Temperature-dependent quantum pair potentials and their application to dense partially ionized hydrogen plasmas

Area of Science:

• Computational Physics
• Quantum Mechanics
• Materials Science

Background:

• Previous work established foundational concepts for pseudopotentials.
• Accurate modeling of two-component Coulomb systems at finite temperatures is crucial for understanding materials under extreme conditions.

Purpose of the Study:

• To provide a detailed discussion on the accuracy and practical applications of various finite-temperature pseudopotentials.
• To develop and validate improved pseudopotentials for simulating strongly coupled hydrogen.

Main Methods:

• Comparison of five different pseudopotentials: diagonal Kelbg, off-diagonal Kelbg, improved diagonal Kelbg, Feynman-Kleinert variational, and exact quantum pair potential.
• Derivation of a temperature-dependent fit for the improved diagonal Kelbg potential.
• Application of derived pseudopotentials in path integral Monte Carlo and molecular-dynamics (MD) simulations.
• Utilizing spin-dependent interaction potentials in classical MD simulations.

Main Results:

• A simple, accurate temperature-dependent fit for the improved diagonal Kelbg potential was derived, reproducing the exact pair potential across the temperature range.
• Classical MD simulations with spin-dependent potentials accurately describe the internal energy of hydrogen in the partially ionized regime down to 60,000 K.
• An important relationship was identified between quantum potentials and effective potentials used in density-functional theory.

Conclusions:

• Finite-temperature pseudopotentials, particularly the improved diagonal Kelbg potential with its derived fit, offer accurate and practical methods for simulating Coulomb systems.
• Classical MD simulations with appropriate potentials are effective for studying the thermodynamics of partially ionized hydrogen.
• The study highlights connections between different theoretical approaches in condensed matter physics.