Nuclear-Electronic Orbital Multistate Density Functional Theory.

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Computational Chemistry

Background:

• Hydrogen tunneling is fundamental to many chemical and biological processes.
• Accurately describing hydrogen tunneling requires accounting for electron-proton correlation, which is computationally challenging.
• Existing multicomponent quantum chemistry methods struggle with both static and dynamic electron-proton correlation.

Purpose of the Study:

• To present a novel computational strategy, the nuclear-electronic orbital multistate density functional theory (NEO-MSDFT) method.
• To enable the inclusion of both static and dynamical electron-proton correlation in hydrogen tunneling calculations.
• To achieve quantitatively accurate predictions of hydrogen tunneling splittings.

Main Methods:

• Combines two localized nuclear-electronic wave functions (from NEO-DFT) using a nonorthogonal configurational interaction approach.
• Generates bilobal, delocalized ground and excited vibronic states.
• Incorporates a correction function for quantitative accuracy in tunneling splittings.

Main Results:

• The NEO-MSDFT approach accurately predicts hydrogen tunneling splittings for model systems like malonaldehyde and acetoacetaldehyde with fixed geometries.
• The method demonstrates computational efficiency.
• It can be integrated with other theories, such as vibronic coupling theory, for dynamics studies.

Conclusions:

• NEO-MSDFT offers a powerful and efficient strategy for describing hydrogen tunneling phenomena.
• The method successfully captures essential electron-proton correlation effects.
• This approach has broad applicability for studying tunneling dynamics and vibronic couplings in diverse systems.