Ionization potential optimized double-hybrid density functional approximations

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Electronic Structure Theory

Background:

• Double-hybrid density functional approximations (DH-DFAs) combine density functional theory and wavefunction theory for accurate molecular electronic structure.
• The Kohn-Sham (KS) potential is crucial for DH-DFA performance, but its accurate generation remains an area of research.

Purpose of the Study:

• To investigate the properties of the potential used in DH-DFAs.
• To develop a method for generating a consistent KS potential for DH-DFAs, including second-order perturbational contributions.
• To propose a strategy for constructing DH-DFAs that yield accurate orbital energies.

Main Methods:

• Utilized the optimized effective potential (OEP) approach to derive the consistent KS potential for DH-DFAs.
• Reparameterized the B2-PLYP functional to create the IP-optimized B2IP-PLYP functional.
• Validated the new functional using a dataset of vertical ionization potentials (IPs) and atomization energies.

Main Results:

• The OEP-derived potential provides improved orbital energies (as vertical IPs) compared to the standard perturbation-free KS potential.
• The reparameterized B2IP-PLYP functional outperforms the original B2-PLYP across various benchmarks.
• B2IP-PLYP demonstrates performance comparable to B2GP-PLYP and excels in difficult electronic and multireference systems.

Conclusions:

• Optimizing the DH-DFA potential for accurate orbital energies is a viable strategy for improving functional performance.
• The B2IP-PLYP functional represents a significant advancement, offering reliability for complex chemical problems.
• This work provides a pathway for developing more accurate and robust DH-DFAs.