On the decomposition of free energies.
The decomposition of free energies and entropies into components has recently been discussed within the framework of the free energy perturbation (FEP) and thermodynamic integration (TI) methods. In FEP, the cumulant expansion of the excess free energy contains coupling terms in second and higher orders. It is shown here that this expansion can be expressed in terms of temperature derivatives of the mean energy, suggesting a natural decomposition of the free energy into components corresponding to each term in the Hamiltonian. This result is derived in such a way that it establishes the equivalence to a particular form of component analysis based on TI in which all terms in the interaction energy are turned on simultaneously using 1/kT as the coupling parameter.
Dept. of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104-6059, USA.
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Brady
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Szabo
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Sharp
D003198:Computer Simulation; D004734:Energy Metabolism; D019277:Entropy; D008962:Models, Theoretical; D013816:Thermodynamics