Analysis of the nuclear-electronic orbital method for model hydrogen transfer systems

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Computational Chemistry

Background:

• The nuclear-electronic orbital (NEO) approach treats nuclei and electrons quantum mechanically.
• This method is applied to hydrogen transfer systems, where nuclei and electrons are treated at the same quantum level.
• Variational optimization of nuclear basis function centers is a key feature.

Purpose of the Study:

• To address fundamental issues in applying the NEO approach to hydrogen transfer systems.
• To analyze technical challenges including basis set flexibility, linear dependency, and optimization convergence.
• To test the accuracy of the NEO method for model systems.

Main Methods:

• Application of the NEO approach to [He-H-He]+ and [He-H-He]++ model systems.
• Quantum mechanical treatment of hydrogen nuclei and all electrons.
• Variational optimization of nuclear basis function center positions.

Main Results:

• Analysis of basis set flexibility for single and double well potential energy surfaces.
• Investigation of linear dependency in hydrogen basis functions and optimization convergence.
• Evaluation of basis set superposition error and comparison with grid calculations.

Conclusions:

• The NEO approach is applicable to hydrogen transfer systems with careful consideration of technical aspects.
• The study identifies and analyzes key challenges in implementing the NEO method for proton transfer.
• Validation against grid calculations confirms the accuracy of the NEO approach for model systems.