Non-adiabatic quantum dynamics without potential energy surfaces based on second-quantized electrons: Application...

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Computational Chemistry

Background:

• The Born-Oppenheimer approximation is a cornerstone of molecular quantum dynamics, but breaks down in non-adiabatic processes.
• Describing coupled electron-nuclear dynamics often relies on computationally expensive potential energy surfaces and non-adiabatic couplings.
• Accurate modeling of quantum interferences and strong electron correlation remains a challenge in molecular dynamics.

Purpose of the Study:

• To introduce a first-principles quantum formalism for non-adiabatic electron-nuclear dynamics.
• To provide an alternative to the Born-Oppenheimer approximation by circumventing potential energy surfaces.
• To demonstrate the formalism's applicability using tensor decomposition methods for wave function propagation.

Main Methods:

• A novel quantum formalism combining second quantization representation (SQR) for electrons and first quantization for nuclei.
• Implementation within the multi-configuration time-dependent Hartree (MCTDH) framework and its multilayer generalization (ML-MCTDH).
• Application to calculate the photodissociation cross section of the HeH+ molecule using Tucker and hierarchical Tucker tensor decompositions.

Main Results:

• The formalism successfully models non-adiabatic effects and quantum interferences in HeH+ photodissociation.
• Calculated photodissociation cross sections show full agreement with results obtained using traditional ab initio potential energy surfaces and non-adiabatic couplings.
• The study highlights the advantages and disadvantages of the new formalism, with potential solutions for drawbacks.

Conclusions:

• The developed quantum formalism offers a viable and accurate alternative to the Born-Oppenheimer approximation for non-adiabatic dynamics.
• The method's compatibility with tensor decomposition techniques facilitates efficient wave function propagation.
• Potential applications include systems with strong static electron correlation coupled with non-adiabatic electronic-nuclear effects.