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Updated: Jul 6, 2025

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Time-dependent coupled cluster with orthogonal adaptive basis functions: General formalism and application to the
Mads Greisen Højlund1, Alberto Zoccante2, Ove Christiansen1
1Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark.
We developed a new method for molecular dynamics, orthogonal time-dependent modal vibrational coupled cluster (oTDMVCC), which shows minor errors compared to exact solutions for molecular systems.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Molecular Dynamics
Background:
- Bivariational wave functions are crucial for describing complex quantum systems.
- Adaptive basis sets offer flexibility in quantum mechanical calculations.
- Coupled cluster methods are standard for high-accuracy electronic structure calculations.
Purpose of the Study:
- To derive equations of motion for bivariational wave functions using orthogonal adaptive basis sets.
- To adapt this formalism to the coupled cluster Ansatz for nuclear dynamics.
- To introduce and implement the orthogonal time-dependent modal vibrational coupled cluster (oTDMVCC) method.
Main Methods:
- Derivation of equations of motion for orthogonal adaptive basis sets.
- Specialization to the coupled cluster Ansatz.
- Implementation and benchmarking of the oTDMVCC method against exact results.
Main Results:
- Amplitude equations in orthogonal and biorthogonal formalisms are identical.
- Basis set time evolution equations differ by symmetrization.
- oTDMVCC shows numerical convergence issues compared to the exact solution, with varying degrees of error across different molecular models.
Conclusions:
- The derived orthogonal formalism provides insights into the relationship between orthogonal and biorthogonal methods.
- While oTDMVCC is computationally efficient, its formal deficiencies can lead to noticeable errors in nuclear dynamics simulations.
- Further development is needed to improve the accuracy of the oTDMVCC method for complex molecular systems.
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