Evaluation of the Adaptive Umbrella Sampling Method

(Received December, 1988) The adaptive umbrella sampling technique, introduced recently to improve the probability ratio method and found to perform more reliably then the customary harmonic umbrella sampling, is tested and compared with other free energy methods. One of the tests applies the method to a transition involving a chemical change: calculation of the hydration free energy difference between acetone and dimethylamine and the other test calculates the conformatonal free energy difference between the C7 and αR conformations of the alanine dipeptide. The dipeptide problem is also treated by two types of thermodynamic integrations and by the perturbation method. The result for the acetone-dimethylamine problem is compared with previous calculations on the same system using the perturbation method, overlap ratio method and finite difference thermodynamic integration. Enhancements to the adaptive umbrella sampling method are also presented.