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Divide and conquer ab initio semiclassical molecular dynamics for spectroscopic calculations of complex systems

Periodic Reporting for period 3 - SEMICOMPLEX (Divide and conquer ab initio semiclassical molecular dynamics for spectroscopic calculations of complex systems)

Reporting period: 2018-11-01 to 2020-04-30

The main idea of this project is based on an ancient military strategy. Like an ancient village succumbing to the classic Roman strategy of divide and conquer, so the complex and counterintuitive features of quantum mechanics in molecules may be uncovered through a collection of innovative semiclassical calculations. Such a powerful mathematically inspired approach paves the way to new and more accurate chemical research of large molecular systems and allows one to detect fundamental quantum mechanical properties. For instance, a close analysis of a molecule’s vibrations yields key information on its structure and constituents. Unfortunately, both theory and experiments in vibrational spectroscopy, the field of chemistry dealing with this type of question, face serious challenges when treating large molecular systems. On one hand, computer simulations entirely based on quantum dynamics are prohibitively expensive. On the other, experiments are difficult to interpret and their features hard to pin down. The computer simulations performed in this project demonstrate how spectroscopy of big molecules (like fullerene, a sixty-atom carbon buckyball) may be successfully implemented to address these problems. By combining efficient classical dynamics simulations with semiclassical mathematical tools, we recover the essential quantum features and project the original problem onto a set of smaller ones. The main beneficial outcomes for the society are in economic and technological terms. On one hand, by enlarging the field of accurate spectroscopic simulations to systems previously accessible only by experimental investigations, this project prospects for the near future the possibility to avoid expensive and sometimes even dangerous lab practices in favor of computer simulations. On the other hand, by increasing the knowledge on molecular and supra-molecular interactions, the project aims at driving the design and synthesis of new remediation materials. The main overall objectives consist in providing the scientific community with a new computational tool to solve the open scientific issue of quantum spectroscopy for large systems, and in providing experimental and industrial partners with an efficient rationalization of the physical and chemical mechanisms at the heart of the production of new materials able to improve air quality. More specifically, the SEMICOMPLEX project is devising (in synergy with experimental partners) conveniently modified nanomaterials made of titanium dioxide to promote the photo-degradation of pollutants. In addition, we are developing a titanium thin film, with specific adsorbed siloxanes, that can be employ for outdoor cultural heritage preservation.
SEMICOMPLEX activities are structured onto different levels that can be seen as concentric spheres.
At the core, there is the scientific research of the PI supported by his team, aimed at developing new theoretical chemistry methods that allow for both the correct interpretation and the prediction of spectroscopic experiments. First, the new methods are implemented into Fortran or C++ codes, and tested on simple and model systems. Then, the codes are further tested on significant real systems to be compared with well-known experimental results. Small molecules, such as water, methane and formaldehyde are our testing benchmarks, because exact calculations are available for these systems. Instead, small amino-acids, such as glycine, represent target systems where exact calculations or analytical results are not available but there are accurate experimental results to compare with. This part of the work has generated internal discussions and group meetings. Furthermore, we have invited external speakers, whose research fields are of particular interest for the SEMICOMPLEX project and we have exploited their knowledge to better understand how to proceed with our work.
At the outer sphere there is the scientific dissemination activity. This activity is mainly composed of oral or poster presentations at scientific meetings plus peer-reviewed journal publications. In detail, our publications of highest impact have appeared in Physical Review Letters, the Journal of Physical Chemistry Letters, and the Journal of Chemical Theory and Computation. Other papers have been published in the Journal of Chemical Physics and in the Journal of Physical Chemistry C. As for scientific meetings, we participated at several national meetings as well as international ones to have the ERC project SEMICOMPLEX well known within the chemistry and physics community. Also, the PI organized in June 2016 a meeting in Lausanne, named “Different Routes to Quantum Molecular Dynamics”. The meeting was entirely sponsored by CECAM (Centre Européen de Calcul Atomique et Moléculaire) and three SEMICOMPLEX team members presented their work to the experts of the field. The new theory and results have been positively accepted by the international community in what we think has been the first step in validating our new methods. This has permitted to further proceed in the development of the SEMICOMPLEX project.
At the outermost sphere, we performed some outreach activities. These actives are aimed at impacting on the ordinary people and can be divided into multimedia ones, such as the project logo and website, plus seminars and conferences. As for the latter, the SEMICOMPLEX team invited and organized at the University of Milan the lecture of Nobel medalist Prof. Martin Karplus. Prof. Karplus, who is nowadays the world’s most eminent theoretical chemist, has been awarded the Nobel Prize in Chemistry in 2013. The choice of Prof. Karplus is motivated by the fact that a Nobel Prize winner can be easily identified by common people as the top representative of the discipline with the possibility to reach a very broad audience. People attending the lecture were composed of colleagues at University of Milan, graduate and undergraduate students in scientific disciplines, people from private companies and institutions related to chemistry, as well as high school students, since several high schools had been notified about the event. Prof. Karplus' visit was important also for the scientific part of the project. In fact, he is considered the father of modern molecular dynamics, the branch of theoretical chemistry to which the ERC SEMICOMPLEX project belongs to. He spent ten days in Milan being hosted by the SEMICOMPLEX team group. We had the possibility to illustrate him the guidelines of the SEMICOMPLEX project, the work of the group and, most importantly, we gathered Prof. Karplus' feedback. His suggestions have been really valuable and they helped us boost and enrich the SEMICOMPLEX project. His visit was fully sponsored by a private company called “Linea Energia”. As a conclusion and summary of this event, the team wrote a newspaper article for the Nuova Energia newspaper. This is a periodic journal that reports about events and progresses related to an environmental-friendly approach to chemistry and other main sciences. The journal targets any Italian citizen, in particular people living in Lombardy. It is available both on-line and on press. It is sponsored by several private companies that are interested to show that they care about environment and copies are sent to customers.
The team also worked as “ERC Community ambassadors” by diffusing the mission of the ERC institution to high school students. Frequently, the young EU citizens are not fully aware of how the national taxpayers’ money is invested at the EU level in research and how each EU citizen can benefit from that. The goal of the “ERC Community ambassador” is to educate high school students toward the importance of the European Research Council, illustrate its activity and explain why the theoretical and computational project SEMICOMPLEX has been financed. Specifically, among the crucial aspects for the modern European society, during these visits, several aspects have been illustrated. These include what theoretical and computational chemistry is (with specific reference to molecular dynamics), the role of the ERC institution and how it works, and the SEMICOMPLEX project. We visited high schools and the Museum of Science in Milan and met students from different year grades. Some of them attended the Nobel lecture described above. Students have shown strong interest about both theoretical chemistry and the ERC institution. They were not aware about the ERC. The visits allowed them to gain a better understanding of how the European Committee spends European taxpayers' money to boost Science and improve the European Society living standards.
The computational chemistry community is roughly divided into static (quantum chemistry) and dynamics (molecular dynamics) communities. Within the molecular dynamics branch, a very small fraction of people is devoted to quantum molecular dynamics because of the inherent difficulties, while a majority of people employ classical molecular dynamics. However, classical molecular dynamics simulations do not include ubiquitous quantum mechanical effects and are heavily limited in the possibility to faithfully reproduce experiments and reliably simulate chemical, physical and biological processes. The SEMICOMPLEX project is progressing beyond the state of the art by introducing semiclassical methodologies that employ classical molecular dynamics information to reproduce quantum mechanical effects in high dimensional molecular systems. The state of the art is represented by semiclassical tools able to mimic quantum effects only for small harmonic-like molecules. We have proved that we can go beyond those systems as we can successfully tackle amino-acids and are currently dealing with big molecules like fullerene, a sixty-atom carbon buckyball, and supra-molecular systems. In the near future, our codes will be consolidated and available as an everyday tool to perform quantum dynamics simulations for a detailed and precise understanding of how matter is behaving. The socio-ecomomic implications will be evident in the medium-long term, when expensive and dangerous experiments are replaced by safe and accurate computer simulations. More specifically, we are working in synergy with experimental groups for developing titania nanoparticles that can be employed for the photodegradation of pollutants. In other words, we want to use efficiently sunlight to clean the atmosphere from pollutants. Our simulations are providing the details on how pollutants are attached to titania nanoparticles and can be photo-degradated. Also, we are devising thin films that can be employed for outdoor cultural heritage preservation by adsorption of specific siloxane molecules on titania.