  We present a tree-tensor-network-state (TTNS) method study of the
ionic-neutral curve crossing of LiF. For this ansatz, the long-range
correlation deviates from the mean-field value polynomially with distance, thus
for quantum chemical applications the computational cost could be significantly
smaller than that of previous attempts using the density matrix renormalization
group (DMRG) method. Optimization of the tensor network topology and
localization of the avoided crossing are discussed in terms of entanglement.
