Numerical simulation of QCD with u, d, s and c quarks in the twisted-mass Wilson formulationT. Chiarappa, F. Farchioni, K. Jansen, I. Montvay, E.E. Scholz, L. Scorzato, T. Sudmann and C. UrbachEur. Phys. J. C, 50 2 (2007) 373-383DOI: https://doi.org/10.1140/epjc/s10052-006-0204-4