Orbital entanglement and correlation from pCCD-tailored coupled cluster wave functions

Area of Science:

• Quantum many-body physics
• Computational chemistry
• Strongly correlated electron systems

Background:

• Electron-pair wave functions offer cost-effective models for quantum many-body problems.
• Strongly correlated electrons require accurate wave function descriptions.
• Broken-pair states necessitate specific corrections for reliable modeling.

Purpose of the Study:

• To evaluate the performance of electron-pair methods in predicting orbital-based correlation spectra.
• To analyze the efficacy of the (orbital-optimized) pair-coupled cluster doubles (pCCD) ansatz with a linearized coupled-cluster (LCC) correction.
• To investigate the determination of orbital-based entanglement and correlation measures from pCCD-tailored wave functions.

Main Methods:

• Utilizing the pair-coupled cluster doubles (pCCD) ansatz with a linearized coupled-cluster (LCC) correction.
• Employing single-orbital entropy, orbital-pair mutual information, and two-orbital reduced density matrices.
• Benchmarking against Density Matrix Renormalization Group (DMRG) calculations for the 1D Hubbard model and N2/F2 molecules.

Main Results:

• The pCCD-LCC method accurately reproduces orbital-pair correlation patterns.
• Performance is validated in the weak correlation limit.
• Reliable wave function predictions are achieved for molecules near equilibrium structure.

Conclusions:

• The pCCD-LCC approach provides a reliable and accurate method for describing orbital-based correlation spectra.
• This method is particularly effective for systems with weak correlation and near-equilibrium molecular structures.
• Electron-pair methods, with appropriate corrections, are valuable tools for quantum many-body problems.