Multicomponent wavefunction-in-DFT embedding for positronium molecules.

Area of Science:

• Quantum chemistry
• Computational chemistry
• Theoretical chemistry

Background:

• The projector operator embedding scheme is extended to a multicomponent (MC) framework.
• A molecular system is partitioned into a wavefunction (WF) subsystem and a density functional theory (DFT) environment.
• This WF-in-DFT approach reduces computational expense by truncating the WF subsystem basis set, introducing controllable error.

Purpose of the Study:

• To explore the applicability of the MC extension of the WF-in-DFT scheme.
• To investigate positron-binding energies in positron-anion complexes.
• To assess the computational cost reduction and accuracy of the embedding scheme.

Main Methods:

• Extension of the Manby et al. projector operator embedding scheme to an MC framework.
• Implementation of third-order propagator-in-DFT calculations.
• Application to positron-anion complexes of alkoxides and carboxylates with varying carbon chain lengths.

Main Results:

• Selecting a WF subsystem with the positron and oxygen atoms yielded errors of 0.1 eV or lower in positron-binding energies.
• Basis set size was reduced by 33% to 55% using the WF-in-DFT partition.
• Computational cost reduction enabled complete basis set limit extrapolations for improved predictions.

Conclusions:

• The WF-in-DFT embedding scheme significantly reduces computational costs while maintaining high accuracy for positron-binding energies.
• Positronium aliphatic alkoxides are predicted to be stable by 0.3 eV with respect to positronium emission.
• Positronium carboxylates (aromatic and aliphatic) are predicted to be stable by 1.3 eV.