Two-dimensional infinite-system density-matrix renormalization-group algorithm

It has proved difficult to extend the density-matrix renormalization-group technique to large two-dimensional systems. I here present an approach where the calculation is done directly in two dimensions. This makes it possible to use an infinite-system method, and the fixed point in two dimensions is studied. By applying several related blocking schemes to the two-dimensional Heisenberg model I find that there exists an algorithm for which the energy per site decreases monotonically as the system size increases, thereby showing the potential feasibility of this method.