  Using both analytical and simulational methods, we study low-temperature
nucleation rates in kinetic Ising lattice-gas models that evolve under two
different Arrhenius dynamics that interpose between the Ising states a
transition state representing a local energy barrier. The two dynamics are the
transition-state approximation [T. Ala-Nissila, J. Kjoll, and S. C. Ying, Phys.
Rev. B 46, 846 (1992)] and the one-step dynamic [H. C. Kang and W. H. Weinberg,
J. Chem. Phys. 90, 2824 (1989)]. Even though they both obey detailed balance
and are here applied to a situation that does not conserve the order parameter,
we find significant differences between the nucleation rates observed with the
two dynamics, and between them and the standard Glauber dynamic [R. J. Glauber,
J. Math. Phys. 4, 294 (1963)], which does not contain transition states. Our
results show that great care must be exercised when devising kinetic Monte
Carlo transition rates for specific physical or chemical systems.
