In our interview series, "A Coffee with…," we give the floor to our awesome colleagues. This time, Stefan takes center stage and sheds light on how chemical simulations and quantum chemistry contribute to the discovery of new materials.

Let’s warm up with a first simple question: Tea, coffee, or water?  
They all have their purposes, but I’ve been enjoying coffee as far back as I can remember.  

What would you title your autobiography?  
“Please Purchase this Book”

What's your favorite element from the periodic table and why?
I should probably say fluorine, because my entire doctoral studies were financed by a special research grant on fluorine chemistry. But I recall while still studying chemistry and working in the lab that I found iodine pretty cool.

Iodine is such a useful reagent in many ways, and compared to other reactive chemicals, it’s not super hazardous to handle. It exists as a shiny crystalline powder that you can pick up with a teaspoon. Later, through quantum chemistry, I realized how fascinating these crystals were as a material. Simply speaking, crystalline iodine to some extent behaves like a metal, much more than chemists would expect from a diatomic molecule.

Cool, let's delve into your area of expertise. Can you tell us how you apply computational techniques to characterize and discover new materials?

Well, the space of possible materials is so immensely huge that we are forced to take on a generalist approach. In the morning, someone wants to learn more about the strength of their new high-entropy alloy. After lunch, it’s all about the diffusion of defects in a semiconductor. And in the late afternoon, the important question is the degradation of surfactant molecules in an oxidizing atmosphere.

Luckily, quantum chemistry provides an extremely robust framework for computer modeling of the fundamental building blocks that make up materials. The interesting challenge lies in applying quantum chemistry as generally and efficiently as possible. That means that we must not only keep the physical equations correct but also use concepts from data science and artificial intelligence to guide the simulations.

As our expert on solid state, surface chemistry, and alloys, what is so challenging in investigating the quantum chemistry of materials?

The sheer size of materials, compared to isolated molecules. The simple water molecule, H2O, has just three atoms and it is very straightforward to computationally model any property of that molecule. Materials, on the other hand, are by definition a huge collection of chemical species that interact as an ensemble. I mean, for example, the quadrillions of atoms that make up a metal sample. More specifically, the challenge for the material quantum chemist is to find a good enough reduced model to understand the question at hand and make sure that accurate results are delivered as quickly as possible.

In your daily work, you support the software development team to implement simulation tools into our platform, QuantistryLab. What are the challenges of translating scientific theories and concepts into a cloud-based platform?
The cloud allows for great flexibility and intelligent planning of the usage of computational resources. This is in contrast to more traditional quantum chemistry simulations on high-performance computers, where the researcher often needs to attend to non-scientific matters, such as raw data validation, hardware usage, and a whole lot of other technical details. This of course leads to many bottlenecks where the calculation servers remain unused. In the cloud-based solution, it’s much easier to keep the flow of calculations running, and it reduces the amount of manual labor greatly.

The challenges often revolve around the fact that we are truly for the first time translating quantum chemistry to cloud architectures. We’ve already had quite some success integrating many known methods in materials modeling and I’m optimistic that we can deliver chemical insights in a modern software solution.

And last but not least: Which scientist from any era would you like to have a coffee with?
I’ll go way out of my field and say Noam Chomsky.

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