Countries, companies and individuals are increasingly aware of the need to keep our world clean by supporting sustainable energy. The landscape is evolving rapidly. Of the various mechanisms considered currently, the potential of solar energy is particularly promising. One of the evolving technologies used to harness radiant light from the sun is photovoltaics technology. Photovoltaic cells are cheap, environmentally friendly, thin, light and very flexible. Developing low-cost and environmentally friendly devices that can be scaled up to industrial production is crucial for the successful and reliable integration of renewable energy.
Photography: Sophie de Kort
From left to right: Dr. Björn Baumeier, Dr. Nicolas Renaud, Dr. Alexey Lyulin, Vivek Sundaram, Dr. Jens Wehner, Dr. Felipe Zapata
In the project MULTIXMAS, Dr. Björn Baumeier and Dr. Alexey Lyulin from TU Eindhoven together with the Netherlands eScience Center, are developing bottom-up simulations of charge-carriers dynamics in large-scale polymer morphologies of some organic solar cells, combining multiscale structure equilibration of a nanomaterial using classical molecular-dynamic simulations with excited state electronic structure theory.
The development of such a multiscale computer simulation approach is the central building block of this project. According to Lyulin, associate professor within the Theory of Polymers and Soft Matter (TPS) Group of the Applied Physics Department at TU Eindhoven, this is an extremely challenging task.
Avoiding the creation of a computational Frankenstein monster
Baumeier, assistant professor at TU Eindhoven´s Scientific Computing Group, says his research is driven both by curiosity and with an eye on applications.
“Molecular materials offer a fascinating playground in this regard since they exhibit electronic behavior that makes them suitable to be used in devices such as organic light-emitting diodes (see OLED displays in mobile phones or TVs) or solar cells. In all cases, the behavior we see and use at the device scale is the result of a very intricate interplay of elementary processes that occur on nano- and macroscales. My goal is to use simulations based on first principles to understand fundamentally how these processes and their interactions give rise to the observable behavior and with this knowledge drive the optimization of materials forward. These simulations need to be accurate and predictive which constitutes challenges on various levels: the multiscale nature of the problem means that one needs combinations of several models, which in turn requires a careful control of the individual methods and how they are combined to avoid the creation of a computational Frankenstein monster.”
Diversity and expertise
Collaboration plays a central role in his group’s research, says Baumeier “From the nature of the problem, it requires expertise in several fields to successfully tackle it. At group level we have people with diverse backgrounds who need to work together to achieve a common goal. The collaboration with eScience Engineers Dr. Nicolas Renaud and Dr. Felipe Zapata, added greatly to this diversity by bringing both domain knowledge and the particular eScience skills that were only marginally present before.”
“Felipe and Nicolas have helped with developments that now allow us to address bigger and therefore more relevant systems than before.” — Dr. B. Baumeier
Baumeier continues: “One of the restrictions of our simulation software is that it is computationally very demanding. This is particularly true for the excited-state quantum-chemical calculations we perform with the help of Green’s functions. Felipe and Nicolas have helped with developments that now allow us to address bigger and therefore more relevant systems than before. Their initial outsiders’ view to the workflow has also been useful in identifying areas of improvement.”
“On the technical side the eScience Center brought a lot of new ideas and opinions to the project, which was very refreshing. I underestimated how important good communication between the parties is to get the process working smoothly.” — Dr. Jens Wehner, Eindhoven University of Technology
Lasting collaboration
Methods developed in MULTIXMAS are not material-specific and will be part of the open-source VOTCA package. Bexause MULTIXMAS’s developments will enter the open source VOTCA software(www.votca.org, github.com/votca),the concept of openness and sharing best practices is very important. Lyulin: “As a general toolkit for multiscale simulation of excitation dynamics in complex molecular systems, with extendable interfaces to standard quantum-chemistry software, we expect a large number of users and long-lasting collaborations beyond the project’s runtime.”
Baumeier agrees: “Openness has been an essential aspect of our work before the project and it continues to be one during the project. I am a strong advocate of open-source software in scientific research and it has always been important for me to be open in our own work and also to be able to make use of other’s research. Frankly, not doing it would be a waste of resources. If we do our job well, our work can be used in a variety of contexts besides the polymer solar cell use case we are currently working on.”
The goal is to bring the quality of simulations, both from a scientific and a software point of view, to a higher level.
“If we do our job well, our work can be used in a variety of contexts besides the polymer solar cell use case we are working on.”
There are already some groups internationally who use and contribute to the research software and Baumeier expects this user group to increase with performance, feature, and usability enhancements.
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