 Restrictions are being progressively lifted, but I mean we are a few tens of people so let's try to be continue to be careful okay, so while enjoying being together, but Careful as carefully as possible Okay, so So the first talk I would like just to introduce some of the philosophy and what we are going to do for next days I mean, what is the goal of the school? Of course the goal of the school cannot be to to transform you in in advanced users of the code and And interrogations about to give you tools and ideas of what to do next Because actually the word of where YAMBO is is working is the giant word of material science and And So the first thing to understand is the tool you you are going to use is something that's been developed along the years for a specific Mission, so why is there and what is more importantly is that after so much coding and so much development the code itself is a Big thing. I mean it's a super monster super tool Complicated with 200 variables and so on and so forth. How do I use it? And so you have to master? First of all the equations that are coded in the code. This is very important. This is something that at me personally I think is the most important part of the story Yes, because actually at the end of the story you have different Communities acting in the word of material science and this is something you realize when you start working in it because if you have Physics so theoretical physics and applications Above this there is the entire world of codes and in recent years Computational physics and even computational theory. So sometimes as a tradition That I've been working from the farm and I've done for so many years I found myself studying the theory of GPUs or theory of theory of linear algebra these kind of things That I never imagined I had to study this is because things have changed So actually you have several actors in this material science and there are traditions There are the runners the guys that run the computer codes trying to get data compared with the experiment and that are the experimentalists and Of course with different. I don't know sure many of you had to fight with the experimentalist and In general at the beginning you spend like six months create a common language. I mean giving same meaning the same words This is very instructive and So thread of physics is something that even if may appear far from the final application Is the real engine of all the story and this is something that we will go through Doing several lectures. So Pedro for example after me will give first lecture about many body This is actually the engine what drives everything. So when you run yambo yambo is just running and solving me that many body equations and Then if you know exactly which kind of equations are solved that you don't know what is the meaning of the variables You don't know absolutely how to set up the variables and in general you most probably you will get garbage you will get numbers, but And and the problem actually of many body is as simple as complicated You have a system of particles of bodies. So those bodies can be anything I mean it can be elections or can be even more advanced stuff and in general they are interacting through a potential The the bad thing of many bodies that is potentially is long range. It's not short range being long range is almost impossible to solve Exactly. So you have to use tricks and there are two main tricks. We are I Mean that are used by by by yambo is density functional theory in many body So they are completely different theories with different approximations and different goals, but there are two pillars So you have DFT and many body So in DFT you actually want to write exactly the ground state problem with many bindings that you want to write exactly the excited state problem And then and then you will see in practice. What doesn't mean all this at the end of the story You get a scheme that is the one Yambo is based on where density function theory is the starting point So you first do a DFT calculation You get the basis of your of your system in practice Actually, you write your emiltonian you were right your emiltonian You start from an emiltonia that is complicated. You have no idea how to solve it. You say, okay Take a second. I Rewrite it using DFT in a mean field class correction and at that point you apply many body The good thing is that you include already some part of the problem you don't know how to solve correlation part in DFT and The price the price to pay instead is that you have to all many body machinery and so on and so forth But in addition as you have started from a density function theory calculation, you are parameter free So your calculation is for silicon for gamma arsenide for the nanotube for the surface for whatever So when you run DFT, you actually create an emiltonia that is specific to your system All the calculations will be done after a specific that system So the numbers you get if correct can be compared to the experiment Now the tools we are going to use are just at the beginning of a lot of a lot there So if you go back to theoretical physics, you know that depending on the experiment you want to study You need to understand which one is the right tool theoretical tool So we will go back to this in a moment But I mean a very mind and many body is I know at the bottom of the ladder because above this there is Non-equilibrium Gibbs function theory. There is a mean field theory and so on and so forth So it depends on what you need to calculate to choose the right the right theory And then we have this last actor entered in the in the in the story that is computational physics Computational science because at the beginning Yumbo was written by me doing my my my PhD. So it was doing my PhD and I started writing yumbo And then it was possible at that time, you know, you write your personal piece of code Then for some reason you decided to push it more and then Potentially you can get after a long evolution After lots of people entering there in developments. You can get something that is stable and and used But the point is that if along the years you create different Applications of the code the point is that you have to oh, sorry. This is I want to tell yes The point is that yes, I want to tell you after but it doesn't matter The point is that you have to find yourself with the fact that the code has to run on machines And this is something that it is a problem for you. It was not a problem for me I mean all my first papers were done on a PC running on a on a UMPC The point is that now instead the materials have increasing complexity and the machines where the code run Increasing complexity. So when you now code and use the code, it's not enough to know the code But it's also important to know how to run it on specific machines So for example, if you want to run, I remember very well that the The first version of yumbo when it was ported for the first time on a eb Supercomputer yambo was not even compiling Not even compiling and after compiling it was giving out a number for months We didn't know what was going on and it was terrible because those machines are very complicated and and they require fine-tuning That sometimes is as important as the coding itself So this means that we will try to give you also some some elemental concepts about Parallel Simulations and also about the more recent event of GPUs graphic cards and so on and so forth Sorry, this is back so last thing I want to tell you is that Yumbo has grown enormously along the years. So what it makes me really Epiode that is that apart from the several developers. We have a different project We managed to create also a user infrastructure So there is a form there is a wiki page with instructions and all this is needed because we really do lots of schools So this is a series of schools that we did in in secum. I forgot to put a t-shirt Okay, there is a t-shirt. I have the t-shirt. I will use it in the next lecture and And lots of schools. So really lots of schools along the years We did tens of schools and next week I will be in Congo in King Shasa to do a school about Yumbo So we are we really travel all over the world and this is really important and it's enriching for us because we met students and We had the opportunity to see what are the problems of the students and how Yumbo eventually can help in science because this is at the key of The school you have to see whether Yumbo can help you Are they're using or other learning how it works and then you have to select the Applications the field and the tool that that the better fits your needs now and now the most important part of the story is How you move from From your unknowledge for lack of knowledge to the knowledge What is the path because at the end of the story you want to get an interpretation a spectrum number something I don't know. Maybe you are interested. I don't know what are your interests at the same point I think that we will maybe we will have chance to discuss it. I don't know in the ring your PhD Your boss told you that there is to interpret the absorption spectrum of a surface to see the effect of the adzopate on the surface if there are peaks moving appearing or not appearing and Sometimes you have a lack enough you have been an experiment to compare with but in general is an observable It can be I don't know our piss I'm gonna resolve for the mission spectrum or x-ray for the mission spectrum or I don't know a temperature a critical temperature a conductivity Can be anything and the point is that okay? How do I calculate this thing? How do I get it and this is the the the the the road you have to take you have the simulation at the end You want to reach this point, but this is at the end of a procedure Because you have the physical phenomenon That is what you have to calculate First you need to understand how do I calculate this physical phenomenon? I mean if it is absorption, you need the response function if it is band structure I'm gonna solve for the mission spectrum. You need the single-part degrees function. There are different objects So you need to understand what is the? Microscopic variable inside the theory that gives what you need Then you have to understand how to calculate this thing I mean if you write on a piece of paper the response function it contains at least two integrals from minus infinity to plus infinity and Outwardly, I mean you need to calculate other you get a model and you get the solution exactly analytically or you need to find a way to Actually implemented numerically Even when is implemented numerically, that's not enough because you have to simulate So you have to understand what? how and where to run it and all this different steps of course are not exact You cannot if you can get exactly What is the object you need to calculate in general you cannot get exactly the theory for that? You cannot get exactly the form for that and you cannot get exactly the numerical implementation You need to find approximations at all the level of the procedure and The quality of the number will produce is Exactly the sum of the quality of the approximations so if any of you for example is interested in the arpus of of Corporates Were in general you see a bar bands. Yumbo cannot give a bar bands Because of the approximation inside the theory we used so you need to go to something else How do you implement this tool or you know? We had to find a way this was done along the years I mean yumbo got more and more tools more and more extensions to calculate more and more stuff Now An example is if you need to calculate absorption there are lectures and references for laughter lot like mother interaction is petroscopy and then Depending on the the theory you are interested in you can use many body that's defunctional and so on and so forth and Then the numeric implementation The numerical implementation can require it the study of how to discretize equations and how to use numerical methods So it's a lot there This is really important So at the end of this week I will be happy if with the umbo you will understand that there is a procedure There is need to study and to get details of what you want to calculate in order to produce Reasonable and meaningful number at the end. Okay, very quickly at every school There is someone asking where is the logo of yambo coming from is from the collaboration from the time where I was working In my my postdoc and meet also was there we were working together and actually it was To do this paper. I was drawing lots of vacuum polarization diagrams So I was really I could really dream them during the night I was in the blackboard everywhere with this vacuum polarization diagrams in Mirtha Seeing all those dagons so that they could translate it in an oyster. So an oyster the oyster yambo is a vacuum polarization diagram And that's all thank you very much other questions. Yeah step by step Yes, I can get you So we have very different types of code in the market these days Yeah, yambo is one of them like you want to solve a specific problem Does it mean they have to read about the theory of all these codes before I start thinking of okay? Which problem particular problem to solve? Well, it depends. It depends. I mean you are you have to have a control. I Mean if now you go by said I don't want to study and then I want to calculate absorption of leading fluoride Then you can find somehow on the web the input files of leading fluoride And then you will ask yambo to give you the input file to do the absorption you will get 20 parameters This is the minimal mode If you increase the verbose you will get 50 parameters and so what? You don't know the numbers you don't know the values you can guess But you don't know so at the end of the story to do a calculation You need to connect what you are calculating with the theory with the object you want to calculate Then of course if now I tell you a response function or even worse I tell you this function is defined on the kelvish contour. You have no idea. What is the kelvish contour? You have to go back The point and the things you need to study It is a matter of experience Of course, there are a series of lectures that are essential to understand the thing But then while the computer runs, maybe you can keep keep studying more more you study and more you have control And control is knowledge Voice coming from yeah, just a second because that we cannot hear you very well hybrid schools Hello It's a number that zoom and my motor bus or volume and also So let me understand if I just the property you say that when you run yambo you can use your personal PC But to do our research in for a specific materials you may need More resources is it right did I get it right? Yes, this is a big problem I totally understand with you. This is one of the biggest problem now in in the extension material science Two parts of the world where there are not so many computational resources. This is a gap to be filled But a gap to be filled. I perfectly know and but but there is still room For lots of work in the sense that me personally most of the papers I did at the beginning were run on a PC I mean, they were not super computers. It's true that science was different But still today it is possible. I mean 90% of the runs to be familiar with yambo can be run on a laptop There is no need of super computers It is true that at the end if you decide to do research on a nanostructure on a big Nanostructure on a surface or a nanotube on whatever with lots of atoms or heavy atoms You need a super computer or you need a machine with lots of memory I totally and agree with you in the case where you need to do a simulation on a large Material and you are in a developing country. There is a big gap still when I think a CDP is working They have an institute in Rwanda in Kigali and partially is providing with Computational resources to students of course this cannot be done for anyone, but things are honestly changing Kubeya, can you unmute yourself? No, it's not muted. Sorry. Can you can you try again? Okay, so clear This actually It's not the right question. I mean the sense that you need to find Can you repeat the questions for the question is what are the the pros in using yambo compared to other codes? Why why should they use yambo? Absolutely You have to find a tool that better fits with your research. If it is yambo, we are happy Otherwise, not a big problem at the moment at doing this school You have to consider yambo as a tool to study the the the procedure to get to the final Observable what we have done in yambo along the heroes is to create as much as possible a user friendly Code so an example. There are tiny examples I mean one example is that for example, I am very bad in memory So I cannot remember things by earth in a way. So yambo is able to create input file itself But this is this is a user pro in the sense that you don't have to go through a Long list of variables to create your input file then is GPU ported and and and heavily paralyzed, but I mean those are technical details that actually Don't decide exactly the code to use So you have to decide the answer to find the answer this question So there are of course many abinishokots around but most of them are focused on DFT density functional theory Instead there are fewer focused on many body perturbation theory. I like yambo is so this also one big difference Okay