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Onsagerのイジング模型の原論文の代用
http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/onsager-lars.pdf
N a t i o n a l a c a d e m y o f s c i e n c e s
L a r s O n s a g e r 1903?1976
A Biographical Memoir by
Christopher Longuet-Higgins and Michael E.Fisher
(抜粋)
The Ising model, which can serve as a model of ferromagnetism,
of antiferromagnetism, of gaseous condensation,
or of phase separation in fluid mixtures and metallic alloys,
looks innocuous enough to the nonspecialist?like the fourcolor
problem in topology (to which, in fact, it is not entirely
unrelated). An Ising model is an assembly of particles or
"spins" located at the vertices of an infinite space lattice?in
the simplest nontrivial case, a two-dimensional planar square
lattice. Each particle or spin can exist in either of two states,
and the total energy of the lattice is additive over neighboring
pairs of particles. The energy of any such pair is either +/
or ?J according as the particles are in the same state or in
different states, or as the spins are parallel or antiparallel.
(Onsager actually considered the significantly more general
problem in which the interaction energy has different magnitudes,/
and/', for the two directions?horizontal and vertical?
of a square lattice. An essentially one-dimensional system
is obtained when J'/J → 0.)

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