Hello, A new project on the LCRC cluster has been requested. Please forward the information on to the LCRC Allocation sub-committee. Applicant's name: John J. Low Applicant's institution: ANL Applicant's division: CLS Project Name: Low-Emissivity-Coats Project title: Molecular Simulations of Low-Emissivity Coatings Associated funding: Other Systems: Science: Emissivity plays a crucial role in energy engineering. As a measure of how effective the surface of a material is to emit energy as thermal radiation becomes increasingly important in the context of functional building materials.[1] Typical buildings loose up to 30 % of energy through the building envelope.[1] Especially windows and glazings represent critical building components. To improve energy efficiency in buildings, energy saving windows are regarded as a promising and efficient strategy to save costs and reduce the heat loss. This can be achieved by low emissivity coatings. Advanced glazing coatings typically consist of one or more layer stacks[2,3,4]. The composition of a typical stack is illustrated in Scheme 1. In state of the art coatings, a high IR reflectance is achieved by using silver. While base and top layers govern the visible optical performance, seed and barrier layers are critical for the emissivity[3]. For the latter, metal oxides like ZnO, SnO2, or TiO2 are used.[5] Apart from the bulk material properties, the layer properties such as thickness and roughness affect the emissivity. Challenges for future developments are to increase the performance, reduce manufacturing cost and provide durability and stability over a wide range of conditions. New combinations of materials and different configurations are regarded as most promising approaches [1,3] Molecular modeling has become a powerful tool in product design because it allows to gain important insights at the atomistic level and to predict material properties efficiently. Ab initio methods have been used to calculate radiative properties and emissivity. These properties can be obtained by calculating the frequency dependent dielectric constant. In the work of Bao et al. [6], ab initio simulations on refractive properties of a semiconductor have been presented, and Avdoshenko et al. [7] have studied the influence of defects and disorder on the high-temperature emissivity of metal oxides. The role of adhesion in the context of emissivity has been discussed by Cornil et al. [5] who characterized the adhesion of silver and metal oxides at ab initio level. The goal of this study is to predict and screen the reflectance and emissivity of metal/metal oxide interfaces based on the frequency dependent dielectric constant and to characterize the adhesion of these interfaces. We will consider such metal/metal oxide combinations that are relevant for low emissivity coatings used in glass and solar heat collector industry. Density functional theory (DFT) calculations will be performed using Quantum Espresso [8] or Abinit [9]. Both software packages use a plane-wave pseudopotential approach and are suited to address questions involving solid state materials. References: [1] B. Jelle, S. Kalnæs, T. Gao, Low-emissivity materials for building applications: A state-of-the-art review and future research perspectives, Energy and Buildings, 96, 2015, 329-356. [2]J. Mohelnikova, 7 - Nanocoatings for architectural glass, In Woodhead Publishing Series in Metals and Surface Engineering, Woodhead Publishing, 2011, 182-202, Nanocoatings and Ultra-Thin Films [3]G. Ding and C. Clavero, Silver-Based Low-Emissivity Coating Technology for Energy- Saving Window Applications, Modern Technologies for Creating the Thin-film Systems and Coatings, Prof. N. Nikitenkov (Ed.), InTech, 2017, DOI:10.5772/67085. [4] J. Finley, PPG Industries, Inc. The future high performance Glazing in commercial buildings, 2008, Available from http://www.lehigh.edu/imi/teched/SolarWS/T6f_Finley.pdf [5] D. Cornil, H. Wiame, B. Lecomte, J. Cornil, and D. Beljonne, Which Oxide for Low-Emissivity Glasses? First-Principles Modeling of Silver Adhesion, ACS Applied Materials & Interfaces, 9 (21), 2017, 18346-18354 [6] H. Bao, X. Ruan, Ab initio calculations of thermal radiative properties: The semiconductor GaAs, International Journal of Heat and Mass Transfer, 53, 2010, 1308–1312 [7] S. M. Avdoshenko and A. Strachan, High-temperature emissivity of silica,zirconia and samaria from ab initio simulations: role of defects and disorder, Modelling Simul. Mater. Sci. Eng., 22, 2014, 075004 [8] Giannozzi, et al., QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials, J.Phys.:Condens.Matter, 21, 2009, 395502. [9] Gonze et al., ABINIT: First-principles approach to material and nanosystem properties, Computer Physics Communications. 180, 2009, 2582. Project description: As it is best practice, we will first carry out a convergence study to find suitable settings for the k-point grid and energy cut-offs. Metal/metal oxide interfaces will be geometry optimized, before calculating the frequency dependent dielectric constant. When investigating interfaces, the match of cell parameters of the different layers is a critical point. Either the cell size of the individual components needs to be scaled, or sufficiently large supercells need to be created to provide a reasonable fit. Following the latter approach leads to larger system sizes which are computationally more demanding, but the first approach can only be used, if the mismatch is only a few percent. For our studies, we will use the supercell approach, since it is generally applicable. Another aspect that needs to be evaluated is the surface plane. Different surface planes need to be evaluated to account for the polarity of the metal oxide surfaces. Also, we will ca lculate the work of adhesion as described by Cornil [5], as this has implications on the thickness of the metal layer which ultimately translates into reduced production costs. In the first part of the project, we will combine silver (Ag) as metal due to its industrial relevance for low-e coatings with several metal oxides that are typically used in the glass industry, i.e. ZnO, TiO2, ZrO2, and SnO2. Also, interfaces with MgO and NiO will be studied, as both oxides have been suggested as alternative seed layers to ZnO [10] because of their better lattice matching with Ag compared to ZnO. Figure 1 shows a possible Ag(200)/NiO(200) interface. In the second part of the project, the influence of the silver layer thickness on the properties will be investigated, because it is a critical factor concerning performance and cost. Three silver layer with varying thicknesses will be built and combined with two different metal oxides. The metal oxides will be chosen based on the results obtained in the first part. Finally, in the third part, ab initio molecular dynamics (AIMD) simulations will be performed to equilibrate three metal oxide/Ag interfaces at elevated temperatures to account for the temperature dependence of the spectral emissivity. This will allow studying the texture of the surfaces and the radiative properties under operating conditions. The metal oxides will be selected based on the results of the preceding parts. The computational effort of this study will be considerable. Ab initio simulations are fairly demanding since they take electronic effects into account in contrast to typical force-field based approaches. Geometry optimizations need to be performed for all systems of the first two parts, i.e. the various metal oxide/Ag combinations (6 combinations), surface planes of the metal oxides (2 surfaces per oxide), and different layer thicknesses of Ag (3 layer thicknesses combined with two metal oxides) which makes in total 18 systems. For the geometry optimized structures, the frequency dependent dielectric constant will be calculated and the work of adhesion which also involves simulations for the individual compounds (19 structures). A single point energy calculation of a 64 atom ZrO2 slab with a volume of 1700 Å^3 using a 5x5x1 k-point grid requires about 45 min on 16 cores. As explained above, the interface structures require large system sizes. An interface structure of ZrO2( 111)/Ag(111) with a cell depths of 4 and 5 for ZrO2 and Ag, respectively, contains about 300 atoms. Including a vacuum space of 20 Å, the cell volume is about 10,000 Å3. For calculating adhesion, 19 simulations will be needed which are expected to take about 2000 CPU hours, In order to geometry optimize the structures, which is computationally more demanding than single-point calculations as it involves several optimization cycles, we estimate about 65,000 CPU hours. For calculating radiative properties of the optimized structure, which is somewhat more demanding than pure energy calculations, about 20,000 CPU hours will be needed. In addition to that, we plan to carry out three AIMD simulations over 10 ps. An AIMD simulation of 6 atoms in a 70 Å^3 cell at the Γ point with a simulation time of 0.1 ps takes about 30 min on 8 cores using QuantumEspresso. Assuming a nearly ideal scaling behavior, 170,000 core hours would be needed for three AIMD simulations of interface str uctures like ZrO2(111)/Ag(111) containing 300 atoms in a 10,000 Å^3 cell at the Γ point. In total, the project is expected to take 265,000 CPU hours. We believe that the study will be valuable for designing optimized low-e coatings and provide important insights for applications in glass and solar industry. References [10] P. Ries, Silver thin films : improving the efficiency of low-E coatings by employing different seed layers, Aachen, Techn. Hochsch., Diss., 2015. Industry partnership: This colloboration with Scienomics. Scienomics was established in 2004 and with selected partnerships with the best-of-the-breed (e.g.: Sandia National Labs, Max Planck Institute, Fraunhofer Institute, University of Illinois, Demokritos, University of Shanghai), Scienomics’s MAPS platform offers a unique and powerful blend of multiscale and multiparadigm modeling and simulation modules. With high quality science and industrial solution oriented applied research, Scienomics has garnered collaborative projects with companies in the areas of energy and green chemistry, alternate fuels, catalysis, polymers, biodefense, auto exhaust, etc. This collaboration encourages the use of high performance computing in industry and should lead to future collaborations with other industries. Project URL: Requested allocation: 265000 Q1: 66250 Q2: 66250 Q3: 66250 Q4: 66250 Justification: Storage requirements: The requester has used undetermined amount hours of their initial startup project. In addition to approving an initial amount, please specify a Category and Subcategory for this project. For a list of the current selection of approved categories, please see: https://wiki.lcrc.anl.gov/wiki/Processes/Categories Once the Allocation committee has approved the project, please go to the Project Management page to create it: https://accounts.lcrc.anl.gov/projects.php Thank You, The LCRC Accounts System