For which $n \times n$ correlation matrix $C$ can one construct Bernoulli random variables $(B_1, \ldots, B_n)$ with correlation $C$ ?
Following the approach described in this MO thread, one can think of the following construction. Define independent Bernoulli random variables $B_{k_1, \ldots, k_n}$ for $(k_1, \ldots, k_n) \in \mathbb{Z}^n$ and another independent $\mathbb{Z}^k$-valued random variable $I=(I_1, \ldots, I_n)$. Then $(B_{I_1}, \ldots, B_{I_n})$ is a correlated Bernoulli vector.
1: Is there any example of correlation structure that cannot be obtained this way ?
2: Any easy example of correlation matrix $C$ that cannot be the correlation matrix of a ${0,1}^n$ \{0,1\}^n$ valued random vector ?
