  We demonstrate how to parallelize the density matrix renormalization group
(DMRG) algorithm in real space through a straightforward modification of serial
DMRG. This makes it possible to apply at least an order of magnitude more
computational power to challenging simulations, greatly accelerating
investigations of two-dimensional systems and large parameter spaces. We
discuss details of the algorithm and present benchmark results including a
study of valence-bond-solid order within the square-lattice Q2 model and Neel
order within the triangular lattice Heisenberg model. The parallel DMRG
algorithm also motivates an alternative canonical form for matrix product
states.
