 First of all I would like to thank the organizers for the max price and also this opportunity to present my work. So I am working on metal organic interfaces and which are there in all organic electronic devices wherever there is a junction between the active organic layer and the metal electrode. And the charge injection across such an interface affects the overall efficiency of such devices. So we study such interfaces with density partial theory and today I would like to present the three systems I have worked on, Pentaxenon Aluminium 001, Coranoline on Silver 111 and then effects of doping of such an organic layer on metal. So I started my journey with Quantum Espresso with this system in 2013. So it is where I started. So experiments for this system was conducted by Dr. Luca Floriano and his group in Electra Synchrotron 3ST and he had performed read, XPS, Nexephys and STM instead I was simulating the results to compare with the experimental results. So I started with finding the most stable configuration for Pentaxenon Silver, sorry, Aluminium 001 and the high symmetry side stop hollow and bridge were considered and again bridge dash and hollow dash two additional ones that is bridge dash is obtained from bridge by rotating either the molecule or substrate by 90 degrees and hollow dash by rotating from hollow by 45 degrees and the interesting thing is that at bridge side the molecule is bent into a V shape and the same results is obtained also for hollow dash with apparent delta Z that is a high difference between the central and the edge carbon atom around 1.35 angstrom. The most stable site anyways remains the bridge site. So we were wondering what is this particular bending, what causes this kind of bending and the interesting fact is that it's the matching distance between the central carbon atoms C1 and C1 dash around 2.82 angstrom very much matching with the two aluminum atoms directly below these carbon atoms. So this constitutes pushes the molecule to deform and bond particularly at that V shape with an angle of around 155 and it's also important to note that without including van der Belz I was also calculating and it was not giving such a result. So these push interactions are really important in such a system. Here I have plotted the conchium orbitals of the gas phase V shape molecule and the planar molecule and what is the main result is homo-lumo gap has been produced by half an AV and there is an lumo plus two, lumo plus three exchange which we can see here just by the V shape bending because these are both gas phase. Now on the surface looking at the molecular orbital projected density of states the lumo is heavily hybridized and the main peak lies below the Fermi level at the bridge site. Instead of top site I have just shown this one because there is where the molecule is planar and the highest stable site where the molecule is planar. Then here the charge arrangements at the most stable site which clearly shows this kind of bonding between the two carbon atoms and the aluminum below where red color shows electron accumulation and blue electron depletion comparison between the XPS results for the experiment which is given by the dotted line and for calculation how I was doing is first I calculate the core level binding energy so subtracting the total energy of the gas of the ground state minus subtracted from the total energy of the system with the full core hole at one in equal of at each in equaling carbon atoms. So here pentasyn has six in equaling carbon atoms and so it was done for six times and then to calculate core level shift as a reference energy I was taking the weighted average of the binding energies. So the result is that I get six sticks which has been brought in by using pseudo void profile to get the final spectra and as we can see bridge site is in very good agreement with the experimental results. Coming to next surface so from next surface we can get two kinds of information that is the structural information and as well as some electronic information. So first of all I would like to say about the electronic information which is okay so first of all the top panel is the experimental one and the bottom panel is the simulated one. So I was simulating using X spectra code in quantum espresso using the transition potential approach. What we can see is the background the shaded one is the gas phase is that of the gas phase and here the dotted one is also the gas phase whereas the solid lines are adsorbed. Compared to the gas phase spectra both in experiment and theory this peak is missing. So the first part of the next surface which is so we know that in next surface what we see is we probe the unoccupied orbitals. So what first peak missing is because before in the MOPidos we saw that at bridge site the LUMO is filled and is below the Fermi level. So it's not present there as an unoccupied orbital anymore. So that is the reason why the first peak is missing in the adsorbed case. So this is the electronic information now coming to structural information. The blue curve is the P-polarization and the red dotted one is the S-polarization. So for a perfectly planar molecule for the S-polarization there should be zero pi star contributions. But instead we see in experiments some non-zero pi star contributions. So this indicates some kind of tilting of the molecule. In my calculation I have some non-zero contributions but not as much as in experiments. So because this non-zero contribution comes from just the V-shaped bending of the molecule. For this let us see the experimental conditions because it was very difficult to prepare the aluminum 001 very pure surface and so we were not able to obtain a very well-ordered monolayer. So from the read it was very strict defraction pattern. So a lot of step edges defects were present on the surface as seen also in the STM. This is STM of the uncovered terraces that after the molecule has been evaporated where we can see some molecule induced reconstruction. Shown by this golden lines. So no long range auto domains were detected. So this could be the reason why we have such a huge amount of pi star contribution in experiments. Finally, STM, simulated STM is given here for the bridge which is corresponding to the experimental image here with very, very good agreement. Also if you look at the line profile the V-shaped contributions also seen in the experiments so this is a very good agreement. So concluding this first part, Pendicin ourselves in V-shape and we see that the lumo is getting filled and this is resulting in the narrowing of the next surface peak. Next I would like to move on to the second system which is Coranulin on silver 111 and so Coranulin is called the Bucky Bowl because it can be obtained from the Bucky Bowl C60 by cutting the 20 top carbon atoms. So it has a pentagon in the middle surrounded by six hexagons. It's a curved molecule and usually one Coranulin bonds with another one like this so convex to concave coupling to maximize the pi-pi bonding. Instead on the surfaces on copper 111 for example it has been reported to absorb on one of the hexagons so in a tilted manner and on copper 110 it is absorbing shown here on one of the carbon carbon bonds of the central pentagon so always in a tilted way. So to study on silver 111 again the experiments were performed by Dr. Luca Floriano and what he was seeing was in scanning Coranulin microscopy the molecules were very mobile so it was very difficult to obtain the STM images however he was seeing income insurance and with the periodicity of around 3.6 and in the refraction pattern he obtained 3 by 3 periodicity as well as this circles which are equivalent to 3.6 periodicity. So however in simulations what we decided to do is we decided to calculate a 3 by 3 and a 4 by 4. So again using quantum as per so and I was as a calculator XPS and XSS to compare with experiments. So for the 4 by 4 we had a wealth of configurations to test because we were doing 3 tilt angles that is 0 degree pentagon 10 degree which is on the carbon carbon bond and 20 degree is one on the hexagon on the 4 high symmetry sites so resulting around 96 configurations instant for 3 by 3 because of steric hindrance we could the only possible confessions were 8 so we did all of these calculations and the most stable ones were 4 by 4 in all cases the molecule was falling flat in the sense that on the pentagon it's absorbing on the pentagon as and whereas on in the case of 4 by 4 in the case of 3 by 3 it was always absorbing on one of the hexagon so with the effective tilt angle. However going from 4 by 4 to 3 by 3 there was a gain of 9 millileve per angstrom square in energy. Now looking at the XPS what we can see is so these ones shown outside the graph is that of the gas phase because quarenoline has 3 in equaling carbon atoms and here is a plot between core level shift and carb height of carbon atom. In the case of 4 by 4 where the molecule is flat what we see is that the C1 C3 differs between the C1 C3 core level shift has reduced and going from flat to tilted so in the case of tilted you have these many dots because when you have a tilted you have the more number of inequality carbon atoms because I cut the molecule in this way and so the whole half of the molecule has been considered and we can see that the core level shift increases with increasing in height of the carbon atom from the surface this is because of the reduced screening as the top most carbon atoms are farthest from the surface so that was an interesting observation however the both the 3 by 3 and the 4 by 4 were giving more or less similar results with respect to the experimental core which is the blue one. Now coming to the XSS of such curved molecules so before I was telling that in the case of a flat molecule it's easier to get the structural information because one it's once it is pretty flat the Picer contributions are not there in a polarization instead in the case of K-curved molecule what happens is since it is already curved there's an intrinsic curvature which however gives some Picer contribution in this polarization so we should be careful while extracting for example tilt angle from such for such systems as shown here this is the next step is for a gas phase coranulin so for as in this position or also in the flat line question on the pentagon you can see that however there are non-zero contributions now while projecting the LUMO onto the PZP XY of the in equaling carbon atoms however we see that there is an average tilt angle of 20 degrees always present even if the molecule is flat now looking at the adsorbed next surface so the blue one is the experimental one and the green 4x4 and red 3x3 from experiments using store analysis they were extracting a tilt angle of 28 degrees whereas from my calculation the ones x the values extracted at 23 and 38 degrees but for 23 degrees means that beta that is the tilt angle of the central pentagon is zero which means that it's flat but with the intrinsic curvature so what does it mean this 20 degree in the experiments it could be it could be between these two cases that is it's neither 3x3 neither 4x4 but somewhere in the middle so the average tilt angle could be 20 degrees which is obtained from the previous graph for example here if you look at the 20 degree true tilt angle you get a value of around 20 a degree in the store analysis so controlling this part store analysis is extended also to the non-planar molecules and average tilt angle could be 20 degrees for this particular system and it's in commensurate around 3.6 periodicity. Now coming to the last part after talking about the organic molecular structural metal now I would also like to say about the doping effects of doping so we have an organic monolayer now what happens when you dope such a monolayer so you can dope in order to tune the energy level alignment of such interfaces doping of organic semiconductors is different from doping in organ semiconductors because in organic you have very low concentration like parts per million but in organic cases since the conductivity is already very low we have higher concentrations like even more or two atoms per molecule and it's a however completely different scenarios so here in my system PTC is the molecule and potassium is the donor so experiments were performed by the group of Frederick Shuler University professor Torsten Fritz and his group and they were performing STHM, LEED, DRS, NYXS, W and UPS. I was performing some of my calculations during my broad period in TU grads where I started with WASP but then on return to my home university I was continuing the post analysis using quantum espresso and YAMBO. So experimentally they were observing two most stable phases of potassium doped PTCD on silver so PTCDA which are given here so two potassium atoms per molecule and here around 3 potassium atoms so this was the starting point and I was I was calculating these systems with exactly these values measured by the experimentalist from STHM, clear STHM images so they were performing the STHM because by conventional STM they were not able to see the potassium atoms because the resolution is not very high but with STHM they were the first people to see or image the doped atoms started with the PTC on silver very very well known system PTCDA LUMO is at Fermi level and it's a very well studied system with PTCDA taking around more than almost two electrons from silver. So for K2 PTCDA I was simulating the exact cell obtained from the experiments and what we can see is unlike the PTCDA where the oxygen are bent towards the silver here the potassium is interacting with the oxygen and bending away from the silver surface. I also simulated the STM images and we can see it's imperfect matching with the STM as well as STHM where we can see these dots are the potassium atoms calculated absorption heights so these are the calculated and these are the experimental ones and we can see that the shaded ones are PTCDA before before doping so the oxygen are below and after doping as we can see the it has bent in the other direction in the U shape very good agreement with the experiments. Now the second doping stage was a little bit tricky because in the experiments they were seeing like around five dots however according to the deposition rate they were expecting three potassium atoms per molecule. However when I simulated this system what happened was the resulting structure was not what we were expecting as it was not what we were seeing in experimental results. So we were thinking since there are like five dots present maybe it's five potassium atoms and I simulated also five K5 PTCDA but then it happened that one of the potassium atoms started to go below the PTCDA by tilting and if there was a tilted PTCDA it would have been clearly visible on the experimental images so this is also not the case. Then I tried K4 PTCDA and the agreement was excellent so the result was that it is four Kp, four potassium atoms per PTCDA not three not five so the question is why or where does it come this central feature in these team images. Then there is the answer is that it is nothing but the loom of a K4 4 plus cluster which means that you have four potassium atoms arranged in such a manner and if such a cluster is charged with one positive one charge on each of them you have the loom of looking like this so it is nothing but in the center is accumulated charge density that is what the image what they imagine the experimental STM so in the STM it's nothing it's just seen as a blob also here but here instead for STHM it has it can be seen as five dots but the central dot is not a potassium atom. Coming to the electronic properties of the system so gas phase PTCDA is the first panel then the second panel is PTCDA on silver where the loom is at the Fermi level so its monolayer of PTCDA on silver shows a metallic character instead with two potassium atoms the loom is narrowed and shift below the Fermi level thereby we have a metal to semiconductor phase transition upon doping then for the doping that is the K4 PTCDA the loom of shifts for the below the Fermi level and it's the calculated density of states are in excellent agreement with the experimental UPS so here I was plotting the k-resol density of states projected onto the atomic wave functions belonging to the atoms of the molecule and what we can see here it is normalized to a one where the the most red colored represents the function which are localized at the molecule so in the first graph where PTCDA on silver we can see that the bands are heavily hybridized and heavy dispersion. Moving to K2 PTCDA it becomes more localized from the molecule which means that the hybridization has reduced so adding potassium it has somehow decoupled structurally and also electronically the molecule from the silver. Further K4 PTCDA we can see that the bands are almost flat that is dispersion has heavily reduced. Now this narrowing of the orbiters have also been seen in the optical spectra so here they have the experimental optical spectra and I have calculated the spectra by Yambo at the independent particle random phase approximation level and it's not quantitatively comparable but qualitatively we have captured all the main features which is the PTCDA on silver at the black curve has a single feature broad one instead the red curve has two peaks resolved and shifted to higher energy which is also here with two peaks shifted to higher energy and again the blue curve is narrower and shifted again to higher energy according to the increased potassium doping you have reduced hybridization with the silver. So concluding two stable doping stages were found for x equal to 2 and 4 and we found for the first doping stage a metal semiconductor phase transition of the organic layer and K atoms decoupled PTCDA both electronically and structurally from silver. So thank you for your attention and I would also like to thank Dr. Gouda Fratesi who was my supervisor at my PhD and also contributed to Quantum Espresso developing. Thank you.