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Excitations in photoactive molecules from quantum Monte Carlo
Friedemann Schautz1, Francesco Buda, Claudia Filippi
1Instituut-Lorentz, Universiteit Leiden, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands.
The Journal of Chemical Physics
|September 16, 2004
Summary
Quantum Monte Carlo accurately estimates excitation energies for photoactive biomolecules. However, discrepancies arise with time-dependent density functional theory and restricted open-shell Kohn-Sham methods in describing excited states and isomerization.
Area of Science:
- Computational chemistry
- Photochemistry
- Biomolecular science
Background:
- Accurate electronic structure methods are crucial for understanding excited states in photoactive biomolecules.
- Photoinduced processes in these molecules remain challenging to describe computationally.
Purpose of the Study:
- To evaluate promising computational approaches for excited potential energy surfaces.
- To assess methods for formaldimine, formaldehyde, and a retinal chromophore model.
Main Methods:
- Quantum Monte Carlo (QMC) with optimized trial wave functions.
- Time-dependent density functional theory (TD-DFT).
- Restricted open-shell Kohn-Sham (ROKS) method.
Main Results:
- QMC accurately estimates excitation energies when trial wave functions are carefully constructed and reoptimized.
- TD-DFT and QMC show agreement in excitation energies but differ qualitatively in describing Schiff base isomerization.
- ROKS and QMC yield differing results for the lowest singlet excited state potential energy surface in low-symmetry structures.
Conclusions:
- QMC offers a reliable route to excited state energies with proper wave function construction.
- Methodological choices significantly impact the description of excited-state dynamics and isomerization in photoactive biomolecules.
- Further investigation is needed to reconcile discrepancies between QMC, TD-DFT, and ROKS for complex systems.