Quantum Proton Effects from Density Matrix Renormalization Group Calculations.

Area of Science:

• Quantum chemistry
• Computational physics
• Molecular dynamics

Background:

• The Born-Oppenheimer approximation is a common simplification in molecular simulations.
• Accurately describing nuclear-electronic correlations is computationally challenging.
• Existing methods often struggle with strong correlation effects in molecular systems.

Purpose of the Study:

• To develop and apply a novel nuclear-electronic Hartree-Fock DMRG (NEHF-DMRG) method.
• To treat nuclei and electrons on an equal footing without the Born-Oppenheimer approximation.
• To accurately capture inter- and intraspecies correlations and detect strong correlation effects.

Main Methods:

• Combining the Density Matrix Renormalization Group (DMRG) method with nuclear-electronic Hartree-Fock (NEHF).
• Utilizing a stochastically optimized orbital basis.
• Extending orbital entanglement and mutual information to nuclear-electronic wave functions.

Main Results:

• Accurate proton densities, ground-state energies, and vibrational frequencies for HeHHe+.
• Improved accuracy for ground-state energy and proton density in HCN compared to state-of-the-art methods.
• Demonstrated reliability of entanglement metrics for detecting strong correlations.

Conclusions:

• The NEHF-DMRG method provides a powerful and accurate approach for quantum chemistry.
• This method overcomes limitations of traditional approaches in handling strong electron-nuclear correlations.
• The developed metrics offer new insights into complex electronic structures.