Developing the MCTDH Quantum Dynamics Code: Accurate Direct Dynamics of Non-Adiabatic Phenomena
Lead Research Organisation:
Imperial College London
Department Name: Chemistry
Abstract
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Organisations
Publications
Richings G
(2015)
Quantum dynamics simulations using Gaussian wavepackets: the vMCG method
in International Reviews in Physical Chemistry
| Description | The goal of this research was to develop software for carrying out quantum molecular dynamics. Understanding the energy flow in molecules after absorbing a photon of light is important to understand their light-activated properties. These are important in a range of technologies, such as harvesting solar energy and data storage, as well as understanding photo-stability and deriving new molecules via photochemical pathways. This energy flow is complex, as a number of different pathways (channels) are available. Of particular importance are what are termed non-adiabatic pathways that allow a molecule to undergo a change of chemical character (electronic state) effectively instantaneously and so dominate the molecular evolution. Unfortunately it is impossible to say a priori which pathways are most important for a particular molecular, and computer simulations have a large role to play in answering this question by modelling the potential energy surfaces and molecular dynamics after excitation. Computer codes for simulating excited-state dynamics are becoming more powerful and useful. At the start of this project there was still no code available that could capture all of the quantum mechanical effects required for larger molecules, that had the potential to be used by non-specialist researchers. This promises to be able to accurately treat the molecules of interest using what is termed direct dynamics, which couples the dynamical simulation of the changes in molecular structure to a separate program that calculates the potential energy surfaces only when required, thus saving much of the work. Initial studies support this. This DD-vMCG code - now available as part of the Quantics package - was developed through this award so that it is more computationally efficient, easier to use, more stable numerically, and can continue to be developed in a sustainable manner. This software engineering work ensures that the method will be able to fulfill its potential after many years of development, and can be used by the scientific community to help understand and engineer how molecules behave and ultimately how they can be controlled in the presence of light. One recent example highlights the potential of the method for such applications in the future. In quantum theory, electrons behave like waves and can therefore interfere, as demonstrated in Young's double-slit experiment. The ability to interfere is related to the 'coherence' of the electron waves: as long as there exists a constant relative displacement between the different electron waves, the system is said to be coherent. However, the electrons are not isolated; their motion is affected by the motion of the nuclei in the molecule (even at absolute zero temperature). Is coherence long enough to be observed by experiment? By using Quantics to carry out dynamics calculations for both electrons and nuclei, researchers have been able to accurately describe this decoherence for the first time, and to show that for many molecules and many electronic states it is almost unavoidable. |
| Exploitation Route | There was no quantum dynamics code available as part of the National Service for Computational Chemistry Software, the UK service run primarily for non-specialist computational chemists. Our long-term goal was to provide such a code, along with the experience to make use of it effective and an active community linking developers and users. As with electronic structure theory, the transition from specialist academic to non-specialist and non-academic use will take time. We cannot guarantee that our nonadiabatic dynamics code will change the way light-driven molecular devices are designed in 20 years time. We have, however, provided a code that, by analogy with electronic structure codes, shows non-specialists the types of calculations they could make and so generates new interest and ideas. NSCCS no longer exists, but the code developed as part of this project - Quantics - is available for specialists and non specialists, with an interest in accurately calculating the dynamical behaviour of multiple electronic states in molecules. |
| Sectors | Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Education,Energy,Environment |
| URL | http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/naturalsciences/chemistry/newssummary/news_8-3-2017-10-57-39 |
| Description | Controlling photophysics and photochemistry via quantum superpositions of electronic states: towards attochemistry |
| Amount | £479,550 (GBP) |
| Funding ID | EP/T006560/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 11/2019 |
| End | 10/2023 |
| Title | Research Software consultancy |
| Description | The IC team for Developing MCTDH engaged a software consultant to redevelop what's now become the Quantics dynamics code. This model is now much more widely used in a different form: EPSRC have championed Research Software Engineering through fellowships, and a number of institutions - including Imperial - are developing teams to take on software engineering projects for research. We're now using this as part a new project EP/T006943/1, with 220 days of RSE time included to tackle software engineering challenges which are not appropriate for a postdoctoral research fellow, in that they won't directly lead to new publications, but they are vital for preparing our codes for the size of simulation needed to engage directly with the experimental project partners. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2017 |
| Provided To Others? | No |
| Impact | The need to improve academic software development has been widely recognised for some time, and there have been multiple initiatives in this area. We benefitted from Software As Infrastructure funding to begin specific software developments for quantum molecular dynamics simulations. We also trialled a model for academic software development that wasn't so widely used at the time. Both are now central to a current funded research project, and the experience from Developing MCTDH, as well as the code itself, will be vital to the success of this project. |
| Title | Quantics |
| Description | The goal of this part of a joint research programme was to transform the MCTDH program for carrying out molecular quantum dynamics calculations, creating a stable new release accessible to a much wider range of researchers, through supporting an academic visitor with detailed knowledge of the methods implemented and a software consultant with database, revision control and code optimisation experience. |
| Type Of Technology | Software |
| Year Produced | 2015 |
| Impact | The Quantics code whose development was supported by this joint award is the closest now available to a general purpose software for molecular quantum dynamics, as well as being a specialised research tool. It was used in modified form as part of the following research which demonstrates that the motion of the nuclei can lead to the loss of quantum coherence of the electrons in molecules, published in Physical Review Letters, highlighted by our communications team: http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/naturalsciences/chemistry/newssummary/news_8-3-2017-10-57-39 |
| URL | https://www2.chem.ucl.ac.uk/worthgrp/quantics/doc/index.html |