Quantum Monte Carlo Calculations in Solids with Downfolded Hamiltonians

Area of Science:

• Condensed matter physics
• Quantum chemistry
• Materials science

Background:

• Accurate theoretical modeling of extended systems is crucial for understanding material properties.
• Traditional many-body methods face challenges with computational cost and pseudopotential approximations.
• Strong electron correlation effects in materials like NiO require advanced computational techniques.

Purpose of the Study:

• To develop and validate a computationally efficient and accurate many-body method for extended systems.
• To eliminate pseudopotential errors in electronic structure calculations.
• To investigate the equation of state of cubic BN and the spin gap in NiO.

Main Methods:

• Combining a downfolding many-body approach with auxiliary-field quantum Monte Carlo (AFQMC).
• Utilizing a systematically improvable Hamiltonian tailored for material-specific properties.
• Employing frozen orbitals constructed adaptively from the solid environment to eliminate pseudopotential errors.

Main Results:

• Achieved excellent accuracy for a diverse range of solids, including semiconductors, ionic insulators, and metals.
• Demonstrated significant reduction in computational cost without compromising accuracy.
• Successfully calculated the equation of state for cubic BN under ultrahigh pressure.
• Determined the spin gap in NiO, a material with strong electron correlation.

Conclusions:

• The presented downfolding many-body + AFQMC approach offers a powerful and efficient tool for accurate electronic structure calculations of solids.
• This method overcomes limitations of traditional approaches, particularly for correlated materials.
• It provides a reliable pathway for predicting material properties under extreme conditions and for complex systems.