  We have proposed a density-matrix renormalization group (DMRG) scheme to
optimize the one-electron basis states of molecules. It improves significantly
the accuracy and efficiency of the DMRG in the study of quantum chemistry or
other many-fermion system with nonlocal interactions. For a water molecule, we
find that the ground state energy obtained by the DMRG with only 61 optimized
orbitals already reaches the accuracy of best quantum Monte Carlo calculation
with 92 orbitals.
