Search NASA⌕ Search

SEARCH · Search NASA

Results for “first principles”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

First-Principles Study of Intrinsic and Extrinsic Point Defects in Lead-Based Hybrid Perovskites.

Intrinsic and extrinsic defects play a major role in determining solar cell efficiencies of lead halide hybrid perovskite absorbers. Here, we present the results of first-principles computations performed on MAPbBr3 (MA = methylammonium) to study the energetics and defect levels of intrinsic point defects, namely vacancy, self-interstitial and anti-site, and extrinsic Pb-substitution defects. While vacancies are the lowest formation energy intrinsic defects and create shallow transition levels, a number of extrinsic defects can have comparable formation energies under desirable chemical potential conditions. therefore, carrier concentrations may be tunable with these substituents. Further, some extrinsic defects create deeper transition levels which can potentially be exploited to enhance solar cell efficiencies via sub-gap absorption.

density functional theory↗
DOE OSTI2018

First-Principles Calculations of Acoustic and Anharmonic Properties of Ferromagnetic Cu{sub 2}MnZ (Z = Al and In) Heusler Alloys

The acoustic and anharmonic properties of ferromagnetic Cu{sub 2}MnZ (Z = Al and In) Heusler alloys have been investigated by first-principles calculations method. The obtained lattice parameters, magnetic moments, elastic properties are found to be in good agreement with the available experimental values. From the elastic properties, the sound velocities and the related Debye temperatures and minimum thermal conductivities have been obtained for the two alloys. The sound velocities and thermal conductivities of both alloys are found to show significant anisotropy, and the Cu{sub 2}MnAl with small density and large elastic constants has large sound velocities, high Debye temperature, and large thermal conductivities. Also, the effective second-order elastic constants, generalized Grüneisen constants, and nonlinear ultrasonic parameters to characterize anharmonic properties have been studied for the two alloys. These predictions on the acoustic and anharmonic properties can provide a valuable guidance or reference for further related investigations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electronic Structures, Magnetic Properties and Half-Metallicity of Heusler Compounds Hf{sub 2}VZ (Z = Ga, In, Tl, Si, Ge, Sn and Pb): First-Principle Calculations

We investigate the electronic structures, magnetic properties and half-metallicity of Heusler compounds Hf{sub 2}VZ (Z = Ga, In, Tl, Si, Ge, Sn and Pb) with Hg{sub 2}CuTi-type structure by using the first-principle calculations based on density-functional theory. It is found that the equilibrium lattice constants of Hf{sub 2}VZ (Z = Ga, In, Tl, Si, Ge, Sn and Pb) compounds are 6.68, 6.88, 6.91, 6.57, 6.63, 6.85 and 6.94 Å, respectively. Hf{sub 2}VZ (Z = Ga, In, Tl, Si and Sn) compounds exhibit half-metallicity at their respective equilibrium lattice constants. Hf{sub 2}VGe and Hf{sub 2}VPb do not exhibit half-metallicity at their equilibrium lattice constants but can present the half-metallicity when the lattice constant decreases to 6.51 and 6.71 Å, respectively. In case of the lattice thermal expansion, the half-metallicity can be kept in the range of 6.30∼ 7.27, 6.36∼ 7.80, 6.46∼ 7.35, 6.00∼ 6.70 and 6.10∼ 6.95 Å (lattice constant) for Hf{sub 2}VZ (Z = Ga, In, Tl, Si and Sn). Under the unaxial strain, the half-metallicity can still be kept for Hf{sub 2}VZ (Z = Ga, In, Tl) when the lattice distortion is up to ± 10% (c/a) and be kept for Hf{sub 2}VZ (Z = Si, Sn) when the lattice distortion is 0.88∼ 1.09, 0.91∼ 1.09 (c/a). For the Hf{sub 2}VZ compounds with half-metallicity, the total magnetic moment is 2 μ{sub B} when Z is the third main group elements and is 1 μ{sub B} when Z is the fourth main group elements. The Hf{sub 2}VZ compounds with half-metallicity obey the Slater-Pauling formula: M{sub t} = 18 − Z{sub t} rule.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

First-Principles Study of Ferroelectric and Optical Properties in Derivatives of Thiourea

Organic ferroelectric materials in the form of molecular crystals are promising alternatives to well-known ferroelectric perovskite oxides due to their structural flexibility, tunability, and ease of processing. First-principles density functional theory calculations combined with group theory analyses are employed in this work to discuss polar nature of a class of derivatives of thiourea: CH 4 N 2 A where A = O, S, Se, and Te. Further, optical properties in the UV range along with thermodynamic and dynamic stability of such materials are also evaluated in the study. We find that CH 4 N 2 Te with bandgap energy of ~3.33 eV shows large spontaneous polarization of P = 10.92 μC/cm 2 . The electronic and optical properties become tunable under strain.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

First-principles study on structural mechanical and thermodynamic properties of HfMoTaTiZr

This study calculates the phase diagram of HfMoTaTiZr using the TCHEA1 database in Thermo-Calc software. Furthermore, it also investigates the structural and mechanical properties of HfMoTaTiZr by applying first-principles calculations. The elastic and other mechanical properties such as Young’s modulus, pugh ratio, hardness, bulk modulus was derived and discussed. These parameters were found to be in good harmony with previously available experimental reports. Vickers hardness of HfMoTaTiZr predicted from the Tians model agrees with the available experimental result. This study also investigates the thermal coefficient of linear expansion and vibrational heat capacity of the HfMoTaTiZr using the Debye–Grüneisen theory.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Discovery of atomic clock-like spin defects in simple oxides from first principles

Virtually noiseless due to the scarcity of spinful nuclei in the lattice, simple oxides hold promise as hosts of solid-state spin qubits. However, no suitable spin defect has yet been found in these systems. Using high-throughput first-principles calculations, we predict spin defects in calcium oxide with electronic properties remarkably similar to those of the NV center in diamond. These defects are charged complexes where a dopant atom — Sb, Bi, or I — occupies the volume vacated by adjacent cation and anion vacancies. The predicted zero phonon line shows that the Bi complex emits in the telecommunication range, and the computed many-body energy levels suggest a viable optical cycle required for qubit initialization. Notably, the high-spin nucleus of each dopant strongly couples to the electron spin, leading to many controllable quantum levels and the emergence of atomic clock-like transitions that are well protected from environmental noise. Specifically, the Hanh-echo coherence time increases beyond seconds at the clock-like transition in the defect with 209 Bi. Our results pave the way to designing quantum states with long coherence times in simple oxides, making them attractive platforms for quantum technologies.

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

The stability, electronic structure, and optical absorption of boron-nitride diamondoids predicted with first-principles calculations

Although diamondoids are broadly studied for their fundamental properties and applications, boron-nitride-based diamondoids are scarcely explored.In this report we predict the stability, electronic structure, and optical absorption spectra of six boron-nitride (BN) diamondoids with first-principles methods based on pseudopotential density functional theory and many-body perturbation methods implemented with a real-space formalism. We find that four of them are thermodynamically stable at room temperature, while B10N8H24 and B6N4H16 show thermodynamic instability in molecular dynamics simulations. With the GW approximation, we predicted the ionization energies and electron affinities of BN-diamondoids and find that the evolution of the electronic structure with size does not follow the same trend as diamondoids, owing to the unbalanced numbers of boron and nitrogen atoms. We show strong photoabsorption of BN-triamantane and BN-adamantane in the infrared and visible ranges and analyze the features of low-energy absorption by examining the characteristics of related orbitals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

First principles study on the electronic transport properties of C{sub 60} and B{sub 80} molecular bridges

The electronic transport properties of molecular bridges constructed by C{sub 60} and B{sub 80} molecules which have the same symmetry are investigated by first principles calculations combined with a non-equilibrium Green's function technique. It is found that, like C{sub 60}, monomer B{sub 80} is a good conductor arising from the charge transfer from the leads to the molecule, while the dimer (B{sub 80}){sub 2} and (C{sub 60}){sub 2} are both insulators due to the potential barrier formed at the molecule-molecule interface. Our further study shows that, although both the homogeneous dimer (B{sub 80}){sub 2} and (C{sub 60}){sub 2} display poor conductivity, the heterogeneous dimer B{sub 80}C{sub 60} shows a very high conductance as a result from the decreased HOMO-LUMO gap and the excess charge redistribution. Finally, we find that the conductivity of both (B{sub 80}){sub 2} and (C{sub 60}){sub 2} can be significantly improved by electron doping, for example, by doping C in (B{sub 80}){sub 2} and doping N in (C{sub 60}){sub 2}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Alloying effects on structural and thermal behavior of Ti{sub 1-x}Zr{sub x}C: A first principles study

The formation energy, equilibrium lattice parameter, bulk modulus, Debye temperature and heat capacity at constant volume have been calculated for TiC, ZrC, and their intermediate alloys (Ti{sub 1-x}Zr{sub x}C, x = 0,0.25.0.5,0.75,1) using first principles approach. The calculated values of lattice parameter and bulk modulus agree well with the available experimental and earlier theoretical reports. The variation of lattice parameter and bulk modulus with the change in concentration of Zr atom in Ti{sub 1-x}Zr{sub x}C has also been reported. The heat capacities of TiC, ZrC, and their intermediate alloys have been calculated by considering both vibrational and electronic contributions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

First-principles study of order-disorder transitions in multicomponent solid-solution alloys

In this paper, we will focus on the recent development of the order-disorder transition in metallic materials. The past decades have witnessed fast development in the first-principles methodologies and their applications to ordering transitions in multi-component alloys, particularly the high-entropy alloys. The driving force for the proceedings comes from (i) the advance of algorithms and increasingly cheaper hardware, and also (ii) the great passion to model alloys with increasing number of components.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

Predicting charge transport in organic molecular crystals is notoriously challenging. Carrier mobility calculations in organic semiconductors are dominated by quantum chemistry methods based on charge hopping, which are laborious and only moderately accurate. We compute from first principles the electron-phonon scattering and the phonon-limited hole mobility of naphthalene crystal in the framework of ab initio band theory. Our calculations combine GW electronic bandstructures, ab initio electron-phonon scattering, and the Boltzmann transport equation. The calculated hole mobility is in very good agreement with experiment between 100–300K, and we can predict its temperature dependence with high accuracy. Here we show that scattering between intermolecular phonons and holes regulates the mobility, though intramolecular phonons possess the strongest coupling with holes. We revisit the common belief that only rigid molecular motions affect carrier dynamics in organic molecular crystals. Our paper provides a quantitative and rigorous framework to compute charge transport in organic crystals and is a first step toward reconciling band theory and carrier hopping computational methods.

36 MATERIALS SCIENCE↗
DOE OSTI2024

First-principles investigation of high capacity, rechargeable CF x cathode batteries based on graphdiyne and “holey” graphene carbon allotropes

Batteries composed of CF x cathodes have high theoretical specific capacities (>860 mA h g -1 ). Attempts at realizing such batteries coupled with Li anodes have failed to deliver on this promise, however, due to a discharge voltage plateau below the theoretical maximum lowering the realized energy density and difficulties with recharging the system. Here, in this study, we use first-principles calculations to investigate novel carbon allotropes for these battery systems: graphdiyne and “holey” graphene. We first identify stable flourination structures and calculate their band gaps. We demonstrate that the holes in these carbon allotropes can induce the formation of an amorphous LiF network within the carbon and that this formation may, in fact, be kinetically favored. For structures where amorphous LiF forms within the carbon, we predict it is easier to recharge and higher discharge voltages can be achieved. If the LiF forms outside the carbon product, however, it will be crystalline in form and lead to lower discharge voltages and more difficulty in recharging the systems. Finally, we simulate XPS spectra of representative cases, demonstrating an experimental pathway for determining the reaction pathway of these systems. Our work suggests CF x allotropes with holes in them as potential targets for high capacity, rechargeable cathodes for Li batteries, provided they lead to the formation of amorphous LiF within the C structure.

25 ENERGY STORAGE↗
DOE OSTI2018

Adhesion of ZrN and Al 2 O 3 coatings on U metal from first-principles

To understand the role of alumina layer in the adhesion of ZrN coating on U-Mo surface using atomic layer deposition (ALD) technique, we investigate the interfaces of ZrN/U, Al 2 O 3 /U, and ZrN/Al 2 O 3 using first-principles density-functional theory calculations. The preferred interfacial plane orientation relationships and terminations for all the interfaces are predicted. Calculations show that both lattice mismatch and interfacial bonding play crucial roles in determining the adhesion strength of ZrN and Al 2 O 3 coatings on U metal surface. The strength of Al 2 O 3 /U and ZrN/Al 2 O 3 interfaces are found to be substantially higher than that of ZrN/U interface. The strong interfacial adhesion of Al 2 O 3 /U and ZrN/Al 2 O 3 interfaces is ascribed to the formation of ionic bonds at the interface, as compared to weak metallic bonds formed in ZrN/U interface. Furthermore, the formation of metal-oxygen ionic bonds at interface explains the role of alumina layer in the improved adhesion of ZrN coating on U-Mo surface.

36 MATERIALS SCIENCE↗
DOE OSTI2018

First-Principles Investigation of Borophene as a Monolayer Transparent Conductor

Two-dimensional boron is promising as a tunable monolayer metal for nano-optoelectronics. We study the optoelectronic properties of two likely allotropes of two-dimensional boron, β12 and δ6, using first-principles density functional theory and many-body perturbation theory. We find that both systems are anisotropic metals, with strong energy- and thickness-dependent optical transparency and a weak (<1%) absorbance in the visible range. Additionally, using state-of-the-art methods for the description of the electron–phonon and electron–electron interactions, we show that the electrical conductivity is limited by electron–phonon interactions. Furthermore, our results indicate that both structures are suitable as a transparent electrode.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Stability of hydrogenated graphene: a first-principles study

In order to explain the disagreement between present theoretical and experimental investigations on the stability of hydrogenated graphene, we have systematically studied hydrogenated graphene with different configurations from the consideration of single-side and double-side adsorption using first-principles calculations. Both binding energy and formation energy are calculated to characterize the stability of the system. It is found that single-side hydrogenated graphene is always unstable. However, for double-side hydrogenation, some configurations are stable due to the increased carbon–carbon sp 3 hybridization compared to single-side hydrogenation. Furthermore, it is found that the system is energetically favorable when an equal number of hydrogen atoms are adsorbed on each side of the graphene.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Pyro-paraelectric and flexocaloric effects in barium strontium titanate: A first principles approach

Inhomogeneous strain allows the manifestation of an unexplored component of stress-driven caloric effect (flexocaloric effect) and enhanced pyroelectric performance, obtainable significantly beyond the Curie point. A peak temperature change of 1.5 K (at 289 K) was predicted from first-principles-based simulations for Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} under the application of a strain gradient of 1.5 μm{sup −1}. Additionally, enhanced pyro-paraelectric coefficient (pyroelectric coefficient in paraelectric phase) and flexocaloric cooling 11 × 10{sup −4} C m{sup −2 }K{sup −1} and 1.02 K, respectively, could be obtained (at 330 K and 1.5 μm{sup −1}). A comparative analysis with prevailing literature indicates huge untapped potential and warrants further research.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Molecule-Adsorbed Topological Insulator and Metal Surfaces: A Comparative First-Principles Study

We compare electronic structure characteristics of three different kinds of benzene-adsorbed (111) surfaces: that of Bi 2 Te 3 , a prototypical topological insulator, that of Au, a prototypical inert metal, and that of Pt, a prototypical catalytic metal. Using first-principles calculations based on dispersion-corrected density functional theory, we show that benzene is chemisorbed on Pt, but physisorbed on Au and Bi 2 Te 3 . Here, the adsorption on Bi 2 Te 3 is particularly weak, consistent with a minimal perturbation of the electronic structure at the surface of the topological insulator, revealed by a detailed analysis of the interaction of the molecular orbitals with the topological surface states.

36 MATERIALS SCIENCE↗
DOE OSTI2024

First-Principles Calculations of the Electrical Conductivity of Carbon Nanotubes Functionalized with Copper and Nitrogen: Implications for Electronics, Energy Storage, and Nanodevices

In this work, we investigate the electrical conductivity of carbon nanotubes (CNTs), with a particular focus on the effects of doping. Using first-principles-based approaches, we study the electronic structure, phonon dispersion, and electron–phonon scattering to understand the finite-temperature electrical transport properties in CNTs. Our study covers both prototypical metallic and semiconducting CNTs, with special emphasis on the influence of typical defects such as vacancies and the incorporation of copper or nitrogen, such as pyridinic N, pyrrolic N, graphitic N, and oxidized N. Our theoretical study shows significant improvements in the electrical conduction properties of copper-CNT composites, especially when semiconducting CNTs are functionalized with nitrogen. Doping is found to cause significant changes in the electronic density of states near the Fermi level, which affects the electrical conductivity. Calculations show that certain types of functional groups, such as N-pyrrolic, result in more than 30-fold increase in the conductivity of semiconducting CNTs compared to Cu-incorporated CNTs alone. For metallic CNTs, the conductivity is in agreement with existing experimental data, and our prediction of significant increases in conductivity with N-pyrrolic functional group is consistent with recent experimental results, demonstrating the effectiveness of doping in modifying conductivity. In conclusion, our study provides valuable insight into the electronic properties of doped CNTs and contributes to the development of ultrahigh conductivity CNT composites.

36 MATERIALS SCIENCE↗