Frederik Tielens (VUB) on Materials Modelling and Theoretical Background of Raman Spectra
Could you please tell us about yourself as a researcher?
The material modelling is like you put your nanoscopic glasses on and you see what is happening in real life but on an atomic scale.
Frederik Tielens (VUB)
I am a chemist. I have been trained as a physical/theoretical chemist at the Vrije Universiteit Brussel in Belgium. Subsequently, I started a PhD in chemistry. I have always been in touch with the characterisation of materials, in line with the CHARISMA project we are now involved in. After finishing my postdoc at ExxonMobil and working at different companies, I wanted to go back to academic research and was able to rejoin the university by going to Spain to the University of Castellon (Universitat Jaume I). I conducted another postdoc in Paris, and in 2007 I got my permanent position in Sorbonne University Paris, which is also a member of the CHARISMA Consortium now. I was an assistant professor there for ten years, then I had the opportunity to go back to Belgium.
At Vrije Universiteit Brussel, I built an independent group on materials modelling in 2017. And now, I am heading the Department of Chemistry there.
How do you describe your role in the CHARISMA Project?
CHARISMA is about the standardisation and harmonisation of Raman spectroscopy. So, Raman is the keyword for the project. Raman is also important in the characterisation of materials, which I studied for 25 years or more. We do that not only experimentally but theoretically as well. So, there is some theory behind that, and we want to understand why we have a specific signal, why we have this tool, why we can use this tool for characterisation. And, my role here is to provide some theoretical spectra of some, let’s say, standard materials which are used in industry or by experimentalists to have a reference: a reference material analysis, theoretically. I produce some spectra from reference materials that need to be compared to the experiments. And I try to understand why they are not all the same, why they sometimes deviate. If we have one reference, it can be used for comparison. Then we can more or less try to calibrate relying on this reference structure (and you can only have that if you have a good theoretical description.) This is my main task for the first part of the CHARISMA Project.
What’s on the horizon for the rest of the project?
The second part of the project, we will do something more adventurous, more challenging. We will look at the chemical phenomena that can be followed with spectroscopy. We will work with companies on applications.
1) We will calculate/predict the Raman spectra of zeolites –zeolite formation/crystallisation– with TOPSOE. It’s quite challenging because it’s a dynamic process. We need to simulate the dynamics of the system on an atomic and molecular level and at the same time, we need to calculate the spectra. There are methods available now and this is what we want to test.
2) Minerals called feldspars and used in some markers like non-reproducible papers (such as bills and banknotes or lottery tickets and so on). There are some Raman signals, interesting phenomena that cannot yet be explained. What I bring here is a molecular picture of the systems and the phenomena the experimentalists investigate.
How would you describe the materials modelling?
The materials modelling is like you put your nanoscopic glasses on and you see what is happening in real life but on an atomic scale. Experimentalists cannot see some signals through the atoms because it is a microscopic phenomena you observe. So, we link the microscopic with the nanoscopic.
We want to understand the very fundamental nature of the matter, which for chemists is the atom.
The atoms get together to make molecules, and molecules can organise in something which is periodic and makes crystals, and on this level one can already trace back the observation of microscopic phenomena. This is what we calculate. In fact, we calculate the electronic structure of the atoms. Since the 1930s, we are able to describe the electronic properties. We know how the electrons behave in these molecules. And since the late 1990s beginning 2000, it is possible to calculate the electronic structure of materials and its derived electronic properties, such as Raman spectra. This is what we do, this is computational quantum chemistry.
Why is the theoretical background vital for CHARISMA’s objectives?
So, the theoretical background is important to make simulations, and with these simulations we try to understand and predict the phenomena of materials that may be difficult to measure experimentally. It is not only the prediction, it is also understanding why one has this signal or behaviour but not another one. In experimental tools, this is much more difficult because you receive the complete spectrum, and that’s it. Are we sure that it is the spectrum of the material we are analysing? Isn’t there any interference by something? It can be the instrument itself, but it can be the material which may not be pure enough.
There is always something in an experiment that you cannot control, and you don’t even know what. In order to filter this out, one can try to or want to have a signal, a spectrum then, which is completely controlled by theory.
Some ask why it is useful. Because in theoretical structures, defectless structures (perfect crystals, monocrystals e.g.) exist, most of the time. So, the spectrum one calculates is not the same as the experimental one. If you even want to subtract that, then you know that some other peaks in the spectra, signals in general, are attributed to the nature of the sample. Therefore, we can say that this is a particularity of the sample or of the instrument, and it was not expected. You cannot expect the signals if you don’t have real material. I think the theory is there to explain and understand the experimental signal.
The theoretical description of the spectra is needed in order to understand the completely experimental spectra.
Let’s take a vibration, which is a typical example to give in a course of modelling: for many years the vibration spectroscopy has been used. And it’s so well-used that most people don’t even think about questioning a spectrum because a lot has been written in papers, in literature and in databases dating from the 1950s-60s. But, in the last 20 years, the materials modelling has gained a lot of impact in research. Before that it was too weak because we did not have computational power. New software and calculation power became available then. We could calculate the unit cell of a crystal rather than a few atoms. One could calculate properties, such as atomic vibrations. In effect, computational chemistry could be used as an experimental tool, a characterisation tool.
What do you like most about the CHARISMA Project and its real life impacts?
First, it is very closely related to what I’ve done before and want to do in the future. The properties I want to calculate, the interaction with the experiments…
There is one interesting application that we want to study in order to test the references and understand this Raman spectra. It is the formation of zeolites. Zeolites are minerals; you can find them in nature but there are a lot of synthesised zeolites nowadays because one can make them more pure. And there are a lot of them used in the industry. You can find them in many applications: for example, the production of gasoline/diesel.
So if you drive a car, zeolites have been in contact with that. But also at home, they are present in washing/cleaning products.
In order that your soap works better or to clean your clothes better, the chalk in the water –the hardness of the water– needs to be taken away. This way, your cleaning products work better and your machine will live longer. The powders and liquids one uses for washing always contain that. Zeolites help achieve such things most efficiently.
Get to know VUB
To learn more about the role of VUB in CHARISMA, please click here.
If you have any questions, feel free to contact CHARISMA.
