A more efficient version of the Expanded Ensembles method for calculation of free energy in molecular-mechanical simulations is proposed. The method is based on the Horowitz L2MC approach to accelerate movement along the "alchemical" coordinate. It is possible to achieve the same efficiency of the algorithm both with the optimal number of "windows" and with a larger number of them compared to the original algorithm. Since the optimal number of windows is unknown a priory, the proposed algorithm is more robust than the traditional one. We can choose the number of windows in excess and do not worry about the loss of efficiency. We illustrate the method's efficiency with the computation of the hydration free energies of pyridine and water.
Keywords: Monte Carlo; algorithm; expanded ensembles; free energy; molecular dynamics.
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