 Hello. Hello, Ali. Hi, I'm Ado. How are you? Fine. Good you. Good morning. Good morning. How are you? Fine. I didn't see you yesterday. No, I was, I was, I was there. Yeah, I was sitting behind, following, waiting for my sessions. I see. Since I'm going to see the whole day today and tomorrow, basically, I see that you are sharing today. Yeah. We are online. So good morning again. Welcome again to the second day of our virtual conference. Welcome everybody. So we have basically today also in the morning, six talks. Each talk will be 20 minutes presentation and five minutes interaction as what we did yesterday. We start with the first presenter today. Stephanie. Can you please, Stephanie came up, shared your screen and the floor is for you. Okay, good. So by the way, my name is Stefan Kenmore. So you should not read the E like the E in English. Today I want to report on what we are doing here at the University of this book essence. So, so we are part of a collaborative project, which is devoted to alcohol oxidations using heterogeneous catalysis. And then our contribution to this project is to study the impact of salvation on the structural and reactivity of the various oxides structures that we are going to use in the project. So we are among the few theoretical groups, which are working with a zoo of experimentalist using various background and techniques to address the topic. Okay, so, as I just said, we are doing heterogeneous catalysis in the liquid phase because this topic is important because as we know, most of the chemicals in the industry in the chemical industry are produced via oxidation. And around more than 500 million tons of chemicals are produced through oxidations every year in the world. And we know already large scale industrial oxidation in the gas phase is well established many people have addressed oxidation using for example metals theoretically and experimentally speaking about theory we know people like Michaelides who have studied metals interaction with water to a very extent, big extent, and other people here in Germany and all over the world. So selective oxidation is also an important process because it allow to functionalize hydrocarbon and many other raw material. So we want to bring oxidation, heterogeneous oxidation on catalysis in the liquid phase to a level understanding that can be equivalent to what is original on metals because in our studies in our project we focused on oxides because as we know oxides are more abundant. Apart from few noble metals, most of the metals forms oxides as soon as they're exposed to the atmosphere. And as we know in the Pairando condition water is always there so it's important to know how water interferes with the chemical processes that we want to address. And as I said already in the first slide here in is a collaborative project is a national project in Germany. And then one of the professors here in the university got a big grant where he wanted to address the topic have been mentioning since the beginning, and then we were we saw the importance of theory because in the first funding period. I think the project was not accepted because there was a few theory in the application. So this is how my boss here was contacted and then we apply for a second round and then got accepted as you can see theories in the center of the project. Telling all this because in Africa sometimes we think that theory is not important, but theory is reaching a level. People are already kind of doing to a certain extent experimental experiment experiment computer experiment using various codes like CP2K or many others. So, concretely, what you want to do is to study the nature of the catalyst the catalyst that we are going to use. Namely, we want to study the nature of the active sites, the reaction mechanism, and also focus on particular oxides that give the best structure to activity. So, precisely we in the project focus on abundant oxides in on earth so in earth sorry, like cobalt and iron oxides. So, in the first step of the project we started with cobalt oxide because cobalt oxide has many beneficial properties, magnetic, electronic and redox property that makes it a potential candidate for many reaction, like water oxidation, selective propranol isopropanol oxidation steam, the forming of ethanol, carbon monoxide oxidation and so on and so forth. So, cobalt oxide nanoparticles that are used for catalysis have this shape, and you see on this shape three phases are mainly exposed to the 101, 111 and 110. And then depending on the application that you want to use, people have developed over the year, in many experimental groups, people have developed technique to allow a selective exposure, right, of the facets that are more active for particular catalytical reactions. And then the 101, the 100 surface, as you can see is a very abundant on the, it's very prominent on nanoparticles. So, this is why we have decided to study this surface orientation. It's first interaction with water, and in the later stage, the oxidation of selected alcohol, namely isopropanol. And we started first by studying water because, as you know, water can promote a metastable reaction by stabilizing in damages or water can also inhibit reactions by blocking the active site. So, how do we do it? So we do a computer experiment and this is the procedure that we follow. So we take the bulk we cut in particular orientations, and then when you do it for cobalt oxide, you end up, if you cut cobalt oxide according to the 100 orientation, you end up with two termination, which are known as the A and B termination. The A is terminated by cobalt two plus atoms. And then the B termination is terminated by a mixture of oxygen and cobalt three plus. So you have cobalt with two different oxidation states, which are two and three. So what do we do? We use what we call a supercell approach in which we put the slabs, so the surfaces. In principle, surfaces are, a surface is not an entity at its own. A surface is always connected to the bulk. So here, when we simulate the surface, we fix some part of our slabs to bulk position to mimic the bulk, and then the upper part of the slab is allowed to relax for the clean surface and also later with water. So as you see my point here, this part here is allowed to relax in here is keep fixed at bulk position to mimic the bulk, the bulk behavior. So, and then we add water on top and then see what happens. So we, we do it at several level of salvation. So first one layer of water, two layers, three layers, and then we go towards, we converge towards bulk water. And then here the dimension of the cells that we use are typically in the nano regime so it's basically 1.5 nanometers four on top of which we put water. So I will skip you from the details here so maybe if one is interested we talk about it during the discussion. And then we address a specific scientific question. First of all, what is the structure by structural response of the interface to what absorption, where and how does water absorb on the surface what is the degree of the association because as we know surface which are very this is what's the driving force for the stabilization of what are the interface what is the nature of the fundamental interaction that stabilize absorb water. What about the hydrogen bond network and the topological realization because as we know the smoother you have the hydrogen bond network. Sometimes the better is for proton transport, which is can be another another pathway for hydrogen evolution for people who do for example water splitting. And then, at the end, after we know how the substrate or the catalyst reacts towards water, then we put the selected alcohol that we want, and then see the effect of the effect of temperature and environment on the oxidation that is oxidation, you can understand the loss of hydrogen from alcohol to create a ketone, for example. So in the case of propanol you can have acetone. So, directs to the first question. So what happens when you have water at the interface. So first we address the clean surface and then you see the A and the B surface. This is before relaxation. And then you see that in the case of case of A, you see these arrows. So the cobalt 2 plus which are green, they move towards the road towards the four fall along the road towards the four fall holocytes that are located here as you see my pointer. So they say construction on the A termination. And as you can see here you have no reconstruction on the B termination so you have small relaxation, so a small magnitude of relaxation. So they are actually ongoing experiment in a group in Free Cyber Institute in Berlin where they are doing STM measurements to try to corroborate what we see from theory. And then what happens when we put water. So for the moment I want to show the water molecule, sorry, I will just show you this small characteristic Raja distribution function. So as theoreticians to see what is happening with what is there the movie is not important, but the physical property so we calculated the distance between cobalt atom at the top most layer the surface and surface oxygens also. And then you see, in the case of the A termination. So we add gradually 16 water molecule that is one layer 24 what this is to and then 32 which is three water monolayers on the surface. And then you see that in the case of the A. This is for example the right distribution in the book you see a kind of, I will say, not allow me to call it narrow peak. Where you have a fixed a fixed peak here, which is not white as when you the surface is relaxing and undergoes construction because you see on this line here that you have the common. Sorry, so the peak is actually within because there is the reconstruction going on on the on the clean surface and then the more you add water you are 1624 and then you go to 32 you see we go you go back towards a bulk like distributions at the interface, which is sort of say that waters favors kind of bulk like environment. So, and then you see that the peaks do not have the eighth of the peak do not have do not have a significant dependence on the water content. So on the cobalt atoms, which are also present on the A termination but on a lower sub layer. So you see similar feature concerning the relaxation on the A on the B. They are less pronounced relaxation of cobalt three atoms. And we actually try to understand what is going on what's the driving force for this behavior and then we perform a thorough analysis that I won't show here. And then we come out with the conclusion that the driving force for this stabilization is the coordination number at the interface. So everybody wants to get his coordination number that he had in the bulk. So, now, what is the structure of the interface, where is what, what do we see how does what is there. So that's for example is not short top view of A and B termination with 16 water layer so one one layer. You have intact water layers like here, and then also dissociated water, you can see the hydroxyl groups. So this is, so the absorption mode in the same is the same on the A and B terminations, just that on the A, you have more dissociation, you have more OH groups compared to the B where molecular water is more prominent. And then, what happens when the more you add water, so how does the dissociation degree in the contact layer depends from what we have seen that the dissociation degree actually does not strongly depends on the water coverage because the dissociation degree is almost 100% on cobalt two plus and 50% on cobalt three plus on the A termination. And then even if you increase the solvation degree, it's still the same. When you go on the B, as I said before, there is less dissociation which is actually almost one quarter of what is associating, and which is also not dependent on the water content. And then we concerning talking about the structure, we also try to, to see what is the, I mean, the, how, how, how do the layers looks at the interface and then we come out with the conclusion that we have actually buckled layer on the A as you can see here. And the buckling is more very important on the A termination compared to the B where layers are almost flat. And this you can see it from this characteristic density profile along the Z direction that we calculated. So, this picks actually at one is attributed to hydrogen bonds that dissociate and go to oxygen on the surface which are located almost at one, one ounce long away, this is the characteristic distance for an OH group on the surface. And then you have other picks here are two, actually the water oxygens, and then you have broadening and picks that are hybridizing somewhere here when water become more important, water content becomes more and more important at the surface. On the B as I said, the structure is a bit more ordered. And then the experimentalists now are also doing some STM images for comparison here. And then they are also doing some another group is doing some XPS chemical XPS measurement to see the chemical state of water. So to confirm that water is really actually part the dissociated and the interface so they actually they do it by calculating. So it's different you have five minutes or zero one S electrodes. So they can also do ambient pressure XPS experiment to determine the thickness of water at the interface. So, that brings me directly to the next point where we have calculated the, the right distribution function of cobalt atom to oxygen to, to, I mean, to, to investigate the strength of interfacial bonds at the surface. These picks are two characteristics for covalent bonds, cobalt to oxygen bonds at the surface. We see some picks at two, which are attributed to molecular water and some other ones are 1.89, which is actually hydroxyls on the group. So the features are almost the same for the A and the B. And then we also address the lateral distribution of species at the interface and then you can see I will just show for the B. You see that this is, for example, water gray here, water sports. So we calculate the XY distribution of ports during molecular dynamic simulation that we did. And then you see that you have rigid oxidants layers, as you can see with the grace. And then which shows that actually on the B term nation water forms epitactic layers on the surface. Also, we studied the hydrogen bond distribution and then we calculated the orientation of OH vectors with respect to the surface normal. And then you can see from distributions that the more water is there, you have a growing edge bonds and more deviation to the surface normal. So we and experimentally together calculating the shift actually direct direct shift in which frequencies to see to have a quantitative quantitative information about what is happening. So these effects are more pronounced on the E and the A term nation concerning this strengthening of the hydrogen bond network. So that brings me to the last slide of my talk. So at this stage we have seen that water actually we have information about the state of water at the interface which actually partially dissociate on both terminations. We have rigid oxygen layers, but I didn't show the proton subsystem because the time is too short. And I saw short in the previous slides, we have the construction on the A, which is driven by this reconstruction is lifted up when water is present and this is due to the increase in the contribution number we have broken layer the dissociation degree. If we summarize is actually 75% with full dissociation on cobalt two plus and 50 and on cobalt three plus. So we have a dynamic interface I didn't show anything about dynamics here. We have a ring construction on the B epitactic layers, 25% dissociation and then the proton transfer mechanism is less reactive. And then this, this conclusion brought us to do. So we asked ourselves, is it because of the fact that what I started, what the OH are tightly bound to cobalt two plus on the A that we have high temperature distortion peaks. Maybe this is the case because an experiment they see it, maybe we have this is the first step to the explanation of that. And then maybe the B termination could be I mean more favorable to large molecule absorption and decomposition, maybe the cobalt three plus actually the active site and then to end up I will just show this movie. This is for example, now we have introduced an alcohol isopropanol. And then as you can see here, when you put it. This is because on the A we have seen nothing the A is not reactive because water is tightly bound the OH bonds are stubborn, not easy to dissolve or to collaborate with other ones to allow the proton transfer. So on the B this what is happening, also nothing is happening but as soon as we play with environment, and then by actually, I mean, creating some defects, you have something happening. Interesting so you have the decomposition of isopropanol to acetone, you see that hydrogen is transferred from the, from the isopropanol to the neighboring oxygen molecules which is actually our target in this, but now we have to do it long scale for a longer simulation time. So, at the later stage we are going to go, we are going to move towards real structure so concept, I've been making the thing more real right by going really to electrochemical environment extra proton and also a real surface composition by allowing metal doping and vacancies. So, I'm done. This is what I wanted to present today. Thank you. Yeah. Thank you, Stefan. So we have five minutes to interact. You can actually unmute yourself and ask a question. But in the meantime, Stefan, there is some questions on the chat. Yeah. Let me just read them. Have you done DFT calculation on water absorption on your on your surface with different terminations to determine the for favorable configuration before doing MD. Yes, that's actually a good question. So we, we didn't do any thermodynamic analysis to see which surface termination is the best. So actually, one could do up initial thermodynamic and then to see in equilibrium condition which one is more stable, but then they are two problems. One is technical. So calculating surface energy and I mean the first phase of water at ambient temperature is not so trivial to handle when you calculate the surface energies. And then secondly, there's no experimental group are working in equilibrium conditions. So this is why we directly study the two of them and be. And then. So that's what I can say at this stage. In line, Azima, let me just read this one and then you will, you will ask your question. So in line with that someone also asking why do you make some layers fixed during during relaxation. Yeah, because as I said, a surface is not an entity at this point, right, the surface is always connected to the bulk. Right, the surface is something different. It's not something different from both days. They are always connected. So this is why to mimic this picture. What we do is that we take the bulk. We caught in particular direction and then we keep some layers fixed to mimic this part of the bulk which is still under the relaxed layer. So, I mean, this is the basic, this is the basic trick that we do in surface sense right to study surfaces. And then and then and then the physical properties are really, really depending on the amount of your slap thickness that you use and so on and so forth. Perfect. So Azima, you can you can ask your question. Okay, so my question is that your the surfaces you consider, did you consider a symmetric surfaces. Actually, you have dipole interactions of adjacent faces if the surfaces are not symmetric. Yeah, and if you didn't did you consider adding some dipole interaction corrections in your calculations. That's a very nice question. Actually I skipped it because I knew any expert would ask me. So actually what you see this, if you are not careful, we actually use symmetric surface you see the terminations are the same. The A is ended by cobalt 2 plus on both sides. This is true. And then we put enough vacuum and then on top of that, we put dipole correction. Why do we put dipole correction because we see the fact that there is an asymmetric. The asymmetry that is created by the fact that you fix some layers at the bottom. When you fix some layer ones are moving then this asymmetry is handled also by putting this dipole correction. So, thank you for the question we didn't want to go to polar surfaces. And so I have a follow up question. So in fixing some of the layers, did you also fix the final term that surface or you, you allowed the symmetric parts to relax in your. Okay, okay, okay. So this is, this is, I mean, okay, we didn't relax both part of the, so the top of the and no, we didn't do it because this technique is, I think it's more computationally demanding because if you do it, you need is, I mean, you need a considerable amount of bulk in the middle. And then for this you have to go to very large slabs to avoid it, we do only one side absorption and then play with the dipole correction. Okay, okay. All right. Thank you. We will continue all these discussions in actually in our discussion time. Let's let's move.