Toward Realistic DFT Description of Complex Systems: Ethylene Epoxidation on Ag-Cu Alloys and RPA Correlation in van der Waals Molecules

In this thesis we have studied two different aspects of Density Functional Theory (DFT): (i) the application of DFT with the generalized gradient approximation (GGA) functional for exchange-correlation energy in modeling an heterogeneous catalysis problem, and (ii) the development of a new self-consistent field (scf) strategy to solve the Kohn-Sham (KS) equations that allows to improve the accuracy of DFT method with exact exchange (EXX) and RPA correlation energy functionals in the description of weak chemical interactions. Ethylene epoxidation, one of the largest-scale catalytic processes in the chemical industry, were studied in Chapter 2 of this thesis. The formation of the desired product ethylene oxide (EO) in this reaction is promoted by a Ag-Cu alloy catalyst. In this study, the oxidation of ethylene is considered to occur on the Ag-Cu structures formed by thin copper-oxide layers on an Ag slab. These structures have been determined by theoretical and experimental works to be the favorable structures on the surfaces of Ag-Cu alloys in the high pressure and temperature conditions relevant to experiment. According to the calculations for reaction pathways, we found that the structures of Ag-Cu alloys are selective towards the formation of the EO final product, rather than the undesired product acetaldehyde (Ac) which is readily converted to carbon dioxide. The selectivity of Ag-Cu alloys is found to be higher than pure Ag, in agreement with experimental results. To do this, we carried out a study of the stability of the surface structures in thermodynamic equilibrium conditions ( at T = 600 K and pO2 = 1 atm), and we have shown that the higher selectivities relate to the formation of copper-oxide layers on the Ag slab. Moreover, our theoretical results show that the high selectivity of a copperoxide layer is maintained even when the thickness of the oxide is increased to two layers. In particular, we have found that a very high selectivity could be obtained by structure containing 1.25 ML of Cu and 0.25 ML of sub-surface oxygen. Another important result is the finding of a selectivity indicator that allows to determine the selectivity of the pure metals and alloy catalysts even with the thin oxide structures in ethylene epoxidation reaction. In further works, this indicator could be applied to predict the selectivity of other Ag-based alloys such as Ag-Pd, Ag-Pt, etc. These alloys were found experimentally to be selective catalysts towards the formation of EO. In spite of the great success of DFT when employing the well-known approximations such as LDA or GGA exchange-correlation functionals, the standard DFT approaches exhibit several serious shortcomings, and one of them is the poor or even wrong evaluation of long-range dispersion interactions (i.e., van der Waals interactions). Calculations with the EXX/RPA-correlation energy within the adiabatic connection uctuation-dissipation theorem (ACFDT) formalism have shown as a promising approach that can give the correct description not only of weak bonds but also of systems with covalent bonds. In Chapter 3, we developed the complete scf procedure that enables the optimization of KS systems whose total energy is computed with the EXX/RPA-correlation energy functionals. The implementation has been applied to the study of some simple molecules. In future work, EXX/RPA calculations could be applied to heterogeneous catalysis systems, where the role of van der Waals interactions is still largely unknown. Moreover, improvement of the accuracy of EXX/RPA calculations is also needed. According to ACFDT, one can go beyond the RPA formalism by taking into account higher-level approximations of the exchange-correlation kernel in the Dyson equation such as the time-dependent EXX kernel

Column tessellations

A new class of random spatial tessellations is introduced -- the so-called column tessellations of three-dimensional space. The construction is based on a stationary planar tessellation. Each cell of the spatial tessellation is a prism whose base facet is congruent to a cell of the planar tessellation. Thus intensities, topological and metric mean values of the spatial tessellation can be calculated by suitably chosen parameters of the planar tessellation. A column tessellation is not facet-to-facet.Comment: 18 pages, 3 figure

Stressors and Coping Styles Among Chronic Hemodialysis Patients in Vietnam

The purpose of this study was to understand stressors experienced and coping styles used by 30 hemodialysis patients in Vietnam and to examine the relationship among stressors, coping styles, and demographics (age, gender, and length of treatment). A quantitative, cross-sectional, descriptive study was conducted. Data collection took place in a government hospital in Ho Chi Minh City. The hospital has 60 hemodialysis machines. The hemodialysis department serves 450 scheduled hemodialysis patients and 60 emergency cases per day. Stressors were divided into two groups: physical and psychosocial. Differences between physical and psychosocial stressors were obtained by dividing raw subscale scores by the number of items in the scale. The mean psychosocial stressor score was higher (1.23) than the mean physical stressor score (1.02). The most frequent stressors were limitation of fluid (1.7), decrease in social life (1.57), limitation of food (1.57), and sleep disturbances (1.57). The least reported stressors were reversal in family roles with the children (.27), fear of being alone (.73), reversal with spouse (.77), and frequent hospitalization (.77). The most common coping style used was emotive and the least common was evasive. The most common coping method used by hemodialysis patients was “Told yourself not to worry because everything would work out fine.” “Told yourself the problem was someone else’s fault” was the least common coping method used. End stage renal disease necessitating hemodialysis could have a significant impact on patients’ quality of life. It is important for hemodialysis providers to understand the stressors these patients experience and the coping methods they use to manage these stressors. Providing sufficient education prior to initiating hemodialysis treatment is an important part of helping patients to manage their stress. The more patients understand about their disease and the impact hemodialysis treatment would have on their lives the more their stress could be managed. Education could specifically be targeted to help patients manage changes to diet, sleep, and their social lives

Predicting League of Legends Ranked Games Outcome

League of Legends (LoL) is the one of most popular multiplayer online battle arena (MOBA) games in the world. For LoL, the most competitive way to evaluate a player’s skill level, below the professional Esports level, is competitive ranked games. These ranked games utilize a matchmaking system based on the player’s ranks to form a fair team for each game. However, a rank game\u27s outcome cannot necessarily be predicted using just players’ ranks, there are a significant number of different variables impacting a rank game depending on how well each team plays. In this paper, I propose a method to predict rank game outcomes based on several different variables that would be collected 14minutes into the games. Using three different machine learning algorithms: Logistic Regression, Random Forest, and Support Vector Machine, I found that game outcomes can be predicted with 79.46% accuracy with all the collected data and newly added variables. I also use the model to show the importance of each variable in helping players make winning decisions. The results show that the difference in gold between the two teams has the most impact on the final result of the games. The skill difference in the three groups can be further examined with extra variables that were not explored during the study

Koopmans-compliant spectral functionals for extended systems

Koopmans-compliant functionals have been shown to provide accurate spectral properties for molecular systems; this accuracy is driven by the generalized linearization condition imposed on each charged excitation - i.e. on changing the occupation of any orbital in the system, while accounting for screening and relaxation from all other electrons. In this work we discuss the theoretical formulation and the practical implementation of this formalism to the case of extended systems, where a third condition, the localization of Koopmans' orbitals, proves crucial to reach seamlessly the thermodynamic limit. We illustrate the formalism by first studying one-dimensional molecular systems of increasing length. Then, we consider the band gaps of 30 paradigmatic solid-state test cases, for which accurate experimental and computational results are available. The results are found to be comparable with the state-of-the-art in diagrammatic techniques (self-consistent many-body perturbation theory with vertex corrections), notably using just a functional formulation for spectral properties and the physics of the generalized-gradient approximation; when ionization potentials are compared, the results are roughly twice as accurate.Comment: 9 pages, 3 figures, 1 supporting informatio

Screening in orbital-density-dependent functionals

Electronic-structure functionals that include screening effects, such as Hubbard or Koopmans' functionals, require to describe the response of a system to the fractional addition or removal of an electron from an orbital or a manifold. Here, we present a general method to incorporate screening based on linear-response theory, and we apply it to the case of the orbital-by-orbital screening of Koopmans' functionals. We illustrate the importance of such generalization when dealing with challenging systems containing orbitals with very different chemical character, also highlighting the simple dependence of the screening on the localization of the orbitals. We choose a set of 46 transition-metal complexes for which experimental data and accurate many-body perturbation theory calculations are available. When compared to experiment, results for ionization potentials show a very good performance with a mean absolute error of $~0.2$ eV, comparable to the most accurate many-body perturbation theory approaches. These results reiterate the role of Koopmans' compliant functionals as simple and accurate quasiparticle approximations to the exact spectral functional, bypassing diagrammatic expansions and relying only on the physics of the local density or generalized-gradient approximation

Management current land use of perennial industrial crops by NDVI index: A case study in Chu Se District, Gia Lai Province, Vietnam: Research article

Remote sensing and Geographic Information System (GIS) - an effective tool for managing naturalresources, is quite common application in establishing thematic maps. However, the application of this modern technology in natural resource management has not yet been popular in Vietnam, particularly mapping the land use/cover. Currently, land use/cover map is constructed as traditional methods and gets limitations of management counting due to time-consuming for mapping andsynthesis the status of land use/cover. Hence, information on the map is often outdated and inaccurate.The main objective of this study is to upgrade the accuracies in mapping current perennialcrops in Chu Se District, Gia Lai Province in Vietnam by interpreted NDVI index (Normalized Difference Vegetation Index) from Landsat 8-OLI (Operational Land Imager). The results of studyis satisfied the urgent of practical requirement and scientific research. There are 3 types of perennial industrial plants in the study area including rubber, coffee, and pepper, in which most coffee isgrown, with an area of over 10,000 hectares. The results also show that integration of remote sensing and GIS technology enables to map current management and distribution of perennial industrialplants timely and accurately. This application is fully consistent with the trend of the world, and in accordance with regulations of established land use/cover map, and the process could be appliedat other districts /towns or in higher administrative units.Viễn thám và hệ thông tin địa lý (GIS) là công cụ hữu hiệu để quản lý tài nguyên thiên nhiên, được ứng dụng khá phổ biến để thành lập các loại bản đồ. Tuy nhiên, việc áp dụng công nghệ hiện đại này trong lĩnh vực quản lý tài nguyên thiên nhiên ở Việt Nam chưa phổ biến, nhất là công tác xây dựng bản đồ hiện trạng sử dụng/độ phủ đất. Việc xây dựng bản đồ hiện trạng hiện nay vẫn theo phương pháp truyền thống, thường gặp nhiều hạn chế do thời gian tổng hợp và xây dựng bản đồ hiện trạng kéo dài, dẫn đến thông tin trên bản đồ bị lạc hậu và không chính xác. Mục tiêu chính của nghiên cứu này là nâng cao độ chính xác kết quả giải đoán ảnh viễn thám Landsat 8 bằng chỉ số NDVI (chỉ số khác biệt thực vật) để thành lập bản đồ hiện trạng sử dụng đất cây công nghiệp lâu năm ở huyện Chư Sê, tỉnh Gia Lai, Việt Nam. Từ đó quản lý hiện trạng sử dụng loại đất này phù hợp yêu cầu cấp bách thực tiễn sản xuất và nghiên cứu khoa học. Kết quả của nghiên cứu cho thấy có 3 loại hình cây công nghiệp trên địa bàn nghiên cứu gồm cây cao su, cà phê và hồ tiêu, trong đó cây cà phê được trồng nhiều nhất, với diện tích hơn 10.000 ha. Nghiên cứu cũng cho thấy, tích hợp công nghệ viễn thám và GIS cho phép quản lý hiện trạng và phân bố cây công nghiệp trong không gian một cách hiệu quả và nhanh chóng. Ứng dụng này hoàn toàn phù hợp với xu hướng của thế giới, đồng thời theo đúng quy định thành lập bản đồ hiện trạng sử dụng đất, và quy trình này có thể thực hiện được ở cấp huyện/thị xã hoặc đơn vị hành chính cấp cao hơn

Asymptotic integration of linear differential-algebraic equations

Abstract. This paper is concerned with the asymptotic behavior of solutions of lin-ear differential-algebraic equations with asymptotically constant coefficients. Some re-sults of asymptotic integration which are well known for ordinary differential equations (ODEs) are extended to differential-algebraic equations (DAEs)

Column tessellations and birth-time distributions of weighted polytopes in STIT tessellations

Das Ziel dieser Arbeit ist die Untersuchung einiger Modelle von zufälligen Mosaiken. Zu diesem Zweck wird zunächst ein neues Modell, das kein flächentreues zufälliges Mosaik im Raum ist, eingeführt – das sogenannte Column Mosaik. Die räumliche Konstruktion basiert auf einem stationären zufälligen ebenen Mosaik mit konvexen polygonalen Zellen. Zu jeder polygonalen Zelle bilden wir einen unendlichen Zylinder, der senkrecht zu der Ebene, die das ebene Mosaik enthält, ist. Jeder Zylinder wird in Zellen des räumlichen Mosaiks durch Schnitte, die zu dieser Ebene parallel sind, unterteilt. Jede räumliche Zelle ist ein gerades Prisma, dessen Grundfläche kongruent zu einer Zelle des ebenen Mosaiks ist. Somit können die Merkmale des resultierenden zufälligen räumlichen Mosaiks, nämlich Intensitäten, topologische/innere Parameter und metrische Mittelwerte von Längen, Flächen und Volumen, aus geeignet gewählten Parametern des zugrundeliegenden zufälligen ebenen Mosaiks berechnet werden. Analoge Merkmale werden für Stratum Mosaike bestimmt. Danach führen wir markierte Poissonsche Hyperebenenprozesse ein. Dieser markierte Prozess erzeugt ein entsprechendes markiertes Poissonsches Hyperebenenmosaik. Die Verteilungen der Lebenszeit und der teilenden Hyperebene eines Objekts im Prozess der markierten Poissonschen Hyperebenenprozesse werden berechnet. Außerdem untersuchen wir die Unabhängigkeit zwischen einem gewichteten Objekt und seinem entsprechenden Geburtszeit-Vektor. Eine Beziehung zwischen Poissonschen Hyperebenenprozessen und STIT Mosaiken wird ebenfalls vorgestellt. Zum Schluss behandeln wir die k-dimensionalen gewichteten maximalen Polytope eines STIT Mosaiks, wobei die inneren Volumina die Gewichte darstellen. Ein k-dimensionales maximales Polytop des STIT Mosaiks ist der Durchschnitt von (d-k) maximalen Polytopen der Dimension (d-1). Im Hinblick auf die räumlich-zeitliche Konstruktion von STIT Mosaiken hat jedes dieser (d-k) Polytope eine wohldefinierte zufällige Geburtszeit. Die gemeinsame Verteilung der Geburtszeiten dieser (d-k) maximalen Polytope wird berechnet und verwendet, um die Wahrscheinlichkeit, dass ein gewisses typisches maximales Segment eine feste Anzahl von inneren Knoten enthält, zu bestimmen