Looking for some free energy? Call JEFREE (…)

In this communication, we present the Jarzynski's Equality FREe Energy (JEFREE) library, an efficient and easy-to-use C++ library targeted to the calculation of the free energy profile along a selected generalized coordinate of a system, within the framework of the nonequilibrium steered transformations as introduced by Jarzynski [Phys. Rev. E, 1997, 56, 5018]. JEFREE can be readily integrated into any code, since both C and FORTRAN wrappers have been developed, and easily customizable by a user thanks to the object-oriented programming paradigm offered by the C++ language. Also, JEFREE implements the novel idea of making a total “morphing” of the system energy landscape before initiating the proper steering stage. This proves to be an efficient mean to overtake the problematic sampling of the initial equilibrium state when the number of degrees of freedom is high and the landscape owns many local minima separated by large energy barriers. The calculation of the free energy profile for the rotation along torsion angles in alkyl chains is presented as an example of application of our tool.