Path-integral renormalization group method with quantum-number projection

We present a quantum-number projection technique and its implementation to the recently proposed path-integral renormalization group (PIRG) method, which has been quite a powerful tool in investigating strongly correlated electron systems. By this extension, the PIRG can handle excited states with different quantum numbers in addition to the ground state and precision of solution is highly improved. By taking Hubbard models as an example, we demonstrate its feasibility.