Monte Carlo simulations are employed to study the rate laws of A+A→0 and A+B→0 diffusion-limited elementary reactions in three dimensions (3D). Using reflective instead of cyclic boundary conditions we do observe the Zeldovich regime in 3D for the A+B reaction. The time and density for the crossover into the Zeldovich regime in 3D agree with the existing scaling laws and provide the hitherto missing scaling coefficient. We show that the behavior of the A+A reaction rates in 1D, 2D, and 3D and the early time behavior of the A+B reaction rate map the rate of distinct sites visited by a single random walker, giving nonclassical kinetics at early times in all cases. We also determine a simple scaling law for crossover to finite size effects, which depends only on the linear lattice length except when the crossover to finite size effects and the crossover to the Zeldovich regime are concomitant. © 1996 The American Physical Society.

• Received 8 September 1995

DOI:https://doi.org/10.1103/PhysRevE.53.1502