Time-dependent multiconfiguration theory for describing molecular dynamics in diatomic-like molecules

Area of Science:

• Quantum chemistry
• Molecular dynamics
• Theoretical chemistry

Background:

• The multiconfiguration time-dependent Hartree-Fock (MCTDHF) theory is established for electronic dynamics in atoms and molecules.
• Existing models often use a clamped nuclear approximation, limiting their scope for nuclear dynamics.

Purpose of the Study:

• To extend MCTDHF theory for describing molecular dynamics involving electrons, protons, and two heavy nuclei.
• To develop a theoretical framework for non-Born-Oppenheimer molecular dynamics in intense laser fields.
• To investigate intramolecular proton migration mechanisms in hydrocarbon molecules.

Main Methods:

• A novel representation of the molecular wave function incorporating electronic and nuclear degrees of freedom.
• Formulation of coupled equations of motion (EOMs) for electron and proton spin-orbitals.
• Introduction of CI-vectors to describe the quantum motion of internuclear distance.
• Two-step derivation of EOMs: classical treatment of internuclear distance followed by quantum mechanical treatment.

Main Results:

• The developed theory enables the description of both electronic and nuclear quantum dynamics.
• Explicit coupled EOMs are derived for electron spin-orbitals, proton spin-orbitals, and CI-vectors.
• The framework allows for the study of non-Born-Oppenheimer effects on molecular dynamics.
• The theory is applicable to diatomic-like molecular systems including electrons, protons, and two heavy nuclei.

Conclusions:

• The extended MCTDHF theory provides a robust framework for studying complex molecular dynamics.
• This approach is crucial for understanding phenomena like intramolecular proton migration in intense laser fields.
• The theory facilitates the investigation of competing processes such as ionization and fragmentation.