A5029423543- Quantum and electron transport phenomena
- Semiconductor materials and devices
- Semiconductor Quantum Structures and Devices
- Advancements in Semiconductor Devices and Circuit Design
- Advanced Chemical Physics Studies
- Quantum Computing Algorithms and Architecture
- Silicon Nanostructures and Photoluminescence
- Quantum-Dot Cellular Automata
- Spectroscopy and Quantum Chemical Studies
- Quantum Information and Cryptography
- Surface and Thin Film Phenomena
- Molecular Junctions and Nanostructures
- Ion-surface interactions and analysis
- Integrated Circuits and Semiconductor Failure Analysis
- Computational Physics and Python Applications
- Advanced Battery Technologies Research
- Force Microscopy Techniques and Applications
- Advancements in Battery Materials
- Porphyrin and Phthalocyanine Chemistry
- Photonic and Optical Devices
- Parallel Computing and Optimization Techniques
- Electron and X-Ray Spectroscopy Techniques
- Advanced Materials Characterization Techniques
- Semiconductor materials and interfaces
- Asymmetric Hydrogenation and Catalysis
Sandia National Laboratories
2011-2023
Sandia National Laboratories California
2006-2022
Centre for Quantum Computation and Communication Technology
2016
UNSW Sydney
2016
Australian Research Council
2016
University of Cambridge
2016
Advanced Device Technology (United States)
2013
University of Washington
2009
University of New Mexico
2006-2009
California Institute of Technology
1990-2007
SymPy is an open source computer algebra system written in pure Python. It built with a focus on extensibility and ease of use, through both interactive programmatic applications. These characteristics have led to become popular symbolic library for the scientific Python ecosystem. This paper presents architecture SymPy, description its features, discussion select submodules. The supplementary material provide additional examples further outline details features SymPy.
Gas phase hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a relatively stable molecule which releases large amount of energy upon decomposition. Although gas-phase unimolecular decomposition experiments suggest at least two major pathways, there no mechanistic understanding the reactions involving RDX or other energetic molecules (such as HMX and TATB), used in applications ranging from automobile air bags to rocket propellants. For RDX, we find three pathways: (i) concerted ring form...
We derive here the form for exact exchange energy density a that decays with Gaussian-type behavior at long range. This functional is intermediate between B88 and PW91 functionals. Using this modified to match expected Gaussian densities, we propose X3LYP extended functional. find significantly outperforms Becke three parameter Lee–Yang–Parr (B3LYP) describing van der Waals hydrogen bond interactions, while performing slightly better than B3LYP predicting heats of formation, ionization...
Molecular compounds—comprised of mechanically interlocked components—such as rotaxanes and catenanes can be designed to display readily controllable internal movements one component with respect the other. Since weak noncovalent bonding interactions that contribute template-directed synthesis such compounds live on between components thereafter, they activated move in either a linear fashion (rotaxanes) or rotary manner (catenanes). These molecules by switching recognition elements off...
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAb Initio Calculations of Free Energy Barriers for Chemical Reactions in SolutionRichard P. Muller and Arieh WarshelCite this: J. Phys. Chem. 1995, 99, 49, 17516–17524Publication Date (Print):December 1, 1995Publication History Published online1 May 2002Published inissue 1 December 1995https://pubs.acs.org/doi/10.1021/j100049a009https://doi.org/10.1021/j100049a009research-articleACS PublicationsRequest reuse permissionsArticle...
An effective approach for ab initio calculations of activation free energies enzymatic reactions is developed and examined. This uses an empirical valence bond (EVB) potential surface as a reference evaluating the hybrid quantum mechanics/molecular mechanics (QM(ai)/MM) surface. procedure involves automated calibration EVB using gas-phase calculations. In addition, strategies treating contact region QM MM atoms well enzyme solvent environments are developed. Two levels used in studying...
SymPy is an open source computer algebra system written in pure Python. It built with a focus on extensibility and ease of use, through both interactive programmatic applications. These characteristics have led to become the standard symbolic library for scientific Python ecosystem. This paper presents architecture SymPy, description its features, discussion select domain specific submodules. The supplementary materials provide additional examples further outline details features SymPy.
The mechanism of hydroarylation olefins by a homogeneous Ph-Ir(acac)2(L) catalyst is elucidated first principles quantum mechanical methods (DFT), with particular emphasis on activation the catalyst, catalytic cycle, and interpretation experimental observations. On basis this mechanism, we suggest new catalysts expected to have improved activity. Initiation from inert trans-form into active cis-form occurs through dissociative pathway calculated ΔH(0 K)⧧ = 35.1 kcal/mol ΔG(298 26.1 kcal/mol....
To improve the mechanistic understanding of possible decomposition in gas phase energetic material HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), we used ab initio calculations to determine various unimolecular channels. We find three distinct mechanisms: (i) homolytic cleavage N−N bond form NO2 (M = 46) and HMR 250) which subsequently decomposes products; (ii) successive HONO eliminations give four 47) plus a stable intermediate 108); (iii) O-migration from one groups neighboring C...
The recently developed frozen density functional theory (FDFT) is extended to ab initio free energy calculations of chemical reactions in solution. This method treats the solute−solvent system as a supermolecule but constrains electron solvent molecules. Unlike hybrid quantum mechanical/molecular mechanics techniques, FDFT represents mechanically. quality interaction potential examined by generating clusters reacting and several molecules comparing DFT energies corresponding energies....
Stimulated by the recent surprising results from Wentworth et al. [Wentworth, A. D., Jones, L. H., Wentworth, P., Janda, K. D. & Lerner, R. (2000) Proc. Natl. Acad. Sci. USA 97, 10930–10935] that Abs efficiently catalyze conversion of molecular singlet oxygen ( 1 O 2 ) plus water to hydrogen peroxide (HOOH), we used quantum chemical methods (B3LYP density functional theory) delineate most plausible mechanisms for observed efficient HOOH. We find two reasonable pathways. In Pathway I, i H...
Using density functional theory (DFT) with gradient-corrected exchange-correlation functionals (B3LYP), we systematically study the electronic structure and bonding of oxygen to various Pt-clusters. Our aim is understand how cluster size shape affect chemistry dispersed catalysts find smallest suitable for modeling surface reactions on Pt(111)-surface. We that dependence binding sites these clusters well described in terms interstitial electron model (IEM). The results show 28-atom...
Last year, Salfi et al. made the first direct measurements of a donor wave function and found extremely good theoretical agreement with atomistic tight-binding theory results [Salfi al., Nat. Mater. 13, 605 (2014)]. Here, we show that multivalley effective mass theory, applied properly, does achieve close hence gives reliable predictions. To demonstrate this, variationally solve coupled six-valley Shindo-Nara equations, including silicon's full Bloch functions. Surprisingly, find functions...
Taking Pd di-imine catalysts as an example, we use first principles density functional theory (B3LYP/6-31G*) to investigate the chain propagation steps for polymerization of polar monomers. We start with complex formed from insertion ethylene into polymer and consider Pd−C bond each four monomers: methyl acrylate, vinyl acetate, chloride, acrylonitrile. find 2,1-insertion is favored in case (by 3 5 kcal/mol), resulting a product strong interaction group growing metal. Next, insert another...
The mechanism of the direct insertion molecular oxygen into a palladium hydride bond has been elucidated using quantum mechanics (B3LYP/LACVP** with PBF continuum solvent model). key step is found to be abstraction hydrogen atom resulting in formation PdI/HO2 (triplet) radical pair, which then proceeds form singlet hydroperoxo species. Potential palladium(0) pathways were explored and inaccessible. results are agreement recent experimental consistent our previously predicted for an analogue system.
The pseudospectral (PS) method for self-consistent-field calculations is extended use in generalized valence-bond and used to calculate singlet–triplet excitation energies methylene, silylene, ethylene molecules bond dissociation twisting ethylene. We find that the PS lead an accuracy total of ≤0.1 kcal/mol ≤0.01 all systems. With effective core potentials on Si, we greatly improved PS.
We use quantum mechanics to characterize the structure and current-voltage performance of Stoddart-Heath rotaxane-based programmable electronic switch. find that current when ring is on DNP 37-58 times TTF, in agreement with experiment (ratio 10-100). This establishes basis for iterative experimental-theoretical efforts optimize systems molecule-based electronics which we illustrate by predicting effect adding a group such as CN rotaxane.
First-principles calculation and x-ray diffraction simulation methods have been used to explore crystal structures reaction mechanisms of the intermediate phases involved in dehydriding LiBH4. LiBH4 was found dehydride via two sequential steps: first through LiBH, followed by LiBH LiB. The step, which releases 13.1wt.% hydrogen, calculated an activation barrier 2.33eV per formula unit endothermic 1.28eV unit, while second step 0.23eV unit. On other hand, if each donated one electron,...
Hydrogenolysis reactions of palladium(II) hydroxide and methoxide complexes to form water methanol, respectively, the corresponding hydride are reported. In presence water, 1 was found exist in solution as a water-bridged dimer; however, kinetic studies suggest reaction H(2) proceeds exclusively through monomer water. Computational four-center intramolecular proton transfer opposed an oxidative addition/reductive elimination pathway.
We present measurements of silicon (Si) metal-oxide-semiconductor (MOS) nanostructures that are fabricated using a process facilitates essentially arbitrary gate geometries. Stable Coulomb-blockade behavior showing single-period conductance oscillations consistent with lithographically defined quantum dot is exhibited in several MOS dots an open-lateral quantum-dot geometry. Decreases mobility and increases charge defect densities (i.e., interface traps fixed-oxide charge) measured for...
A phase field model is presented to capture the formation of a solid electrolyte interface (SEI) layer on anode surface in lithium ion batteries. In this model, an SEI treated as transformation process where transformed due electrochemical reactions at SEI/electrolyte during growth. Numerical results show that growth exhibits power-law scaling with respect time and limited by diffusion electrons across layer. It found growth, gradients both electric potential concentrations species are built...
Albany is a multiphysics code constructed by assembling set of reusable, general components. It an implicit, unstructured grid finite element that hosts advanced features are readily combined within single analysis run. uses template-based generic programming methods to provide extensibility and flexibility; it employs residual evaluation interface support the easy addition modification physics. This coupled powerful automatic differentiation utilities used implement efficient nonlinear...