  Gutzwiller-projected fermionic states can be efficiently implemented within
quantum Monte Carlo calculations to define extremely accurate variational wave
functions for Heisenberg models on frustrated two-dimensional lattices, not
only for the ground state but also for low-energy excitations. The application
of few Lanczos steps on top of these states further improves their accuracy,
allowing calculations on large clusters. In addition, by computing both the
energy and its variance, it is possible to obtain reliable estimations of exact
results. Here, we report the cases of the frustrated Heisenberg models on
square and Kagome lattices.
