2018 Fiscal Year Research-status Report
Efficient simulation of coupled electronic and nuclear motion in molecules in intense laser fields
| Project/Area Number |
18K05024
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| Research Institution | The University of Tokyo |
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Principal Investigator |
LOETSTEDT ERIK 東京大学, 大学院理学系研究科(理学部), 助教 (80632984)
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| Project Period (FY) |
2018-04-01 – 2021-03-31
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| Keywords | Strong-field physics / TDSE / Hartree-Fock |
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| Outline of Annual Research Achievements |
My research efforts during FY2018 have been concentrated on two research projects:
(1) The application of the extended multiconfiguration time-dependent Hartree-Fock (Ex-MCTDHF) method to the simulation of laser-induced ionization, excitation and dissociation of the hydrogen molecular ion H2+. In the Ex-MCTDHF method the total time-dependent wave function of a molecule, including both the electronic as well as the nuclear degrees of freedom, can be calculated without using potential energy surfaces. However, the Ex-MCTDHF method had not been shown to work efficiently for molecules in laser fields. I showed that the Ex-MCTDHF method can indeed describe both vibrational excitation, dissociation, and ionization of H2+, demonstrating that the Ex-MCTDHF method is a promising method for the simulation of the coupled electron-nuclear dynamics of small molecules in intense laser fields.
(2) In the Ex-MCTDHF method as well as in the related MCTDHF method for electrons, the equation of motion for the electronic orbitals is a non-linear equation. I showed, together with collaborators from Germany and Hungary, that this non-linearity may result in an unphysical oscillation of the population of excited states during field-free propagation of the wave function. Stationary populations can be obtained if the number of active orbitals is large enough. I carried out numerical calculations of the time-dependent populations in the excited states of a helium atom exposed to intense VUV laser pulses. These results are currently being prepared for publication.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
An important step was achieved by the successful simulation of excitation and dissociation of H2+ in intense laser fields, as described above in “Summary of research achievements”. This simulation showed that the Ex-MCTDHF method can describe ionization, electronic and vibrational excitation and dissociation occurring simultaneously in an intense laser field. Because this first, proof-of-principle simulation succeeded, it is meaningful to proceed further and apply the Ex-MCTDHF method to the simulation of larger molecules, and also to try to make the simulation procedure more efficient.
The findings described above under item (2) are important, since they suggest a way of assessing the accuracy of theories such as MCTDHF and Ex-MCTDHF. An (Ex-)MCTDHF wave function can be considered to be converged with respect to the number of time-dependent orbitals when the populations are stationary under field-free propagation.
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| Strategy for Future Research Activity |
During FY2019, the main effort will be spent on applying the Ex-MCTDHF method to the hydrogen molecule, H2. H2 contains 2 electrons, and is therefore more demanding than H2+, since a proper treatment of the electron-electron interaction has to be considered. I aim to simulate the complete electro-nuclear wave function of H2, including all degrees of freedom: rotational, vibrational, and electronic. If successful, a simulation of the complete rovibronic wave function of H2 in intense laser fields with the Ex-MCTDHF method would be the first of its kind. As a first step, I will implement the Ex-MCTDHF equations of motion and calculate the ground state wave function by imaginary time propagation. After confirming that the rovibronic ground state of H2 can be obtained within the Ex-MCTDHF method and checking that the results are consistent with other calculations, real-time simulations can be initialized.
I will also consider how the Ex-MCTDHF method can be further optimized, or how the simulations can be performed in a more efficient way. The optimization will be pursued along the lines in the submitted proposal: (i) Combining the Ex-MCTDHF method with the standard BO approximation, and (ii) Dynamical configuration-space adaptation.
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| Causes of Carryover |
When a new workstation was to be purchased in February 2019, a Dell workstation with the desired specification was found to be slightly cheaper than expected.
The remaining amount will be used to purchase reference literature during FY 2019.
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| Remarks |
Publications related to the research project will be announced at the web page of the Yamanouchi lab.
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Research Products
(12 results)
