Quantum Monte-Carlo method without negative-sign problem for   two-dimensional electron systems under strong magnetic fields
  The quantum Monte-Carlo method is applied to two-dimensional electron systems under strong magnetic fields. The negative-sign problem involved by this method can be avoided for certain filling factors by modifying interaction parameters from those of the Coulomb interaction. Our techniques for obtaining sign-problem-free parameters are described in detail. Calculated results on static observables are also reported for Landau level filling $\nu = 1/3$. 
Sei Suzuki and Tatsuya Nakajima