The Truncated Polynomial Expansion Monte Carlo Method for Fermion Systems Coupled to Classical Fields: A Model Independent Implementation

A software library is presented for the polynomial expansion method (PEM) of the density of states (DOS) developed by two of the authors (N.F. and Y. M.). The library provides all necessary functions for the use of the PEM and its truncated version (TPEM) in a model independent way. The PEM/TPEM replaces the exact diagonalization of the one electron sector in models for fermions coupled to classical fields. The computational cost of the algorithm is O(N) -- with N the number of lattice sites -- for the TPEM which should be contrasted with the computational cost of the diagonalization technique that scales as O(N^4). The method is applied for the first time to a double exchange model with finite Hund coupling and also to diluted spin-fermion models.