A5113488730- High-pressure geophysics and materials
- Advanced Chemical Physics Studies
- Quantum, superfluid, helium dynamics
- Astro and Planetary Science
- Laser-Plasma Interactions and Diagnostics
- nanoparticles nucleation surface interactions
- Radio Frequency Integrated Circuit Design
- Diamond and Carbon-based Materials Research
- Advanced Power Amplifier Design
- Surface and Thin Film Phenomena
- Spectroscopy and Quantum Chemical Studies
- Energetic Materials and Combustion
- Atomic and Molecular Physics
- Machine Learning in Materials Science
- Magnetic confinement fusion research
- Semiconductor materials and devices
- Advanced Materials Characterization Techniques
- Combustion and Detonation Processes
- Radioactive element chemistry and processing
- Gas Dynamics and Kinetic Theory
- Phase Equilibria and Thermodynamics
- Electromagnetic Compatibility and Noise Suppression
- Nuclear Physics and Applications
- Planetary Science and Exploration
- Metal and Thin Film Mechanics
GKN (Sweden)
2024
Sandia National Laboratories
2014-2024
Los Alamos National Laboratory
2022
Applied Pulsed Power (United States)
2018
University of Michigan
2018
Sandia National Laboratories California
2004-2017
Ericsson (Sweden)
1992-2016
General Atomics (United States)
2016
Washington State University
2016
University of Rostock
2008
The radii and orbital periods of 4,000+ confirmed/candidate exoplanets have been precisely measured by the Kepler mission. show a bimodal distribution, with two peaks corresponding to smaller planets (likely rocky) larger intermediate-size planets, respectively. While only masses orbiting brightest stars can be determined ground-based spectroscopic observations, these observations allow calculation their average densities placing constraints on bulk compositions internal structures. However,...
Density functional theory (DFT) methods for calculating the quantum mechanical ground states of condensed matter systems are now a common and significant component materials research. The growing importance DFT reflects development sufficiently accurate functionals, efficient algorithms continuing improvements in computing capabilities. As problems to which is applied have become large complex, so sets calculations necessary investigating given problem. Highly versatile, powerful codes exist...
Density functional theory (DFT) molecular dynamics (MD) and classical MD simulations of the principal shock Hugoniot are presented for two hydrocarbon polymers, polyethylene (PE) poly(4-methyl-1-pentene) (PMP). DFT results in excellent agreement with experimental data, which is currently available up to 80 GPa. Further, we predict PE PMP Hugoniots 350 200 GPa, respectively. For comparison, studied reactive nonreactive interaction potentials. latter, exp-6 Borodin et al. showed much better...
Driving liquid deuterium into metal Quick and powerful compression can force materials to change their properties dramatically. Knudson et al. compressed extreme temperatures pressures using high-energy magnetic pulses at the Sandia Z-machine (see Perspective by Ackland). Deuterium began reflect like a mirror during compression, as electrical conductivity sharply increased. The observed conditions for metallization of hydrogen help us build theoretical models universe's most abundant...
We have revealed, and resolved, an apparent inability of density functional theory, within the local generalized gradient approximations, to describe vacancies in Al accurately consistently. The shortcoming is due electron correlation effects near electronic edges we show how correct for them. find that divacancy energetically unstable anharmonic atomic vibrations explain non-Arrhenius temperature dependence vacancy concentration.
We show that the AM05 functional [Armiento and Mattsson, Phys. Rev. B 72, 085108 (2005)] has same excellent performance for solids as hybrid density functionals tested in Paier et al. [J. Chem. 124, 154709 (2006); 125, 249901 (2006)]. This confirms original finding performs exceptionally well surfaces. Hartree-Fock calculations are typically an order of magnitude slower than local or semilocal such AM05, which is a regular generalized gradient approximation form. The on average found to be...
We present QMD simulations of water in the ultra-high-pressure regime up to conditions typical for deep interior Jupiter and Saturn. calculate equation state Hugoniot curve study structural properties via pair correlation functions self-diffusion coefficients. In ultradense superionic phase, we find a continuous transition protonic structure. With rising density, mobile protons stay with increasing probability at octahedral sites while leaving ice X positions same degree unoccupied. Water...
The predictive power of first-principles calculations vacancy formation energies in metals (Pt, Pd, Mo) is improved by adding a correction for the intrinsic surface error current implementations density functional theory. derived given as function electron density; it can be explicitly applied to wide range systems. Density theory, contrary claims previous work, underestimates energy when structural relaxation included. This case whether using local density- or generalized gradient...
Two of the most popular generalized gradient approximations used in applications density functional theory, PW91 and PBE, are generally regarded as essentially equivalent. They produce similar numerical results for many simple properties, such lattice constants, bulk moduli, atomization energies. We examine more complex properties systems with electronic surface regions, specific application monovacancy formation energies Pt Al. A surprisingly large consistent discrepancy between PBE is...
Recently there has been tremendous increase in the number of identified extra-solar planetary systems. Our understanding their formation is tied to exoplanet internal structure models, which rely upon equations state light elements and compounds like water. Here we present shock compression data for water with unprecedented accuracy that shows commonly used modeling significantly overestimate compressibility at conditions relevant interiors. Furthermore, show its behavior these conditions,...
We present experimental results from the first systematic study of performance scaling with drive parameters for a magnetoinertial fusion concept. In magnetized liner inertial experiments, burn-averaged ion temperature doubles to 3.1 keV and primary deuterium-deuterium neutron yield increases by more than an order magnitude 1.1×10^{13} (2 kJ deuterium-tritium equivalent) through simultaneous increase in applied magnetic field (from 10.4 15.9 T), laser preheat energy 0.46 1.2 kJ), current...
The electrical conductivity and structure of water between $2000--70\text{ }000\text{ }\text{ }\mathrm{K}$ $0.1--3.7\text{ }\mathrm{g}/{\mathrm{cm}}^{3}$ is studied by finite temperature density functional theory (DFT). Proton conduction investigated quantitatively analyzing diffusion, the pair-correlation function, Wannier center locations, while electronic calculated in Kubo-Greenwood formalism. formulation valid across three phase transitions (molecular liquid, ionic superionic, liquid)....
Metals deposited in vacuum on metal oxides such as alumina normally grow three-dimensional clusters because of weak adatom-substrate interactions. This tendency hinders our ability to form interfaces ultrathin, laminar films for use microelectronics and other technologies where nanostructural control is desired. We present experimental theoretical results showing that room temperature Co deposition fully hydroxylated clean sapphire (α-Al 2 O 3 ) produces a surface chemical reaction leads...
Current equation of state (EOS) models for xenon show substantial differences in the Hugoniot above 100 GPa, prompting need an improved understanding xenon's behavior at extreme conditions. We performed shock compression experiments on liquid to determine up 840 using these results validate density functional theory (DFT) simulations. Despite nearly fivefold compression, we find that limiting Thomas-Fermi theory, exact high limit, does not accurately describe system. Combining experimental...
The moon-forming impact and the subsequent evolution of proto-Earth is strongly dependent on properties materials at extreme conditions generated by this violent collision. We examine high pressure behavior MgO, one dominant constituents in Earth's mantle, using high-precision, plate shock compression experiments performed Sandia National Laboratories' Z Machine extensive quantum calculations density functional theory (DFT) Monte Carlo (QMC) methods. combined data span from ambient to 1.2...
We apply diffusion quantum Monte Carlo (DMC) to a broad set of solids, benchmarking the method by comparing bulk structural properties (equilibrium volume and modulus) experiment DFT based theories. The test includes materials with many different types binding including ionic, metallic, covalent van der Waals. show that, on average, accuracy is comparable or better than that density functional theory (DFT) when using new generation functionals, one hybrid two dispersion corrected...
By combining experiments and modeling from three US national laboratories, we explore compressive strength in a well-characterized material, tantalum, across pressures zero to over 350 GPa, strain-rates 10−3/s 108/s temperatures 148 K 3800 K. Strength values 40+ are shown vary by nearly two orders of magnitude, 0.15 GPa 10 GPa. Cross-comparison these results allows pressure strain-rate dependencies be isolated, increases more significantly with than strain rate the range studied. Simulations...
Mechanisms for enhanced low-dose-rate sensitivity are described. In these mechanisms, bimolecular reactions dominate the kinetics at high dose rates thereby causing a sub-linear dependence on total dose, and this leads to dose-rate dependence. These mechanisms include electron-hole recombination, hydrogen recapture source sites, dimerization form molecules. The essence of each is dominance over radiolysis reaction rates. However, low rates, dominates leading maximum effect radiation.
A technique for the automatic correction of errors in RF quadrature modulators is described. The method uses a diode detector to provide amplitude feedback guide adaption baseband circuits that correct carrier leak, differential gain and phase mismatch errors.
We calculate the electrical conductivity of water for ultrahigh pressures up to 80 Mbar and temperatures $130\text{ }000\text{ }\text{K}$ as relevant planetary physics by using ab initio molecular-dynamics simulations. The electron system is treated within density-functional theory electronic obtained from an evaluation Kubo-Greenwood formula. ionic determined via diffusion coefficients. Our calculations reproduce most available experimental data error bars while plateau measured Mitchell...
A VCO is implemented in an RF 90 nm CMOS process and covers the frequency range 2.55-4.08 GHz. Drawing 19 mA from 1.2 V, phase noise at 20 MHz offset a 3.7 GHz carrier -156 dBc/Hz, meeting requirement for GSM/EDGE SAW-less WCDMA transmitter after division by 2 or 4. second version of additional 4.90-5.75 range, expense higher added band. In this way, all currently operational WCDMA/EDGE bands can be synthesized single working double quadruple desired
We have performed quantum molecular dynamics simulations for dense helium to study the nonmetal-to-metal transition at high pressures. present new results equation of state and Hugoniot curve in warm matter region. The optical conductivity is calculated via Kubo-Greenwood formula from which dc derived. identified about 1 g/ccm. compare with experimental as well other theoretical approaches, especially predictions chemical models.
Lithium is a prototypical simple metal at standard conditions which well described within the nearly free electron model. However, by changing density towards expanded or compressed states, electrical conductivity shows strong and partly unexpected variations. We have performed quantum molecular dynamics simulations for fluid lithium wide range of densities temperatures in order to derive equation state, conductivity, information about structural electronic changes along expansion...