Density matrix technique for ground state calculations

The density matrix approach is a technique to calculate the lowest eigenval ue of a large matrix such as occurring in quantum mechanical systems. So fa r the method works very well for systems with a linear structure. The limit ations for a planar structure, from critical correlations and from slowdown , due to the existence of slow modes, will be discussed using the transvers e Ising model as illustration. (C) 1999 Elsevier Science B.V. All rights re served.