Accelerated convergence in exact-diagonalization studies.

A simple method is proposed and tested for obtaining accelerated convergence of quantum systems on small lattices with N sites. The main idea is to perform exact diagonalizations with some added irrelevant parameter, and use this parameter to accelerate the convergence to the infinitelattice limit. In this paper di8'erent boundary conditions are used to improve the convergence for the Heisenberg model. In particular, we find that the application of the method to the d=l antiferromagnetic Heisenberg model changes the rate of convergence of the ground-state energy per site, ~EO(N) —Eo(oo)~ N, to x = 4 from the value z = 2, which is found using only periodic boundary conditions.