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Rydberg states with quantum Monte Carlo
Annika Bande1, Arne Lüchow, Fabio Della Sala
1Institut für Physikalische Chemie, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany.
The Journal of Chemical Physics
|March 25, 2006
Summary
Quantum Monte Carlo methods accurately calculate Rydberg state excitation energies. Variational Monte Carlo (VMC) calculations precisely reproduce experimental results for both excitation energies and singlet-triplet splittings in atoms and molecules.
Area of Science:
- Quantum chemistry
- Computational physics
- Atomic and molecular physics
Background:
- Rydberg states are highly excited electronic states.
- Accurate calculations of excitation energies and singlet-triplet splittings are crucial for understanding chemical bonding and reactivity.
- Quantum Monte Carlo (QMC) methods offer a powerful approach for electronic structure calculations.
Purpose of the Study:
- To calculate excitation energies and singlet-triplet splittings for Rydberg states using QMC methods.
- To investigate the accuracy of the fixed-node diffusion quantum Monte Carlo (FN-DMC) method, particularly concerning nodal artefacts.
- To compare the performance of FN-DMC and Variational Monte Carlo (VMC) methods against experimental data.
Main Methods:
- Utilized quantum Monte Carlo (QMC) methods, specifically fixed-node diffusion quantum Monte Carlo (FN-DMC).
- Employed Kohn-Sham wave functions derived from open-shell localized Hartree-Fock orbitals as trial and guide functions.
- Investigated nodal artefacts in the FN-DMC ground state calculations for the carbon atom.
Main Results:
- FN-DMC yielded accurate excitation energies for the studied model systems (carbon atom and carbon monoxide).
- FN-DMC showed less accuracy in predicting singlet-triplet splittings compared to experimental values.
- Variational Monte Carlo (VMC) calculations successfully reproduced experimental results for both excitation energies and singlet-triplet splittings.
Conclusions:
- FN-DMC is effective for calculating excitation energies but requires careful consideration of nodal artefacts for accurate singlet-triplet splitting predictions.
- VMC provides a reliable and accurate alternative for determining both excitation energies and singlet-triplet splittings, closely matching experimental observations.