A simple method for sampling partition function ratios

A simple simulation method is proposed for calculating partition function ratios with emphasis on computing transition state theory rate constants. Potential energy histograms are calculated in one single high temperature simulation. Partition function ratios can then be computed for a wide range of temperatures from this information. We apply this high-temperature configuration-space exploration (HTCE) method to a model problem. We find that HTCE quantitatively reproduces rate constants evaluated using brute-force molecular dynamics, and using Voter’s displacement vector method. HTCE is extremely straightforward to implement and it offers other system information that targeted free-energy simulations may not.