A method to compute absolute free energies or enthalpies of fluids

We propose a new method to compute the free energy or enthalpy of fluids or disordered solids by computer simulation . The main idea is to construct a reference system by freezing one representative configuration, and then carry out a thermodynamic integration. We present a strategy and an algorithm which allows to sample the thermodynamic integration path even in the case of liquids, despite the fact that the particles can diffuse freely through the system. The method is described in detail and illustrated with applications to hard sphere fluids and solids with mobile defects.

💡 Research Summary

The paper introduces a novel computational strategy for obtaining absolute free energies (or enthalpies) of fluids and disordered solids directly from molecular simulations. Traditional free‑energy methods rely on a well‑defined reference state, typically a crystalline lattice, which is unavailable for liquids or highly defective solids. To overcome this limitation, the authors construct a reference system by “freezing” a single representative configuration extracted from an equilibrated simulation. This frozen configuration is enforced by an external potential that tethers each particle to its original position, thereby creating a deterministic reference state that shares the same particle number and interaction model as the target system.

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