Glauber dynamics in Ising systems: A general approach
Shaon Sahoo, Soumya Kanti Ganguly
Abstract
In the Glauber model, the only restriction on the choice of the transition rates ($w_j$'s) is that these rates must satisfy the equation of detailed balance at equilibrium for all possible configurations. Though a linear form for $w_j$'s works best for analytical study of dynamics, generally it is not possible to get this form for which the above condition is obeyed. In this paper we discuss the best possible way of writing $w_j$'s in a linear form for a generic system where a spin is coupled to $z$ neighbors with different coupling constants. In our approach, the linear form of a $w_j$ involves $z$ independent parameters whose optimal values are derived by a linear regression. Generically, the Moore-Penrose pseudoinverse matrix involved in the regression is obtained solely from the configuration matrix and takes a simple form of dimension $z \times 2^z$. The fact that the pseudoinverse matrix does not depend on the Hamiltonian parameters or dimensionality of system makes our approach more appealing. In the second part of the paper we use our new approach to study Ising systems in different dimensions; in particular, we analyze the relaxation time and find out the critical temperatures ($T_C$) for two and three dimensional systems. It is easy to study the effect of magnetic field ($H$) within our approach; our analysis shows that $T_C$ decreases quadratically with (weak) magnetic field ($\delta T_C/T_C\propto -H^2$).