Periodic Reporting for period 1 - SICMA (Simulating Intramolecular Charge Migration on Attosecond timescales)
Reporting period: 2020-08-01 to 2022-07-31
With the advent of attosecond laser pulses in the extreme-ultraviolet regime, ultrafast molecular dynamics can be probed with unprecedented time resolution. The fundamental challenge of attosecond science is to understand the creation of coherent superposition of electronic states (upon shining a laser pulse) and the manipulation of electronic coherence (by overcoming the nuclei-induced decoherence).
Long-lived quantum coherence is already predicted for the efficient energy transfer in photosynthetic complexes at physiological temperatures. Quantum coherence is also indispensable in quantum technologies, such as, sensing, transduction, and computing – to outperform their classical counterparts.
The overall objectives of SICMA are two-fold: (i) to ascertain the role of nuclear motion in governing the electronic motion following the creation of a non-stationary electronic state, and (ii) to investigate fundamentally new ways to “steer” the correlated electron-nuclear motion and the resulting ultrafast charge migration.
The results indicate the vital role played by the nuclear degrees-of-freedom in the overall decoherence. However, by invoking a simple, and effective laser control strategy long-lived coherences can still be achieved.
Long-lived quantum coherence is already predicted for the efficient energy transfer in photosynthetic complexes at physiological temperatures. Quantum coherence is also indispensable in quantum technologies, such as, sensing, transduction, and computing – to outperform their classical counterparts.
The overall objectives of SICMA are two-fold: (i) to ascertain the role of nuclear motion in governing the electronic motion following the creation of a non-stationary electronic state, and (ii) to investigate fundamentally new ways to “steer” the correlated electron-nuclear motion and the resulting ultrafast charge migration.
The results indicate the vital role played by the nuclear degrees-of-freedom in the overall decoherence. However, by invoking a simple, and effective laser control strategy long-lived coherences can still be achieved.
The work performed during the project includes:
• Development of a project plan, project coordination and management.
• Development of a data management plan.
• Detailed review on charge migration in polyatomic molecules driven by intense, ultra-short laser pulses, including the technical aspects such as theoretical modelling and issues related to the choice of system.
• Development of a vibronic coupling Hamiltonian model by performing electronic structure calculations, in particular, CASSCF and CASPT2 using MOLCAS and GAUSSIAN softwares and fitting the ab inito data with VCHam program available in the QUANTICS suite of programs.
• Numerically exact quantum dynamical simulations of charge migration following the multiconfigurational time-dependent Hartree (MCTDH) algorithm and its multi-layer variant (ML-MCTDH) as implemented in the QUANTICS suite of programs.
• Incorporation of the electron continua model within the dynamical simulations to deal with the outgoing electron.
• Calculation of photoionization cross-sections using the ezDyson code of the Q-Chem 5.3 program.
• Comparative analysis of the explicit inclusion of a laser pulse in the simulations to the sudden ionization picture.
• Development of laser control schemes to control the charge migration over the molecular backbone.
• Analysis of the numerical simulations and interpretation of the results.
• Presentation of project results at national and international conferences, seminars, and meetings.
• Presentation of project results at department events/meetings.
• Outreach activities through participation in: (i) monthly coffee mornings, and (ii) weekly Chemistry, Light and Dynamics (CLD) seminars.
The main results achieved so far are as follows:
1. We have demonstrated how to create a coherent superposition of electronic states, i.e. electronic wavepacket, via photoionization using broadband XUV pulses.
2. We have carefully studied the validity of the widely used sudden ionization model and put forward the necessity of incorporating the laser pulse explicitly in the simulations.
3. We have demonstrated how the electron dynamics will affect the subsequent nuclear dynamics in a charge migration process.
4. We have demonstrated a simple and effective laser control scheme to control the correlated electron-nuclear motion to retain the electronic coherence for a longer time period.
Earlier, electronic coherences was reported to survive for smaller time scales, roughly 10 fs. Our results suggest that with a simple and effective laser control scheme the electronic coherences can be retained for much longer time periods.
The outcomes and results have so far been disseminated in 1 peer-reviewed scientific journal of international repute, which will be available as open-source. In addition, 2 more papers will be published shortly in peer-reviewed journals targeting researchers researching in atomic, molecular and optical physics. The project activities will be disseminated via social media (e.g. Linkedin, Twitter, arXiv, ResearchGate) and the project website. The work was done in close collaboration with the secondment host at Heidelberg University and upon discussion with our experimental and theoretical collaborators at Imperial College London that has resulted in an effective transfer of the results to those research groups. The project results were also presented (oral and poster) in several conferences, seminars and meetings in the UK and abroad.
• Development of a project plan, project coordination and management.
• Development of a data management plan.
• Detailed review on charge migration in polyatomic molecules driven by intense, ultra-short laser pulses, including the technical aspects such as theoretical modelling and issues related to the choice of system.
• Development of a vibronic coupling Hamiltonian model by performing electronic structure calculations, in particular, CASSCF and CASPT2 using MOLCAS and GAUSSIAN softwares and fitting the ab inito data with VCHam program available in the QUANTICS suite of programs.
• Numerically exact quantum dynamical simulations of charge migration following the multiconfigurational time-dependent Hartree (MCTDH) algorithm and its multi-layer variant (ML-MCTDH) as implemented in the QUANTICS suite of programs.
• Incorporation of the electron continua model within the dynamical simulations to deal with the outgoing electron.
• Calculation of photoionization cross-sections using the ezDyson code of the Q-Chem 5.3 program.
• Comparative analysis of the explicit inclusion of a laser pulse in the simulations to the sudden ionization picture.
• Development of laser control schemes to control the charge migration over the molecular backbone.
• Analysis of the numerical simulations and interpretation of the results.
• Presentation of project results at national and international conferences, seminars, and meetings.
• Presentation of project results at department events/meetings.
• Outreach activities through participation in: (i) monthly coffee mornings, and (ii) weekly Chemistry, Light and Dynamics (CLD) seminars.
The main results achieved so far are as follows:
1. We have demonstrated how to create a coherent superposition of electronic states, i.e. electronic wavepacket, via photoionization using broadband XUV pulses.
2. We have carefully studied the validity of the widely used sudden ionization model and put forward the necessity of incorporating the laser pulse explicitly in the simulations.
3. We have demonstrated how the electron dynamics will affect the subsequent nuclear dynamics in a charge migration process.
4. We have demonstrated a simple and effective laser control scheme to control the correlated electron-nuclear motion to retain the electronic coherence for a longer time period.
Earlier, electronic coherences was reported to survive for smaller time scales, roughly 10 fs. Our results suggest that with a simple and effective laser control scheme the electronic coherences can be retained for much longer time periods.
The outcomes and results have so far been disseminated in 1 peer-reviewed scientific journal of international repute, which will be available as open-source. In addition, 2 more papers will be published shortly in peer-reviewed journals targeting researchers researching in atomic, molecular and optical physics. The project activities will be disseminated via social media (e.g. Linkedin, Twitter, arXiv, ResearchGate) and the project website. The work was done in close collaboration with the secondment host at Heidelberg University and upon discussion with our experimental and theoretical collaborators at Imperial College London that has resulted in an effective transfer of the results to those research groups. The project results were also presented (oral and poster) in several conferences, seminars and meetings in the UK and abroad.
Previous theoretical simulations of charge migration in polyatomic molecules was limited to the sudden ionization picture. SICMA goes beyond that traditional model by incorporating the laser pulse explicitly in the simulation, draws a comparison between the two approaches and discusses the merits and demerits of both. These complete simulations were undertaken for a particular system. We believe similar conclusions can be drawn for other molecules under study and maybe for any molecule in general. Quantum coherence and control is a topic of considerable interest in diverse areas of research, including the development of artificial photosynthesis devices and the design of future devices related to quantum computing and therefore SICMA highlights potential for further advancement in those fields too.