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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Leveraging a Neural Network-Enhanced Reproducing Kernel Particle Method for Multiphysics Degradation Modeling of Energy Storage Materials

Energy storage materials exhibit strong electro-chemo-mechanical coupling and highly anisotropic material properties, contributing to the formation and propagation of micro-cracking during charge/discharge cycling and resulting in reduced performance and service life. A coupled electro-chemo-mechanical reproducing kernel particle method (RKPM) formulation has been developed to analyze this system. With microstructural images supplied by the National Renewable Energy Laboratory (NREL), pixel-based model construction by RKPM is used to represent the complex material microstructures that dictate the coupled physics of these systems. Traditional electro-chemo-mechanical models rely on mesh-based finite element methods, which can lead to difficulties in meshing such complex geometries and capturing crack propagation due to mesh dependency. Here, a neural network-enhanced reproducing kernel particle method (NN-RKPM) [1, 2] is introduced to effectively model damage and crack propagation in the material microstructures; the location, orientation, and solution transition near a localization are automatically captured by superimposed block-level NN optimizations. This NN enrichment approach allows for effective modeling of localizations via a fixed background discretization, relieving tedious efforts for adaptive refinement in traditional mesh-based methods. Applications to the heterogeneous microstructures of Li-ion battery cathodes will be presented to demonstrate the effectiveness of the proposed methods. NN-RKPM is additionally used to inform how crack opening and closure in turn affect the coupled chemical equations and material microstructure. Reference: [1] Baek, J., Chen, J. S., Susuki, K., "Neural Network enhanced Reproducing Kernel Particle Method for Modeling Localizations," International Journal for Numerical Methods in Engineering, Vol. 123, pp 4422-4454, https://doi.org/10.1002/nme.7040, 2022. [2] Baek, J., Chen, J. S., "A Neural Network-Based Enrichment of Reproducing Kernel Approximation for Modeling Brittle Fracture", Computer Methods in Applied Mechanics and Engineering Vol. 410, 116590, 2024.

degradation↗
DOE OSTI2014

How to remove the spurious resonances from ring polymer molecular dynamics

Two of the most successful methods that are presently available for simulating the quantum dynamics of condensed phase systems are centroid molecular dynamics (CMD) and ring polymer molecular dynamics (RPMD). Despite their conceptual differences, practical implementations of these methods differ in just two respects: the choice of the Parrinello-Rahman mass matrix and whether or not a thermostat is applied to the internal modes of the ring polymer during the dynamics. Here, we explore a method which is halfway between the two approximations: we keep the path integral bead masses equal to the physical particle masses but attach a Langevin thermostat to the internal modes of the ring polymer during the dynamics. We justify this by showing analytically that the inclusion of an internal mode thermostat does not affect any of the established features of RPMD: thermostatted RPMD is equally valid with respect to everything that has actually been proven about the method as RPMD itself. In particular, because of the choice of bead masses, the resulting method is still optimum in the short-time limit, and the transition state approximation to its reaction rate theory remains closely related to the semiclassical instanton approximation in the deep quantum tunneling regime. In effect, there is a continuous family of methods with these properties, parameterised by the strength of the Langevin friction. Here, we explore numerically how the approximation to quantum dynamics depends on this friction, with a particular emphasis on vibrational spectroscopy. We find that a broad range of frictions approaching optimal damping give similar results, and that these results are immune to both the resonance problem of RPMD and the curvature problem of CMD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

First-principles investigation of the thermo-physical properties of Ca{sub 3}Si{sub 4}

The first-principles calculations were applied to investigate the thermo-physical properties of Ca{sub 3}Si{sub 4} compound with increasing pressure. Those properties are based on density functional theory (DFT) method within the generalized gradient approximation (GGA) and local density approximation (LDA) for exchange and correlation. The optimized lattice constant and formation enthalpy are in good agreement with the experimental data and other theoretical data available. The calculated band structures confirm that Ca{sub 3}Si{sub 4} is a semiconductor with an indirect band gap of 0.363 eV (GGA) and 0.311 eV (LDA) at 0 GPa, and the calculated band gap decreased with the increasing pressure. The elastic constants, elastic anisotropy, elastic moduli and Poisson's ratio of Ca{sub 3}Si{sub 4} have also been obtained under high pressures. The Debye temperature, heat capacity, coefficient of thermal expansion and Grueneisen parameter have also been calculated in the quasiharmonic Debye model. - Graphical abstract: The Partial Density of States and Band Structure of Ca{sub 3}Si{sub 4}. Highlights: Black-Right-Pointing-Pointer The thermo-physical properties of Ca{sub 3}Si{sub 4} have been investigated. Black-Right-Pointing-Pointer Ca{sub 3}Si{sub 4} is a semiconductor with an indirect band gap. Black-Right-Pointing-Pointer The mechanical properties of Ca{sub 3}Si{sub 4} have been studied. Black-Right-Pointing-Pointer The heat capacity and thermal expansion have been obtained.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

The Fourth-Order Symmetry Energy of Finite Nuclei

The fourth-order symmetry energy E{sub sym,4}(A) of heavy nuclei is investigated based on the Skyrme energy density functional in combination with a local density approximation. Unlike some previous works, in our method, the interferences from the other energy terms are removed since it is completely isolated from the rest of energy terms. The calculated E{sub sym,4}(A) is much less than that extracted from nuclear masses. The underlying reason for the big difference is discussed. The Brueckner theory also gives a small fourth-order symmetry energy coefficient of nuclear matter, which is also different from recent conclusions with another methods.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Mapping Thermal Conductivity at the Atomic Scale: A Step toward the Thermal Design of Materials

We describe a spatial decomposition of the thermal conductivity, termed site-projected thermal conductivity, which quantifies the thermal conduction activity at each atomic site—a critical parameter for the thermal design of materials. The method is based on the Green–Kubo formula and the harmonic approximation and requires the force-constant and dynamical matrices, as well as a relaxed structural model. Throughout the study, it uses high quality models previously tested and compared to many experiments. It discusses the method and underlying approximations for amorphous silicon, carries the detailed analysis for amorphous silicon, and then examines an amorphous-crystal silicon interface and representative carbon materials. This study identifies the sites and local structures that reduce heat transport, and quantify these (estimate the spatial range) over which these “thermal defects” are effective. It identifies filamentary structures in the amorphous silicon network which impact heat transport and electronic structure (the Urbach edge) and electronic transport.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Half-metallicity and stability of the rock salt BaC and SrC (111) surfaces: A density functional study

The electronic structure and magnetic properties of relaxed (111) surfaces of the alkaline-earth monocarbides BaC and SrC in the stable rock salt structure, are calculated on the basis of first principle density functional theory within the framework of self-consistent field plane wave pseudo-potential method, using the generalized gradient approximation for the exchange-correlation functional. The results of this study reveal that the C-terminated (111) surfaces retain the bulk half-metallic property in both BaC and SrC. The half-metallicity of the C-terminated BaC surface is found to be more robust compared to the bulk BaC due to the larger half-metallic energy gap. In contrast, the half-metallic energy gap of the C-terminated SrC surface is found to be smaller than that of the bulk. The Ba-terminated surface of BaC and the Sr-terminated surface of SrC, however, lose their bulk half-metallicity due to the formation of surface states in the majority spin band gap. The calculations also show that the atomic magnetic moments at the half-metallic C-terminated surfaces in both BaC and SrC increase considerably with respect to the corresponding bulk values, which is explained in terms of an increase in the number of unpaired 2p electrons of the carbon atom at the surface. We also discuss the stability of the surfaces via the calculated bulk formation energies. The bulk formation energies for both BaC and SrC in the rock salt structure are found to be positive, which indicate that the surfaces are not stable at normal pressure and temperature conditions, and non-equilibrium growth techniques may be required for the realization of BaC and SrC thin films.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Half-Metallic and Half-Semiconductor Gaps in Cr-Based Chalcogenides: DFT + U Calculations

Using full-potential linear-augmented plane waves plus local orbitals (FP-LAPW) method, within the generalized gradient approximation (GGA) and GGA + U (Hubbard Coulomb onsite correction) as well as the modified Becke-Johnson approach (mBJ-GGA and mBJ-GGA + U), we have carried out a systematic investigation of the structural, electronic, and magnetic properties of CrS, CrSe, and CrTe compounds in two competing phases: the zinc-blende (ZB) and wurtzite (WZ) structures. We obtained half-metallic (HM) gaps of 1.35 (2.32), 1.65 (2.49), and 1.52 (1.80) for the CrS, CrSe, and CrTe compounds, respectively, in the ZB phase within the GGA + U (mBJ-GGA + U) approach. The HM gaps are 1.78, 2.11, and 1.53 for CrS, CrSe, and CrTe compounds, respectively, in the WZ phase using the GGA + U. Notably, the CrSe and CrTe using the mBJ-GGA + U approach are a half-semiconductor (HSC) in the WZ phase. The HSC gaps are 0.94 and 0.25 eV for CrSe and CrTe compounds, respectively, while CrS has a HM gap of 2.30 eV. We observed a HSC-to-HM transition for the CrSe and CrTe crystal structures on application of strain. The CrS, CrSe, and CrTe compounds have a total magnetic moment of 4.0 µ{sub B} per formula unit with the magnetization predominantly from the Cr ion. The main features observed from the density of states and strain evolution should motivate further experimental exploration on the possible application of the CrS, CrSe, and CrTe compounds for spintronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Vibrational frequency scaling factors for correlation consistent basis sets and the methods CC2 and MP2 and their spin-scaled SCS and SOS variants

We present scaling factors for vibrational frequencies calculated within the harmonic approximation and the correlated wave-function methods coupled cluster singles and doubles model (CC2) and Møller-Plesset perturbation theory (MP2) with and without a spin-component scaling (SCS or spin-opposite scaling (SOS)). Frequency scaling factors and the remaining deviations from the reference data are evaluated for several non-augmented basis sets of the cc-pVXZ family of generally contracted correlation-consistent basis sets as well as for the segmented contracted TZVPP basis. We find that the SCS and SOS variants of CC2 and MP2 lead to a slightly better accuracy for the scaled vibrational frequencies. The determined frequency scaling factors can also be used for vibrational frequencies calculated for excited states through response theory with CC2 and the algebraic diagrammatic construction through second order and their spin-component scaled variants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Particle acceleration and energy conservation in particle in cell simulations

Particle acceleration is a process of great importance in all areas of plasma physics. In most cases, kinetic effects are dominant and require a full kinetic treatment, such as the particle in cell (PIC) method. PIC methods are widely used in all aspects of plasma physics, proving to be a precious and irreplaceable tool. Yet all methods in use and published conserve energy to a good approximation, but not exactly. A well known property of PIC methods, documented extensively in all textbooks, is that energy is not conserved exactly. In fact, the particle noise is a unphysical source of energy that, when insufficient resolution is used, can make the simulations go unstable. In the present paper, we apply a new exactly energy conserving scheme and demonstrate that indeed exact energy conservation plays a key role in determining the correct spectrum of the accelerated particles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Block Preconditioners for Stable Mixed Nodal and Edge finite element Representations of Incompressible Resistive MHD

The scalable iterative solution of strongly coupled three-dimensional incompressible resistive magnetohydrodynamics (MHD) equations is quite challenging because disparate time scales arise from the electromagnetics, the hydrodynamics, as well as the coupling between these systems. This study considers a mixed finite element discretization of a dual saddle point formulation of the incompressible resistive MHD equations using a stable nodal (Q2/Q1) discretization for the hydrodynamics and a stable edge-node discretization of a reduced form of the Maxwell equations. This paper introduces new approximate block factorization preconditioners for this system which reduce the system to approximate Schur complement systems that can be solved using algebraic multilevel methods. These preconditioners include a new augmentation-based approximation for the magnetic induction saddle point system as well as efficient approximations of the Schur complements that arise from the complex coupling between the Navier--Stokes equations and the Maxwell equations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Model-based predictive control of multi-zone commercial building with a lumped building modelling approach

Here this study investigates the applicability of a lumped building modeling approach to model-based predictive control (MPC) to alleviate the complex modeling process of the grey-box multi-zone building model. Based on experimental data, two building models were estimated in this study. The detailed model as a reference case and a lumped model were estimated with decentralized and conventional approaches, respectively. Then, simulations were performed with two boundary conditions, including the comfort bound and electricity cost structure. The performances of the MPC with the detailed and lumped models were analyzed compared to the feedback control. More savings was achieved with a larger comfort bound and more aggressive electricity cost structure. The savings potential of the proposed lumped model approach was not as high as that of the detailed model. However, the proposed method yields good control performance, whose savings was approximately 8.6% over that of feedback control. These results suggest that the proposed method can be used to facilitate MPC implementation in multi-zone building applications.

42 ENGINEERING↗
DOE OSTI2021

Scalable ab initio fragmentation methods based on a truncated expansion of the non-orthogonal molecular orbital model

An alternative formulation of the non-orthogonal molecular orbital model of electronic structure theory is developed based on the expansion of the inverse molecular orbital overlap matrix. From this model, a hierarchy of ab initio fragment-based quantum chemistry methods, referred to as the nth-order expanded non-orthogonal molecular orbital methods, are developed using a minimal number of approximations, each of which is frequently employed in intermolecular interaction theory. These novel methods are compared to existing fragment-based quantum chemistry methods, and the implications of those significant differences, where they exist, between the methods developed herein and those already existing methods are examined in detail. Computational complexities and theoretical scaling are also analyzed and discussed. Future extensions for the hierarchy of methods, to account for additional intrafragment and interfragment interactions, are outlined.

Westheimer, Bryce M. (ORCID:0000000267645714)↗
DOE OSTI2018

PV Inverter Fault Response Including Momentary Cessation, Frequency-Watt, and Virtual Inertia

This paper presents two photovoltaic (PV) inverter control methods and an analysis of the two under a significant three-phase transmission line fault contingencies in the Hawaiian island of Oahu power system. Simulations are presented for the two control methods on the island power system with a high penetration of PV generation, approximately 40% of the total. The two control methods discussed are similar: one is a proportional frequency-watt controller, and the second is a proportional-derivative controller, a frequency-watt controller with virtual inertia. Both methods can be beneficial for fast frequency support. The inverter model also emulates inverter fault response including 'momentary cessation' and recovery during low voltage events. The study presented in this paper utilizes a validated power system model of the Hawaiian island of Oahu, modified to include PV resources with the two custom developed control models. Dynamic simulations with PSS/E are presented during a significant transmission line three-phase fault contingency. Simulations are presented with and without PV reserve margin. In addition, a parameter sensitivity analysis is presented for the control methods. Results indicate both methods can significantly improve system response during fault events. Findings indicate that transmission faults can produce severe frequency events, and that fast recovery from momentary cessation is crucial to mitigate severity.

14 SOLAR ENERGY↗
DOE OSTI2011

Extended Brueckner-Hartree-Fock theory with pionic correlation in finite nuclei

Highlights: > We formulate a many-body theory with explicit treatment of tensor correlations. > The Hartree-Fock (HF) model space is extended to include 2-particle 2-hole states. > This extended HF equation has a structure of the Brueckner theory. > Single-particle states are obtained under the influence of the tensor correlation. > This framework is interpreted by the Feshbach projection method. - Abstract: We formulate a nuclear many-body theory with explicit treatment of the strong tensor correlation caused by the pion-exchange interaction. To do this, we have to extend the Hartree-Fock variational model space to include 2-particle 2-hole (2p-2h) states, which are able to handle the tensor correlation and to contain high momentum components originating from its pseudo-scalar nature of the pion. We take the variational principle of the total energy, and obtain equations of motion for the variational parameters as the Hartree-Fock single particle states and 2p-2h states. As for the short range repulsion, we use the unitary correlation operator method (UCOM) to express the short range correlation in the ground state wave function. We then arrive at an extended Hartree-Fock equation with the inclusion of the effect of the pion exchange and short range repulsive interactions. We find this extended Hartree-Fock equation has a structure of the Brueckner theory. Thus, we name the present theoretical framework as an extended Brueckner-Hartree-Fock (EBHF) theory. We compare the EBHF theory with the Feshbach projection method and the Brueckner-Hartree-Fock theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A new insight into neutrino energy loss by electron capture of iron group nuclei in magnetar surfaces

Based on the relativistic mean-field effective interactions theory, and the Lai dong model, we discuss the influences of superstrong magnetic fields (SMFs) on electron Fermi energy, nuclear blinding energy, and single-particle level structure in magnetar surfaces. Using the Shell-Model Monte Carlo method and the Random Phase Approximation theory, we analyze the neutrino energy loss rates (NELRs) by electron capture for iron group nuclei in SMFs. First, when B {sub 12} < 100, we find that the SMFs have a slight influence on the NELRs for most nuclides at relativistic low temperatures (e.g., T {sub 9} = 0.233); nevertheless, the NELRs increase by more than four orders of magnitude at relativistic high temperatures (e.g., T {sub 9} = 15.53). When B {sub 12} > 100, the NELRs decrease by more than three orders of magnitude (e.g., at T {sub 9} = 15.53 for {sup 52–61}Fe, {sup 55–60}Co, and {sup 56–63}Ni). Second, for a certain value of magnetic field and temperature, the NELRs increase by more than four orders of magnitude when ρ{sub 7}⩽10{sup 3}, but as the density increases (i.e., when ρ{sub 7}>10{sup 3}), there is almost no influence on the density of NELRs. For the density around ρ{sub 7}=10{sup 2}, there is an abrupt increase in NELRs when B {sub 12} ≥ 10{sup 3.5}. Such jumps are an indication that the underlying shell structure has changed due to single-particle behavior by SMFs. Finally, we compare our NELRs with those of Fuller et al. (FFN) and Nabi and Klapdor-Kleingrothaus (NKK). For the case without SMFs, one finds that our rates for certain nuclei are close to about five orders of magnitude lower than FFN and NKK at relativistic low temperatures (e.g., T {sub 9} = 1). However, at a relativistic high temperature (e.g., T {sub 9} = 3), our results are in good agreement with NKK, but about one order of magnitude lower than FFN. For the case with SMFs, our NELRs for some iron group nuclei can be about five orders of magnitude higher than those of FFN and NKK. (Note that B {sub 12}, T {sub 9}, and ρ {sub 7} are in units of 10{sup 12} G, 10{sup 9} K, and 10{sup 7} g cm{sup −3}, respectively.)

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Hyperfine interactions for small systems including transition-metal elements using self-interaction corrected density-functional theory

The interactions between the electronic magnetic moment and the nuclear spin moment, i.e., magnetic hyperfine (HF) interactions, play an important role in understanding electronic properties of magnetic systems and in realizing platforms for quantum information science applications. We investigate the HF interactions for atomic systems and small molecules, including Ti or Mn, by using Fermi–Löwdin orbital (FLO) based self-interaction corrected (SIC) density-functional theory. We calculate the Fermi contact (FC) and spin-dipole terms for the systems within the local density approximation (LDA) in the FLO-SIC method and compare them with the corresponding values without SIC within the LDA and generalized-gradient approximation (GGA), as well as experimental data. For the moderately heavy atomic systems (atomic number Z ≤ 25), we find that the mean absolute error of the FLO-SIC FC term is about 27 MHz (percentage error is 6.4%), while that of the LDA and GGA results is almost double that. Therefore, in this case, the FLO-SIC results are in better agreement with the experimental data. For the non-transition-metal molecules, the FLO-SIC FC term has the mean absolute error of 68 MHz, which is comparable to both the LDA and GGA results without SIC. For the seven transition-metal-based molecules, the FLO-SIC mean absolute error is 59 MHz, whereas the corresponding LDA and GGA errors are 101 and 82 MHz, respectively. Therefore, for the transition-metal-based molecules, the FLO-SIC FC term agrees better with experiment than the LDA and GGA results. We observe that the FC term from the FLO-SIC calculation is not necessarily larger than that from the LDA or GGA for all the considered systems due to the core spin polarization, in contrast to the expectation that SIC would increase the spin density near atomic nuclei, leading to larger FC terms.

Chemistry↗
DOE OSTI2017

Optical potential from first principles

Here, we develop a method to construct a microscopic optical potential from chiral interactions for nucleon-nucleus scattering. The optical potential is constructed by combining the Green’s function approach with the coupled-cluster method. To deal with the poles of the Green’s function along the real energy axis we employ a Berggren basis in the complex energy plane combined with the Lanczos method. Using this approach, we perform a proof-of-principle calculation of the optical potential for the elastic neutron scattering on 16 O. For the computation of the ground-state of 16 O, we use the coupled-cluster method in the singles-and-doubles approximation, while for the A ±1 nuclei we use particle-attached/removed equation-of-motion method truncated at two-particle-one-hole and one-particle-two-hole excitations, respectively. We verify the convergence of the optical potential and scattering phase shifts with respect to the model-space size and the number of discretized complex continuum states. We also investigate the absorptive component of the optical potential (which reflects the opening of inelastic channels) by computing its imaginary volume integral and find an almost negligible absorptive component at low-energies. To shed light on this result, we computed excited states of 16 O using equation-of-motion coupled-cluster method with singles-and- doubles excitations and we found no low-lying excited states below 10 MeV. Furthermore, most excited states have a dominant two-particle-two-hole component, making higher-order particle-hole excitations necessary to achieve a precise description of these core-excited states. We conclude that the reduced absorption at low-energies can be attributed to the lack of correlations coming from the low-order cluster truncation in the employed coupled-cluster method.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Real-space density kernel method for Kohn–Sham density functional theory calculations at high temperature

Kohn–Sham density functional theory calculations using conventional diagonalization based methods become increasingly expensive as temperature increases due to the need to compute increasing numbers of partially occupied states. In this work, we present a density matrix based method for Kohn–Sham calculations at high temperatures that eliminates the need for diagonalization entirely, thus reducing the cost of such calculations significantly. Specifically, we develop real-space expressions for the electron density, electronic free energy, Hellmann–Feynman forces, and Hellmann–Feynman stress tensor in terms of an orthonormal auxiliary orbital basis and its density kernel transform, the density kernel being the matrix representation of the density operator in the auxiliary basis. Using Chebyshev filtering to generate the auxiliary basis, we next develop an approach akin to Clenshaw–Curtis spectral quadrature to calculate the individual columns of the density kernel based on the Fermi operator expansion in Chebyshev polynomials and employ a similar approach to evaluate band structure and entropic energy components. We implement the proposed formulation in the SPARC electronic structure code, using which we show systematic convergence of the aforementioned quantities to exact diagonalization results, and obtain significant speedups relative to conventional diagonalization based methods. Finally, we employ the new method to compute the self-diffusion coefficient and viscosity of aluminum at 116 045 K from Kohn–Sham quantum molecular dynamics, where we find agreement with previous more approximate orbital-free density functional methods.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗