Thermal decay rate of a metastable state with two degrees of freedom: Dynamical modelling versus approximate analytical formula

Accuracy of the Kramers approximate formula for the thermal decay rate of the metastable state is studied for the two-dimensional potential pocket. This is done by comparing with the quasistationary rate resulting from the dynamical modelling. It is shown that the Kramers rate is in agreement with the quasistationary rate within the statistical errors provided the absorptive border is far enough from the potential ridge restricting the metastable state. As the absorptive border (or its part) gets closer to the ridge, the Kramers formula underestimates the quasistationary rate. The difference reaches approximately the factor of 2 when the absorptive border coincides with the ridge.