Atomically thin, magnetic materials have recently gained a lot of attention in the field of two-dimensional (2D) materials. Single magnetic layers with critical temperature above room-temperature are extremely attractive for fundamental studies and could potentially be the basis for a new class of information storage. In order to shed light on the intriguing phenomena of 2D magnetism, we present theoretical investigations in the framework of the density functional theory (DFT) of the structural, electronic and optical properties of the layered material such as MnPS3, NiPS3 as well as a mixed systems MnxNi1-xPS3. These materials are important examples from the large family of transition metal phosphorus trisulfide (MPS3). We also discuss the influence of the substrate (graphene layer) on the properties of NiPS3 material. In this seminar we will answer important questions concerning 2D magnetic materials, such as: Can we probe the magnetic properties optically at the nanolevel scale?Is there a difference between 3D and 2D magnetism?Does the graphene layer affect NiPS3 properties?How to obtain ferromagnetic semiconductor from the antifferomagnetic material?
Zapraszamy do sali 1.03, ul. Pasteura 5 o godzinie 15:15
prof. dr hab. Adam Kubas (Institute of Physical Chemistry, Polish Academy of Sciences)
Polyene retinoids are an important class of biologically active molecules involved in many facets of human physiology. The geometric configurations of retinoids have enormous impact on their chemical and biological properties. For example the Z-isomeric form of retinal plays an important role as a chromophore of rod and cone photoreceptor cells in the visual cycle. Genetic or environmental factors affecting chromophore production can lead to diseases of the retina and eventually blindness. Pharmacological interventions by means of Z-isomers of retinal and retinyl acetate are used to maintain vision in inherited retinal degenerative disease [1].We recently developed three paths to access such biologically relevant 9-cis and 13-cis retinoid derivatives: (a) palladium-based catalytic approach [2], (b) direct monochromatic photoisomerisation [3] and (c) photocatalytic isomerization using iridium catalyst [3]. The single-step protocols are easily scalable and allows for gram-scale synthesis of the Z-isomers. However, depending on the method and the nature of all-trans substrate various distributions of Z-isomers were observed. To understand the distribution of the products we carried out extensive quantum chemical calculations [2,3]. Our multi-level approach include geometry optimizations at the density functional theory (DFT) level, single-point energy refinements at the local coupled-cluster level and excitation energies calculations at the (simplified) time-dependent DFT level. In the case of catalytic reaction we showed that the active catalyst exists in a dimeric form and the reaction proceeds via six-membered chair-like chloropalladate intermediate. We related the distribution of photochemical products with the relative energy ordering of the intermediates at the excited potential energy surface. In addition, we developed the “local polarization change” (LPC) model that explains photoisomerisation product distribution using only HOMO and LUMO atomic populations.[1] P. D. Kiser, K. Palczewski, Annu. Rev. Vis. Sci. 2, 197-234 (2016).space[2] S. Kahremany, A. Kubas, G. P. Tochtrop, K. Palczewski, Dalton Trans. 48, 10581 (2019).[3] S. Kahremany, C. L. Sander, G. P. Tochtrop, A. Kubas, K. Palczewski, Org. Biomol. Chem. accepted, DOI: 10.1039/C9OB01645G (2019).
Zapraszamy do sali 1.03, ul. Pasteura 5 o godzinie 15:15
dr Paweł Bączyk (IFT UW)
Modelling of isospin-symmetry-breaking (ISB) effects in atomic nuclei is a long-standing problem first tackled by Nolen and Schiffer in 1969. Since then, the interplay of electromagnetic and strong-force-rooted effects has been studied in many models. Our approach based on the Density Functional Theory (DFT) turns out to be very successful in this matter.During the seminar I will present how to reproduce binding energy differences of nuclei with N~Z in a broad range of masses (A=6-75) and what can we learn about the strong nuclear interaction using an effective theory. What is more, I will present calculations of nuclear structure and beta decay properties going beyond mean-field approximation.
Zapraszamy do sali 1.03, ul. Pasteura 5 o godzinie 15:15
dr Max P. Cooper (IFT UW)
When acid is injected into soluble rocks such as limestone channels,termed "wormholes", are formed due to a reaction-infiltrationinstability arising from heterogeneity within the rock. The continuedgrowth of the wormhole is controlled by the coupling of flow andgeometry of both the wormhole and pre-existing pores in the rock.Previous studies have attempted to capture the evolution of flow andgeometry in models, starting with initial pore geometry fromtomographic scans of rocks and compare the model output to scans ofthe acidize rock. This study steps back from modeling and directlyobserves the evolution of wormhole formation. Rock cores are subjectedto acid injection in a cell, with parameters such as injection rateand acid concentration are controlled. To observe evolution this cellis placed in a tomograph and scans are performed while the rock isbeing acidized. The evolution of the flow field is also captured byinjecting a contrasting agent such as potassium iodide or heavy waterwhen scanned with X-Ray or neutron tomography, respectively. Initialresults show wormhole growth is controlled by focused flow at the tipof the wormhole and the character of wormhole geometry is stronglycontrolled by the pore space.
Zapraszamy do sali 1.03, ul. Pasteura 5 o godzinie 15:15
DR Jacek Konieczny (Nauto, CA USA)
The lecture presents practical insights into training of Deep Neural Networks. We will start by introducing basic components of modern Artificial Neural Networks and explain why the training of such networks is not a trivial task. Next, we will discuss the most important approaches to training neural networks, including Stochastic Gradient Descent and Adam, show practical variants of the methods improving their performance and convergence time and discuss applicability of the methods. Finally, we will take a look into the most recent advances in the field of optimizing neural networks, including Circular Learning Rates, warm-up and Lookahead optimizer.
Zapraszamy do sali 1.03, ul. Pasteura 5 o godzinie 15:15
Jacek A. Majewski (IFT UW)