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  1. Kohn–Sham accuracy from orbital-free density functional theory via Δ-machine learning

    Kumar, Shashikant; Jing, Xin; Pask, John; ... - Journal of Chemical Physics
    Here, we present a Δ-machine learning model for obtaining Kohn–Sham accuracy from orbital-free density functional theory (DFT) calculations. In particular, we employ a machine-learned force field (MLFF) scheme based on the kernel method to capture the difference between Kohn–Sham and orbital-free DFT energies/forces. We implement this model in the context of on-the-fly molecular dynamics simulations and study its accuracy, performance, and sensitivity to parameters for representative systems. We find that the formalism not only improves the accuracy of Thomas–Fermi–von Weizsäcker orbital-free energies and forces by more than two orders of magnitude but is also more accurate than MLFFs based solelymore » on Kohn–Sham DFT while being more efficient and less sensitive to model parameters. We apply the framework to study the structure of molten Al0.88Si0.12, the results suggesting no aggregation of Si atoms, in agreement with a previous Kohn–Sham study performed at an order of magnitude smaller length and time scales.« less

  2. GDB-9-Ex_TD-DFT-PBE0: Dataset containing Time Dependent Density Functional Theory (TDDFT) calculations for organic molecules of the GDB-9-Ex dataset.

    Mehta, Kshitij; Lupo Pasini, Massimiliano; Irle, Stephan; ...
    This dataset contains data-intensive quantum chemical electronic structure calculations for 96,766 organic molecules of the GDB-9-Ex dataset. Calculations were performed using the Time Dependent Density Functional Theory (TDDFT) first principles method using the ORCA software. It provides UV-vis spectra calculations of molecules with a high level of accuracy. The optical spectra behavior was collected based on the optimized molecular geometries in the DFTB method with 3ob parameters. All calculations utilized the def2-TZVP basis sets with the auxiliary def2/J and def2-TZVP/C basis sets. The time-dependent density-functional theory (TDDFT) approach with the PBE0 exchange-correlation functional and ORCAs default integration grid was employed.more » For the excitation energy calculations, the lowest 50 excitation states were calculated.« less

  3. Defect-induced states, defect-induced phase transition, and excitonic states in bent tungsten disulfide (WS2) nanoribbons: Density functional vs. many body theory

    Neupane, Santosh; Tang, Hong; Ruzsinszky, Adrienn - Physical Review Materials
    Two-dimensional (2D) transition metal dichalcogenide (TMD) materials have versatile electronic and optical properties. TMD nanoribbons exhibit interesting properties due to reduced dimensionality, quantum confinement, and edge states, which make them suitable for various electronic and optoelectronic applications. In a previous work conducted by our group, we demonstrated that the edge bands evolved with bending can tune the optical properties for various widths of TMD nanoribbons. Defects are commonly present in 2D TMD materials, and can dramatically change the material properties. Here, in this following work, we investigate the interaction between the edge and the defect states in tungsten disulfide (WS2)more » nanoribbons with lines of W- or S-atom vacancies defects under different bending conditions, using density functional theory (DFT). To gain understanding about the limits of density functional approximations, we compare results on band gaps and energies of defect states with quasiparticle GW. We reveal interesting semiconductor-metal phase transitions, suggesting potential applications in nanoelectronics or molecular electronics. We also calculate the optical absorption of the bent and defective nanoribbons with the many-body GW-BSE (Bethe-Salpeter equation) approach, revealing a tunable optical spectrum and diverse exciton states in the defective WS2 nanoribbons.« less

  4. Discovery of Stable Surfaces with Extreme Work Functions by High‐Throughput Density Functional Theory and Machine Learning

    Schindler, Peter; Antoniuk, Evan; Cheon, Gowoon; ... - Advanced Functional Materials
    Abstract The work function is the key surface property that determines the energy required to extract an electron from the surface of a material. This property is crucial for thermionic energy conversion, band alignment in heterostructures, and electron emission devices. This work presents a high‐throughput workflow using density functional theory (DFT) to calculate the work function and cleavage energy of 33,631 slabs (58,332 work functions) that are created from 3,716 bulk materials. The number of calculated surface properties surpasses the previously largest database by a factor of ≈27. Several surfaces with an ultra‐low (<2 eV) and ultra‐high (>7 eV) workmore » function are identified. Specifically, the (100)‐Ba‐O surface of BaMoO 3 and the (001)‐F surface of Ag 2 F have record‐low (1.25 eV) and record‐high (9.06 eV) steady‐state work functions. Based on this database a physics‐based approach to featurize surfaces is utilized to predict the work function. The random forest model achieves a test mean absolute error (MAE) of 0.09 eV, comparable to the accuracy of DFT. This surrogate model enables rapid predictions of the work function (≈ 10 5 faster than DFT) across a vast chemical space and facilitates the discovery of material surfaces with extreme work functions for energy conversion and electronic device applications.« less

  5. A Study on the Role of Electric Field in Low-Temperature Plasma Catalytic Ammonia Synthesis via Integrated Density Functional Theory and Microkinetic Modeling

    Shao, Ketong; Mesbah, Ali - JACS Au
    Low-temperature plasma catalysis has shown promise for various chemical processes such as light hydrocarbon conversion, volatile organic compounds removal, and ammonia synthesis. Plasma-catalytic ammonia synthesis has the potential advantages of leveraging renewable energy and distributed manufacturing principles to mitigate the pressing environmental challenges of the energy-intensive Haber-Bosh process, towards sustainable ammonia production. However, lack of foundational understanding of plasma-catalyst interactions poses a key challenge to optimizing plasma-catalytic processes. Recent studies suggest electro- and photoeffects, such as electric field and charge, can play an important role in enhancing surface reactions. These studies mostly rely on using density functional theory (DFT) tomore » investigate surface reactions under these effects. However, integration of DFT with microkinetic modeling in plasma catalysis, which is crucial for establishing a comprehensive understanding of the interplay between the gas-phase chemistry and surface reactions, remains largely unexplored. This paper presents a first-principles framework coupling DFT calculations and microkinetic modeling to investigate the role of electric field on plasma-catalytic ammonia synthesis. The DFT-microkinetic model shows more consistent predictions with experimental observations, as compared to the case wherein the variable effects of plasma process parameters on surface reactions are neglected. In particular, predictions of the DFT-microkinetic model indicate electric field can have a notable effect on surface reactions relative to other process parameters. A global sensitivity analysis is performed to investigate how ammonia synthesis pathways will change in relation to different plasma process parameters. The DFT-microkinetic model is then used in conjunction with active learning to systematically explore the complex parameter space of the plasma-catalytic ammonia synthesis to maximize the amount of produced ammonia while inhibiting reactions dissipating energy, such as the recombination of H2 through gas-phase H radicals and surface-adsorbed H. This paper demonstrates the importance of accounting for the effects of electric field on surface reactions when investigating and optimizing the performance of plasma-catalytic processes.« less

  6. Spectral-partitioned Kohn-Sham density functional theory

    Sadigh, Babak; Åberg, Daniel; Pask, John - Physical Review. E
    Here we introduce a general, variational scheme for systematic approximation of a given Kohn-Sham free-energy functional by partitioning the density matrix into distinct spectral domains, each of which may be spanned by an independent diagonal representation without requirement of mutual orthogonality. It is shown that by generalizing the entropic contribution to the free energy to allow for independent representations in each spectral domain, the free energy becomes an upper bound to the exact (unpartitioned) Kohn-Sham free energy, attaining this limit as the representations approach Kohn-Sham eigenfunctions. A numerical procedure is devised for calculation of the generalized entropy associated with spectralmore » partitioning of the density matrix. The result is a powerful framework for Kohn-Sham calculations of systems whose occupied subspaces span multiple energy regimes. As a case in point, we apply the proposed framework to warm- and hot-dense matter described by finite-temperature density functional theory, where at high energies the density matrix is represented by that of the free-electron gas, while at low energies it is variationally optimized. We derive expressions for the spectral-partitioned Kohn-Sham Hamiltonian, atomic forces, and macroscopic stresses within the projector-augmented wave (PAW) and the norm-conserving pseudopotential methods. It is demonstrated that at high temperatures, spectral partitioning facilitates accurate calculations at dramatically reduced computational cost. Moreover, as temperature is increased, fewer exact Kohn-Sham states are required for a given accuracy, leading to further reductions in computational cost. Finally, it is shown that standard multiprojector expansions of electronic orbitals within atomic spheres in the PAW method lack sufficient completeness at high temperatures. Spectral partitioning provides a systematic solution for this fundamental problem.« less

  7. Binding of radionuclides and surrogate to 18-crown-6 ether by density functional theory

    Liu, Yuan; Ta, An; Park, Kyoung; ... - Microporous and Mesoporous Materials
    For this work, we use density functional theory to investigate the interactions of cerium, americium, and curium cations with crown ethers. Our calculations reveal that the modeled structure of cerium integrated within the crown ether is in good agreement with experimental data, with the negative binding energy indicating that capturing the cerium nitrates is thermodynamically favorable. Our results demonstrate that crown ethers can also bind americium and curium, providing insights into the potential applications of crown ether in radionuclide sequestration. Finally, we explore the impact of the skeleton modification of different crown ethers through by substitution of nitrogen atoms inmore » the core of the crown ether for oxygen atoms and find that this structural modification significantly increases the radionuclide binding energies. These findings provide insights on the potential for the use of organic linkers such as crown ethers to address the urgent needs in radionuclide sequestration, separation and sensing.« less

  8. Binding of uranyl cations to a Zr-based metal-organic framework by density functional theory

    Liu, Yuan; Ta, An; Pandey, Shubham; ... - Computational Materials Science
    Zr-based metal–organic frameworks (Zr-MOFs) have been widely used as ion adsorbents for the removal or extraction of toxic and/or radionuclide species from aqueous solutions. However, the mechanisms by which uranyl cations (UO22+) interact with Zr-MOFs have not been established. In this work, the nature of the bonding of uranyl cations with a Zr-MOF was determined using density functional theory for nineteen structurally distinct candidate complexes. Further, the results showed that in all cases the binding energy was of the order of 1.5 eV, but depended on the specific bonding site. The most stable structure involved coordination of the uranyl cationmore » and two structurally distinct oxygens in the Zr-MOF metal node. It was also found that higher degree of deprotonation in Zr-MOF correlated with higher binding energy between the Zr-MOF and uranyl cations. These insights can aid in the design of Zr-MOFs with optimized features for efficient capture of uranyl cations.« less

  9. Synthesis, characterization, and density functional theory investigation of (CH 6 N 3 ) 2 [NpO 2 Cl 3 ] and Rb[NpO 2 Cl 2 (H 2 O)] chain structures

    Rajapaksha, Harindu; Benthin, Grant; Markun, Emma; ... - Dalton Transactions
    The actinyl tetrachloro complex [An(V/VI)O2Cl4]2-/3- tends to form discrete molecular units in both solution and solid state materials, but related aquachloro complexes have been observed as both discrete coordination compounds and 1-D chain topologies. Subtle differences in the inner sphere coordination significantly influence the formation of structural topologies in the actinyl chloride system, but the exact reasoning for these variations has not been delineated. In the current study, we present the synthesis, structural characterization, and vibrational analysis of two 1-D neptunyl(V) chain compounds: (CH6N3)2[NpO2Cl3] (Np-Gua) and Rb[NpO2Cl2(H2O)] (Np-Rb). Bonding and non-covalent interactions (NCIs) in the systems were evaluated using periodicmore » Density Functional Theory (DFT) to link these properties to related phases. We observed ~6.5% and ~3.9% weakening of Np$$=$$O bonds in Np-Gua and Np-Rb compared to the reference Cs3[NpO2Cl4]. NCI analysis distinguished specific assembly modes, where Np-Gua was connected via hydrogen bonding (N-H...Cleq and N-H...Oyl) and Np-Rb contained both cation interactions (Rb+...Oyl and Rb+...Cleq) and hydrogen bonding (Oeq-H...Oyl) networks. Thermodynamically viable formation pathways for both compounds were explored using DFT methodology. The [NpO2Cl4](aq)3- and [NpO2Cl3(H2O)](aq)2- substructures were identified as precursors to Np-Gua and [NpO2Cl3(H2O)](aq)2- and [NpO2Cl2(H2O)2](aq)- were isolated as the primary building units of Np-Rb. Finally, we utilized DFT to analyze the vibrational modes for Np-Gua and Np-Rb, where we found evidence of the Np$$=$$O bond weakening within the Np(V) chain structures compared to [NpO2Cl4]3-.« less

  10. $$\mathrm{DRAGON}$$: A multi-GPU orbital-free density functional theory molecular dynamics simulation package for modeling of warm dense matter

    Mihaylov, Deyan; Hu, S.; Karasiev, Valentin - Computer Physics Communications
    As progress in electronic structure theoretical methods is made, ab initio molecular dynamics (MD) based on orbital-free density functional theory (OF-DFT) is becoming increasingly more successful at substituting the traditional, very accurate but computationally costly Kohn–Sham (KS) approach for simulations of matter at the challenging warm dense matter (WDM) regime. However, despite the significant cost alleviation of eliminating the dependence on the KS orbitals, OF-DFT MD runs require ~102 to 103 CPU cores running for days, or even weeks, for simulations of systems comprised of 102 to 103 atoms, depending on thermodynamic conditions. Here we present DRAGON, a multi-GPU OF-DFTmore » MD code for fast and efficient simulations of WDM. With a relatively small allocation of resources (4 to 8 GPU devices) it can provide an order of magnitude speedup for simulations containing $$\mathscr{O}$$(104) atoms and target systems composed of $$\mathscr{O}$$(105) atoms at conditions within the WDM regime, which is currently outside the capabilities of CPU codes.« less
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