  1 is the sign 
  p  |  ± 
  
  The perturbation on y-links is 