Low energy constants from the chirally improved Dirac operator D_CI
  The leading order low energy parameters like the pion decay constant or the quark condensate are well-known from "classical" low energy theorems and experiments. It is a challenge, however, to find these parameters based exclusively on an ab-initio QCD calculation. We discuss results of a quenched lattice calculation of low energy constants using the chirally improved Dirac operator. Several lattice sizes at different lattice spacings are studied, using pseudoscalar and axial vector correlators. We find consistent results for f_\pi = 96(2) MeV, f_K = 105(2) MeV, \Sigma = -(286(4) MeV)^3, the average light quark mass m = 4.1(2.4) MeV and m_s = 101(8) MeV. 
Christof Gattringer, Philipp Huber, and C. B. Lang