We present an impurity solver based on adaptively truncated Hilbert spaces.
The solver is particularly suitable for dynamical mean-field theory in
circumstances where quantum Monte Carlo approaches are ineffective. It exploits
the sparsity structure of quantum impurity models, in which the interactions
couple only a small subset of the degrees of freedom. We further introduce an
adaptive truncation of the particle or hole excited spaces, which enables
computations of Green functions with an accuracy needed to avoid unphysical
(sign change of imaginary part) self-energies. The method is benchmarked on the
one-dimensional Hubbard model.Comment: 10 pages, 7 figure
