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Arias, T. A.

Publications and source records attributed to Arias, T. A..

18 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

JDFTx: Software for joint density-functional theory

Density-functional theory (DFT) has revolutionized computational prediction of atomic-scale properties from first principles in physics, chemistry and materials science. Continuing development of new methods is necessary for accurate predictions of new classes of materials and properties, and for connecting to nano- and mesoscale properties using coarse-grained theories. JDFTx is a fully-featured open-source electronic DFT software designed specifically to facilitate rapid development of new theories, models and algorithms. Using an algebraic formulation as an abstraction layer, compact C++11 code automatically performs well on diverse hardware including GPUs (Graphics Processing Units). This code hosts the development of joint density-functional theory (JDFT) that combines electronic DFT with classical DFT and continuum models of liquids for first-principles calculations of solvated and electrochemical systems. In addition, the modular nature of the code makes it easy to extend and interface with, facilitating the development of multi-scale toolkits that connect to ab initio calculations, e.g. photo-excited carrier dynamics combining electron and phonon calculations with electromagnetic simulations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Computationally efficient dielectric calculations of molecular crystals

The microscopic dielectric response is a key quantity for electronic materials such as organic semiconductors. Calculations of this response for molecular crystals are currently either expensive or rely on extreme simplifications such as multipole expansions which lack microscopic detail. We present an alternate approach using a microscopic analogue of the Clausius-Mossotti equation, which constructs the dielectric response of a crystal from an eigenvalue decomposition of the dielectric response of individual molecules. This method can potentially be used to examine the effects of defects, disorder, and surfaces on the dielectric properties of molecular solids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Spicing up continuum solvation models with SaLSA: The spherically averaged liquid susceptibility ansatz

Continuum solvation models enable electronic structure calculations of systems in liquid environments, but because of the large number of empirical parameters, they are limited to the class of systems in their fit set (typically organic molecules). Here, we derive a solvation model with no empirical parameters for the dielectric response by taking the linear response limit of a classical density functional for molecular liquids. This model directly incorporates the nonlocal dielectric response of the liquid using an angular momentum expansion, and with a single fit parameter for dispersion contributions it predicts solvation energies of neutral molecules with a RMS error of 1.3 kcal/mol in water and 0.8 kcal/mol in chloroform and carbon tetrachloride. We show that this model is more accurate for strongly polar and charged systems than previous solvation models because of the parameter-free electric response, and demonstrate its suitability for ab initio solvation, including self-consistent solvation in quantum Monte Carlo calculations.

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

Weighted-density functionals for cavity formation and dispersion energies in continuum solvation models

Continuum solvation models enable efficient first principles calculations of chemical reactions in solution, but require extensive parametrization and fitting for each solvent and class of solute systems. Here, we examine the assumptions of continuum solvation models in detail and replace empirical terms with physical models in order to construct a minimally-empirical solvation model. Specifically, we derive solvent radii from the nonlocal dielectric response of the solvent from ab initio calculations, construct a closed-form and parameter-free weighted-density approximation for the free energy of the cavity formation, and employ a pair-potential approximation for the dispersion energy. We show that the resulting model with a single solvent-independent parameter: the electron density threshold (n{sub c}), and a single solvent-dependent parameter: the dispersion scale factor (s{sub 6}), reproduces solvation energies of organic molecules in water, chloroform, and carbon tetrachloride with RMS errors of 1.1, 0.6 and 0.5 kcal/mol, respectively. We additionally show that fitting the solvent-dependent s{sub 6} parameter to the solvation energy of a single non-polar molecule does not substantially increase these errors. Parametrization of this model for other solvents, therefore, requires minimal effort and is possible without extensive databases of experimental solvation free energies.

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

A recipe for free-energy functionals of polarizable molecular fluids

Classical density-functional theory is the most direct approach to equilibrium structures and free energies of inhomogeneous liquids, but requires the construction of an approximate free-energy functional for each liquid of interest. We present a general recipe for constructing functionals for small-molecular liquids based only on bulk experimental properties and ab initio calculations of a single solvent molecule. This recipe combines the exact free energy of the non-interacting system with fundamental measure theory for the repulsive contribution and a weighted density functional for the short-ranged attractive interactions. We add to these ingredients a weighted polarization functional for the long-range correlations in both the rotational and molecular-polarizability contributions to the dielectric response. We also perform molecular dynamics calculations for the free energy of cavity formation and the high-field dielectric response, and show that our free-energy functional adequately describes these properties (which are key for accurate solvation calculations) for all three solvents in our study: water, chloroform, and carbon tetrachloride.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Implicit solvation model for density-functional study of nanocrystal surfaces and reaction pathways

Solid-liquid interfaces are at the heart of many modern-day technologies and provide a challenge to many materials simulation methods. A realistic first-principles computational study of such systems entails the inclusion of solvent effects. In this work, we implement an implicit solvation model that has a firm theoretical foundation into the widely used density-functional code Vienna ab initio Software Package. The implicit solvation model follows the framework of joint density functional theory. We describe the framework, our algorithm and implementation, and benchmarks for small molecular systems. We apply the solvation model to study the surface energies of different facets of semiconducting and metallic nanocrystals and the S N 2 reaction pathway. We find that solvation reduces the surface energies of the nanocrystals, especially for the semiconducting ones and increases the energy barrier of the S N 2 reaction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1986

Analysis of Jovian decamteric data: Study of radio emission mechanisms

This research effort involved careful examination of Jovian radio emission data below 40 MHz, with emphasis on the informative observations of the Planetary Radio Astronomy experiment (PRA) on the Voyager 1 and 2 spacecraft. The work is divided into three sections, decametric arcs, decametric V bursts, and hectometric modulated spectral activity (MSA).

Staelin, D. H.↗
NASA NTRS1985

Analysis of Jovian decametric data: Study of radio emission mechanisms

Data gathered by the Voyager 1 and Voyager 2 Planetary Radio Astronomy Experiments (PRA) are unique in many ways including their frequency range, time resolution, polarization information and geometric characteristics. Studies of rapidly varying phenomena have thus far been hampered by paper display techniques which require large amounts of paper to exploit the full PRA time resolution. A software package capable of effectively displaying full 6s resolution PRA dynamic spectra on a high quality video monitor while compensating for the aforementioned variations was developed. The most striking phenomena revealed by the new display techniques is called Modulated Spectral Activity (MSA) because of its appearance in dynamic spectra as a series at least two parallel emission bands which drift back and forth in frequency on time scales of tens of seconds. In an attempt to locate and understand the MSA source mechanism, a catalogue has been compiled of the start and end of all known MSA events.

Staelin, D. H.↗
NASA NTRS1985

Analysis of Jovian decametric data: Study of radio emission mechanisms

The Voyager 1 and Voyager 2 Planetary Radio Astronomy Experiments (PRA) have produced the finest set of Jovian decametric radio emission data ever obtained. Jovian decametric L-burst and S-burst arcs were characterized and the data reconciled with models for the radio emission geometry and mechanisms. The first major results involve comparisons of the distribution of arc separations with longitudes. The identification and analyses of systematic variations in the PRA data have yielded interesting results, but only the most obvious features of the data were examined. Analyses of the PRA data were extended with the use of new 6-Sec formats that are more sensitive to the S-bursts.

Staelin, D. H.↗