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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Properties of Medium Nuclei from First Principles

During this project we have extended the Auxiliary Field Diffusion Monte Carlo (AFDMC) to calculate several properties of light/medium nuclei. In particular, we have included and tested several models of three-body forces and the associated approximations required, and the comparison with other exact calculations for simpler problems demonstrated the accuracy of the AFDMC method. In this project we have also developed new subroutines to solve for the ground-state of open shell nuclei. This case requires very complex wave function with respect to the case of closed-shell nuclei. We have used the AFDMC code to calculate many properties of nuclei up to the Oxygen, including energies, radii, spatial and momentum distributions and others.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Diffusion Models to Construct a First Principles Multipole-Based Cable Braid Model for Conducting Wires in the Time Domain

We describe here diffusion models apt to construct a multipole-based, cable braid time domain model for conducting wires. Implementation details of both a ladder network valid for time-domain signals with all frequency content and an approximate single-stage circuit valid for low-frequency dominated time signals (such as electromagnetic pulses) are reported. This time domain model can be leveraged to treat system-generated electromagnetic pulse events, as well as used to further confirm the correctness of the multipole-based, cable braid frequency domain model.

42 ENGINEERING↗
DOE OSTI2021

Towards Realistic Models of Heterogeneous Catalysis: Simulations of Oxidation Catalysis from First Principles

Among the most significant developments in heterogeneous catalysis in the last 20 years is the emergence of microkinetic models, often parameterized from density functional theory (DFT) calculations, used to quantify observed catalyst performance and to guide the discovery of new catalytic materials. While DFT directly reports binding energies and elementary step activation energies, the free energies that enter into microkinetic models must be computed from additional approximations. Frequently these free energy approximations assume ideal behavior—that adsorbates do not interact with one another, or that adsorbates are immobile or vibrate harmonically about a binding site. These assumptions can and do have an impact on predicted catalyst performance and potentially even on predicted trends. Our work relates to three categories of non-idealities, explored in the context of nitrogen oxidation and reduction catalysis on metal surfaces. One component relates to adsorbate translational free energy, the contribution least well described by conventional models, in which we develop modeling approaches that improve accuracy with limited increase in computational expense. A second component relates adsorbate-adsorbate interactions, in which we develop benchmark on-lattice interaction models and compare kinetic predictions with conventional mean-field models, in an effort to develop more robust coverage-dependent mean field modeling approaches. The last relates the most fundamental assumption of all—that of energy equipartition—in an effort to rationalize and guide plasma-enhanced catalysis.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2021

First-principles Studies of Tritium Species Formation on and Desorption from Surfaces of $γ- LiAlO_2$ Pellets with Related Secondary Phase

The $γ- LiAlO_2$ ceramics enriched with the $^6Li$ isotope are used in the form of annular pellets in tritium-producing burnable absorber rods (TPBARs). When irradiated in a pressurized water reactor (PWR), the $^6Li$ absorbs neutrons, simulating the nuclear characteristics of a burnable absorber rod, and produces tritium $(_{1}^{3}H, T)$. Once the $_{1}^{3}H$ is produced in the bulk of $γ- LiAlO_2$, it diffuses to its surface, forming different $_{1}^{3}H$ species (possibly $T, OT, T_2, or T_2O$). The $T_2O$ is expected to be generated from experiment, to avoid $_{1}^{3}H$ leakage. However, up to now, it is still not clear which $_{1}^{3}H$ species are formed on the $γ- LiAlO_2$ surface and travel to the getter. Besides, with the dramatic Li loss under irradiation, the secondary phase (possibly $LiAl_5O_8$) precipitates and participates into the $_{1}^{3}H$ diffusivity and $_{1}^{3}H$ species formation. Therefore, exploring $_{1}^{3}H$ species formation on and desorption from surfaces of $γ- LiAlO_2$ with related secondary phases becomes a very important task to provide a better understanding of $_{1}^{3}H$H species escaping from pellets.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

First-principles Search for Compact Optical Materials [Slides]

Optoelectronics can increase speed and efficiency of information technology. There is a need to miniaturize components below the difrraction limit. Computational pre-screening increases the speed of materials discovery. Factors that must be accounting for beyond raw performance are material stability, cost, and environmental impact.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Structure of the Pion and Kaon from First-Principles Calculation in Lattice QCD

I outline recent developments in lattice QCD that enable the computation of the x-dependent Parton Distribution Functions, and then present recent calculations of the valence PDF of the pion by the HadStruct collaboration. I describe the challenges and opportunities to compute the gluon and sea-quark contributions to meson structure, and how such lattice calculations can form a key part of the physics goals of the EIC.

Richards, David↗
DOE OSTI2023

Energy Frontier Research Centers: Center for the Computational Design of Functional Layered Materials (CCDM) August 1, 2014 - July 31, 2018; Center for Complex Materials from First Principles (CCM) August 1, 2018 - July 31, 2021 (Final Report)

The mission of the DOE Energy Frontier Research Centers CCDM (2014-2018) and CCM (2018-2021) was to theoretically develop, computationally apply, and experimentally validate electronic structure methods for all materials, with a focus on the complex materials, especially layered and two-dimensional materials, strongly-correlated materials, and liquid water. This was achieved by over 200 published journal articles authored by about 17 senior investigators from physics and chemistry and from theory, computation, and experiment, plus their collaborators. In particular, the Centers confirmed the predictive power of the SCAN (strongly constrained and appropriately normed) density functional, which was constructed to satisfy 17 known exact constraints and several appropriate norms. Without being fitted to real bonded systems, and at a modest computational cost, SCAN correctly predicted covalent, ionic, metallic, hydrogen, and van der Waals bonds in many challenging materials. SCAN gave an improved description of defects in semiconductors, surface properties of metals, seven phases of ice, liquid water, liquid and supercooled silicon, subtle structural distortions in ferroelectrics, formation energies and structural predictions for solids, and critical pressures for structural phase transitions. Perhaps most remarkably, SCAN correctly described some strongly-correlated materials that were previously believed to be beyond the reach of density-functional approximations. SCAN is the only density functional that correctly predicts the band gap closing under chemical doping of the cuprate high-temperature superconducting materials. SCAN also predicts a landscape of competing stripe and magnetic phases in the cuprates. For some materials with some codes, SCAN has convergence problems that are greatly reduced by the CCM-developed r 2 SCAN, without loss of accuracy or rigor. SCAN and r 2 SCAN still make some self-interaction error, which is greatly reduced by the CCDM/ CCM-developed local orbital scaling correction (LOSC). These Centers further proved that the fundamental energy gaps of a solid from an orbital energy difference and from total energy differences are the same for a large class of generalized Kohn-Sham (GKS) functionals, including SCAN and standard hybrid functionals, and that symmetry breaking arises when a dynamic density fluctuation drops to zero frequency. The Centers identified new mechanisms for catalysis in layered materials with ions intercalated between the layers, investigated charge density waves both in model systems and in real layered materials, studied changes of band gap with the number of layers, and explored topological ultrathin films, bent nanoribbons, and defects.

08 HYDROGEN↗