  We develop a correction to the density matrix used in density matrix
renormalization group calculations to take into account the incompleteness of
the environment block. The correction allows successful calculations using only
a single site in the center of the system, rather than the standard two sites,
improving typical computation times by a factor of two to four. In addition, in
many cases where ordinary DMRG can get stuck in metastable configurations, the
correction eliminates the sticking. We test the new method on the Heisenberg
S=1 chain.
