ESpinS: A program for classical Monte-Carlo simulations of spin systems

Abstract We present ESpinS  (Esfahan Spin Simulation) package to evaluate the thermodynamic properties of spin systems described by a spin model Hamiltonian. In addition to the Heisenberg exchange term, the spin Hamiltonian in ESpinS  can contain interactions such as bi-quadratic, Dzyaloshinskii–Moriya, and single-ion anisotropy. By applying the classical Monte Carlo simulation, ESpinS  simulates the behavior of spin systems with respect to temperature. ESpinS  can calculate the specific heat, susceptibility, staggered magnetization, energy histogram, fourth-order Binder cumulants, and neutron scattering structure factor. Further, it can compute the user-defined magnetic order parameter, that is, the summation of the projection of spins on the user-defined directions and the physical quantities based on it. ESpinS  works with both a local update algorithm and a parallel tempering algorithm. The latter is an appropriate option for considering frustrated and spin-glass magnetic systems. ESpinS  is written in Fortran 90 and can be run in single or parallel mode. The package is freely available under the GPL license ( https://github.com/nafiserb/ESpinS ).