Constrained nuclear-electronic orbital density functional theory: Energy surfaces with nuclear quantum effects

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• The nuclear-electronic orbital (NEO) framework accounts for nuclear quantum effects by treating nuclei and electrons quantum mechanically.
• Conventional NEO methods rely on the Born-Oppenheimer approximation, limiting the potential energy surface to classical nuclear coordinates.
• This limitation hinders accurate modeling of systems where quantum nuclei significantly influence molecular properties.

Purpose of the Study:

• To develop a novel computational method, constrained nuclear-electronic orbital density functional theory (cNEO-DFT), that overcomes limitations of conventional NEO.
• To incorporate nuclear quantum effects directly into the energy surface calculation by constraining quantum nuclear positions.
• To enable a more accurate representation of molecular energies and facilitate the study of chemical dynamics.

Main Methods:

• Developed cNEO-DFT by imposing a constraint on the expectation value of quantum nuclear positions.
• Derived an extended NEO energy surface dependent on both electron and quantum nuclear coordinates.
• Applied cNEO-DFT to investigate the impact of nuclear quantum effects on energy profiles and stationary states.

Main Results:

• The extended NEO energy surface obtained from cNEO-DFT explicitly includes nuclear quantum effects.
• This approach yields a more accurate energy profile compared to conventional DFT.
• cNEO-DFT effectively facilitates the identification of NEO stationary states, crucial for chemical reaction analysis.

Conclusions:

• cNEO-DFT offers a significant advancement in computational chemistry by incorporating nuclear quantum effects directly into the energy surface.
• The method enhances the accuracy of energy calculations and provides a robust framework for locating stationary states.
• This approach holds potential for applications in geometry optimization, transition state searches, and reaction dynamics calculations.