4,922 research outputs found
Joint density-functional theory for electronic structure of solvated systems
We introduce a new form of density functional theory for the {\em ab initio}
description of electronic systems in contact with a molecular liquid
environment. This theory rigorously joins an electron density-functional for
the electrons of a solute with a classical density-functional theory for the
liquid into a single variational principle for the free energy of the combined
system. A simple approximate functional predicts, without any fitting of
parameters to solvation data, solvation energies as well as state-of-the-art
quantum-chemical cavity approaches, which require such fitting.Comment: Fixed typos and minor updates to tex
Validação de um método para detecção e quantificação de soja culticance tolerante a herbicidas imidazolinonas por PCR convencional e quantitativo.
bitstream/item/71972/1/ID-30956.pd
Ab Initio Study of Screw Dislocations in Mo and Ta: A new picture of plasticity in bcc transition metals
We report the first ab initio density-functional study of screw
dislocations cores in the bcc transition metals Mo and Ta. Our results suggest
a new picture of bcc plasticity with symmetric and compact dislocation cores,
contrary to the presently accepted picture based on continuum and interatomic
potentials. Core energy scales in this new picture are in much better agreement
with the Peierls energy barriers to dislocation motion suggested by
experiments.Comment: 3 figures, 3 table
Large Scale Electronic Structure Calculations with Multigrid Acceleration
We have developed a set of techniques for performing large scale ab initio
calculations using multigrid accelerations and a real-space grid as a basis.
The multigrid methods permit efficient calculations on ill-conditioned systems
with long length scales or high energy cutoffs. The technique has been applied
to systems containing up to 100 atoms, including a highly elongated diamond
cell, an isolated C molecule, and a 32-atom cell of GaN with the Ga
d-states in valence. The method is well suited for implementation on both
vector and massively parallel architectures.Comment: 4 pages, 1 postscript figur
Nitrogen Doped Graphene Generated by Microwave Plasma and Reduction Expansion Synthesis
The article of record as published may be found at http://dx.doi.org/10.1166/nnl.2016.2055This work aimed to produce nitrogen doped graphene from Graphite Oxide (GO) by combining the
Expansion Reduction Synthesis (RES) approach, which utilizes urea as doping/reducing agent, with
the use of an Atmospheric Plasma torch (Plasma), which provides the high temperature reactor
environment known to thermally exfoliate it. The use of this combined strategy (Plasma-RES) was
tried in an attempt to increase the surface area of the products. The amount of nitrogen doping
was controlled by varying the urea/GO mass ratios in the precursor powders. X-ray diffraction
analysis, SEM, TEM, BET surface areas and conductivity measurements of the diverse products
are presented. Nitrogen inclusion in the graphene samples was corroborated by the mass spectral
signal of the evolved gases generated during thermal programmed oxidation experiments of the
products and by EDX analysis. We found that the Plasma-RES method can successfully generate
doped graphene in situ as the urea and GO precursors simultaneously decompose and reduce
in the discharge zone. When using the same amount of urea in the precursor mixture, samples obtained by Plasma-RES have higher surface area than those generated by RES, however, they contain a smaller nitrogen content
Fracture in Mode I using a Conserved Phase-Field Model
We present a continuum phase-field model of crack propagation. It includes a
phase-field that is proportional to the mass density and a displacement field
that is governed by linear elastic theory. Generic macroscopic crack growth
laws emerge naturally from this model. In contrast to classical continuum
fracture mechanics simulations, our model avoids numerical front tracking. The
added phase-field smoothes the sharp interface, enabling us to use equations of
motion for the material (grounded in basic physical principles) rather than for
the interface (which often are deduced from complicated theories or empirical
observations). The interface dynamics thus emerges naturally. In this paper, we
look at stationary solutions of the model, mode I fracture, and also discuss
numerical issues. We find that the Griffith's threshold underestimates the
critical value at which our system fractures due to long wavelength modes
excited by the fracture process.Comment: 10 pages, 5 figures (eps). Added 2 figures and some text. Removed one
section (and a figure). To be published in PR
Ferromagnetic resonance in periodic particle arrays
We report measurements of the ferromagnetic resonance (FMR) spectra of arrays
of submicron size periodic particle arrays of permalloy produced by
electron-beam lithography. In contrast to plane ferromagnetic films, the
spectra of the arrays show a number of additional resonance peaks, whose
position depends strongly on the orientation of the external magnetic field and
the interparticle interaction. Time-dependent micromagnetic simulation of the
ac response show that these peaks are associated with coupled exchange and
dipolar spin wave modesComment: 4 pages, 4 figure
Generator coordinate method calculations of one-nucleon removal reactions on Ca
An approach to the Generator Coordinate Method (GCM) using Skyrme-type
effective forces and Woods-Saxon construction potential is applied to calculate
the single-particle proton and neutron overlap functions in Ca. The
relationship between the bound-state overlap functions and the one-body density
matrix has been used. These overlap functions are applied to calculate the
cross sections of one-nucleon removal reactions such as (), ()
and () on Ca on the same theoretical footing. A consistent
description of data for the different reactions is achieved. The shapes of the
experimental cross sections for transitions to the ground state and
the first excited state of the residual nuclei are well reproduced by
the overlap functions obtained within the GCM. An additional spectroscopic
factor accounting for correlations not included in the overlap function must be
applied to the calculated results to reproduce the size of the experimental
cross sections.Comment: 16 pages, 6 figures, to be published in Phys. Rev.
Two-nucleon emission in the longitudinal response
The contribution of the two-nucleon emission in the longitudinal response for
inclusive electron scattering reactions is studied. The model adopted to
perform the calculations is based upon Correlated Basis Function theory but it
considers only first order terms in the correlation function. The proper
normalization of the wave function is ensured by considering, in addition to
the usually evaluated two-point diagrams, also the three-point diagrams.
Results for the 12C nucleus in the quasi-elastic region are presented.Comment: 7 pages, 4 Postscript figure
Micromagnetic simulations of interacting dipoles on a fcc lattice: Application to nanoparticle assemblies
Micromagnetic simulations are used to examine the effects of cubic and axial
anisotropy, magnetostatic interactions and temperature on M-H loops for a
collection of magnetic dipoles on fcc and sc lattices. We employ a simple model
of interacting dipoles that represent single-domain particles in an attempt to
explain recent experimental data on ordered arrays of magnetoferritin
nanoparticles that demonstrate the crucial role of interactions between
particles in a fcc lattice. Significant agreement between the simulation and
experimental results is achieved, and the impact of intra-particle degrees of
freedom and surface effects on thermal fluctuations are investigated.Comment: 10 pages, 9 figure
- …