Correcting density-driven errors in projection-based embedding.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Materials Science

Background:

• Projection-based embedding offers a robust framework for multiscale wavefunction-in-density-functional-theory (WF-in-DFT) calculations.
• The accuracy of WF-in-DFT relies on the low-level density functional theory (DFT) accurately describing subsystem energetics and coupling.

Purpose of the Study:

• Investigate errors in WF-in-DFT embedding calculations caused by delocalization errors in model systems.
• Address the spurious delocalization of singly occupied orbitals in open-shell doublet systems due to self-interaction errors.

Main Methods:

• Studied model systems exhibiting delocalization errors that affect the total density description.
• Proposed a method to mitigate self-interaction errors by using a more accurate self-consistent density for DFT energy evaluation.

Main Results:

• Identified substantial errors in WF-in-DFT embedding calculations for open-shell doublet systems.
• Demonstrated that evaluating DFT energy with Hartree-Fock (HF) theory density significantly reduces errors.

Conclusions:

• Wavefunction-in-(Hartree-Fock-DFT) (WF-in-(HF-DFT)) calculations show excellent convergence towards full-system wavefunction calculations.
• The proposed WF-in-(HF-DFT) approach effectively resolves delocalization and self-interaction errors in embedding calculations.