An improvement of the Energy Renormalization Group method is proposed for systems with small gap, based on the projection methods developed by H. Feshbach. It is tested for the ground state energy of the one-dimensional tight-binding model.
@article{arxiv.cond-mat/0310569,
title = {Projection method for rapid ab initio calculations of metals},
author = {A. Kenoufi and J. Polonyi},
journal= {arXiv preprint arXiv:cond-mat/0310569},
year = {2010}
}