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: Alper Kinaci Applicant's institution: ANL Applicant's division: NST Project Name: VO2_conductivity Project title: First principles studies of electronic transport properties in Vanadium Dioxide Associated funding: This work is funded by a work-for-other proposal sponsored by the Toyota Motor Engineering & Manufacturing North America (TEMA). Other Systems: Carbon cluster at the Center for Nanoscale Materials, rapid access proposal pending. Science: Metal to insulator transition (MIT) is an intriguing phenomenon that may be facilitated by electron localization, carrier doping and electron-phonon coupling. The localization effects can be introduced via disorder (Anderson transition) [1] imposing a strong random potential or strong Coulomb (Mott–Hubbard transition) [2] repulsion between electrons. Electron-phonon coupling (Peierls transition) [3] also contributes to the opening of a band gap by periodic lattice distortion. Since in many systems, the MIT is accompanied by phase transformation, the primary cause of the change in conductivity (i.e. Mott–Hubbard or Peierls) is elusive [4]. Vanadium dioxide, VO2, is one of the appealing materials due to its near room temperature (T-MIT=340 K) transformation from monoclinic insulating phase to metallic rutile phase as temperature is increased [5]. Above the transition temperature, the electronic conductivity dramatically increases by several orders of magnitude [6]. According Wiedemann-Franz law, the MIT also affects the electronic contribution to the thermal conductivity. As a consequence, the electronic thermal conductivity of VO2 also increases when the temperature reaches the transformation temperature. Thus, near room temperature switching is possible for not only electronic but also thermal conductivity. These properties open many opportunities for device applications by tuning various ambient parameters. The switching can be induced by electric field [7-9], photons [10, 11] and pressure [12]. The structural transformation of vanadium dioxide also results in significant changes in its optical properties which can be manipulated to produce thermochromic windows [13] around ambient temperature. By using different dopants and alloying elements, it is possible to manipulate MIT phenomena in strongly correlated systems. Suppression of transition, changing T-MIT, phase separation and structural modification are some outcomes of doping and alloying [14-17]. In this project, we will analyze the effect of alloying/doping elements on the structure and the conductivity of VO2 in both conductive and insulating phases. For this purpose, density functional theory (DFT) calculations along with Boltzmann transport equation (BTE) will be employed. To model these strongly correlated systems, performance of DFT calculations with different exchange-correlation functionals will be tested. [1] P. W. Anderson, Phys. Rev. 109, 1492 (1958). [2] N. F. Mott, “Metal-Insulator Transitions” (Taylor and Francis, London 1990). [3] G. Gruner, Rev. Mod. Phys. 60 1129 (1988). [4] A. Perucchi, L. Baldassarre, P. Postorino and S. Lupi, J. Phys.: Condens. Matter 21, 323202 (2009). [5] R. M. Wentzcovitch, W. W. Schulz and P. B. Allen, Phys. Rev. Lett. 72, 3389 (1994). [6] F. J. Morin, Phys. Rev. Lett. 3, 34 (1959). [7] D. Ruzmetov, G. Gopalakrishnan, C. Ko, V. Narayanamurti, and S. Ramanathan, J. Appl. Phys. 107, 114516 (2010). [8] H.-T. Kim, B.-G. Chae, D.-H. Youn, G. Kim, K.-Y. Kang, S.-J. Lee, K. Kim, and Y.-S. Lim, Appl. Phys. Lett. 86 242101 (2005). [9] Nakano, M., Shibuya, K., Okuyama, D., Hatano, T., Ono, S., Kawasaki, M., Iwasa, Y. & Tokura, Nature 487, 459 (2012). [10] M. Nakajima, N. Takubo, Z. Hiroi, Y. Ueda, and T. Suemoto, Appl. Phys. Lett. 92, 011907 (2008). [11] A. Cavalleri, Th. Dekorsy, H. H. W. Chong, J. C. Kieffer, and R. W. Schoenlein, Phys. Rev. B 70, 161102(R) (2004). [12] E. Arcangeletti, L. Baldassarre, D. Di Castro, S. Lupi, L. Malavasi, C. Marini, A. Perucchi, and P. Postorino, Phys. Rev. Lett. 98, 196406 (2007). [13] H. Kakiuchida, P. Jin, M. Tazawa, Sol. Energ. Mat. Sol. C. 92, 1279 (2008). [14] C. Marini, E. Arcangeletti, D. Di Castro, L. Baldassare, A. Perucchi, S. Lupi, L. Malavasi, L. Boeri, E. Pomjakushina, K. Conder, and P. Postorino, Phys. Rev. B 77, 235111 (2008). [15] K. Shibuya, M. Kawasaki, and Y. Tokura, Phys. Rev. B 82, 205118 (2010). [16] K. W. Kim, J. S. Lee, and T. W. Noh, S. R. Lee and K. Char, Phys. Rev. B 71, 125104 (2005). [17] R. Shabna, P. M. Sarun, S. Vinu, A. Biju and U. Syamaprasad, Supercond. Sci. Technol. 22, 045016 (2009). Project description: Density functional theory calculations will be performed using the plane wave code VASP. Boltzmann transport equation calculations will be performed with the BoltzTraP code. (1) We will test DFT with semilocal, and hybrid functionals, as well as DFT+U method for VO2. A direct or indirect comparison with the experimental data is necessary to choose the most appropriate method for the next step. Since there is indication that the density of states (DOS) at the Fermi level for the metallic state near a MIT is related to the conductivity, we will investigate the validity of using the DOS as a proxy for electronic conductivity. (2) With the appropriate calculation method available, the next step is to model the electronic conductivity of MIT material with dopants. Different dopants can differ significantly in the following properties: a. Vary the electrical conductivity compared to the parent material. b. Solubility in the parent material. c. Induce structural changes after doping. Initially 5 different transition metals (Ti, Cr, Zr, Nb, Mo) will be evaluated for their solubility and substitutional defect formation energies. Thermodynamic analysis will be carried out to ensure phase stability of the doped compound. The deformation of the lattice will also be inspected. To study smaller dopant concentrations, 2x2x2 or 3x3x3 supercells will be used. (3) To further corroborate the results, BTE calculations will be performed using experimental relaxation times to estimate the electrical conductivity in pristine structure evaluated with different methods. The electronic transport in doped structures will also be investigated using BTE. The DFT calculations will be performed using the plane wave DFT code VASP. The code is tested in Blues with a 350 electron system and 65%-80% scaling efficiency is obtained 64 to 128 cores compared to 16 cores. In Fusion where the code has been tested for systems having up to 7000 electrons, the code showed 70%-80% scaling efficiency for 64 to 128 cores compared to 8 cores. Given this performance, the VASP code has the efficiency to simulate large number configurations in reasonable amount of time. Based on the previous experience on Fusion, the time estimates for each item are listed below. BoltzTraP is a serial code and only 1 core will be used for each calculation. The total time required for the 1 core simulations are estimated to be 2.5% of all requested time. The time estimates for the various parts above, based on benchmark results with VASP, are listed below. 1) Testing different functionals and U parameters on VO2: 100,000 core hours (include testing of various convergence parameters) 2) Doping studies: 250,000 core hours (5 TM species * 4 compositions * 10 atomic configurations * 1250 core-hours) 3) Boltzmann transport calculations: a- 40,000 core hours (increased k-point density for Boltzmann transport calculations). b- 10,000 core hours (BoltzTraP calculations). The total requested time is 400,000 core-hours. Dr. Alper Kinaci and Dr. Maria Chan will be responsible for carrying out the simulations. Industry partnership: The project is funded by TEMA and is part of an ongoing partnership between Argonne and Toyota in the experimental and computational investigations of novel ways to control thermal transport. Project URL: Requested allocation: 400000 Q1: 100000 Q2: 150000 Q3: 100000 Q4: 50000 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