Dual-Topology Hamiltonian-Replica-Exchange Overlap Histogramming Method   to Calculate Relative Free Energy Difference in Rough Energy Landscape
  A novel overlap histogramming method based on Dual-Topology Hamiltonian-Replica-Exchange simulation technique is presented to efficiently calculate relative free energy difference in rough energy landscape, in which multiple conformers coexist and are separated by large energy barriers. The proposed method is based on the realization that both DT-HERM exchange efficiency and confidence of free energy determination in overlap histogramming method depend on the same criteria: neighboring states' energy derivative distribution overlap. In this paper, we demonstrate this new methodology by calculating free energy difference between amino acids: Leucine and Asparagine, which is an identified chanllenging system for free energy simulations. 
Donghong Min, Hongzhi Li, Guohui Li, Ryan Bitter-Putzer, Wei Yang