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Layered materials that perform mixed electron and ion transport are promising for energy harvesting, water desalination, and bioinspired functionalities. These functionalities depend on the interaction between ionic and electronic charges...

Sublattice melting is the loss of order of one lattice component in binary or ternary ionic crystals upon increase in temperature. A related transition has been predicted in colloidal crystals. To understand the nature of this transition, we study delocalization in self-assembled, size asymmetric binary colloidal crystals using a generalized molecular dynamics model. Focusing on BCC lattices, we observe a smooth change from localized-to-delocalized interstitial particles for a variety of interaction strengths. Thermodynamic arguments, mainly the absence of a discontinuity in the heat capacity, suggest that the passage from localization-to-delocalization is continuous and not a phase transition. This change is enhanced by lattice vibrations, and the temperature of the onset of delocalization can be tuned by the strength of the interaction between the colloid species. Therefore, the localized and delocalized regimes of the sublattice are dominated by enthalpic and entropic driving forces, respectively. This work sets the stage for future studies of sublattice melting in colloidal systems with different stoichiometries and lattice types, and it provides insights into superionic materials, which have potential for application in energy storage technologies., Hector Lopez-Rios and Ali Ehlen contributed equally

The evolving nature of electricity production, transmission, and consumption necessitates an update to the IEEE's Reliability Test System (RTS), which was last modernized in 1996. The update presented here introduces a generation mix more representative of modern power systems, with the removal of several nuclear and oil-generating units and the addition of natural gas, wind, solar photovoltaics, concentrating solar power, and energy storage. The update includes assigning the test system a geographic location in the southwestern United States to enable the integration of spatio-temporally consistent wind, solar, and load data with forecasts. Additional updates include common RTS transmission modifications in published literature, definitions for reserve product requirements, and market simulation descriptions to enable benchmarking of multi-period power system scheduling problems. The final section presents example results from a production cost modeling simulation on the updated RTS system data.

Label-free in situ X-ray scattering from protein spherical nucleic acids (Pro-SNAs, consisting of protein cores densely functionalized with covalently bound DNA) was used to elucidate the enzymatic reaction pathway for the DNase I-induced degradation of DNA. Time-course small-angle X-ray scattering (SAXS) and gel electrophoresis reveal a two-state system with time-dependent populations of intact and fully degraded DNA in the Pro-SNAs. SAXS shows that in the fully degraded state, the DNA strands forming the outer shell of the Pro-SNA were completely digested. SAXS analysis of reactions with different Pro-SNA concentrations reveals a reaction pathway characterized by a slow, rate determining DNase I-Pro-SNA association, followed by rapid DNA hydrolysis. Molecular dynamics (MD) simulations provide the distributions of monovalent and divalent ions around the Pro-SNA, relevant to the activity of DNase I. Taken together, in situ SAXS in conjunction with MD simulations yield key mechanistic and structural insights into the interaction of DNA with DNase I. The approach presented here should prove invaluable in probing other enzyme-catalyzed reactions on the nanoscale.

Polydispersity and random sequences are ubiquitous features of polymers, and molecular dynamics simulations can help elucidate the impact of disorder in polymer systems. However, currently available packages for building polymer topologies do not enable the user to include randomness in a straightforward fashion. Here, we introduce Hoobas, a molecular builder package that easily handles polydispersity using a prototype-builder design pattern. This enables fast and easy building of systems comprised of thousands of distinct objects. It is written in the Python programming language, which ensures compatibility with a wide range of molecular dynamics packages and tools, as well as easy integration into most workflows.

Colloidal crystals formed by size-asymmetric binary particles co-assemble into a wide variety of colloidal compounds with lattices akin to ionic crystals. Recently, a transition from a compound phase with a sublattice of small particles to a metal-like phase in which the small particles are delocalized has been predicted computationally and observed experimentally. In this colloidal metallic phase, the small particles roam the crystal maintaining the integrity of the lattice of large particles, as electrons do in metals. A similar transition also occurs in superionic crystals, termed sublattice melting. Here, we use energetic principles and a generalized molecular dynamics model of a binary system of functionalized nanoparticles to analyze the transition to sublattice delocalization in different co-assembled crystal phases as a function of T, number of grafted chains on the small particles, and number ratio between the small and large particles $n_s$:$n_l$. We find that $n_s$:$n_l$ is the primary determinant of crystal type due to energetic interactions and interstitial site filling, while the number of grafted chains per small particle determines the stability of these crystals. We observe first-order sublattice delocalization transitions as T increases, in which the host lattice transforms from low- to high-symmetry crystal structures, including A20 to BCT to BCC, Ad to BCT to BCC, and BCC to BCC/FCC to FCC transitions and lattices. Analogous sublattice transitions driven primarily by lattice vibrations have been seen in some atomic materials exhibiting an insulator-metal transition also referred to as metallization. We also find minima in the lattice vibrations and diffusion coefficient of small particles as a function of $n_s$:$n_l$, indicating enhanced stability of certain crystal structures for $n_s$:$n_l$ values that form compounds., Comment: AE and HL-R contributed equally to this work

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Integration of large scale renewables into the electrical grid is currently one of the major challenges and priorities for many countries. The Government of India (GOI) has committed to install 175 GW renewable energy (RE) by 2022. Due to favorable policies, RE capacity in India recently exceeded 60 GW, overtaking hydropower as the second largest fleet. To assess the impact of large scale RE on the power system, three studies (one national and two regional) were undertaken jointly by the United States Agency for International Development (USAID) and the Ministry of Power (MOP), GOI. The studies used production cost models to simulate the Indian electricity system for each 15-minute time block of the year 2022 to understand potential future operational challenges and opportunities for more cost-effective integration. This paper is an abridged version of the national study titled, “Greening the Grid: Pathways to Integrate 175 Gigawatts of Renewable Energy into India’s Electric Grid, Vol. I — National Study” (June 2017). The study concluded that the integration of 175 GW of RE, equivalent to 370 TWh annual generation and 22% demand penetration, is achievable at 15-minute operational timescales with minimal RE curtailment. If the thermal fleet exploits their ramping capabilities and lower minimum generation levels, the Indian power system has sufficient flexibility to manage net load changes and RE forecast errors. Along with thermal fleet flexibility, the latent flexibility in hydroelectric generation is critical in maintaining system balance. The study analyzed integration strategies that may generate cost savings and lower RE curtailment. Coordinated scheduling across regional and national levels, which increases the size of the balancing areas, lowers RE curtailment and reduces annual production costs. Reducing the technical minimum of thermal plants has the biggest impact on reducing RE curtailment. The study’s implications to policy makers, planners, and regulators include coordinated transmission planning, better coordination among states for scheduling and dispatch, and incentives for system flexibility.

Author(s): Palchak, D; Cochran, J; Deshmukh, R; Ehlen, A; Soonee, S; Narasimhan, S; Joshi, M; McBennett, B; Milligan, M; Sreedharan, P; Chernyakhovskiy, I; Abhyankar, N | Abstract: The use of renewable energy (RE) sources, primarily wind and solar generation, is poised to grow significantly within the Indian power system. The Government of India has established an installed capacity target of 175 gigawatts (GW) RE by 2022 that includes 60 GW of wind and 100 GW of solar, up from current capacities of 29 GW wind and 9 GW solar. India’s contribution to global efforts on climate mitigation extends this ambition to 40% non-fossil-based generation capacity by 2030. Global experience demonstrates that power systems can integrate wind and solar at this scale; however, evidence-based planning is important to achieve wind and solar integration at least cost. The purpose of this analysis is to evaluate the operation of India’s power grid with 175 GW of RE in order to identify potential cost and operational concerns and actions needed to efficiently integrate this level of wind and solar generation.

Author(s): Palchak, D; Cochran, J; Deshmukh, R; Ehlen, A; Soonee, R; Narasimhan, S; Joshi, M; McBennett, B; Milligan, M; Sreedharan, P; Chernyakhovskiy, I; Abhyankar, N | Abstract: The use of renewable energy (RE) sources, primarily wind and solar generation, is poised to grow significantly within the Indian power system. The Government of India has established a target of 175 gigawatts (GW) of installed RE capacity by 2022, including 60 GW of wind and 100 GW of solar, up from 29 GW wind and 9 GW solar at the beginning of 2017. Using advanced weather and power system modeling made for this project, the study team is able to explore operational impacts of meeting India’s RE targets and identify actions that may be favorable for integration. Our primary tool is a detailed production cost model, which simulates optimal scheduling and dispatch of available generation in a future year (2022) by minimizing total production costs subject to physical, operational, and market constraints. Our team comprises a core group from the Power System Operation Corporation, Ltd. (POSOCO), which is the national grid operator (with representation from the National, Southern, and Western Regional Load Dispatch Centers) under Ministry of Power, National Renewable Energy Laboratory (NREL), and Lawrence Berkeley National Laboratory (Berkeley Lab), and a broader modeling team that includes Central Electricity Authority (CEA), POWERGRID (the central transmission utility, CTU), and State Load Dispatch Centers in Maharashtra, Gujarat, Tamil Nadu, Karnataka, Rajasthan, and Andhra Pradesh. Our model includes high-resolution wind and solar data (forecasts and actuals), unique properties for each generator, CEA/CTU’s anticipated buildout of the power system, and enforced state-to-state transmission flows. Assuming the fulfillment of current efforts to provide better access to the physical flexibility of the power system, we find that power system balancing with 100 GW of solar and 60 GW of wind is achievable at 15-minute operational timescales with minimal RE curtailment. This RE capacity meets 22% of total projected 2022 electricity consumption in India with annual RE curtailment of 1.4%, in line with experiences in other countries with significant RE penetrations (Bird et al. 2016). Changes to operational practice can further reduce the cost of operating the power system and reduce RE curtailment. Coordinating scheduling and dispatch over a broader area is the largest driver to reduce costs, saving INR 6300 crore (USD 980 million) annually when optimized regionally. Lowering minimum operating levels of coal plants (from 70% to 40%) is the biggest driver to reduce RE curtailment—from 3.5% down to 0.76%. In fact, this operating property is more influential than faster thermal generation ramp rates in lowering the projected levels of curtailment. While this study does not answer every question relevant to planning for India’s 2022 RE targets, it is an important step toward analyzing operational challenges and cost saving opportunities using state-of-the-art power system planning tools. Further analysis can build upon this basis to explore optimal renewable resource and intrastate transmission siting, system stability during contingencies, and the influence of total power system investment costs on customer tariffs.