  We study the bipartite entanglement of strongly correlated systems using
exact diagonalization techniques. In particular, we examine how the
entanglement changes in the presence of long-range interactions by studying the
Pariser-Parr-Pople model with long-range interactions. We compare the results
for this model with those obtained for the Hubbard and Heisenberg models with
short-range interactions. This study helps us to understand why the density
matrix renormalization group (DMRG) technique is so successful even in the
presence of long-range interactions. To better understand the behavior of
long-range interactions and why the DMRG works well with it, we study the
entanglement spectrum of the ground state and a few excited states of finite
chains. We also investigate if the symmetry properties of a state vector have
any significance in relation to its entanglement. Finally, we make an
interesting observation on the entanglement profiles of different states
(across the energy spectrum) in comparison with the the corresponding profile
of the density of states. We use isotropic chains and a molecule with
non-Abelian symmetry for these numerical investigations.
