Constrained nuclear-electronic orbital second-order Møller-Plesset perturbation theory

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Molecular Physics

Background:

• Accurate calculation of molecular properties requires accounting for nuclear quantum effects.
• Existing methods for incorporating nuclear vibrations are often computationally expensive and require multiple steps.

Purpose of the Study:

• To develop and implement a novel multicomponent second-order Møller-Plesset perturbation theory (MP2) method within the constrained nuclear-electronic orbital (CNEO) framework.
• To enable the simultaneous calculation of electronic-nuclear and nuclear correlation for vibrationally averaged molecular properties.
• To provide a more efficient approach for capturing nuclear quantum effects like vibrational averaging, isotopic effects, and zero-point energy.

Main Methods:

• Derivation and implementation of the multicomponent CNEO-MP2 method based on a generalized Hylleraas functional.
• Inclusion of electronic-nuclear and nuclear correlation effects.
• Benchmarking the CNEO-MP2 method on diatomic and small polyatomic molecules and ions.

Main Results:

• The CNEO-MP2 method successfully incorporates nuclear quantum effects into a single calculation or geometry optimization.
• Calculated internuclear distances, bond angles, potential energy surfaces, and vibrational frequencies demonstrate the method's accuracy.
• The method eliminates the need for costly post-calculation steps to determine vibrational effects on molecular properties.

Conclusions:

• The developed CNEO-MP2 method accurately captures the influence of nuclear vibrational motion on molecular properties.
• This new approach offers a significant computational advantage for studying nuclear quantum effects in molecules.
• CNEO-MP2 provides a robust framework for future investigations in computational and molecular physics.