  Based on the contractor renormalization group (CORE) method and the density
matrix renormalization group (DMRG) method, a new computational scheme, which
is called the block density matrix renormalization group with effective
interactions (BDMRG-EI), is proposed to deal with the numerical computation of
quantum correlated systems. Different from the convential CORE method in the
ways of calculating the blocks and the fragments, where the DMRG method instead
of the exact diagonalization is employed in BDMRG-EI, DMRG-EI makes the
calculations of larger blocks and fragments applicable. Integrating DMRG's
advantage of high accuracy and CORE's advantage of low computational costs,
BDMRG-EI can be widely used for the theoretical calculations of the ground
state and low-lying excited states of large systems with simple or complicated
connectivity. Test calculations on a 240 site one-dimensional chain and a
double-layer polyacene oligomer containing 48 hexagons demonstrate the
efficiency and potentiality of the method.
