  An extension of the projected entangled-pair states (PEPS) algorithm to
infinite systems, known as the iPEPS algorithm, was recently proposed to
compute the ground state of quantum systems on an infinite two-dimensional
lattice. Here we investigate a modification of the iPEPS algorithm, where the
environment is computed using the corner transfer matrix renormalization group
(CTMRG) method, instead of using one-dimensional transfer matrix methods as in
the original proposal. We describe a variant of the CTMRG that addresses
different directions of the lattice independently, and use it combined with
imaginary time evolution to compute the ground state of the two-dimensional
quantum Ising model. Near criticality, the modified iPEPS algorithm is seen to
provide a better estimation of the order parameter and correlators.
