Enhanced Twist-Averaging Technique for Magnetic Metals: Applications Using Quantum Monte Carlo

Area of Science:

• Computational Physics
• Quantum Chemistry
• Materials Science

Background:

• Quantum Monte Carlo (QMC) methods are powerful tools for electronic structure calculations.
• Accurate sampling of the Brillouin zone is crucial for metallic systems.
• Existing twist-averaging (TA) schemes can suffer from energy fluctuations and require postprocessing.

Purpose of the Study:

• To propose an improved twist-averaging (TA) scheme for QMC methods.
• To enhance the convergence of total energy and magnetism for magnetic and nonmagnetic materials.
• To avoid energy fluctuations and the need for postprocessing corrections.

Main Methods:

• Developed a novel TA scheme using converged Kohn-Sham or Hartree-Fock orbitals as reference.
• Tailored the scheme for Brillouin zone sampling in magnetic metals, applicable to nonmagnetic conductors.
• Applied Diffusion Monte Carlo (DMC) to nonmagnetic Aluminum (Al) and ferromagnetic alpha-Iron (α-Fe).

Main Results:

• The proposed TA scheme demonstrates robust convergence of total energy and magnetism towards the thermodynamic limit (TDL).
• Achieves charge neutrality by construction, eliminating large energy fluctuations.
• DMC calculations on Al show excellent agreement between TDL cohesive energy and experimental results.
• Magnetic moments in α-Fe converge rapidly with an increasing number of twists.

Conclusions:

• The improved TA scheme offers a more robust and efficient approach for QMC calculations of metallic systems.
• It provides accurate results for cohesive energies and magnetic properties.
• This method is particularly beneficial for studying magnetic materials and their properties.