To accelerate convergence, the relevant range of the collective variable can be divided into several regions or "windows" to which the ABF algorithm is applied simultaneously. This approach is known as the stratification scheme. The length of these windows should not be too small, as restricting the range of the colvar too much in a single simulation may lead to a slowdown in convergence or even a loss of ergodicity. In other words, the simulation should visit the same configurations and in the same proportion as it would do using a much larger window, so that the artificial limit to the colvar explored in each window does not introduce a bias in the sampling.