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) introduced in Ref [1, 2]. 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[3] which should be contrasted with the computational cost of the diagonalization technique that scales as O(N). The method is applied for the first time to a double exchange model with finite Hund coupling and also to diluted spin-fermion models.