Solid Free Energy

This skill calculates the absolute free energy of a crystalline solid using Frenkel-Ladd switching, which is a specific form of Thermodynamic Integration (TI).

Thermodynamic integration computes the free energy difference between two states by integrating the derivative of the Hamiltonian along a continuous coupling path. In this skill, the path interpolates between a physical MLIP Hamiltonian (the target state) and a harmonic Einstein-crystal reference (where the exact absolute free energy is analytically known).

Goal

Compute the Helmholtz free energy $F$ of a pre-equilibrated periodic solid at a target temperature, and optionally the Gibbs free energy $G = F + PV$ if pressure is supplied.

Prerequisites

• A pre-equilibrated periodic solid structure in an ASE-readable format such as CIF or POSCAR.
• The transferable MLIP wrapper stack must be available in the target repo via src.utils.mlips.loader.load_wrapper(...).
• ASE and pymatgen must be installed in the relevant conda environment.

[!IMPORTANT] This skill only performs the Frenkel-Ladd free-energy workflow. It does not relax the structure, build a supercell, equilibrate the volume, perform alchemical switching, or apply center-of-mass corrections.