2019 Fiscal Year Research-status Report
Efficient simulation of coupled electronic and nuclear motion in molecules in intense laser fields
| Project/Area Number |
18K05024
|
|---|
| Research Institution | The University of Tokyo |
|---|
Principal Investigator |
LOETSTEDT ERIK 東京大学, 大学院理学系研究科(理学部), 助教 (80632984)
|
|---|
| Project Period (FY) |
2018-04-01 – 2021-03-31
|
| Keywords | Strong-field physics / TDSE / Hartree-Fock / Particle correlation |
|---|
| Outline of Annual Research Achievements |
My research efforts during FY2019 have been concentrated on two research directions:
(1) Application of the Extended multiconfiguration time-dependent Hartree-Fock (Ex-MCTDHF) method to the calculation of a complete rovibronic wave function of H2. Preliminary calculations have shown that an approximation for the ground state rovibronic wave function can be obtained by including only one protonic and one electronic orbital in the wave function expansion
(2) Method for calculation of excited states within the multiconfiguration time-dependent Hartree-Fock (MCTDHF) method and application to He. Together with collaborators from Germany and Hungary, I demonstrated how excited state wave functions can be calculated within the MCTDHF method. I calculated the time-dependent populations in laser-driven He and showed that unless a sufficiently large number of active orbitals are included in the expansion of the time-dependent wave function, unphysical oscillations of the populations occur after the laser-atom interaction.
(3) Application of the MCTDHF method to the calculation of tunneling and over-the-barrier ionization rates of He-like ions. Reliable ionization rates for He-like ions are important for the implementation of a recently proposed scheme for determining the laser intensity of ultra-intense laser pulses. Together with a collaborator from the Czech Republic, I have shown that a modified Perelemov-Popov-Terentev formula provides an analytical approximation to the ionization rate which deviates from the reference rates calculated by the MCTDHF method by less than 10%.
|
| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
(1) If the Ex-MCTDHF method can be demonstrated to be able to simulate complete time-dependent vibronic wave functions, it would be major breakthrough in the area of simulation of laser-molecule interaction. Therefore, the derivation of the Hartree-Fock type of rovibronic wave function for H2 is an important step forward.
(2) Previously, it was not known how to deal with excited states in the MCTDHF theory. My results establish a general definition of excited states within the MCTDHF theory, and also provide a method for obtaining these excited states in a practical way via imaginary time propagation. It is expected that our proposed method can be applied both as a general method in the quantum chemistry community, and that it can also be adapted to other methods having nonlinear equations of motion, such as the multiconfiguration time-dependent Hartree method.
(3)The results on the ionization rates for He-like ions are important in two aspects. (i) I established the applicability of the MCTDHF method for the calculation of ionization rates both in the tunneling and in the over-the-barrier regime of strong-field ionization. For the ionization rates of He, the results calculated with the MCTDHF method agree well with the results calculated with other, explicitly correlated methods. (ii) The analytic formula proposed by us and verified by the comparison with MCTDHF results is expected to be useful in the practical implementation of a scheme for measuring the intensity of ultra-intense laser pulses (intensity larger than 10^20 W/cm2).
|
| Strategy for Future Research Activity |
During the last year of this project, FY2020, I will concentrate on two related projects.
(1) Calculation of a time-dependent rovibrational wave function of H2 using the Ex-MCTDHF method. The preliminary Hartree-Fock type wave function will be extended to a multiconfiguration-type wave function. As a first step, the ground state wave function will be obtained, and the convergence with respect to the number of protonic and electronic orbitals included in the wave function expansion will be investigated. Particular emphasis will be put on confirming that the electron-electron and electron-proton correlation in the ground state wave function can be adequately reproduced. After obtaining the ground state, time-dependent dynamics in an intense laser pulse will be investigated.
(2) Implementation of a mixed Born-Oppenheimer--Ex-MCTDHF (BO-ExMCTDHF) method for laser-molecule interaction. The idea is here to combine two methods, (i) the BO approximation, which is efficient for the description of dissociation, and (ii) the Ex-MCTDHF which can describe ionization, into a combined method which can efficiently describe both ionization and dissociation. As a first step, the equations of motion for the BO-ExMCTDHF method will be derived. Second, the BO-ExMCTDHF method will be applied to a one-dimensional model of H2+. The results obtained by this new method will compared with the results of the BO approximation, the Ex-MCTDHF method, and a numerically exact method where no approximations are employed.
|
| Causes of Carryover |
An amount of approximately 30000 yen reserved for the update of Matlab software was not used, since the University-wide Matlab license became available.
This amount will be spent next fiscal year for updates of other software.
|
| Remarks |
Research results are posted at the webpage of Yamanouchi lab at The University of Tokyo.
|
