  In this article we present the exact representation of a fully correlated
electronic wavefunction as the single-particle basis approaches completeness.
It consists of a half-infinite chain of matrices of exponentially increasing
size. The complete basis limit is illustrated numerically using the density
matrix renormalization group method by computing the core-valence entanglement
in the C$_2$ ground state in increasing subsets of cc-pVTZ and pVQZ bases until
convergence is reached.
