A Novel NPT Thermodynamic Integration Scheme to Derive Rigorous Gibbs Free Energies for Crystalline Solids

Abstract

Thermodynamic Integration (TI) is the state-of-the-art computational technique for accurate Gibbs free energy predictions of solids. Conventional TI schemes start from an NVT harmonic reference and require three successive corrections to recover the Gibbs free energy of the real crystal in the NPT ensemble. However, the NVT-to-NPT correction neglects full cell flexibility. Here, we present a rigorous (and only) two-step TI scheme that operates entirely in the NPT ensemble, eliminating the need for the approximate NVT-to-NPT step. The key methodological advancement is the novel NPT reference that explicitly accounts for full cell fluctuations. The new approach is compared with the conventional one via two complementary case studies. For ice polymorphs, having simple cell-shape distributions, the new approach reproduces conventional TI results with excellent agreement. For CsPbI3, whose black phase exhibits complex cell-shape behavior, we demonstrate that our novel method provides more accurate Gibbs free energy differences than the conventional one. Moreover, the proposed framework maintains comparable computational cost while offering a simplified workflow. Overall, the new NPT TI scheme provides rigorous and direct Gibbs free energy calculations for solids.

References in corpus (12)

• Parallel Tempering: Theory, Applications, and New Perspectives
• The first-principles phase diagram of monolayer nanoconfined water
• Hydrogen bonds and van der Waals forces in ice at ambient and high pressures
• Advances in the experimental exploration of water's phase diagram
• Anharmonic and Quantum Fluctuations in Molecular Crystals: A First-Principles Study of the Stability of Paracetamol
• Computing the Absolute Gibbs Free Energy in Atomistic Simulations: Applications to Defects in Solids
• A complete description of thermodynamic stabilities of molecular crystals
• Quantum-mechanical exploration of the phase diagram of water
• i-PI 3.0: a flexible and efficient framework for advanced atomistic simulations
• A streamlined molecular-dynamics workflow for computing solubilities of molecular and ionic crystals
• Training Dataset Matters for Machine Learning Interatomic Potentials: Water Simulation as an Example
• Harmonic-to-anharmonic thermodynamic integration made simple using REG TI