====== イジング模型 ======
$$
s_{i} = \left\{\begin{array}{l}1\\-1\end{array}\right.
$$

$$
{\cal H} = \displaystyle\sum_{i}h_{i} s_{i} + \sum_{\langle i, j\rangle}J_{ij} s_{i} s_{j} + \cdots
$$


===== Si(001) =====