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Mean-Field Theory

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Abstract

The zero-field Ising Hamiltonian

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Notes

  1. 1.

    For large \(n\)

    $$\begin{aligned} \ln (n!)=\left( n+{\textstyle \frac{1}{2}}\right) \ln (n)-n+{\textstyle \frac{1}{2}}\ln (2\pi )+\mathrm {O}(1/n). \end{aligned}$$
  2. 2.

    In an accurate treatment, which must include the effect of local fluctuations, the susceptibility divergence is sharper.

  3. 3.

    We are interested is in deriving the part of the phase diagram in the plane shown in Fig. 4.3a, b.

  4. 4.

    Of course, with this layered model on a \(d\)-dimensional hypercubic lattice , , but and are used in the interests of generality.

  5. 5.

    For the simple cubic lattice , .

  6. 6.

    Here we encounter the usual problem in statistical mechanics that, whereas the equations take a simpler form in terms of couplings and , physical insight is helped by presenting figures in terms of the fields \(T\) and . We shall, therefore, in the discussion make free use of both sets of variables.

  7. 7.

    With , and remembering that in Sect. 6.1 \(:=J/T\) not .

  8. 8.

    As indicated in Sect. 5.5, for the exponents we simply omit the ‘\(\mathrm {p}\)’.

  9. 9.

    The case shown here is for \(\lambda =1\), \(T_{\mathrm {t}}>0\); the differences that occur when \(\lambda <\frac{1}{3}\), \(T_{\mathrm {t}}<0\) are discussed below.

  10. 10.

    There is also a mirror-image transition line in the half-plane, but we need consider only the line explicitly.

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Correspondence to David A. Lavis .

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© 2015 Springer Science+Business Media Dordrecht

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Lavis, D.A. (2015). Mean-Field Theory. In: Equilibrium Statistical Mechanics of Lattice Models. Theoretical and Mathematical Physics. Springer, Dordrecht. https://doi.org/10.1007/978-94-017-9430-5_6

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