QC-DMRG study of the ionic-neutral curve crossing of LiF

We have studied the ionic - neutral curve crossing between the two lowest (1)Sigma(+) states of LiF in order to demonstrate the efficiency of the quantum chemistry version of the density-matrix renormalization group method (QC-DMRG). We show that QC-DMRG is capable of calculating the ground and several low-lying excited state energies within the error margin set up in advance of the calculation, while with standard quantum chemical methods it is difficult to obtain a good approximation to full configuration-interaction property values at the point of the avoided crossing. We have calculated the dipole moment as a function of bond length, which in fact provides a smooth and continuous curve even close to the avoided crossing, in contrast to other standard numerical treatments.