Arbey, A.; Mahmoudi, F.
2010-07-01
We describe SuperIso Relic, a public program for evaluation of relic density and flavor physics observables in the minimal supersymmetric extension of the Standard Model (MSSM). SuperIso Relic is an extension of the SuperIso program which adds to the flavor observables of SuperIso the computation of all possible annihilation and coannihilation processes of the LSP which are required for the relic density calculation. All amplitudes have been generated at the tree level with FeynArts/FormCalc, and widths of the Higgs bosons are computed with FeynHiggs at the two-loop level. SuperIso Relic also provides the possibility to modify the assumptions of the cosmological model, and to study their consequences on the relic density. Catalogue identifier: AEGD_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEGD_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: yes No. of lines in distributed program, including test data, etc.: 2 274 720 No. of bytes in distributed program, including test data, etc.: 6 735 649 Distribution format: tar.gz Programming language: C (C99 Standard compliant) and Fortran Computer: 32- or 64-bit PC, Mac Operating system: Linux, MacOS RAM: 100 Mb Classification: 1.9, 11.6 External routines: ISASUGRA/ISAJET and/or SOFTSUSY, FeynHiggs Does the new version supersede the previous version?: No (AEAN_v2_0) Nature of problem: Calculation of the lightest supersymmetric particle relic density, as well as flavor physics observables, in order to derive constraints on the supersymmetric parameter space. Solution method: SuperIso Relic uses a SUSY Les Houches Accord file, which can be either generated automatically via a call to SOFTSUSY or ISAJET, or provided by the user. This file contains the masses and couplings of the supersymmetric particles. SuperIso Relic then computes the lightest supersymmetric particle relic density as well as the most constraining flavor physics
Harz, Julia; Klasen, Michael; Kovařík, Karol; Steppeler, Patrick
2015-01-01
The latest Planck data allow one to determine the dark matter relic density with previously unparalleled precision. In order to achieve a comparable precision on the theory side, we have calculated the full $\\mathcal{O}(\\alpha_s)$ corrections to the most relevant annihilation and coannihilation processes for relic density calculations within the Minimal Supersymmetric Standard Model (MSSM). The interplay of these processes is discussed. The impact of the radiative corrections on the resulting relic density is found to be larger than the experimental uncertainty of the Planck data.
micrOMEGAs 2.0: A program to calculate the relic density of dark matter in a generic model
Bélanger, G.; Boudjema, F.; Pukhov, A.; Semenov, A.
2007-03-01
micrOMEGAs 2.0 is a code which calculates the relic density of a stable massive particle in an arbitrary model. The underlying assumption is that there is a conservation law like R-parity in supersymmetry which guarantees the stability of the lightest odd particle. The new physics model must be incorporated in the notation of CalcHEP, a package for the automatic generation of squared matrix elements. Once this is done, all annihilation and coannihilation channels are included automatically in any model. Cross-sections at v=0, relevant for indirect detection of dark matter, are also computed automatically. The package includes three sample models: the minimal supersymmetric standard model (MSSM), the MSSM with complex phases and the NMSSM. Extension to other models, including non-supersymmetric models, is described. Program summaryTitle of program:micrOMEGAs2.0 Catalogue identifier:ADQR_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADQR_v2_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computers for which the program is designed and others on which it has been tested:PC, Alpha, Mac, Sun Operating systems under which the program has been tested:UNIX (Linux, OSF1, SunOS, Darwin, Cygwin) Programming language used:C and Fortran Memory required to execute with typical data:17 MB depending on the number of processes required No. of processors used:1 Has the code been vectorized or parallelized:no No. of lines in distributed program, including test data, etc.:91 778 No. of bytes in distributed program, including test data, etc.:1 306 726 Distribution format:tar.gz External routines/libraries used:no Catalogue identifier of previous version:ADQR_v1_3 Journal reference of previous version:Comput. Phys. Comm. 174 (2006) 577 Does the new version supersede the previous version:yes Nature of physical problem:Calculation of the relic density of the lightest stable particle in a generic new model of particle physics. Method
micrOMEGAs 2.0.7: a program to calculate the relic density of dark matter in a generic model
Bélanger, G.; Boudjema, F.; Pukhov, A.; Semenov, A.
2007-12-01
micrOMEGAs2.0.7 is a code which calculates the relic density of a stable massive particle in an arbitrary model. The underlying assumption is that there is a conservation law like R-parity in supersymmetry which guarantees the stability of the lightest odd particle. The new physics model must be incorporated in the notation of CalcHEP, a package for the automatic generation of squared matrix elements. Once this is done, all annihilation and coannihilation channels are included automatically in any model. Cross-sections at v=0, relevant for indirect detection of dark matter, are also computed automatically. The package includes three sample models: the minimal supersymmetric standard model (MSSM), the MSSM with complex phases and the NMSSM. Extension to other models, including non supersymmetric models, is described. Program summaryTitle of program:micrOMEGAs2.0.7 Catalogue identifier:ADQR_v2_1 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADQR_v2_1.html Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions:Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.:216 529 No. of bytes in distributed program, including test data, etc.:1 848 816 Distribution format:tar.gz Programming language used:C and Fortran Computer:PC, Alpha, Mac, Sun Operating system:UNIX (Linux, OSF1, SunOS, Darwin, Cygwin) RAM:17 MB depending on the number of processes required Classification:1.9, 11.6 Catalogue identifier of previous version:ADQR_v2_0 Journal version of previous version:Comput. Phys. Comm. 176 (2007) 367 Does the new version supersede the previous version?:Yes Nature of problem:Calculation of the relic density of the lightest stable particle in a generic new model of particle physics. Solution method:In numerically solving the evolution equation for the density of dark matter, relativistic formulae for the thermal average are used. All tree
Improved calculation of relic gravitational waves
2007-01-01
In this paper, we have improved the calculation of the relic gravitational waves (RGW) in two aspects. First, we investigate the transfer function by taking into consideration the redshift-suppression effect, the accelerating expansion effect, the damping effect of free-streaming relativistic particles, and the damping effect of cosmic phase transition, and give a simple approximate analytic expression, which clearly illustrates the dependence on the cosmological parameters.Second, we develop a numerical method to calculate the primordial power spectrum of RGW in a very wide frequency range, where the observed constraints on ns (the scalar spectral index) and Ps(ko) (the amplitude of primordial scalar spectrum) and the Hamilton-Jacobi equation are used. This method is applied to two kinds of inflationary models,which satisfy the current constraints on ns, α (the running of ns) and r (the tensor-scalar ratio). We plot them in the r - Ωg diagram, where Ωg is the strength of RGW, and study their measurements from the cosmic microwave background (CMB) experiments and laser interferometers.
Predicting the neutralino relic density in the MSSM more precisely
Harz, Julia; Klasen, Michael; Kovařík, Karol; Steppeler, Patrick
2016-01-01
The dark matter relic density being a powerful observable to constrain models of new physics, the recent experimental progress calls for more precise theoretical predictions. On the particle physics side, improvements are to be made in the calculation of the (co)annihilation cross-section of the dark matter particle. We present the project DM@NLO which aims at calculating the neutralino (co)annihilation cross-section in the MSSM including radiative corrections in QCD. In the present document, we briefly review selected results for different (co)annihilation processes. We then discuss the estimation of the associated theory uncertainty obtained by varying the renormalization scale. Finally, perspectives are discussed.
Precise Prediction of the Dark Matter Relic Density within the MSSM
Harz, J.; Herrmann, B.; Klasen, M.; Kovarik, K.; Steppeler, P.
With the latest Planck results the dark matter relic density is determined to an unprecedented precision. In order to reduce current theoretical uncertainties in the dark matter relic density prediction, we have calculated next-to-leading order SUSY-QCD corrections to neutralino (co)annihilation processes including Coulomb enhancement effects. We demonstrate that these corrections can have significant impact on the cosmologically favoured MSSM parameter space and are thus of general interest for parameter studies and global fits.
Precise Prediction of the Dark Matter Relic Density within the MSSM
Harz, Julia; Klasen, Michael; Kovarik, Karol; Steppeler, Patrick
2015-01-01
With the latest Planck results the dark matter relic density is determined to an unprecedented precision. In order to reduce current theoretical uncertainties in the dark matter relic density prediction, we have calculated next-to-leading order SUSY-QCD corrections to neutralino (co)annihilation processes including Coulomb enhancement effects. We demonstrate that these corrections can have significant impact on the cosmologically favoured MSSM parameter space and are thus of general interest for parameter studies and global fits.
Neutralino Relic Density in a Supersymmetric U(1)' Model
Barger, V; Langacker, P; Lee, H S; Barger, Vernon; Kao, Chung; Langacker, Paul; Lee, Hye-Sung
2004-01-01
We study properties of the lightest neutralino (\\chi) and calculate its cosmological relic density in a supersymmetric U(1)' model with a secluded U(1)' breaking sector (the S-model). The lightest neutralino mass is smaller than in the minimal supersymmetric standard model; for instance, m_\\chi < 100 GeV in the limit that the U(1)' gaugino mass is large compared to the electroweak scale. We find that the Z-\\chi-\\chi coupling can be enhanced due to the singlino components in the extended neutralino sector. Neutralino annihilation through the Z-resonance then reproduces the measured cold dark matter density over broad regions of the model parameter space.
Relic density computations at NLO: infrared finiteness and thermal correction
Beneke, Martin; Hryczuk, Andrzej
2014-01-01
There is an increasing interest in accurate dark matter relic density predictions, which requires next-to-leading order (NLO) calculations. The method applied up to now uses zero-temperature NLO calculations of annihilation cross sections in the standard Boltzmann equation for freeze-out, and is conceptually problematic, since it ignores the finite-temperature infrared (IR) divergences from soft and collinear radiation and virtual effects. We address this problem systematically by starting from non-equilibrium quantum field theory, and demonstrate on a realistic model that soft and collinear temperature-dependent divergences cancel in the collision term. Our analysis provides justification for the use of the freeze-out equation in its conventional form and determines the leading finite-temperature correction to the annihilation cross section. This turns out to have a remarkably simple structure.
Relic density of dark matter in the NMSSM
Bélanger, G; Hugonie, C; Pukhov, A E; Semenov, A
2005-01-01
We present a code to compute the relic density of dark matter in the Next-to-Minimal Supersymmetric Standard Model (NMSSM). Dominant corrections to the Higgs masses are calculated with NMHDECAY as well as theoretical and collider constraints. All neutralino annihilation and coannihilation processes are then computed with an extended version of micrOMEGAs, taking into acount higher order corrections to Higgs vertices. We explore the parameter space of the NMSSM and consider in particular the case of a bino LSP, of a mixed bino-higgsino LSP and of a singlino LSP. As compared to the MSSM, neutralino annihilation is often more efficient as it can take place via (additional) Higgs resonances as well as annihilation into light Higgs states. Models with a large singlino component can be compatible with WMAP constraints.
Quintessence and the relic density of neutralinos
Salati, Pierre
2003-10-09
The archetypal model for the recently discovered dark energy component of the universe is based on the existence of a scalar field whose dynamical evolution comes down today to a non-vanishing cosmological constant. In the past - before big-bang nucleosynthesis for that matter - that scalar field could have gone through a period of kination during which the universe has expanded at a much higher pace than what is currently postulated in the standard radiation dominated cosmology. I examine here the consequences of such a period of kination on the relic abundance of neutralinos and find that the latter could be much higher - by three orders of magnitude - than what is estimated in the canonical derivation. I shortly discuss the implications of this scenario for the dark matter candidates and their astrophysical signatures.
SUSY constraints from relic density: High sensitivity to pre-BBN expansion rate
Arbey, A. [Universite de Lyon, Lyon F-69000 (France); Universite Lyon 1, Villeurbanne F-69622 (France); Centre de Recherche Astrophysique de Lyon, Observatoire de Lyon, 9 avenue Charles Andre, Saint-Genis Laval cedex F-69561 (France); CNRS, UMR 5574, Ecole Normale Superieure de Lyon, Lyon (France)], E-mail: arbey@obs.univ-lyon1.fr; Mahmoudi, F. [High Energy Physics, Uppsala University, Box 535, 75121 Uppsala (Sweden)
2008-10-30
The sensitivity of the lightest supersymmetric particle relic density calculation to the variation of the cosmological expansion rate before nucleosynthesis is discussed. Such a modification of the expansion rate, even extremely modest and with no consequence on the cosmological observations, can greatly enhance the calculated relic density, and therefore change the constraints on the SUSY parameter space drastically. We illustrate this variation in two examples of SUSY models, and show that it is unsafe to use the lower bound of the WMAP limits in order to constrain supersymmetry. We therefore suggest to use only the upper value {omega}{sub DM}h{sup 2}<0.135.
Dark matter relic density in Gauss-Bonnet braneworld cosmology
Meehan, Michael T
2014-01-01
The relic density of symmetric and asymmetric dark matter in the Gauss-Bonnet braneworld cosmology is investigated. The reduced expansion rate in this scenario delays particle freeze-out, leading to relic abundances which are suppressed by up to $\\mathcal{O}(10^{-3})$. In this case the annihilation cross section must be reduced by up to two orders of magnitude below the canonical value $\\langle\\sigma v\\rangle \\approx 2\\times 10^{-26}$ cm$^3$s$^{-1}$ to reconcile the predicted dark matter density with observation. We use the latest observational bound $\\Omega_{DM}h^2 = 0.1187 \\pm 0.0017$ to constrain the various model parameters and discuss the implications for direct/indirect dark matter detection experiments as well as dark matter particle models.
Neutralino Relic Density in the CPVMSSM at the ILC
Bélanger, G; Kraml, S; Martyn, H U; Pukhov, A
2009-01-01
We discuss ILC measurements for a specific MSSM scenario with CP phases, where the lightest neutralino, a candidate for dark matter, annihilates through t-channel exchange of light staus. These prospective ILC measurements are used to fit the underlying model parameters. A collider prediction of the relic density of the neutralino from this fit gives 0.116
Dark matter relic density in Gauss-Bonnet braneworld cosmology
Meehan, Michael T.; Whittingham, Ian B., E-mail: Michael.Meehan@my.jcu.edu.au, E-mail: Ian.Whittingham@jcu.edu.au [College of Science, Technology and Engineering, James Cook University, 1 James Cook Dr., Townsville 4811 (Australia)
2014-12-01
The relic density of symmetric and asymmetric dark matter in a Gauss-Bonnet (GB) modified Randall-Sundrum (RS) type II braneworld cosmology is investigated. The existing study of symmetric dark matter in a GB braneworld (Okada and Okada, 2009) found that the expansion rate was reduced compared to that in standard General Relativity (GR), thereby delaying particle freeze-out and resulting in relic abundances which are suppressed by up to O(10{sup −2}). This is in direct contrast to the behaviour observed in RS braneworlds where the expansion rate is enhanced and the final relic abundance boosted. However, this finding that relic abundances are suppressed in a GB braneworld is based upon a highly contrived situation in which the GB era evolves directly into a standard GR era, rather than passing through a RS era as is the general situation. This collapse of the RS era requires equating the mass scale m{sub α} of the GB modification and the mass scale m{sub σ} of the brane tension. However, if the GB contribution is to be considered as the lowest order correction from string theory to the RS action, we would expect m{sub α} > m{sub σ}. We investigate the effect upon the relic abundance of choosing more realistic values for the ratio R{sub m} ≡ m{sub α}/m{sub σ} and find that the relic abundance can be either enhanced or suppressed by more than two orders of magnitude. However, suppression only occurs for a small range of parameter choices and, overwhelmingly, the predominant situation is that of enhancement as we recover the usual Randall-Sundrum type behaviour in the limit R{sub m} >> 1. We use the latest observational bound Ω{sub DM}h{sup 2} = 0.1187 ± 0.0017 to constrain the various model parameters and briefly discuss the implications for direct/indirect dark matter detection experiments as well as dark matter particle models.
Neutralino relic density from ILC measurements in the CPV MSSM
Bélanger, G; Kraml, Sabine; Martyn, H -U; Pukhov, A
2008-01-01
We discuss ILC measurements for a specific MSSM scenario with CP phases, where the lightest neutralino is a good candidate for dark matter, annihilating efficiently through t-channel exchange of light staus. These prospective (CP-even) ILC measurements are then used to fit the underlying model parameters. A collider prediction of the relic density of the neutralino from this fit gives 0.116
Radiative corrections for the direct detection of neutralino dark matter and its relic density
Steppeler, Patrick Norbert
2016-07-01
entering the Boltzmann equation in many scenarios of the MSSM. The Boltzmann equation allows to determine the neutralino relic density, i.e. to predict their present abundance. This prediction can be checked experimentally and is thus of great phenomenological relevance. Measurements of the temperature fluctuations of the cosmic microwave background permit to determine the relic density precisely. Comparing the theoretical prediction with the experimental finding allows to exclude large fractions of the MSSM parameter space. In order to maximally benefit from the experimental precision, it is necessary to minimise theoretical uncertainties and to include the aforementioned radiative corrections. The radiative corrections to the elastic neutralino-nucleon scattering and the corresponding relic density have been implemented into the numerical package Dark matter at next-to-leading order. With the help of this program, we perform a phenomenological investigation and analyse the impact of the radiative corrections. It turns out that the neutralino relic density depends not on a single but a multitude of gaugino (co)annihilation processes in parallel quite often. The calculated radiative corrections lead to a relative shift of the relic density of up to 10%, which is significantly larger than the experimental uncertainty (±2% at the 1σ confidence level) and demonstrates that these corrections should be included when identifying the cosmologically preferred region of the MSSM. Moreover, we investigate the relation between the relic density and the neutralino-nucleon cross sections. In the spin-independent case, the inclusion of radiative corrections leads to a relative shift roughly +14% in comparison to a tree-level calculation. This shift is comparable to typical recent nuclear uncertainties, which influence the prediction as well. The spin-dependent cross section is subject to even larger shifts and modified by up to -50% by radiative corrections.
Klasen, M.; Kovařík, K.; Steppeler, P.
2016-11-01
In this paper, we perform a full next-to-leading order (NLO) QCD calculation of neutralino scattering on protons or neutrons in the minimal supersymmetric standard model. We match the results of the NLO QCD calculation to the scalar and axial-vector operators in the effective field theory approach. These govern the spin-independent and spin-dependent detection rates, respectively. The calculations have been performed for general bino, wino and higgsino decompositions of neutralino dark matter and required a novel tensor reduction method of loop integrals with vanishing relative velocities and Gram determinants. Numerically, the NLO QCD effects are shown to be of at least of similar size and sometimes larger than the currently estimated nuclear uncertainties. We also demonstrate the interplay of the direct detection rate with the relic density when consistently analyzed with the program dm@nlo.
Relic density of wino-like dark matter in the MSSM
Beneke, M; Dighera, F; Hellmann, C; Hryczuk, A; Recksiegel, S; Ruiz-Femenia, P
2016-01-01
The relic density of TeV-scale wino-like neutralino dark matter in the MSSM is subject to potentially large corrections as a result of the Sommerfeld effect. A recently developed framework enables us to calculate the Sommerfeld-enhanced relic density in general MSSM scenarios, properly treating mixed states and multiple co-annihilating channels as well as including off-diagonal contributions. Using this framework, including on-shell one-loop mass splittings and running couplings and taking into account the latest experimental constraints, we perform a thorough study of the regions of parameter space surrounding the well known pure-wino scenario: namely the effect of sfermion masses being non-decoupled and of allowing non-negligible Higgsino or bino components in the lightest neutralino. We further perform an investigation into the effect of thermal corrections and show that these can safely be neglected. The results reveal a number of phenomenologically interesting but so far unexplored regions where the Somm...
Harz, J; Klasen, M; Kovarik, K; Steppeler, P
2016-01-01
For particle physics observables at colliders such as the LHC at CERN, it has been common practice for many decades to estimate the theoretical uncertainty by studying the variations of the predicted cross sections with a priori unpredictable scales. In astroparticle physics, this has so far not been possible, since most of the observables were calculated at Born level only, so that the renormalization scheme and scale dependence could not be studied in a meaningful way. In this paper, we present the first quantitative study of the theoretical uncertainty of the neutralino dark matter relic density from scheme and scale variations. We first explain in detail how the renormalization scale enters the tree-level calculations through coupling constants, masses and mixing angles. We then demonstrate a reduction of the renormalization scale dependence through one-loop SUSY-QCD corrections in many different dark matter annihilation channels and enhanced perturbative stability of a mixed on-shell/$\\bar{\\rm DR}$ renor...
Dark matter relic density from observations of supersymmetry at the ILC
Lehtinen, Suvi-Leena; List, Jenny
2016-01-01
Supersymmetry can explain the observed dark matter relic density with a neutralino dark matter particle and a coannihilating, almost mass-degenerate sparticle. If this were the case in nature, a linear electron positron collider like the ILC could discover the two sparticles if their masses are in the kinematic reach of the collider. This contribution discusses which observations are necessary at the ILC for predicting the dark matter relic density correctly and for confirming that the observed lightest neutralino is the only kind of dark matter. We take the case of stau coannihilation as an example.
Relating the baryon asymmetry to the thermal relic dark matter density
McDonald, John
2011-04-01
We present a generic framework, baryomorphosis, which modifies the baryon asymmetry to be naturally of the order of a typical thermal relic weakly interacting massive particle (WIMP) density. We consider a simple scalar-based model to show how this is possible. This model introduces a sector in which a large initial baryon asymmetry is injected into particles (”annihilons”), ϕB, ϕ^B, of mass ˜100GeV-1TeV. ϕBϕ^B annihilations convert the initial ϕB, ϕ^B asymmetry to a final asymmetry with a thermal relic WIMP-like density. This subsequently decays to a conventional baryon asymmetry whose magnitude is naturally related to the density of thermal relic WIMP dark matter. In this way the two coincidences of baryons and dark matter, i.e. why their densities are similar to each other and why they are both similar to a WIMP thermal relic density (the “WIMP miracle”), may be understood. The model may be tested by the production of annihilons at colliders.
Harz, J.; Herrmann, B.; Klasen, M.; Kovařík, K.; Steppeler, P.
2016-06-01
For particle physics observables at colliders such as the LHC at CERN, it has been common practice for many decades to estimate the theoretical uncertainty by studying the variations of the predicted cross sections with a priori unpredictable scales. In astroparticle physics, this has so far not been possible, since most of the observables were calculated at Born level only, so that the renormalization scheme and scale dependence could not be studied in a meaningful way. In this paper, we present the first quantitative study of the theoretical uncertainty of the neutralino dark matter relic density from scheme and scale variations. We first explain in detail how the renormalization scale enters the tree-level calculations through coupling constants, masses and mixing angles. We then demonstrate a reduction of the renormalization scale dependence through one-loop SUSY-QCD corrections in many different dark matter annihilation channels and enhanced perturbative stability of a mixed on-shell /DR ¯ renormalization scheme over a pure DR ¯ scheme in the top-quark sector. In the stop-stop annihilation channel, the Sommerfeld enhancement and its scale dependence are shown to be of particular importance. Finally, the impact of our higher-order SUSY-QCD corrections and their scale uncertainties are studied in three typical scenarios of the phenomenological minimal supersymmetric standard model with eleven parameters (pMSSM-11). We find that the theoretical uncertainty is reduced in many cases and can become comparable to the size of the experimental one in some scenarios.
Relic density and CMB constraints on dark matter annihilation with Sommerfeld enhancement
Zavala, Jesús; Vogelsberger, Mark; White, Simon D. M.
2010-04-01
We calculate how the relic density of dark matter particles is altered when their annihilation is enhanced by the Sommerfeld mechanism due to a Yukawa interaction between the annihilating particles. Maintaining a dark matter abundance consistent with current observational bounds requires the normalization of the s-wave annihilation cross section to be decreased compared to a model without enhancement. The level of suppression depends on the specific parameters of the particle model, with the kinetic decoupling temperature having the most effect. We find that the cross section can be reduced by as much as an order of magnitude for extreme cases. We also compute the μ-type distortion of the CMB energy spectrum caused by energy injection from such Sommerfeld-enhanced annihilation. Our results indicate that in the vicinity of resonances, associated with bound states, distortions can be large enough to be excluded by the upper limit |μ|≤9.0×10-5 found by the FIRAS (Far Infrared Absolute Spectrophotometer) instrument on the COBE (Cosmic Background Explorer) satellite.
Relic density and CMB constraints on dark matter annihilation with Sommerfeld enhancement
Zavala, Jesus; White, Simon D M
2009-01-01
We calculate how the relic density of dark matter particles is altered when their annihilation is enhanced by the Sommerfeld mechanism due to a Yukawa interaction between the annihilating particles. Maintaining a dark matter abundance consistent with current observational bounds requires the normalization of the s-wave annihilation cross section to be decreased compared to a model without enhancement. The level of suppression depends on the specific parameters of the particle model, with the kinetic decoupling temperature having the most effect. We find that the cross section can be reduced by as much as an order of magnitude for extreme cases. We also compute the mu-type distortion of the CMB energy spectrum caused by energy injection from such Sommerfeld-enhanced annihilation. Our results indicate that in the vicinity of resonances, associated with bound states, distortions can be large enough to be excluded by the upper limit |mu|<9.0x10^(-5) found by the COBE/FIRAS experiment.
Impact of SUSY-QCD corrections to neutralino-squark coannihilation on the dark matter relic density
Harz, Julia [Deutsches Elektronen-Synchrotron, Hamburg (Germany); Herrmann, Bjoern [Laboratoire d' Annecy de Physique Theorique, Annecy-le-Vieux (France); Klasen, Michael [Institute for Theoretical Physics, University of Muenster (Germany); Kovarik, Karol [Karlsruhe Institute of Technology, Karlsruhe (Germany); Le Boulc' h, Quentin [Laboratoire de Physique Subatomique et de Cosmologie, Grenoble (France)
2012-07-01
A powerful method to constrain the parameter space of theories beyond the Standard Model is to compare the predicted dark matter relic density with data from cosmological precision measurements, in particular from the WMAP satellite. On the particle physics side, the main uncertainty on the relic density arises from the (co-)annihilation cross sections of the dark matter particle. After a motivation for including higher order corrections in the prediction of the relic density, the project DM rate at NLO is presented. This software package allows one to compute the neutralino (co-)annihilation cross sections including SUSY-QCD corrections at the one-loop level and to evaluate their effect on the relic density using a link to the public codes MicrOMEGAs and DarkSUSY. Recent results of the impact of SUSY-QCD corrections on the neutralino pair annihilation cross section are discussed, and first results on neutralino-squark coannihilation are shown.
Klasen, Michael; Steppeler, Patrick
2016-01-01
In this paper, we perform a full next-to-leading order (NLO) QCD calculation of neutralino scattering on protons or neutrons in the MSSM. We match the results of the NLO QCD calculation to the scalar and axial-vector operators in the effective field theory approach. These govern the spin-independent and spin-dependent detection rates, respectively. The calculations have been performed for general bino, wino and higgsino decompositions of neutralino dark matter and required a novel tensor reduction method of loop integrals with vanishing relative velocities and Gram determinants. Numerically, the NLO QCD effects are shown to be of at least of similar size and sometimes larger than the currently estimated nuclear uncertainties. We also demonstrate the interplay of the direct detection rate with the relic density when consistently analyzed with the program \\texttt{DMNLO}.
Toma, Takashi
2013-08-30
A gamma-ray excess from the Galactic center consistent with line emission around 130 GeV was recently found in the Fermi-LAT data. Although the Fermi-LAT Collaboration has not confirmed its significance, such a signal would be a clear signature of dark matter annihilation. Until now, there have been many attempts to explain the excess by dark matter. However, these efforts tend to give too-small cross sections into photons if consistency with the correct thermal relic density of dark matter is required. In this Letter, we consider a simple Yukawa interaction that can be compatible with both aspects and show which parameters are favored.
Dark matter relic density from observations of supersymmetry at the ILC
Lehtinen, Suvi-Leena; List, Jenny; Berggren, Mikael [DESY, Hamburg (Germany)
2016-07-01
If supersymmetric particles were discovered at the International Linear Collider (ILC), would we be able to prove that the dark matter candidate discovered is the only dark matter particle? This was investigated using a scenario with a mostly bino lightest supersymmetric particle and a coannihilating stau. In this scenario, the ILC could find the sleptons and lighter gauginos, while the LHC could discover and measure parts of the coloured spectrum. We will demonstrate which measurements and precisions are needed to determine whether the observed dark matter candidate is the sole constituent of the dark matter relic density. The required precisions will be compared to the predicted precisions at the ILC.
Radiative Neutrino Mass with $Z_3$ Dark matter: From Relic Density to LHC Signatures
Ding, Ran; Liao, Yi; Xie, Wan-Peng
2016-01-01
In this work we give a comprehensive analysis on the phenomenology of a specific $\\mathbb{Z}_3$ dark matter (DM) model in which neutrino mass is induced at two loops by interactions with a DM particle that can be a complex scalar or a Dirac fermion. Both the DM properties in relic density and direct detection and the LHC signatures are examined in great detail, and indirect detection for gamma-ray excess from the Galactic Center is also discussed briefly. On the DM side, both semi-annihilation and co-annihilation processes play a crucial role in alleviating the tension of parameter space between relic density and direct detection. On the collider side, new decay channels resulting from $\\mathbb{Z}_3$ particles lead to distinct signals at LHC. Currently the trilepton signal is expected to give the most stringent bound for both scalar and fermion DM candidates, and the signatures of fermion DM are very similar to those of electroweakinos in simplified supersymmetric models.
Impact of SUSY-QCD corrections on neutralino-stop co-annihilation and the neutralino relic density
Harz, J; Klasen, M; Kovarik, K; Boulc'h, Q Le
2013-01-01
We have calculated the full O(alpha_s) supersymmetric QCD corrections to neutralino-stop co-annihilation into electroweak vector and Higgs bosons within the Minimal Supersymmetric Standard Model (MSSM). We performed a parameter study within the phenomenological MSSM and demonstrated that the studied co-annihilation processes are phenomenologically relevant, especially in the context of a 126 GeV Higgs-like particle. By means of an example scenario we discuss the effect of the full next-to-leading order corrections on the co-annihilation cross section and show their impact on the predicted neutralino relic density. We demonstrate that the impact of these corrections on the cosmologically preferred region of parameter space is larger than the current experimental uncertainty of WMAP data.
Impact of SUSY-QCD corrections on neutralino-stop co-annihilation and the neutralino relic density
Harz, Julia [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Herrmann, Bjoern [Savoie Univ./CNRS, Annecy-le-Vieux (France). LAPTh; Klasen, Michael [Muenster Univ. (Germany). Inst. fuer Theoretische Physik 1; Kovarik, Karol [Karlsruher Institut fuer Technologie, Karlsruhe (Germany). Inst. fuer Theoretische Physik; Le Boulc' h, Quentin [Grenoble Univ./CNRS-IN2P3/INPG, Grenoble (France). Lab. de Physique Subatomique et de Cosmologie
2013-02-15
We have calculated the full O({alpha}{sub s}) supersymmetric QCD corrections to neutralino-stop coannihilation into electroweak vector and Higgs bosons within the Minimal Supersymmetric Standard Model (MSSM).We performed a parameter study within the phenomenological MSSM and demonstrated that the studied co-annihilation processes are phenomenologically relevant, especially in the context of a 126 GeV Higgs-like particle. By means of an example scenario we discuss the effect of the full next-to-leading order corrections on the co-annihilation cross section and show their impact on the predicted neutralino relic density. We demonstrate that the impact of these corrections on the cosmologically preferred region of parameter space is larger than the current experimental uncertainty of WMAP data.
$E_6$ Inspired SUSY Benchmarks, Dark Matter Relic Density and a 125 GeV Higgs
Athron, P; Nevzorov, R; Williams, A G
2015-01-01
We explore the relic density of dark matter and the particle spectrum within a constrained version of an $E_6$ inspired SUSY model with an extra $U(1)_N$ gauge symmetry. In this model a single exact custodial symmetry forbids tree-level flavor-changing transitions and the most dangerous baryon and lepton number violating operators. We present a set of benchmark points showing scenarios that have a SM-like Higgs mass of 125 GeV and sparticle masses above the LHC limits. They lead to striking new physics signatures which may be observed during run II of the LHC and can distinguish this model from the simplest SUSY extensions of the SM. At the same time these benchmark scenarios are consistent with the measured dark matter abundance and necessarily lead to large dark matter direct detection cross sections close to current limits and observable soon at the XENON1T experiment.
SUSY-QCD corrections to (co)annihilation and their impact on the relic density
Harz, Julia [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Herrmann, Bjoern [Laboratoire d' Annecy de Physique Theorique, Annecy-le-Vieux (France); Klasen, Michael [Institute for Theoretical Physics, University of Muenster (Germany); Kovarik, Karol [Karlsruher Institut fuer Technologie (KIT), Karlsruhe (Germany); Le Boulc' h, Quentin [Laboratoire de Physique Subatomique et de Cosmologie, Grenoble (France)
2013-07-01
We computed the full O(α{sub s}) supersymmetric QCD corrections for neutralino-stop co-annihilation in the Minimal Supersymmetric Standard Model (MSSM). It is shown that these annihilation channels are phenomenologically relevant within the so-called phenomenological MSSM, in particular in the light of the observation of a Higgs-like particle with a mass of about 126 GeV at the LHC. Numerical results for the co-annihilation cross sections and the predicted neutralino relic density are presented. It will be demonstrated that the impact of including these corrections on the cosmologically preferred region of parameter space is larger than the current experimental uncertainty from WMAP data.
Neutralino relic density from ILC measurements in the CP-violating MSSM
Bélanger, G.; Kittel, O.; Kraml, S.; Martyn, H.-U.; Pukhov, A.
2008-07-01
We discuss ILC measurements for a specific MSSM scenario with CP phases, where the lightest neutralino is a good candidate for dark matter, annihilating efficiently through t-channel exchange of light staus. These prospective (CP-even) ILC measurements are then used to fit the underlying model parameters. A collider prediction of the relic density of the neutralino from this fit gives 0.116<Ωh2<0.19 at 95% C.L. CP-odd observables, while being a direct signal of CP violation, do not help in further constraining Ωh2. The interplay with (in)direct detection of dark matter and with measurements of electric dipole moments is also discussed. Finally we comment on collider measurements at higher energies for refining the prediction of Ωh2.
E6 inspired SUSY benchmarks, dark matter relic density and a 125 GeV Higgs
Athron, Peter; Harries, Dylan; Nevzorov, Roman; Williams, Anthony G.
2016-09-01
We explore the relic density of dark matter and the particle spectrum within a constrained version of an E6 inspired SUSY model with an extra U(1)N gauge symmetry. In this model a single exact custodial symmetry forbids tree-level flavor-changing transitions and the most dangerous baryon and lepton number violating operators. We present a set of benchmark points showing scenarios that have a SM-like Higgs mass of 125 GeV and sparticle masses above the LHC limits. They lead to striking new physics signatures which may be observed during run II of the LHC and can distinguish this model from the simplest SUSY extensions of the SM. At the same time these benchmark scenarios are consistent with the measured dark matter abundance and necessarily lead to large dark matter direct detection cross sections close to current limits and observable soon at the XENON1T experiment.
Chu, Xiaoyong; Hambye, Thomas
2016-01-01
Motivated by the hypothesis that dark matter self-interactions provide a solution to the small-scale structure formation problems, we investigate the possibilities that the relic density of a self-interacting dark matter candidate can proceed from the thermal freeze-out of annihilations into Standard Model particles. We find that scalar and Majorana dark matter in the mass range of $10-500$ MeV, coupled to a slightly heavier massive gauge boson, are the only possible candidates in agreement with multiple current experimental constraints. Here dark matter annihilations take place at a much slower rate than the self-interactions simply because the interaction connecting the Standard Model and the dark matter sectors is small. We also discuss prospects of establishing or excluding these two scenarios in future experiments.
Relic abundance of WIMPs in non-standard cosmological scenarios
Yimingniyazi, W.
2007-08-06
In this thesis we study the relic density n{sub {chi}} of non--relativistic long--lived or stable particles {chi} in various non--standard cosmological scenarios. First, we discuss the relic density in the non--standard cosmological scenario in which the temperature is too low for the particles {chi} to achieve full chemical equilibrium. We also investigated the case where {chi} particles are non--thermally produced from the decay of heavier particles in addition to the usual thermal production. In low temperature scenario, we calculate the relic abundance starting from arbitrary initial temperatures T{sub 0} of the radiation--dominated epoch and derive approximate solutions for the temperature dependence of the relic density which can accurately reproduces numerical results when full thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz no longer reproduces the correct temperature dependence of the {chi} number density. However, we can contrive a semi-analytic formula which gives the correct final relic density, to an accuracy of about 3% or better, for all cross sections and initial temperatures. We also derive the lower bound on the initial temperature T{sub 0}, assuming that the relic particle accounts for the dark matter energy density in the universe. The observed cold dark matter abundance constrains the initial temperature T{sub 0} {>=}m{sub {chi}}/23, where m{sub {chi}} is the mass of {chi}. Second, we discuss the {chi} density in the scenario where the the Hubble parameter is modified. Even in this case, an approximate formula similar to the standard one is found to be capable of predicting the final relic abundance correctly. Choosing the {chi} annihilation cross section such that the observed cold dark matter abundance is reproduced in standard cosmology, we constrain possible modifications of the expansion rate at T {proportional_to}m{sub {chi}}/20, well before Big Bang Nucleosynthesis. (orig.)
The Milky Way Hot Baryons and their Peculiar Density Distribution: a Relic of Nuclear Activity
Nicastro, F; Krongold, Y; Mathur, S; Elvis, M
2016-01-01
We know that our Galaxy is permeated by tenuous, hot, metal-rich gas. However much remains unknown about its origin, the portion of the Galaxy that it permeates, its total mass, as any role it may play in regulating activity in the Galaxy. In a Letter currently in the press with the ApJ, we show that this hot gas permeates both the disk of the Galaxy and a large spherical volume, centered on the Galactic nucleus, and extending out to distances of at least 60-200 kpc from the center. This gas displays a peculiar density distribution that peaks about 6 kpc from the Galaxy's center, likely witnessing a period of strong activity of the central super-massive black hole of the Milky Way that occurred 6 Myrs ago. With our study we are also able to update the total baryonic mass of the Galaxy to Mb = (0.8-4)x1e11 Solar Masses, sufficient to close the Galaxy's baryon census.
Program Calculates Current Densities Of Electronic Designs
Cox, Brian
1996-01-01
PDENSITY computer program calculates current densities for use in calculating power densities of electronic designs. Reads parts-list file for given design, file containing current required for each part, and file containing size of each part. For each part in design, program calculates current density in units of milliamperes per square inch. Written by use of AWK utility for Sun4-series computers running SunOS 4.x and IBM PC-series and compatible computers running MS-DOS. Sun version of program (NPO-19588). PC version of program (NPO-19171).
Arnowitt, Richard; Gurrola, Alfredo; Kamon, Teruki; Krislock, Abram; Toback, David
2008-01-01
We examine the stau-neutralino co-annihilation mechanism of the early universe. We use the minimal supergravity (mSUGRA) model and show that from measurements at the LHC one can predict the dark matter relic density with an uncertainty of 6% with 30 fb-1 of data, which is comparable to the direct measurement by WMAP. This is possible by introducing measurements involving b-quark jets to determine the mSUGRA parameters A0 and tan(beta) without direct measurements of the stop and sbottom masses. Our methods provide precision mass measurements of the gauginos, squark, and lighter stau without the mSUGRA assumption.
Radio Relics in Cosmological Simulations
M. Hoeft; S. E. Nuza; S. Gottlöber; R. J. van Weeren; H. J. A. Röttgering; M. Brüggen
2011-12-01
Radio relics have been discovered in many galaxy clusters. They are believed to trace shock fronts induced by cluster mergers. Cosmological simulations allow us to study merger shocks in detail since the intra-cluster medium is heated by shock dissipation. Using high resolution cosmological simulations, identifying shock fronts and applying a parametric model for the radio emission allows us to simulate the formation of radio relics. We analyze a simulated shock front in detail. We find a rather broad Mach number distribution. The Mach number affects strongly the number density of relativistic electrons in the downstream area, hence, the radio luminosity varies significantly across the shock surface. The abundance of radio relics can be modeled with the help of the radio power probability distribution which aims at predicting radio relic number counts. Since the actual electron acceleration efficiency is not known, predictions for the number counts need to be normalized by the observed number of radio relics. For the characteristics of upcoming low frequency surveys we find that about thousand relics are awaiting discovery.
Density functional calculations of nanoscale conductance
Koentopp, Max; Chang, Connie [Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854 (United States); Burke, Kieron [Department of Chemistry, UC Irvine, 1102 Natural Sciences 2, Irvine, CA 92697 (United States); Car, Roberto [Department of Chemistry and Princeton Institute for the Science and Technology of Materials (PRISM), Princeton University, Princeton, NJ 08544 (United States)
2008-02-27
Density functional calculations for the electronic conductance of single molecules are now common. We examine the methodology from a rigorous point of view, discussing where it can be expected to work, and where it should fail. When molecules are weakly coupled to leads, local and gradient-corrected approximations fail, as the Kohn-Sham levels are misaligned. In the weak bias regime, exchange-correlation corrections to the current are missed by the standard methodology. For finite bias, a new methodology for performing calculations can be rigorously derived using an extension of time-dependent current density functional theory from the Schroedinger equation to a master equation. (topical review)
Realistic level density calculation for heavy nuclei
Cerf, N. [Institut de Physique Nucleaire, Orsay (France); Pichon, B. [Observatoire de Paris, Meudon (France); Rayet, M.; Arnould, M. [Institut d`Astronomie et d`Astrophysique, Bruxelles (Belgium)
1994-12-31
A microscopic calculation of the level density is performed, based on a combinatorial evaluation using a realistic single-particle level scheme. This calculation relies on a fast Monte Carlo algorithm, allowing to consider heavy nuclei (i.e., large shell model spaces) which could not be treated previously in combinatorial approaches. An exhaustive comparison of the predicted neutron s-wave resonance spacings with experimental data for a wide range of nuclei is presented.
Perturbation calculation of thermodynamic density of states.
Brown, G; Schulthess, T C; Nicholson, D M; Eisenbach, M; Stocks, G M
2011-12-01
The density of states g (ε) is frequently used to calculate the temperature-dependent properties of a thermodynamic system. Here a derivation is given for calculating the warped density of states g*(ε) resulting from the addition of a perturbation. The method is validated for a classical Heisenberg model of bcc Fe and the errors in the free energy are shown to be second order in the perturbation. Taking the perturbation to be the difference between a first-principles quantum-mechanical energy and a corresponding classical energy, this method can significantly reduce the computational effort required to calculate g(ε) for quantum systems using the Wang-Landau approach.
Relic galaxies: where are they?
Peralta de Arriba, P.; Quilis, V.; Trujillo, I.; Cebrián, M.; Balcells, M.
2017-03-01
The finding that massive galaxies grow with cosmic time fired the starting gun for the search of objects which could have survived up to the present day without suffering substantial changes (neither in their structures, neither in their stellar populations). Nevertheless, and despite the community efforts, up to now only one firm candidate to be considered one of these relics is known: NGC 1277. Curiously, this galaxy is located at the centre of one of the most rich near galaxy clusters: Perseus. Is its location a matter of chance? Should relic hunters focus their search on galaxy clusters? In order to reply this question, we have performed a simultaneous and analogous analysis using simulations (Millennium I-WMAP7) and observations (New York University Value-Added Galaxy Catalogue). Our results in both frameworks agree: it is more probable to find relics in high density environments.
Pressure Correction in Density Functional Theory Calculations
Lee, S H
2008-01-01
First-principles calculations based on density functional theory have been widely used in studies of the structural, thermoelastic, rheological, and electronic properties of earth-forming materials. The exchange-correlation term, however, is implemented based on various approximations, and this is believed to be the main reason for discrepancies between experiments and theoretical predictions. In this work, by using periclase MgO as a prototype system we examine the discrepancies in pressure and Kohn-Sham energy that are due to the choice of the exchange-correlation functional. For instance, we choose local density approximation and generalized gradient approximation. We perform extensive first-principles calculations at various temperatures and volumes and find that the exchange-correlation-based discrepancies in Kohn-Sham energy and pressure should be independent of temperature. This implies that the physical quantities, such as the equation of states, heat capacity, and the Gr\\"{u}neisen parameter, estimat...
Scalar modes of the relic gravitons
Giovannini, Massimo
2015-01-01
In conformally flat background geometries the long wavelength gravitons can be described in the fluid approximation and they induce scalar fluctuations both during inflation and in the subsequent radiation-dominated epoch. While this effect is minute and suppressed for a de Sitter stage of expansion, the fluctuations of the energy-momentum pseudo-tensor of the graviton fluid lead to curvature perturbations that increase with time all along the post-inflationary evolution. An explicit calculation of these effects is presented for a standard thermal history and it is shown that the growth of the curvature perturbations caused by the long wavelength modes is approximately compensated by the slope of the power spectra of the energy density, pressure and anisotropic stress of the relic gravitons.
Relics: penguin population programs.
Sun, L; Xie, Z
2001-01-01
What has been responsible for the increase in Chinstrap penguin populations during the past 40 years in maritime Antarctica? One view ascribes it to an increase in availability of their prey brought on by the decrease in baleen whale stocks. The contrary opinion, attributes it to environmental warming. This causes a gradual decrease in the frequency of cold years with extensive winter sea ice cover. A number of penguin monitoring programs are in progress and are expected to provide some answers to these questions. Unfortunately, it is not easy to distinguish natural variability from anthropogenic change since penguins are easily accessible predators of krill and the feeding range of the penguins has almost overlapped with the krill fishery in time and space in the last four decades. Therefore it is important to reconstruct the change of ancient penguin abundance and distribution in the absence of human activity. Many efforts have focused on surveying the abandoned penguin rookeries, but this method has not been able to give a continuous historical record of penguin populations. In several recent studies, ancient penguin excreta was scooped from the penguin relics in the sediments of the lake on penguin rookery, Ardley Island, maritime Antarctica. In these studies, penguin droppings or guano soil deposited in the lake and changes in sediment geochemistry have been used to calculate penguin population changes based upon the geochemical composition of the sediment core. The results suggest that climate change has a significant impact on penguin populations.
Energy-Momentum Pseudo-Tensor of Relic Gravitational Wave of Both the Polarized States
ZHANG Xian-Hong; LI Fang-Yu
2006-01-01
Unlike usual celestial gravitational waves, the relic gravitational waves (RGWs) form random signals in curved spacetime background. We calculate the energy-momentum pseudo-tensor of a certain component of the RGWs propagating along arbitrary directions in Cartesian coordinates. It is found that the energy density of RGWs is positive definitely, and the momentum density components have reasonable behaviour. Such results may provide a theoretical basis for the detection of RGWs.
Chang, S.; Coriano, C. [Florida Univ., Gainesville, FL (United States). Inst. for Fundamental Theory; Faraggi, A.E. [Florida Univ., Gainesville, FL (United States). Inst. for Fundamental Theory]|[Inst. for Advanced Study, Princeton, NJ (United States). School of Natural Sciences
1996-05-15
The authors investigate the cosmological constraints on exotic stable matter states which arise in realistic free fermionic superstring models. These states appear in the superstring models due to a ``Wilson-line`` breaking of the unifying non-Abelian gauge symmetry. In the models that they consider the unifying SO(10) gauge symmetry is broken at the string level to SO(6) x SO(4), SU(5) x U(1) or SU(3) x SU(2) x U(1). The exotic matter states are classified according to the patterns of the SO(10) symmetry breaking. In SO(6) x XO(4) and SU(5) x U(1) type models one obtains fractionally charged states with Q{sub e.m.} = {+-}1/2. In SU(3) x SU(2) x U(1) type models one also obtains states with the regular charges under the Standard Model gauge group but with ``fractional`` charges under the U(1){sub z{prime}} symmetry. These states include down-like color triplets and electroweak doublets, as well as states which are Standard Model singlets. By analyzing the renormalizable and nonrenormalizable terms of the superpotential in a specific superstring model, the authors show that these exotic states can be stable. They investigate the cosmological constraints on the masses and relic density of the exotic states. They propose that, while the abundance and the masses of the fractionally charged states are highly constrained, the Standard Model-like states, and in particular the Standard Model singlet, are good dark matter candidates.
Relic Gravitational Waves and Trans-Planckian Physics
WU Pu-Xun; YU Hong-Wei
2005-01-01
@@ Assuming that the effects of trans-Planckian physics are encoded in the choice of initial conditions, mode by mode, for vacuum states at the time when its wavelength becomes equal to the scale of new physics (Planck's scale for example), we calculate the spectrum of energy densities of total relic gravitational waves from de Sitter inflation to the matter dominated universe. Our results show that the spectrum acquires corrections due to the consideration of trans-Planckian physics and these corrections depend sensitively on the vacuum state that was actually realized at the beginning of the inflation.
Density functional calculations on hydrocarbon isodesmic reactions
Fortunelli, Alessandro; Selmi, Massimo
1994-06-01
Hartree—Fock, Hartree—Fock-plus-correlation and self-consistent Kohn—Sham calculations are performed on a set of hydrocarbon isodesmic reactions, i.e. reactions among hydrocarbons in which the number and type of carbon—carbon and carbon—hydrogen bonds is conserved. It is found that neither Hartree—Fock nor Kohn—Sham methods correctly predict standard enthalpies, Δ Hr(298 K), of these reactions, even though — for reactions involving molecules containing strained double bonds — the agreement between the theoretical estimates and the experimental values of Δ Hr seems to be improved by the self-consistent solution of the Kohn—Sham equations. The remaining discrepancies are attributed to intramolecular dispersion effects, that are not described by ordinary exchange—correlation functionals, and are eliminated by introducing corrections based on a simple semi-empirical model.
Exploring the spectroscopic properties of relic radiogalaxies
Capetti, Alessandro; Baldi, Ranieri D; Buttiglione, Sara; Axon, David J; Celotti, Annalisa; Chiaberge, Marco
2013-01-01
From an optical spectroscopic survey of 3CR radiogalaxies (RGs) with z<0.3, we discovered three objects characterized by an extremely low level of gas excitation and a large deficit of line emission with respect to RGs of similar radio luminosity. We interpreted these objects as relic active galactic nuclei (AGN), i.e., sources observed after a large drop in their nuclear activity. We here present new spectroscopic observations for these three galaxies and for a group of "candidate" relics. None of the candidates can be convincingly confirmed. From the new data for the three relics, we estimate the density of the line-emitting gas. This enables us to explore the temporal evolution of the line ratios after the AGN "death". The characteristic timescale is the light-crossing time of the emission line region, a few thousand years, too short to correspond to a substantial population of relic RGs. Additional mechanisms of gas ionization, such as "relic shocks" from their past high power phase or stellar sources,...
2008-01-01
Quake damage leaves worst cultural relic loss in 60 years The deadly earthquake in Sichuan has not only taken tens of thousand of lives and left millions homeless, but it has also had a cultural impact. Standing on the rubble of a temple in Dujiangyan City that was heavily dam- aged after the May 12 earthquake,
A density gradient theory based method for surface tension calculations
Liang, Xiaodong; Michelsen, Michael Locht; Kontogeorgis, Georgios
2016-01-01
The density gradient theory has been becoming a widely used framework for calculating surface tension, within which the same equation of state is used for the interface and bulk phases, because it is a theoretically sound, consistent and computationally affordable approach. Based on the observation...... that the optimal density path from the geometric mean density gradient theory passes the saddle point of the tangent plane distance to the bulk phases, we propose to estimate surface tension with an approximate density path profile that goes through this saddle point. The linear density gradient theory, which...... assumes linearly distributed densities between the two bulk phases, has also been investigated. Numerical problems do not occur with these density path profiles. These two approximation methods together with the full density gradient theory have been used to calculate the surface tension of various...
Galactic abundances as a relic neutrino detection scheme
Riis, Anna Sejersen; Thomas Zinner, Nikolaj; Hannestad, Steen
2011-01-01
We propose to use the threshold-free process of neutrino capture on beta-decaying nuclei (NCB) using all available candidate nuclei in the Milky Way as target material in order to detect the presence of the Cosmic neutrino background. By integrating over the lifetime of the galaxy one might be able....... Secondly, relic neutrinos have so low energy that their de Broglie wavelengths are macroscopic and they may therefore scatter coherently on the electronic cloud of the candidate atoms. One must therefore compare the cross sections for the two processes (induced beta-decay by neutrino capture, and coherent...... scattering of the neutrinos on atomic nuclei) before drawing any conclusions. Finally, the density of target nuclei in the galaxy must be calculated. We assume supernovae as the only production source and approximate the neutrino density as a homogenous background. Here we perform the full calculation...
Density functional calculations of spin-wave dispersion curves.
Kleinman, Leonard; Niu, Qian
1998-03-01
Extending the density functional method of Kubler et al( J. Kubler et al, J. Phys. F 18, 469 (1983) and J. Phys. Condens. Matter 1, 8155 (1989). ) for calcuating spin density wave ground states (but not making their atomic sphere approximation which requires a constant spin polarization direction in each WS sphere) we dicuss the calculation of frozen spin-wave eigenfunctions and their total energies. From these and the results of Niu's talk, we describe the calculation of spin-wave frequencies.
Background Study on Supernova Relic Neutrinos Search in SuperK-Gd
Zhang, Yang
2016-01-01
The detection of supernova relic neutrinos could provide precious information on the evolution of the universe, the formation of stars, the mechanism of supernova bursts and the related neutrino physics. Many experiments, such as Kamland, Borexino, Sudbury Neutrino Observatory and Super-Kamiokande have conducted searches for the supernova relic neutrinos. However, no supernova relic neutrino signal has been observed until now. This paper reports the background study on the supernova relic neutrinos search for the future neutrino experiment in SuperK-Gd project. The expected event rate for various background sources and supernova relic neutrino models are calculated, respectively.
MATERIAL COMPOSITIONS AND NUMBER DENSITIES FOR NEUTRONICS CALCULATIONS
D. A. Thomas
1996-01-02
The purpose of this analysis is to calculate the number densities and isotopic weight percentages of the standard materials to be used in the neutronics (criticality and radiation shielding) evaluations by the Waste Package Development Department. The objective of this analysis is to provide material number density information which can be referenced by future neutronics design analyses, such as for those supporting the Conceptual Design Report.
Joint Density of States Calculation Employing Wang-Landau Algorithm
Kalyan, M. Suman; Bharath, R.; Sastry, V. S. S.; Murthy, K. P. N.
2016-04-01
Joint density of states (JDoS), which depends both on energy and another variable like order parameter provides more information than the conventional density of states (DoS) which depend only on energy. Calculation of JDoS requires huge computational time. In this paper we employ two level method to calculate JDoS which requires relatively much less computational time. We demonstrate this method on a two dimensional Ising spin system, lattice spin model of double strand DNA (dsDNA) and Heisenberg ferromagnet.
Benchmark density functional theory calculations for nanoscale conductance
Strange, Mikkel; Bækgaard, Iben Sig Buur; Thygesen, Kristian Sommer;
2008-01-01
We present a set of benchmark calculations for the Kohn-Sham elastic transmission function of five representative single-molecule junctions. The transmission functions are calculated using two different density functional theory methods, namely an ultrasoft pseudopotential plane-wave code...... in combination with maximally localized Wannier functions and the norm-conserving pseudopotential code SIESTA which applies an atomic orbital basis set. All calculations have been converged with respect to the supercell size and the number of k(parallel to) points in the surface plane. For all systems we find...
Stochastic backgrounds of relic gravitons: a theoretical appraisal
Giovannini, Massimo
2010-01-01
Stochastic backgrounds or relic gravitons, if ever detected, will constitute a prima facie evidence of physical processes taking place during the earliest stages of the evolution of the plasma. The essentials of the stochastic backgrounds of relic gravitons are hereby introduced and reviewed. The pivotal observables customarily employed to infer the properties of the relic gravitons are discussed both in the framework of the $\\Lambda$CDM paradigm as well as in neighboring contexts. The complementarity between experiments measuring the polarization of the Cosmic Microwave Background (such as, for instance, WMAP, Capmap, Quad, Cbi, just to mention a few) and wide band interferometers (e.g. Virgo, Ligo, Geo, Tama) is emphasized. While the analysis of the microwave sky strongly constrains the low-frequency tail of the relic graviton spectrum, wide-band detectors are sensitive to much higher frequencies where the spectral energy density depends chiefly upon the (poorly known) rate of post-inflationary expansion.
Auxiliary Density Matrix Methods for Hartree-Fock Exchange Calculations.
Guidon, Manuel; Hutter, Jürg; VandeVondele, Joost
2010-08-10
The calculation of Hartree-Fock exchange (HFX) is computationally demanding for large systems described with high-quality basis sets. In this work, we show that excellent performance and good accuracy can nevertheless be obtained if an auxiliary density matrix is employed for the HFX calculation. Several schemes to derive an auxiliary density matrix from a high-quality density matrix are discussed. Key to the accuracy of the auxiliary density matrix methods (ADMM) is the use of a correction based on standard generalized gradient approximations for HFX. ADMM integrates seamlessly in existing HFX codes and, in particular, can be employed in linear scaling implementations. Demonstrating the performance of the method, the effect of HFX on the structure of liquid water is investigated in detail using Born-Oppenheimer molecular dynamics simulations (300 ps) of a system of 64 molecules. Representative for large systems are calculations on a solvated protein (Rubredoxin), for which ADMM outperforms the corresponding standard HFX implementation by approximately a factor 20.
Relic Radio Bubbles and Cluster Cooling Flows
De Young, D S
2003-01-01
Recent suggestions that buoyant radio emitting cavities in the intracluster medium can cause significant reheating of cooling flows are re-examined when the effects of the intracluster magnetic field are included. Expansion of the cavity creates a tangential magnetic field in the ICM around the radio source, and this field can suppress instabilities that mix the ICM and the radio source. The onset of instability can be delayed for ~100 million years, and calculation of the actual reheating time shows that this may not occur until about 1Gy after creation of the cavity. These results may explain why the relic radio bubbles are still intact at such late times, and it may imply that the role of radio sources in reheating the ICM should be re-examined. In addition, the existence of relic radio cavities may also imply that the particle content of radio source lobes is primarily electrons and protons rather than electrons and positrons.
Density Functional Calculations for the Neutron Star Matter at Subnormal Density
Kashiwaba, Yu; Nakatsukasa, Takashi
The pasta phases of nuclear matter, whose existence is suggested at low density, may influence observable properties of neutron stars. In order to investigate properties of the neutron star matter, we calculate self-consistent solutions for the ground states of slab-like phase using the microscopic density functional theory with Bloch wave functions. The calculations are performed at each point of fixed average density and proton fraction (\\bar{ρ },Yp), varying the lattice constant of the unit cell. For small Yp values, the dripped neutrons emerge in the ground state, while the protons constitute the slab (crystallized) structure. The shell effect of protons affects the thickness of the slab nuclei.
Linear Scaling Density Functional Calculations with Gaussian Orbitals
Scuseria, Gustavo E.
1999-01-01
Recent advances in linear scaling algorithms that circumvent the computational bottlenecks of large-scale electronic structure simulations make it possible to carry out density functional calculations with Gaussian orbitals on molecules containing more than 1000 atoms and 15000 basis functions using current workstations and personal computers. This paper discusses the recent theoretical developments that have led to these advances and demonstrates in a series of benchmark calculations the present capabilities of state-of-the-art computational quantum chemistry programs for the prediction of molecular structure and properties.
Relic gravitational waves from quintessential inflation
Ahmad, Safia; Myrzakulov, R.; Sami, M.
2017-09-01
We study relic gravitational waves in the paradigm of quintessential inflation. In this framework, irrespective of the underlying model, inflation is followed by the kinetic regime. Thereafter, the field energy density remains subdominant before the onset of acceleration. We carry out model-independent analysis to obtain the temperature at the end of inflation and the estimate for the upper bound on the Hubble parameter to circumvent the problem due to relic gravitational waves. In this process, we use Planck 2015 data to constrain the inflationary phase. We demonstrate that the required temperature can be produced by the mechanism of instant preheating. The generic feature of the scenario includes the presence of the kinetic regime after inflation, which results in the blue spectrum of gravitational wave background at high frequencies. We discuss the prospects of detection of relic gravitational wave background in the advanced LIGO and LISA space-born gravitational wave missions. Finally, we consider a concrete model to realize the paradigm of quintessential inflation and show that inflationary as well as postinflationary evolution can be successfully described by the inflaton potential, V (ϕ )∝Exp (-λ ϕn/MPln)(n >1 ) , by suitably constraining the parameters of the model.
Kaluza-Klein relics from warped reheating
Berndsen, Aaron; Stoica, Horace
2007-01-01
It has been suggested that after brane-antibrane inflation in a Klebanov-Strassler (KS) warped throat, metastable Kaluza-Klein (KK) excitations can be formed due to nearly-conserved angular momenta along isometric directions in the throat. If sufficiently long-lived, these relics could conflict with big bang nucleosynthesis or baryogenesis by dominating the energy density of the universe. We make a detailed estimate of the decay rate of such relics using the low energy effective action of type IIB string theory compactified on the throat geometry, with attention to powers of the warp factor. We find that it is necessary to turn on SUSY-breaking deformations of the KS background in order to ensure that the most dangerous relics will decay. The decay rate is found to be much larger than the naive guess based on the dimension of the operators which break the angular isometries of the throat. For an inflationary warp factor of order w ~ 10^{-4}, we obtain the bound M_{3/2} > 10^8 GeV on the scale of SUSY breaking...
Can cluster merger shocks reproduce the luminosity and shape distribution of radio relics?
Nuza, Sebastián E.; Gelszinnis, Jakob; Hoeft, Matthias; Yepes, Gustavo
2017-09-01
Radio relics in galaxy clusters are believed to trace merger shock fronts. If cosmological structure formation determines the luminosity, size and shape distributions of radio relics, then merger shocks need to be lighted up in a homogeneous way. We investigate if a mock relic sample, obtained from zoomed galaxy cluster simulations, is able to match the properties of relics measured in the NRAO VLA Sky Survey (NVSS). We compile a list of all radio relics known to date and homogeneously measure their parameters in all NVSS images and apply the same procedure to relics in our simulations. Number counts in the mock relic sample increase more steeply towards lower relic flux densities, suggesting an incompleteness of NVSS in this regime. Overall, we find that NVSS and mock samples show similar properties. However, large simulated relics tend to be somewhat smaller and closer to the cluster centre than observed ones. Besides this, the mock sample reproduces very well-known correlations for radio relics, in particular those relating the radio luminosity with the largest linear size and the X-ray luminosity. We show that these correlations are largely governed by the sensitivity of the NVSS observations. Mock relics show a similar orientation with respect to the direction to the cluster centre as the NVSS sample. Moreover, we find that their maximum radio luminosity roughly correlates with cluster mass, although displaying a large scatter. The overall good agreement between NVSS and the mock sample suggests that properties of radio relics are indeed governed by merger shock fronts, emitting in a homogeneous fashion. Our study demonstrates that the combination of mock observations and data from upcoming radio surveys will allow us to shed light on both the origin of radio relics and the nature of the intracluster medium.
On high-order perturbative calculations at finite density
Ghisoiu, Ioan
2017-01-01
We discuss the prospects of performing high-order perturbative calculations in systems characterized by a vanishing temperature but finite density. In particular, we show that the determination of generic Feynman integrals containing fermionic chemical potentials can be reduced to the evaluation of three-dimensional phase space integrals over vacuum on-shell amplitudes. Applications of these rules will be discussed in the context of the thermodynamics of cold and dense QCD, where it is argued that they facilitate an extension of the Equation of State of cold quark matter to higher perturbative orders.
On high-order perturbative calculations at finite density
Ghişoiu, Ioan; Gorda, Tyler; Kurkela, Aleksi; Romatschke, Paul; Säppi, Matias; Vuorinen, Aleksi
2017-02-01
We discuss the prospects of performing high-order perturbative calculations in systems characterized by a vanishing temperature but finite density. In particular, we show that the determination of generic Feynman integrals containing fermionic chemical potentials can be reduced to the evaluation of three-dimensional phase space integrals over vacuum on-shell amplitudes - a result reminiscent of a previously proposed "naive real-time formalism" for vacuum diagrams. Applications of these rules are discussed in the context of the thermodynamics of cold and dense QCD, where it is argued that they facilitate an extension of the Equation of State of cold quark matter to higher perturbative orders.
Self-interaction corrected local spin density calculations of actinides
Petit, Leon; Svane, Axel; Szotek, Z
2010-01-01
We use the self-interaction corrected local spin-density approximation in order to describe localization-delocalization phenomena in the strongly correlated actinide materials. Based on total energy considerations, the methodology enables us to predict the ground-state valency configuration...... of the actinide ions in these compounds from first principles. Here we review a number of applications, ranging from electronic structure calculations of actinide metals, nitrides and carbides to the behaviour under pressure of intermetallics, and O vacancies in PuO2....
Calculations of Optical Rotation from Density Functional Theory
António Canal Neto; Francisco Elias Jorge
2007-01-01
Density function theory calculations of frequency-dependent optical rotations [α]ω for three rigid chiral molecules are reported. Calculations have been carried out at the sodium D line frequency, using the ADZP basis set and a wide variety of functionals. Gauge-invariant atomic orbitals are used to guarantee origin-independent values of [α]D. In addition, study of geometry dependence of [α]D. Is reported. Using the geometries optimized at the B3LYP/ADZP level, the mean absolute deviation of B3LYP/ADZP and experimental [α]D values yields 60.1°/(dm g/cm3). According to our knowledge, this value has not been achieved until now with any other model.
Reliability of Calculated Low-Density Lipoprotein Cholesterol.
Meeusen, Jeffrey W; Snozek, Christine L; Baumann, Nikola A; Jaffe, Allan S; Saenger, Amy K
2015-08-15
Aggressive low-density lipoprotein cholesterol (LDL-C)-lowering strategies are recommended for prevention of cardiovascular events in high-risk populations. Guidelines recommend a 30% to 50% reduction in at-risk patients even when LDL-C concentrations are between 70 and 130 mg/dl (1.8 to 3.4 mmol/L). However, calculation of LDL-C by the Friedewald equation is the primary laboratory method for routine LDL-C measurement. We compared the accuracy and reproducibility of calculated LDL-C <130 mg/dl (3.4 mmol/L) to LDL-C measured by β quantification (considered the gold standard method) in 15,917 patients with fasting triglyceride concentrations <400 mg/dl (4.5 mmol/L). Both variation and bias of calculated LDL-C increased at lower values of measured LDL-C. The 95% confidence intervals for a calculated LDL-C of 70 mg/dl (1.8 mmol/L) and 30 mg/dl (0.8 mmol/L) were 60 to 86 mg/dl (1.6 to 2.2 mmol/L) and 24 to 60 mg/dl (0.6 to 1.6 mmol/L), respectively. Previous recommendations have emphasized the requirement for a fasting sample with triglycerides <400 mg/dl (4.5 mmol/L) to calculate LDL-C by the Friedewald equation. However, no recommendations have addressed the appropriate lower reportable limit for calculated LDL-C. In conclusion, calculated LDL-C <30 mg/dl (0.8 mmol/L) should not be reported because of significant deviation from the gold standard measured LDL-C results, and caution is advised when using calculated LDL-CF values <70 mg/dl (1.8 mmol/L) to make treatment decisions.
Dark Matter Relic Abundance and Light Sterile Neutrinos
Tang, Yi-Lei
2016-01-01
In this paper, we calculate the relic abundance of the dark matter particles when they can annihilate into sterile neutrinos with the mass $\\lesssim 100 \\text{ GeV}$ in a simple model. Unlike the usual standard calculations, the sterile neutrino may fall out of the thermal equilibrium with the thermal bath before the dark matter freezes out. In such case, if the Yukawa coupling between Higgs and sterile neutrino $y_N$ is small, this process gives rise to a larger $\\Omega_{\\text{DM}} h^2$ so we need a larger coupling between dark matter and the sterile neutrino for a correct relic abundance.
Tran, Fabien; Blaha, Peter
2017-05-04
Recently, exchange-correlation potentials in density functional theory were developed with the goal of providing improved band gaps in solids. Among them, the semilocal potentials are particularly interesting for large systems since they lead to calculations that are much faster than with hybrid functionals or methods like GW. We present an exhaustive comparison of semilocal exchange-correlation potentials for band gap calculations on a large test set of solids, and particular attention is paid to the potential HLE16 proposed by Verma and Truhlar. It is shown that the most accurate potential is the modified Becke-Johnson potential, which, most noticeably, is much more accurate than all other semilocal potentials for strongly correlated systems. This can be attributed to its additional dependence on the kinetic energy density. It is also shown that the modified Becke-Johnson potential is at least as accurate as the hybrid functionals and more reliable for solids with large band gaps.
Accurate ionization potential of semiconductors from efficient density functional calculations
Ye, Lin-Hui
2016-07-01
Despite its huge successes in total-energy-related applications, the Kohn-Sham scheme of density functional theory cannot get reliable single-particle excitation energies for solids. In particular, it has not been able to calculate the ionization potential (IP), one of the most important material parameters, for semiconductors. We illustrate that an approximate exact-exchange optimized effective potential (EXX-OEP), the Becke-Johnson exchange, can be used to largely solve this long-standing problem. For a group of 17 semiconductors, we have obtained the IPs to an accuracy similar to that of the much more sophisticated G W approximation (GWA), with the computational cost of only local-density approximation/generalized gradient approximation. The EXX-OEP, therefore, is likely as useful for solids as for finite systems. For solid surfaces, the asymptotic behavior of the vx c has effects similar to those of finite systems which, when neglected, typically cause the semiconductor IPs to be underestimated. This may partially explain why standard GWA systematically underestimates the IPs and why using the same GWA procedures has not been able to get an accurate IP and band gap at the same time.
Direct detection of relic active and sterile neutrinos
Li, Yu-Feng
2016-01-01
Both active and sterile sub-eV neutrinos can form the cosmic neutrino background in the early Universe. We consider the beta-decaying (e.g., $^3$H) and EC-decaying (e.g., $^{163}$Ho) nuclei as the promising targets to capture relic neutrinos in the laboratory. We calculate the capture rates of relic electron neutrinos and antineutrinos against the corresponding beta decay or electron capture (EC) decay backgrounds in the (3+$N_{\\rm s}$) flavor mixing scheme, and discuss the future prospect in terms of the PTOLEMY project. We stress that such direct measurements of hot DM might not be hopeless in the long term.
Velders, G.J.M.; Feil, D.
1989-01-01
Quantum-chemical density-functional theory (DFT) calculations, using the local-density approximation (LDA), have been performed for hydrogen-bounded silicon clusters to determine the electron density distribution of the Si-Si bond. The density distribution in the bonding region is compared with calc
Relic Radiation from an Evaporating Black Hole
Farley, A N St J
2007-01-01
We present a non-string-theoretic calculation of the microcanonical entropy of relic integer-spin Hawking radiation -- at fixed total energy $E$. The only conserved macroscopic quantity is the total energy $E$ (the total energy of the relic radiation). Data for a boundary-value approach, with massless, integer-spin perturbations, are set on initial and final space-like hypersurfaces. In the resulting 1-dimensional statistical-mechanics problem, the real part of the (complex) time separation at spatial infinity, $T = {\\mid}T{\\mid}\\exp(-i\\delta), \\delta >0$, is the variable conjugate to the total energy. We count the number of weak-field configurations on the final space-like hypersurface with energy $E$. One recovers the Cardy formula and the Bekenstein-Hawking entropy, if Re(T) is of the order of the black-hole life- time, leading to a statistical interpretation of black-hole entropy. The microcanonical entropy includes a logarithmic correction to the black-hole area law, which is {\\it universal} (independent...
The death of FRII radio sources and their connection with radio relics
Kaiser, C R; Kaiser, Christian R.; Cotter, Garret
2002-01-01
Radio relic sources in galaxy clusters are often described as the remnants of powerful radio galaxies. Here we develop a model for the evolution of such relics after the jets cease to supply energy to the lobes. This includes the treatment of a relic overpressured with respect to its gaseous surroundings even after the jets switch off. We also determine the radio emission of relics for a large variety of assumptions. We take into account the evolution of the strength of the magnetic field during the phase of relativistic particle injection into the lobes. The resulting spectra show mild steepening at around 1 GHz but avoid any exponential spectral cut-offs. The model calculations are used to fit the observed spectra of six radio relics. The quality of the fits is excellent for {\\it all} models discussed. Unfortunately, this implies that it is virtually impossible to determine any of the important source parameters from the observed radio emission alone.
Time dependent density functional calculation of plasmon response in clusters
Wang Feng(王锋); Zhang Feng-Shou(张丰收); Eric Suraud
2003-01-01
We have introduced a theoretical scheme for the efficient description of the optical response of a cluster based on the time-dependent density functional theory. The practical implementation is done by means of the fully fledged timedependent local density approximation scheme, which is solved directly in the time domain without any linearization.As an example we consider the simple Na2 cluster and compute its surface plasmon photoabsorption cross section, which is in good agreement with the experiments.
Inverse Calculation of Power Density for Laser Surface Treatment
Römer, G.R.B.E.; Meijer, J.
2000-01-01
Laser beam surface treatment requires a well-defined temperature profile. In this paper an analytic method is presented to solve the inverse problem of heat conduction in solids, based on the 2-dimensional Fourier transform. As a result, the required power density profile of the laser beam can be ca
Orbital-Free Density Functional Theory for Molecular Structure Calculations
Huajie Chen; Aihui Zhou
2008-01-01
We give here an overview of the orbital-free density functional theory that is used for modeling atoms and molecules. We review typical approximations to the kinetic energy, exchange-correlation corrections to the kinetic and Hartree energies, and constructions of the pseudopotentials. We discuss numerical discretizations for the orbital-free methods and include several numerical results for illustrations.
Inverse calculation of power density for laser surface treatment
Römer, Gerardus Richardus, Bernardus, Engelina; Meijer, J.
2000-01-01
Laser beam surface treatment requires a well-defined temperature profile. In this paper an analytic method is presented to solve the inverse problem of heat conduction in solids, based on the 2-dimensional Fourier transform. As a result, the required power density profile of the laser beam can be
Reproducibility in density functional theory calculations of solids
Lejaeghere, Kurt; Bihlmayer, Gustav; Björkman, Torbjörn
2016-01-01
The widespread popularity of density functional theory has given rise to an extensive range of dedicated codes for predicting molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions about the reproducibility of such predictions. We r...
Inverse calculation of power density for laser surface treatment
Römer, Gerardus Richardus, Bernardus, Engelina; Meijer, J.
2000-01-01
Laser beam surface treatment requires a well-defined temperature profile. In this paper an analytic method is presented to solve the inverse problem of heat conduction in solids, based on the 2-dimensional Fourier transform. As a result, the required power density profile of the laser beam can be ca
RELICS: Reionization Lensing Cluster Survey
Coe, Dan A.; RELICS Team
2017-01-01
Hubble and Spitzer imaging programs observing galaxy cluster lenses have delivered some of the highest redshift galaxy candidates to date (z ~ 9 - 11, or 540 - 410 Myr after the Big Bang). These magnified galaxies are intrinsically faint, and thus more representative of the sources believed to be primarily responsible for reionization. Magnified galaxies are also observed brightly enough to be prime targets for detailed follow-up study with current and future observatories, including JWST. Building on the successes of CLASH and the Frontier Fields, we have begun RELICS, the Reionization Lensing Cluster Survey. By observing 41 massive clusters for the first time at infrared wavelengths, RELICS will deliver more of the best and brightest high-redshift candidates to the community in time for the November 2017 JWST GO Cycle 1 call for proposals. I will present our early results. I will also discuss prospects for JWST to follow-up known candidates and discover new galaxies at even higher redshifts (z > 11). The discovery efficiency gains from lensing will be even more pronounced at z > 11 if luminosity function faint end slopes are steeper than alpha ~ -2, as suggested by current models and observational extrapolations.
Reproducibility in density functional theory calculations of solids
2016-01-01
This is the author accepted manuscript.The final version is available from the American Association for the Advancement of Science via http://dx.doi.org/10.1126/science.aad3000 The widespread popularity of density-functional theory has given rise to a vast range of dedicated codes to predict molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions on the reproducibility of such predictions. We report the results of a community-...
Calculate Electric Field Gradient of TiO2 Within Density Functional Theory
2008-01-01
<正>TiO2 electric field gradient has been calculated utilizing WIEN2K program, which is ab initio based on density function theory (DFT). DFT uses the charge density as a variable instead of electronic wave
Relic abundance of MeV millicharged particles
Dolgov, A D
2016-01-01
The relic abundance of light millicharged particles (MCP) with the electric charge $e' = 5\\cdot 10^{-5} e$ and with the mass slightly below or above the electron mass is calculated. The abundance depends on the mass ratio $\\eta=m_X/m_e$ and for $\\eta<1$ can be high enough to allow MCP to be the cosmological dark matter or to make a noticeable contribution to it. On the other hand, for $\\eta \\gtrsim 1$ the cosmological energy density of MCPs can be quite low, $\\Omega_X h_0^2 \\simeq 0.02$ for scalar MCPs, and $\\Omega_X h_0^2 \\simeq 0.001$ for spin 1/2 fermions. But even the lowest value of $\\Omega_X h_0^2$ is in tension with several existing limits on the MCP abundances and parameters. However, these limits have been derived under some natural or reasonable assumptions on the properties of MCPs. If these assumptions are relaxed, a patch in the mass-charge plot of MCPs may appear, permitting them to be dark matter particles.
Spectrum of the Supernova Relic Neutrino Background and Metallicity Evolution of Galaxies
Nakazato, Ken'ichiro; Niino, Yuu; Suzuki, Hideyuki
2015-01-01
The spectrum of the supernova relic neutrino (SRN) background from past stellar collapses including black hole formation (failed supernovae) is calculated. The redshift dependence of the black hole formation rate is considered on the basis of the metallicity evolution of galaxies. Assuming the mass and metallicity ranges of failed supernova progenitors, their contribution to SRNs is quantitatively estimated for the first time. Using this model, the dependences of SRNs on the cosmic star formation rate density, shock revival time and equation of state are investigated. The shock revival time is introduced as a parameter that should depend on the still unknown explosion mechanism of core collapse supernovae. The dependence on equation of state is considered for failed supernovae, whose collapse dynamics and neutrino emission are certainly affected. It is found that the low-energy spectrum of SRNs is mainly determined by the cosmic star formation rate density. These low-energy events will be observed in the Supe...
Shock Acceleration Model for the Toothbrush Radio Relic
Kang, Hyesung; Ryu, Dongsu; Jones, T. W.
2017-05-01
Although many of the observed properties of giant radio relics detected in the outskirts of galaxy clusters can be explained by relativistic electrons accelerated at merger-driven shocks, significant puzzles remain. In the case of the so-called Toothbrush relic, the shock Mach number estimated from X-ray observations ({M}{{X}}≈ 1.2{--}1.5) is substantially weaker than that inferred from the radio spectral index ({M}{rad}≈ 2.8). Toward understanding such a discrepancy, we here consider the following diffusive shock acceleration (DSA) models: (1) weak-shock models with {M}{{s}}≲ 2 and a preexisting population of cosmic-ray electrons (CRe) with a flat energy spectrum, and (2) strong-shock models with {M}{{s}}≈ 3 and either shock-generated suprathermal electrons or preexisting fossil CRe. We calculate the synchrotron emission from the accelerated CRe, following the time evolution of the electron DSA, and the subsequent radiative cooling and postshock turbulent acceleration (TA). We find that both models could reproduce reasonably well the observed integrated radio spectrum of the Toothbrush relic, but the observed broad transverse profile requires the stochastic acceleration by downstream turbulence, which we label “turbulent acceleration” or TA to distinguish it from DSA. Moreover, to account for the almost uniform radio spectral index profile along the length of the relic, the weak-shock models require a preshock region over 400 kpc with a uniform population of preexisting CRe with a high cutoff energy (≳ 40 {GeV}). Due to the short cooling time, it is challenging to explain the origin of such energetic electrons. Therefore, we suggest the strong-shock models with low-energy seed CRe (≲ 150 {MeV}) are preferred for the radio observations of this relic.
Density functional theory calculations on dipeptide gallic acid interaction
Madhan, B.; Parthasarathi, R.; Subramanian, V.; Raghava Rao, J.; Nair, Balachandran Unni; Ramasami, T.
2003-02-01
In the present investigation, an attempt has been made to study the interaction of dipeptides with gallic acid, using Becke3 parameter Lee Yang Parr (B3LYP) method employing 3-21G*, 6-31G* and 6-31+G* basis sets. The interaction energies of the dipeptide-gallic acid complexes are in the range of -5 to -18 kcal/mol depending on the mode of intermolecular complexation. Calculated molecular electrostatic potential (MESP) for the various intermolecular complexes revealed the electrostatic nature of the interaction. Qualitative estimations based on chemical hardness and chemical potential demonstrated fractional electron transfer from dipeptide to gallic acid.
Advanced density matrix renormalization group method for nuclear structure calculations
Legeza, Ö; Poves, A; Dukelsky, J
2015-01-01
We present an efficient implementation of the Density Matrix Renormalization Group (DMRG) algorithm that includes an optimal ordering of the proton and neutron orbitals and an efficient expansion of the active space utilizing various concepts of quantum information theory. We first show how this new DMRG methodology could solve a previous $400$ KeV discrepancy in the ground state energy of $^{56}$Ni. We then report the first DMRG results in the $pf+g9/2$ shell model space for the ground $0^+$ and first $2^+$ states of $^{64}$Ge which are benchmarked with reference data obtained from Monte Carlo shell model. The corresponding correlation structure among the proton and neutron orbitals is determined in terms of the two-orbital mutual information. Based on such correlation graphs we propose several further algorithmic improvement possibilities that can be utilized in a new generation of tensor network based algorithms.
Advanced density matrix renormalization group method for nuclear structure calculations
Legeza, Ã.-.; Veis, L.; Poves, A.; Dukelsky, J.
2015-11-01
We present an efficient implementation of the Density Matrix Renormalization Group (DMRG) algorithm that includes an optimal ordering of the proton and neutron orbitals and an efficient expansion of the active space utilizing various concepts of quantum information theory. We first show how this new DMRG methodology could solve a previous 400 keV discrepancy in the ground state energy of 56Ni. We then report the first DMRG results in the p f +g 9 /2 shell model space for the ground 0+ and first 2+ states of 64Ge which are benchmarked with reference data obtained from a Monte Carlo shell model. The corresponding correlation structure among the proton and neutron orbitals is determined in terms of two-orbital mutual information. Based on such correlation graphs we propose several further algorithmic improvement possibilities that can be utilized in a new generation of tensor network based algorithms.
Alhassid Y.
2014-04-01
Full Text Available The shell model Monte Carlo (SMMC method enables calculations in model spaces that are many orders of magnitude larger than those that can be treated by conventional methods, and is particularly suitable for the calculation of level densities in the presence of correlations. We review recent advances and applications of SMMC for the microscopic calculation of level densities. Recent developments include (i a method to calculate accurately the ground-state energy of an odd-mass nucleus, circumventing a sign problem that originates in the projection on an odd number of particles, and (ii a method to calculate directly level densities, which, unlike state densities, do not include the spin degeneracy of the levels. We calculated the level densities of a family of nickel isotopes 59−64Ni and of a heavy deformed rare-earth nucleus 162Dy and found them to be in close agreement with various experimental data sets.
Alhassid, Y; Liu, S; Mukherjee, A; Nakada, H
2014-01-01
The shell model Monte Carlo (SMMC) method enables calculations in model spaces that are many orders of magnitude larger than those that can be treated by conventional methods, and is particularly suitable for the calculation of level densities in the presence of correlations. We review recent advances and applications of SMMC for the microscopic calculation of level densities. Recent developments include (i) a method to calculate accurately the ground-state energy of an odd-mass nucleus, circumventing a sign problem that originates in the projection on an odd number of particles, and (ii) a method to calculate directly level densities, which, unlike state densities, do not include the spin degeneracy of the levels. We calculated the level densities of a family of nickel isotopes $^{59-64}$Ni and of a heavy deformed rare-earth nucleus $^{162}$Dy and found them to be in close agreement with various experimental data sets.
Challenging Density Functional Theory Calculations with Hemes and Porphyrins
Sam P. de Visser
2016-04-01
Full Text Available In this paper we review recent advances in computational chemistry and specifically focus on the chemical description of heme proteins and synthetic porphyrins that act as both mimics of natural processes and technological uses. These are challenging biochemical systems involved in electron transfer as well as biocatalysis processes. In recent years computational tools have improved considerably and now can reproduce experimental spectroscopic and reactivity studies within a reasonable error margin (several kcal·mol−1. This paper gives recent examples from our groups, where we investigated heme and synthetic metal-porphyrin systems. The four case studies highlight how computational modelling can correctly reproduce experimental product distributions, predicted reactivity trends and guide interpretation of electronic structures of complex systems. The case studies focus on the calculations of a variety of spectroscopic features of porphyrins and show how computational modelling gives important insight that explains the experimental spectra and can lead to the design of porphyrins with tuned properties.
Antisites in III-V semiconductors: Density functional theory calculations
Chroneos, A.
2014-07-14
Density functional based simulation, corrected for finite size effects, is used to investigate systematically the formation of antisite defects in III-V semiconductors (III=Al, Ga, and In and V=P, As, and Sb). Different charge states are modelled as a function of the Fermi level and under different growth conditions. The formation energies of group III antisites (III V q) decrease with increasing covalent radius of the group V atom though not group III radius, whereas group V antisites (V I I I q) show a consistent decrease in formation energies with increase in group III and group V covalent radii. In general, III V q defects dominate under III-rich conditions and V I I I q under V-rich conditions. Comparison with equivalent vacancy formation energy simulations shows that while antisite concentrations are always dominant under stoichiometric conditions, modest variation in growth or doping conditions can lead to a significantly higher concentration of vacancies. © 2014 AIP Publishing LLC.
Antisites in III-V semiconductors: Density functional theory calculations
Chroneos, A., E-mail: alex.chroneos@open.ac.uk [Engineering and Innovation, The Open University, Milton Keynes MK7 6AA (United Kingdom); Tahini, H. A. [Department of Materials, Imperial College London, London SW7 2AZ (United Kingdom); PSE Division, KAUST, Thuwal 23955-6900 (Saudi Arabia); Schwingenschlögl, U., E-mail: udo.schwingenschlogl@kaust.edu.sa [PSE Division, KAUST, Thuwal 23955-6900 (Saudi Arabia); Grimes, R. W., E-mail: r.grimes@imperial.ac.uk [Department of Materials, Imperial College London, London SW7 2AZ (United Kingdom)
2014-07-14
Density functional based simulation, corrected for finite size effects, is used to investigate systematically the formation of antisite defects in III-V semiconductors (III = Al, Ga, and In and V = P, As, and Sb). Different charge states are modelled as a function of the Fermi level and under different growth conditions. The formation energies of group III antisites (III{sub V}{sup q}) decrease with increasing covalent radius of the group V atom though not group III radius, whereas group V antisites (V{sub III}{sup q}) show a consistent decrease in formation energies with increase in group III and group V covalent radii. In general, III{sub V}{sup q} defects dominate under III-rich conditions and V{sub III}{sup q} under V-rich conditions. Comparison with equivalent vacancy formation energy simulations shows that while antisite concentrations are always dominant under stoichiometric conditions, modest variation in growth or doping conditions can lead to a significantly higher concentration of vacancies.
A shock at the radio relic position in Abell 115
Botteon, A; Brunetti, G; Dallacasa, D
2016-01-01
We analyzed a deep Chandra observation (334 ks) of the galaxy cluster Abell 115 and detected a shock co-spatial with the radio relic. The X-ray surface brightness profile across the shock region presents a discontinuity, corresponding to a density compression factor $\\mathcal{C}=2.0\\pm0.1$ leading to a Mach number $\\mathcal{M}=1.7\\pm0.1$ ($\\mathcal{M}=1.4-2$ including systematics). Temperatures measured in the upstream and downstream regions are consistent with what expected for such a shock: $T_u=4.3^{+1.0}_{-0.6}\\:\\rm{keV}$ and $T_d=7.9^{+1.4}_{-1.1}\\:\\rm{keV}$ respectively, implying a Mach number $\\mathcal{M}=1.8^{+0.5}_{-0.4}$. So far, only few other shocks discovered in galaxy clusters are consistently detected from both density and temperature jumps. The spatial coincidence between this discontinuity and the radio relic edge strongly supports the view that shocks play a crucial role in powering these synchrotron sources. We suggest that the relic is originated by shock re-acceleration of relativistic el...
Magnetic domain walls of relic neutrinos as Dark Energy
Yajnik, U A
2006-01-01
The observed Dark Energy component of the cosmic energy density is well fitted by domain wall matter which scales as $S(t)^{-1}$ where $S$ is the Friedmann-Robertson-Walker (FRW) scale factor. We show that relic neutrinos of the Big Bang can enter a ferromagnetic state governed by Stoner theory provided they are a degenerate gas and possess a magnetic moment. The domain walls of this ferromagnetism behave as Dark Energy. The degeneracy requirement accords with Big Bang nucleosynthesis expectations of large chemical potentials for neutrinos and provides an estimate for the same. At least one of the the mass eigenstate neutrinos would have to possess a magnetic moment greater than $10^{-9}$ Bohr magneton. Any other relic contributing to Hot Dark Matter could also provide an interesting candidate.
Informing saccharide structural NMR studies with density functional theory calculations.
Klepach, Thomas; Zhao, Hongqiu; Hu, Xiaosong; Zhang, Wenhui; Stenutz, Roland; Hadad, Matthew J; Carmichael, Ian; Serianni, Anthony S
2015-01-01
Density functional theory (DFT) is a powerful computational tool to enable structural interpretations of NMR spin-spin coupling constants ( J-couplings) in saccharides, including the abundant (1)H-(1)H ( JHH), (13)C-(1)H ( JCH), and (13)C-(13)C ( JCC) values that exist for coupling pathways comprised of 1-4 bonds. The multiple hydroxyl groups in saccharides, with their attendant lone-pair orbitals, exert significant effects on J-couplings that can be difficult to decipher and quantify without input from theory. Oxygen substituent effects are configurational and conformational in origin (e.g., axial/equatorial orientation of an OH group in an aldopyranosyl ring; C-O bond conformation involving an exocyclic OH group). DFT studies shed light on these effects, and if conducted properly, yield quantitative relationships between a specific J-coupling and one or more conformational elements in the target molecule. These relationships assist studies of saccharide structure and conformation in solution, which are often challenged by the presence of conformational averaging. Redundant J-couplings, defined as an ensemble of J-couplings sensitive to the same conformational element, are particularly helpful when the element is flexible in solution (i.e., samples multiple conformational states on the NMR time scale), provided that algorithms are available to convert redundant J-values into meaningful conformational models. If the latter conversion is achievable, the data can serve as a means of testing, validating, and refining theoretical methods like molecular dynamics (MD) simulations, which are currently relied upon heavily to assign conformational models of saccharides in solution despite a paucity of experimental data needed to independently validate the method.
The origin of linear scaling Fock matrix calculation with density prescreening
Mitin, Alexander V., E-mail: mitin@phys.chem.msu.ru [Chemistry Department, Moscow State University, Moscow, 119991 (Russian Federation)
2015-12-31
A theorem was proven, which reads that the number of nonzero two-electron integrals scales linearly with respect to the number of basis functions for large molecular systems. This permits to show that linear scaling property of the Fock matrix calculation with using density prescreening arises due to linear scaling properties of the number of nonzero two-electron integrals and the number of leading matrix elements of density matrix. This property is reinforced by employing the density prescreening technique. The use of the density difference prescreening further improves the linear scaling property of the Fock matrix calculation method. As a result, the linear scaling regime of the Fock matrix calculation can begin from the number of basis functions of 2000–3000 in dependence on the basis function type in molecular calculations. It was also shown that the conventional algorithm of Fock matrix calculation from stored nonzero two-electron integrals with density prescreening possesses linear scaling property.
Relic Gravitational Waves and Their Detection
Grishchuk, L P
2001-01-01
The range of expected amplitudes and spectral slopes of relic (squeezed)gravitational waves, predicted by theory and partially supported byobservations, is within the reach of sensitive gravity-wave detectors. In themost favorable case, the detection of relic gravitational waves can be achievedby the cross-correlation of outputs of the initial laser interferometers inLIGO, VIRGO, GEO600. In the more realistic case, the sensitivity of advancedground-based and space-based laser interferometers will be needed. The specificstatistical signature of relic gravitational waves, associated with thephenomenon of squeezing, is a potential reserve for further improvement of thesignal to noise ratio.
Numeric Spectrum of Relic Gravitational Waves in Accelerating Universe
ZHANG Yang; ZHAO Wen; YUAN Ye-Fei; XIA Tian-Yang
2005-01-01
@@ The accelerating expansion of the Universe in the present stage is a process that will change the spectrum of relic gravitational waves. Here we present a numerical calculation for the power spectrum of relic gravitational waves in the accelerating Universe. The results show that although the overall features of the power spectrum are similar to those in the non-accelerating models, the amplitude is smaller in order of 10-1. We also find that the spectrum is very sensitive to the index β of the inflationary expansion with the scale factor a(τ) ∝ |τ|1+β. With increase of β, the resulting spectrum tends to be flatter with more power on high frequencies, and the sensitivity of the second science run of the LIGO detectors puts a restriction on the parameterβ＜ -1.8. The influence of reheating followed by the inflation has been examined.
Special Stamps:Historical Relic Beacons
2002-01-01
In May 2002, the State Postal Bureau issued a set of five stamps picturing historical relic beacons. They are the Mao Beacon, the Jiangxinyu Twin Beacon, the Huaniaoshan Beacon, the Laotieshan Beacon, and
Cosmic relics from the big bang
Hall, L.J.
1988-12-01
A brief introduction to the big bang picture of the early universe is given. Dark matter is discussed; particularly its implications for elementary particle physics. A classification scheme for dark matter relics is given. 21 refs., 11 figs., 1 tab.
Toward a better parameterization of nuclear density for α-decay calculation
Ismail, M.; Ellithi, A.Y. [Physics Department, Faculty of Science, Cairo University, Giza (Egypt); Adel, A. [Physics Department, Faculty of Science, Cairo University, Giza (Egypt); Physics Department, College of Science, Majmaah University, Al Zulfi (Saudi Arabia); Abdulghany, A.R., E-mail: abdulghany@sci.cu.edu.eg [Physics Department, Faculty of Science, Cairo University, Giza (Egypt)
2016-03-15
Starting from three-parameter Fermi distribution of nuclear densities, we used two formulas, for calculating the half-density radius, to study the effect of variation of radius of daughter nucleus on both α-decay half-life and α-preformation factor. We compared the results of the aforementioned two formulas with the corresponding results obtained from the nuclear densities of Hartree–Fock calculation derived from the BSk2 Skyrme force. We considered >60 isotopes of Po and Rn α-emitter elements and studied the variation of half-life and preformation factor with density parameters. We found that the variation of density parameters of daughter nuclei highly affects the calculated half-life and the extracted value of preformation factor, but the behavior of these two quantities with variation of parent neutron number is almost independent of the density parameters.
Relic Gravitational Waves and Their Detection
Grishchuk, L. P.
2000-01-01
The range of expected amplitudes and spectral slopes of relic (squeezed) gravitational waves, predicted by theory and partially supported by observations, is within the reach of sensitive gravity-wave detectors. In the most favorable case, the detection of relic gravitational waves can be achieved by the cross-correlation of outputs of the initial laser interferometers in LIGO, VIRGO, GEO600. In the more realistic case, the sensitivity of advanced ground-based and space-based laser interferom...
Relics and episcopal Authority in Sasanian Iran
Héctor Ricardo Francisco
2017-06-01
Full Text Available This paper analyzes the relationship between episcopacy and the cult of the relics in Sasanian Empire. It will be argued that the cult of martyrs’ relics contributed to the shift in the definition of episcopal Authority in the Church of the East in Fifth Century. In this regard, the tensions over the control of Christian shrines cannot be understood as an actual conflict between preexistent lay and clerical elites.
Relic Abundance in Secluded Dark Matter Scenario with Massive Mediator
Okawa, Shohei; Yamanaka, Masato
2016-01-01
The relic abundance of the dark matter (DM) particle $d$ is studied in a secluded DM scenario, in which the $d$ number decreasing process dominantly occurs not through the pair annihilation of $d$ into the standard model particles, but via the $dd \\to mm$ scattering process with a subsequently decaying mediator particle $m$. It is pointed out that the cosmologically observed relic abundance of DM can be accomplished even with a massive mediator having a mass $m_m$ non-negligibly heavy compared with the DM particle mass $m_d$. In the degenerated $d$-$m$ case ($m_d=m_m$), the DM relic abundance is realized by adjusting the $dd \\to mm$ scattering amplitude large enough and by choosing an appropriate mediator particle life-time. The DM evolution in the early universe exhibits characteristic "terrace" behavior, or two-step number density decreasing behavior, having a "fake" freeze-out at the first step. Based on these observations, a novel possibility of the DM model buildings is introduced in which the mediator p...
Kreutzfeldt, C
1980-10-01
A calculation program is proposed suitable for programmable pocket calculators (e.g. HP series) to estimate s20,w f omega2 dt values from density gradient centrifugation data. The program can be applied to linear or exponential density gradients prepared from sucrose or glycerol solutions spun in zonal rotors or swinging bucket rotors. A wide solute concentration range and temperature range is accounted for. Constants for empirical density calculation of glycerol and sucrose solutions concentrated in % (w/v) are estimated. Experimental verification of the program was carried out.
Lutnæs, Ola B.; Teale, Andrew M.; Helgaker, Trygve; Tozer, David J.; Ruud, Kenneth; Gauss, Jürgen
2009-10-01
An accurate set of benchmark rotational g tensors and magnetizabilities are calculated using coupled-cluster singles-doubles (CCSD) theory and coupled-cluster single-doubles-perturbative-triples [CCSD(T)] theory, in a variety of basis sets consisting of (rotational) London atomic orbitals. The accuracy of the results obtained is established for the rotational g tensors by careful comparison with experimental data, taking into account zero-point vibrational corrections. After an analysis of the basis sets employed, extrapolation techniques are used to provide estimates of the basis-set-limit quantities, thereby establishing an accurate benchmark data set. The utility of the data set is demonstrated by examining a wide variety of density functionals for the calculation of these properties. None of the density-functional methods are competitive with the CCSD or CCSD(T) methods. The need for a careful consideration of vibrational effects is clearly illustrated. Finally, the pure coupled-cluster results are compared with the results of density-functional calculations constrained to give the same electronic density. The importance of current dependence in exchange-correlation functionals is discussed in light of this comparison.
Two new confirmed massive relic galaxies: red nuggets in the present-day Universe
Ferré-Mateu, Anna; Trujillo, Ignacio; Martín-Navarro, Ignacio; Vazdekis, Alexandre; Mezcua, Mar; Balcells, Marc; Domínguez, Lilian
2017-01-01
We confirm two new local massive relic galaxies, i.e. untouched survivors of the early universe massive population: Mrk 1216 and PGC 032873. Both show early and peaked formation events within very short timescales (formation histories remain virtually unchanged out to several effective radii, even when considering the steeper IMF values inferred out to ˜3 effective radii. Their morphologies, kinematics and density profiles are like those found in the z>2 massive population, setting them apart of the typical z˜0 massive early-type galaxies. We find that there seems to exist a degree of relic that is related on how far into the path to become one of these typical z˜0 massive galaxies the compact relic has undergone. This path is partly dictated by the environment the galaxy lives in. For galaxies in rich environments, such as the previously reported relic galaxy NGC 1277, the most extreme properties (e.g. sizes, short formation timescales, larger super-massive black holes) are expected, while lower density environments will have galaxies with delayed and/or extended star formations, slightly larger sizes and not that extreme black hole masses. The confirmation of 3 relic galaxies up to a distance of 106 Mpc implies a lower limit in the number density of these red nuggets in the local universe of 6× 10-7 Mpc3, which is within the theoretical expectations.
Herceg, Matija; Artemieva, Irina; Thybo, Hans
2016-01-01
We investigate how uncertainties in seismic and density structure of the crust propagate to uncertainties in mantle density structure. The analysis is based on interpretation of residual upper-mantle gravity anomalies which are calculated by subtracting (stripping) the gravitational effect of the...
Zobelli, Alberto [Laboratoire de Physique des Solides, Univ. Paris Sud, CNRS UMR, Orsay (France); Ivanovskaya, Viktoria; Wagner, Philipp; Yaya, Abu; Ewels, Chris P. [Institut des Materiaux Jean Rouxel (IMN), CNRS UMR, University of Nantes (France); Suarez-Martinez, Irene [Nanochemistry Research Institute, Curtin University of Technology, Perth, Western Australia (Australia)
2012-02-15
The density functional tight binding approach (DFTB) is well adapted for the study of point and line defects in graphene based systems. After briefly reviewing the use of DFTB in this area, we present a comparative study of defect structures, energies, and dynamics between DFTB results obtained using the dftb+ code, and density functional results using the localized Gaussian orbital code, AIMPRO. DFTB accurately reproduces structures and energies for a range of point defect structures such as vacancies and Stone-Wales defects in graphene, as well as various unfunctionalized and hydroxylated graphene sheet edges. Migration barriers for the vacancy and Stone-Wales defect formation barriers are accurately reproduced using a nudged elastic band approach. Finally we explore the potential for dynamic defect simulations using DFTB, taking as an example electron irradiation damage in graphene. DFTB-MD derived sputtering energy threshold map for a carbon atom in a graphene plane. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Introduction to Density Functional Theory: Calculations by Hand on the Helium Atom
Baseden, Kyle A.; Tye, Jesse W.
2014-01-01
Density functional theory (DFT) is a type of electronic structure calculation that has rapidly gained popularity. In this article, we provide a step-by-step demonstration of a DFT calculation by hand on the helium atom using Slater's X-Alpha exchange functional on a single Gaussian-type orbital to represent the atomic wave function. This DFT…
Full charge-density calculation of the surface energy of metals
Vitos, Levente; Kollár, J..; Skriver, Hans Lomholt
1994-01-01
of the linear-muffin-tin-orbitals (LMTO) method and the ASA in surface calculations. We find that the full charge-density functional improves the agreement with recent full-potential LMTO calculations to a level where the average deviation in surface energy over the 4d series is down to 10%....
Pillai, Sharad Babu; Narayan, Som; Jha, Prafulla K.
2017-05-01
The present paper reports the study of phonon properties of a two dimensional antimony nanosheet under the biaxial strain using first principles calculation based on density functional theory. Our calculations shows that the strain turns the quadratic dependence of wave vector on frequency to the linear dependency which can be linked with the removal of rippling in nanosheets.
Introduction to Density Functional Theory: Calculations by Hand on the Helium Atom
Baseden, Kyle A.; Tye, Jesse W.
2014-01-01
Density functional theory (DFT) is a type of electronic structure calculation that has rapidly gained popularity. In this article, we provide a step-by-step demonstration of a DFT calculation by hand on the helium atom using Slater's X-Alpha exchange functional on a single Gaussian-type orbital to represent the atomic wave function. This DFT…
First-principle Calculations of Equation of State for Metals at High Energy Density
Minakov, Dmitry; Levashov, Pavel; Khishchenko, Konstantin
2012-02-01
In this work, we present quantum molecular dynamics calculations of the shock Hugoniots of solid and porous samples as well as release isentropes and isentropic sound velocity behind the shock front for aluminum. Also we perform similar calculations for nickel and iron. We use the VASP code with ultrasoft and PAW pseudopotentials and GGA exchange-correlation functional. Up to 512 particles have been used in calculations. To calculate Hugoniots we solve the Hugoniot equation numerically. To obtain release isentropes, we use Zel'dovich's approach and integrate an ordinary differential equation for the temperature thus restoring all thermodynamic parameters. Isentropic sound velocity is calculated by differentiation of pressure along isentropes. The results of our calculations are in good agreement with experimental data at densities both higher and lower than the normal one. Thus, quantum molecular dynamics results can be effectively used for verification or calibration of semiempirical equations of state under conditions of lack of experimental information at high energy densities.
Density-functional calculations for rare-earth atoms and ions
Forstreuter, J.; Steinbeck, L.; Richter, M.; Eschrig, H.
1997-04-01
Relativistic local-spin-density (RLSD) and self-interaction-corrected (SIC) RLSD calculations were performed for the whole series of the rare-earth elements. Ionization potentials and radial expectation values with 4f wave functions were calculated. Improvement on nearly all quantities is found for SIC calculations. Comparison with other calculational methods shows that for a description of rare-earth elements SIC-RLSD competes well in accuracy with all of them, including the most accurate quantum-chemical approach. This is important since the SIC calculation has the advantage of being suited for a description of localized f states in solids with a comparatively moderate effort.
Density functional calculation of equilibrium geometry and electronic structure of pyrite
邱冠周; 肖奇; 胡岳华; 徐竞
2001-01-01
The equilibrium geometry and electronic structure of pyrite has been studied using self-consistent density-functional theory within the local density approximation (LDA). The optimum bulk geometry is in good agreement with crystallographic data. The calculated band structure and density of states in the region around the Fermi energy show that valence-band maximum (VBM) is at X (100), and the conduction-band minimum (CBM) is at G (000). The indirect and direct band gaps are 0.6eV and 0.74eV, respectively. The calculated contour map of difference of charge density shows excess charge in nonbonding d electron states on the Fe sites. The density increases between sulfur nuclei and between iron and sulfur nuclei qualitatively reveal that S-S bond and Fe-S bond are covalent binding.
Washiyama, K; Avez, B; Bender, M; Heenen, P -H; Hellemans, V
2012-01-01
[Background] Symmetry restoration and configuration mixing in the spirit of the generator coordinate method based on energy density functionals have become widely used techniques in low-energy nuclear structure physics. Recently, it has been pointed out that these techniques are ill-defined for standard Skyrme functionals, and a regularization procedure has been proposed to remove the resulting spuriosities from such calculations. This procedure imposes an integer power of the density for the density dependent terms of the functional. At present, only dated parameterizations of the Skyrme interaction fulfill this condition. [Purpose] To construct a set of parameterizations of the Skyrme energy density functional for multi-reference energy density functional calculations with regularization using the state-of-the-art fitting protocols. [Method] The parameterizations were adjusted to reproduce ground state properties of a selected set of doubly magic nuclei and properties of nuclear matter. Subsequently, these ...
Relics as Probes of Galaxy Cluster Mergers
R. J. van Weeren; M. Brüggen; H. J. A. Röttgering; M. Hoeft
2011-12-01
Galaxy clusters grow by mergers with other clusters and galaxy groups. These mergers create shocks within the intracluster medium (ICM). It is proposed that particles can be accelerated to extreme energies within the shocks. In the presence of a magnetic field these particles should then form large regions emitting synchrotron radiation, creating the so-called radio relics. An example of a cluster with relics is CIZA J2242.8+5301. Here we present hydrodynamical simulations of idealized binary cluster collisions with the aim of constraining the merger scenario for this cluster. We conclude that by using the location, size and width of double radio relics we can set constraints on the mass ratios, impact parameters, time scales, and viewing geometries of binary cluster merger events.
Semilocal and Hybrid Density Embedding Calculations of Ground-State Charge-Transfer Complexes
Laricchia, S; Della Sala, F; 10.1063/1.4795825
2013-01-01
We apply the frozen density embedding method, using a full relaxation of embedded densities through a freeze-and-thaw procedure, to study the electronic structure of several benchmark ground-state charge-transfer complexes, in order to assess the merits and limitations of the approach for this class of systems. The calculations are performed using both semilocal and hybrid exchange-correlation (XC) functionals. The results show that embedding calculations using semilocal XC functionals yield rather large deviations with respect to the corresponding supermolecular calculations. Due to a large error cancellation effect, however, they can often provide a relatively good description of the electronic structure of charge-transfer complexes, in contrast to supermolecular calculations performed at the same level of theory. On the contrary, when hybrid XC functionals are employed, both embedding and supermolecular calculations agree very well with each other and with the reference benchmark results. In conclusion, fo...
Li, Hui; Shi, LiLi; Zhang, Min; Su, Zhongmin; Wang, XiuJun; Hu, LiHong; Chen, GuanHua
2007-04-14
The combination of genetic algorithm and neural network approach (GANN) has been developed to improve the calculation accuracy of density functional theory. As a demonstration, this combined quantum mechanical calculation and GANN correction approach has been applied to evaluate the optical absorption energies of 150 organic molecules. The neural network approach reduces the root-mean-square (rms) deviation of the calculated absorption energies of 150 organic molecules from 0.47 to 0.22 eV for the TDDFTB3LYP6-31G(d) calculation, and the newly developed GANN correction approach reduces the rms deviation to 0.16 eV.
Beckwith, A W
2008-01-01
We present a way to accomodate relic graviton production via worm hole transitions of prior universe thermal / energy density values to our present universe. This is done in the context of providing a mechanism for thermally driven relic gravitons, and also to explain how Park's 2003 observation as to how a thermally scaled vacuum energy value plays a role in forming the early universe emergent field dynamics
Tellgren, E I; Teale, A M; Furness, J W; Lange, K K; Ekström, U; Helgaker, T
2014-01-21
We present a novel implementation of Kohn-Sham density-functional theory utilizing London atomic orbitals as basis functions. External magnetic fields are treated non-perturbatively, which enable the study of both magnetic response properties and the effects of strong fields, using either standard density functionals or current-density functionals-the implementation is the first fully self-consistent implementation of the latter for molecules. Pilot applications are presented for the finite-field calculation of molecular magnetizabilities, hypermagnetizabilities, and nuclear magnetic resonance shielding constants, focusing on the impact of current-density functionals on the accuracy of the results. Existing current-density functionals based on the gauge-invariant vorticity are tested and found to be sensitive to numerical details of their implementation. Furthermore, when appropriately regularized, the resulting magnetic properties show no improvement over standard density-functional results. An advantage of the present implementation is the ability to apply density-functional theory to molecules in very strong magnetic fields, where the perturbative approach breaks down. Comparison with high accuracy full-configuration-interaction results show that the inadequacies of current-density approximations are exacerbated with increasing magnetic field strength. Standard density-functionals remain well behaved but fail to deliver high accuracy. The need for improved current-dependent density-functionals, and how they may be tested using the presented implementation, is discussed in light of our findings.
Tellgren, E. I., E-mail: erik.tellgren@kjemi.uio.no; Lange, K. K.; Ekström, U.; Helgaker, T. [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); Teale, A. M., E-mail: andrew.teale@nottingham.ac.uk [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom); Furness, J. W. [School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)
2014-01-21
We present a novel implementation of Kohn–Sham density-functional theory utilizing London atomic orbitals as basis functions. External magnetic fields are treated non-perturbatively, which enable the study of both magnetic response properties and the effects of strong fields, using either standard density functionals or current-density functionals—the implementation is the first fully self-consistent implementation of the latter for molecules. Pilot applications are presented for the finite-field calculation of molecular magnetizabilities, hypermagnetizabilities, and nuclear magnetic resonance shielding constants, focusing on the impact of current-density functionals on the accuracy of the results. Existing current-density functionals based on the gauge-invariant vorticity are tested and found to be sensitive to numerical details of their implementation. Furthermore, when appropriately regularized, the resulting magnetic properties show no improvement over standard density-functional results. An advantage of the present implementation is the ability to apply density-functional theory to molecules in very strong magnetic fields, where the perturbative approach breaks down. Comparison with high accuracy full-configuration-interaction results show that the inadequacies of current-density approximations are exacerbated with increasing magnetic field strength. Standard density-functionals remain well behaved but fail to deliver high accuracy. The need for improved current-dependent density-functionals, and how they may be tested using the presented implementation, is discussed in light of our findings.
Calculating electron momentum densities and Compton profiles using the linear tetrahedron method.
Ernsting, D; Billington, D; Haynes, T D; Millichamp, T E; Taylor, J W; Duffy, J A; Giblin, S R; Dewhurst, J K; Dugdale, S B
2014-12-10
A method for computing electron momentum densities and Compton profiles from ab initio calculations is presented. Reciprocal space is divided into optimally-shaped tetrahedra for interpolation, and the linear tetrahedron method is used to obtain the momentum density and its projections such as Compton profiles. Results are presented and evaluated against experimental data for Be, Cu, Ni, Fe3Pt, and YBa2Cu4O8, demonstrating the accuracy of our method in a wide variety of crystal structures.
Density-functional calculation of van der Waals forces for free-electron-like surfaces
Hult, E.; Hyldgaard, P.; Rossmeisl, Jan;
2001-01-01
A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well as for the in......A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well...... as for the interaction between the surfaces themselves. The densities and static image-plane positions that are needed as input in the van der Waals functional are calculated self-consistently within density-functional theory using the generalized-gradient approximation, pseudopotentials, and plane waves. This study...... shows that the van der Waals density functional is applicable to realistic surfaces. The need for physically correct surface models, especially for open surfaces, is also illustrated. Finally the parameters for the anisotropic interaction of O-2 with Al are calculated....
Ringholm, Magnus; Ruud, Kenneth [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø – The Arctic University of Norway, 9037 Tromsø (Norway); Bast, Radovan [Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, AlbaNova University Center, S-10691 Stockholm (Sweden); PDC Center for High Performance Computing, Royal Institute of Technology, S-10044 Stockholm (Sweden); Oggioni, Luca [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø – The Arctic University of Norway, 9037 Tromsø (Norway); Department of Physics G. Occhialini, University of Milano Bicocca, Piazza della scienza 3, 20126 Milan (Italy); Ekström, Ulf [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, 0315 Oslo (Norway)
2014-10-07
We present the first analytic calculations of the geometrical gradients of the first hyperpolarizability tensors at the density-functional theory (DFT) level. We use the analytically calculated hyperpolarizability gradients to explore the importance of electron correlation effects, as described by DFT, on hyper-Raman spectra. In particular, we calculate the hyper-Raman spectra of the all-trans and 11-cis isomers of retinal at the Hartree-Fock (HF) and density-functional levels of theory, also allowing us to explore the sensitivity of the hyper-Raman spectra on the geometrical characteristics of these structurally related molecules. We show that the HF results, using B3LYP-calculated vibrational frequencies and force fields, reproduce the experimental data for all-trans-retinal well, and that electron correlation effects are of minor importance for the hyper-Raman intensities.
Ringholm, Magnus; Bast, Radovan; Oggioni, Luca; Ekström, Ulf; Ruud, Kenneth
2014-10-01
We present the first analytic calculations of the geometrical gradients of the first hyperpolarizability tensors at the density-functional theory (DFT) level. We use the analytically calculated hyperpolarizability gradients to explore the importance of electron correlation effects, as described by DFT, on hyper-Raman spectra. In particular, we calculate the hyper-Raman spectra of the all-trans and 11-cis isomers of retinal at the Hartree-Fock (HF) and density-functional levels of theory, also allowing us to explore the sensitivity of the hyper-Raman spectra on the geometrical characteristics of these structurally related molecules. We show that the HF results, using B3LYP-calculated vibrational frequencies and force fields, reproduce the experimental data for all-trans-retinal well, and that electron correlation effects are of minor importance for the hyper-Raman intensities.
Density functional theory approach for calculation of dielectric properties of warm dense matter
Saitov, Ilnur
2015-06-01
The reflectivity of shocked xenon was measured in the experiments of Mintsev and Zaporoghets for wavelength 1064 nm. But there is no adequate theoretical explanation of these reflectivity results in the framework of the standard methods of nonideal plasma theory. The assumption of significant width to the shock front gives a good agreement with the experimental data. However, there are no evidences of this effect in the experiment. Reflectivity of shocked compressed xenon plasma is calculated in the framework of the density functional theory approach as in. Dependencies on the frequency of incident radiation and on the plasma density are analyzed. The Fresnel formula for the reflectivity is used. The longitudinal expression in the long wavelength limit is applied for the calculation of the imaginary part of the dielectric function. The real part of the dielectric function is calculated by means of the Kramers-Kronig transformation. The approach for the calculation of plasma frequency is developed.
Roondhe, Basant; Upadhyay, Deepak; Som, Narayan; Pillai, Sharad B.; Shinde, Satyam; Jha, Prafulla K.
2017-03-01
The structural, electronic, dynamical and thermodynamical properties of CmX (X = N, P, As, Sb, and Bi) compounds are studied using first principles calculations within density functional theory. The Perdew-Burke-Ernzerhof spin polarized generalized gradient approximation and Perdew-Wang (PW) spin polarized local density approximation as the exchange correlational functionals are used in these calculations. There is a good agreement between the present and previously reported data. The calculated electronic density of states suggests that the curium monopnictides are metallic in nature, which is consistent with earlier studies. The significant values of magnetic moment suggest their magnetic nature. The phonon dispersion curves and phonon density of states are also calculated, which depict the dynamical stability of these compounds. There is a significant separation between the optical and acoustical phonon branches. The temperature dependence of the thermodynamical functions are also calculated and discussed. Internal energy and vibrational contribution to the Helmholtz free energy increases and decreases, respectively, with temperature. The entropy increases with temperature. The specific heat at constant volume and Debye temperature obey Debye theory. The temperature variation of the considered thermodynamical functions is in line with those of other crystalline solids.
Challenges to our understanding of radio relics: X-ray observations of the Toothbrush cluster
Ogrean, G. A.; Brüggen, M.; van Weeren, R. J.; Röttgering, H.; Croston, J. H.; Hoeft, M.
2013-07-01
The cluster 1RXS J0603.3+4214 is a merging galaxy cluster that hosts three radio relics and a giant radio halo. The northern relic, the Toothbrush, is 1.9 Mpc long and has an unusual linear morphology. According to simple diffusive shock acceleration theory, its radio spectral index indicates a Mach number of 3.3-4.6. Here, we present results from a deep XMM-Newton observation of the cluster. We observe two distinct cluster cores that have survived the merger. The presence of three shocks at or near the locations of the radio relics is confirmed by density and temperature discontinuities. However, the observation poses several puzzles that challenge our understanding of radio relics: (i) at the Toothbrush, the shock Mach number is not larger than 2, in apparent conflict with the shock strength predicted from the radio spectrum; (ii) at the Toothbrush, the shock front is, in part, spatially offset from the radio emission; (iii) at the eastern relic, we detect a temperature jump corresponding to a Mach number of approximately 2.5, but there is no associated surface brightness discontinuity. We discuss possible explanations for these findings.
Challenges to our understanding of radio relics: X-ray observations of the Toothbrush cluster
Ogrean, G A; van Weeren, R J; Röttgering, H; Croston, J H; Hoeft, M
2013-01-01
The cluster 1RXS J0603.3+4214 is a merging galaxy cluster that hosts three radio relics and a giant radio halo. The northern relic, the Toothbrush, is 1.9-Mpc long and has an unusual linear morphology. According to simple diffusive shock acceleration theory, its radio spectral index indicates a Mach number of 3.3-4.6. Here, we present results from a deep XMM-Newton observation of the cluster. We observe two distinct cluster cores that have survived the merger. The presence of three shocks at or near the locations of the radio relics is confirmed by density and temperature discontinuities. However, the observation poses several puzzles that challenge our understanding of radio relics: (i) at the Toothbrush, the shock Mach number is not larger than 2, in apparent conflict with the shock strength predicted from the radio spectrum; (ii) at the Toothbrush, the shock front is, in part, spatially offset from the radio emission; (iii) at the eastern relic, we detect a temperature jump corresponding to a Mach number o...
Jacobsen, C.J.H.; Dahl, Søren; Boisen, A.
2002-01-01
For ammonia synthesis catalysts a volcano-type relationship has been found experimentally. We demonstrate that by combining density functional theory calculations with a microkinetic model the position of the maximum of the volcano curve is sensitive to the reaction conditions. The catalytic ammo......-principle quantum mechanical calculations of gas-surface interactions, reactor design, and catalyst selection has been established for the first time....
Hybrid density functional theory LCAO calculations on phonons in Ba (Ti,Zr,Hf) O3
Evaestov, Robert A
2010-01-01
Phonon frequencies at {\\Gamma},X,M,R-points of Brilloin zone in cubic phase of Ba(Ti,Zr,Hf)O3 were first time calculated by frozen phonon method using density functional theory (DFT) with hybrid exchange correlation functional PBE0. The calculations use linear combination of atomic orbitals (LCAO) basis functions as implemented in CRYSTAL09 computer code. The Powell algorithm was applied for basis set optimization. In agreement with the experimental observations the structural instability via...
Green Function Approach to the Calculation of the Local Density of States in the Graphitic Nanocone
Smotlacha Jan
2016-01-01
Full Text Available Graphene and other nanostructures belong to the center of interest of today’s physics research. The local density of states of the graphitic nanocone influenced by the spin–orbit interaction was calculated. Numerical calculations and the Green function approach were used to solve this problem. It was proven in the second case that the second order approximation is not sufficient for this purpose.
HU Xiangqian; LI Lemin
2004-01-01
The regionalized computational method is extended to the non-relativistic, scalar and 2-component relativistic density functional calculation of large systems containing transition series or heavy main-group metal elements. A large system is divided into several regions which can be considered as relatively independent quantum mechanical subsystems. Taking into account the Coulomb and exchange-correlation potentials as well as the Pauli repulsion exerted by the other subsystems, the Kohn-Sham equation related to subsystem K can be written as: (FK+FKP)CK =SKCKεK K=A,B,C,…，where FK,CK,SK,εK are the Fock matrix, the matrix of combination coefficients of orbitals, the overlap matrix of basis sets and the energy eigenvalue matrix, respectively. The matrix FKP reflects the Pauli repulsion from the other subsystems.FK may be non-relativistic, scalar or 2-component relativistic Fock matrix determined by the theoretical method related to the density functional calculations. The other matrices are mated with FK. Solving the Kohn-Sham equation for every subsystem and combining the results from the subsystem calculations, the electronic structural information of the whole system is derived. The density functional calculation of several molecules containing transition metal Ni or heavy main-group metal Tl or Bi is performed by the afore-mentioned regionalization algorithm. The obtained results for each molecule are compared with those from the density functional calculation of that molecule in its entirety in order to check the feasibility of the regionalization algorithm. It is found that with sufficiently large regional basis set in the subsystem calculation the accuracy of the results calculated by the regionalization algorithm is essentially the same as that from the calculation of the molecule in its entirety. With proper smaller regional basis sets the accuracy of the results calculated with the regionalization algorithm can still match the actual accuracy of the
Wampler, William R.; Myers, Samuel M.; Modine, Normand A.
2017-09-01
The energy-dependent probability density of tunneled carrier states for arbitrarily specified longitudinal potential-energy profiles in planar bipolar devices is numerically computed using the scattering method. Results agree accurately with a previous treatment based on solution of the localized eigenvalue problem, where computation times are much greater. These developments enable quantitative treatment of tunneling-assisted recombination in irradiated heterojunction bipolar transistors, where band offsets may enhance the tunneling effect by orders of magnitude. The calculations also reveal the density of non-tunneled carrier states in spatially varying potentials, and thereby test the common approximation of uniform- bulk values for such densities.
China＇s New Cultural Relics Protection Law
XinYuan
2003-01-01
The 30th session of the standing committee of the ninth National People's Congress approved the amended Cultural Relics Protection Law of the People's Republic of China. The new 12，000-word law has a total of 80 articles in eight chapters: General Principles, Unmovable Cultural Relics, Archaeological Excavation, Nuseums' Cultural Relics,
Washiyama, K.; Bennaceur, K.; Avez, B.; Bender, M.; Heenen, P.-H.; Hellemans, V.
2012-11-01
Background: Symmetry restoration and configuration mixing in the spirit of the generator coordinate method based on energy density functionals have become widely used techniques in low-energy nuclear structure physics. Recently, it has been pointed out that these techniques are ill defined for standard Skyrme functionals, and a regularization procedure has been proposed to remove the resulting spuriosities from such calculations. This procedure imposes an integer power of the density for the density-dependent terms of the functional. At present, only dated parametrizations of the Skyrme interaction fulfill this condition.Purpose: To construct a set of parametrizations of the Skyrme energy density functional for multireference energy density functional calculations with regularization using the state-of-the-art fitting protocols.Method: The parametrizations were adjusted to reproduce ground-state properties of a selected set of doubly magic nuclei and properties of nuclear matter. Subsequently, these parameter sets were validated against properties of spherical and deformed nuclei.Results: Our parameter sets successfully reproduce the experimental binding energies and charge radii for a wide range of singly magic nuclei. Compared to the widely used SLy5 and to the SIII parametrization that has integer powers of the density, a significant improvement of the reproduction of the data is observed. Similarly, a good description of the deformation properties at A˜80 was obtained.Conclusions: We have constructed new Skyrme parametrizations with integer powers of the density and validated them against a broad set of experimental data for spherical and deformed nuclei. These parametrizations are tailor-made for regularized multireference energy density functional calculations and can be used to study correlations beyond the mean field in atomic nuclei.
A collocation method for surface tension calculations with the density gradient theory
Larsen, Peter Mahler; Maribo-Mogensen, Bjørn; Kontogeorgis, Georgios M.
2016-01-01
Surface tension calculations are important in many industrial applications and over a wide range of temperatures, pressures and compositions. Empirical parachor methods are not suitable over a wide condition range and the combined use of density gradient theory with equations of state has been...... proposed in literature. Often, many millions of calculations are required in the gradient theory methods, which is computationally very intensive. In this work, we have developed an algorithm to calculate surface tensions an order of magnitude faster than the existing methods, with no loss of accuracy...
Rezende, Carlos A; San Gil, Rosane A S; Borré, Leandro B; Pires, José Ricardo; Vaiss, Viviane S; Resende, Jackson A L C; Leitão, Alexandre A; De Alencastro, Ricardo B; Leal, Katia Z
2016-09-01
The experiments of carvedilol form II, form III, and hydrate by (13)C and (15)N cross-polarization magic-angle spinning (CP MAS) are reported. The GIPAW (gauge-including projector-augmented wave) method from DFT (density functional theory) calculations was used to simulate (13)C and (15)N chemical shifts. A very good agreement was found for the comparison between the global results of experimental and calculated nuclear magnetic resonance (NMR) chemical shifts for carvedilol polymorphs. This work aims a comprehensive understanding of carvedilol crystalline forms employing solution and solid-state NMR as well as DFT calculations.
Effects of QCD bound states on dark matter relic abundance
Liew, Seng Pei
2016-01-01
We study scenarios where there exists an exotic massive particle charged under QCD in the early Universe. We calculate the formation and dissociation rates of bound states formed by pairs of these particles, and apply the results in dark matter (DM) coannihilation scenarios, including also the Sommerfeld effect. We find that on top of the Sommerfeld enhancement, bound-state effects can further significantly increase the largest possible DM masses which can give the observed DM relic abundance, by $\\sim 30 - 100\\%$ with respect to values obtained by considering the Sommerfeld effect only, for the color triplet or octet exotic particles we consider. In particular, it indicates that the Bino DM mass in the right-handed stop-Bino coannihilation scenario in the Minimal Supersymmetric extension of the Standard Model (MSSM) can reach $\\sim 2.5$ TeV. We also apply the bound-state effects in the calculations of relic abundance of long-lived or metastable massive colored particles, and discuss the implications on the B...
Effects of QCD bound states on dark matter relic abundance
Liew, Seng Pei; Luo, Feng
2017-02-01
We study scenarios where there exists an exotic massive particle charged under QCD in the early Universe. We calculate the formation and dissociation rates of bound states formed by pairs of these particles, and apply the results in dark matter (DM) coannihilation scenarios, including also the Sommerfeld effect. We find that on top of the Sommerfeld enhancement, bound-state effects can further significantly increase the largest possible DM masses which can give the observed DM relic abundance, by ˜ 30-100% with respect to values obtained by considering the Sommerfeld effect only, for the color triplet or octet exotic particles we consider. In particular, it indicates that the Bino DM mass in the right-handed stop-Bino coannihilation scenario in the Minimal Supersymmetric extension of the Standard Model (MSSM) can reach ˜ 2.5 TeV, even though the potential between the stop and antistop prior to forming a bound state is repulsive. We also apply the bound-state effects in the calculations of relic abundance of long-lived or metastable massive colored particles, and discuss the implications on the BBN constraints and the abundance of a super-weakly interacting DM. The corrections for the bound-state effect when the exotic massive colored particles also carry electric charges, and the collider bounds are also discussed.
Towards the detection of cosmological relic neutrino with neutrino capture on a beta decaying nuclei
Messina, M; Mangano, G
2010-01-01
In this paper we report on recent results in the Þeld of the phenomenology of very low energy neutrino interactions. We brießy describe the cross section calculation for Neutrino Capture on Beta decay nuclei (NCB). We show that the resulting cross section open the possibility to detect the cosmological relic neutrinos. With this achievement, the relic neutrino detection has been downscaled from a principle problem to a technological challenge. We also summarise the state of the art about possible detection techniques.
Abild-Pedersen, Frank; Nørskov, Jens Kehlet; Rostrup-Nielsen, Jens;
2006-01-01
Mechanisms and energetics of graphene growth catalyzed by nickel nanoclusters were studied using ab initio density functional theory calculations. It is demonstrated that nickel step-edge sites act as the preferential growth centers for graphene layers on the nickel surface. Carbon is transported...
Density functional calculations of elastic properties of portlandite, Ca(OH)(2)
Laugesen, Jakob Lund
2005-01-01
The elastic constants of portlandite, Ca(OH)(2), are calculated by use of density functional theory. A lattice optimization of an infinite (periodic boundary conditions) lattice is performed on which strains are applied. The elastic constants are extracted by minimizing Hooke's law of linear...
The oxygen reduction reaction mechanism on Pt(111) from density functional theory calculations
Tripkovic, Vladimir; Skulason, Egill; Siahrostami, Samira;
2010-01-01
We study the oxygen reduction reaction (ORR) mechanism on a Pt(1 1 1) surface using density functional theory calculations We find that at low overpotentials the surface is covered with a half dissociated water layer We estimate the barrier for proton transfer to this surface and the barrier for ...
first-principle calculation of electrons charge density in the diamond ...
DR. AMINU
In a typical modern electronic structure calculation, the charge density is obtained from a certain ... normalized Slater atomic orbital for multi-electron atoms and ions. Since the spherical .... are used as a first approximation (John and Stefan, 2003). 124 ..... Dalton, and Thomas R. Kochler (Plenum Press, New. York) p. 183.
Johnsen, Kristinn; Yngvason, Jakob
1996-01-01
and the electron number N tend to infinity with N/Z fixed, and the magnetic field B tends to infinity in such a way that B/Z4/3→∞. We have calculated electronic density profiles and ground-state energies for values of the parameters that prevail on neutron star surfaces and compared them with results obtained...
BDEN: A timesaving computer program for calculating soil bulk density and water content.
Lynn G. Starr; Michael J. Geist
1983-01-01
This paper presents an interactive computer program written in BASIC language that will calculate soil bulk density and moisture percentage by weight and volume. Coarse fragment weights are required. The program will also summarize the resulting data giving mean, standard deviation, and 95-percent confidence interval on one or more groupings of data.
A New Calculation Method of Dynamic Kill Fluid Density Variation during Deep Water Drilling
Honghai Fan
2017-01-01
Full Text Available There are plenty of uncertainties and enormous challenges in deep water drilling due to complicated shallow flow and deep strata of high temperature and pressure. This paper investigates density of dynamic kill fluid and optimum density during the kill operation process in which dynamic kill process can be divided into two stages, that is, dynamic stable stage and static stable stage. The dynamic kill fluid consists of a single liquid phase and different solid phases. In addition, liquid phase is a mixture of water and oil. Therefore, a new method in calculating the temperature and pressure field of deep water wellbore is proposed. The paper calculates the changing trend of kill fluid density under different temperature and pressure by means of superposition method, nonlinear regression, and segment processing technique. By employing the improved model of kill fluid density, deep water kill operation in a well is investigated. By comparison, the calculated density results are in line with the field data. The model proposed in this paper proves to be satisfactory in optimizing dynamic kill operations to ensure the safety in deep water.
Density-functional calculations for rare-earth atoms and ions
Forstreuter, J.; Steinbeck, L.; Richter, M.; Eschrig, H. [Technische Universitaet Dresden, MPG-Arbeitsgruppe Elektronensysteme, D-01062 Dresden (Germany)
1997-04-01
Relativistic local-spin-density (RLSD) and self-interaction-corrected (SIC) RLSD calculations were performed for the whole series of the rare-earth elements. Ionization potentials and radial expectation values with 4f wave functions were calculated. Improvement on nearly all quantities is found for SIC calculations. Comparison with other calculational methods shows that for a description of rare-earth elements SIC-RLSD competes well in accuracy with all of them, including the most accurate quantum-chemical approach. This is important since the SIC calculation has the advantage of being suited for a description of localized f states in solids with a comparatively moderate effort. {copyright} {ital 1997} {ital The American Physical Society}
Liu, Yuan; Ning, Chuangang
2015-10-01
Recently, the development of photoelectron velocity map imaging makes it much easier to obtain the photoelectron angular distributions (PADs) experimentally. However, explanations of PADs are only qualitative in most cases, and very limited works have been reported on how to calculate PAD of anions. In the present work, we report a method using the density-functional-theory Kohn-Sham orbitals to calculate the photodetachment cross sections and the anisotropy parameter β. The spherical average over all random molecular orientation is calculated analytically. A program which can handle both the Gaussian type orbital and the Slater type orbital has been coded. The testing calculations on Li-, C-, O-, F-, CH-, OH-, NH2-, O2-, and S2- show that our method is an efficient way to calculate the photodetachment cross section and anisotropy parameter β for anions, thus promising for large systems.
Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework.
Berger, Daniel; Logsdail, Andrew J; Oberhofer, Harald; Farrow, Matthew R; Catlow, C Richard A; Sherwood, Paul; Sokol, Alexey A; Blum, Volker; Reuter, Karsten
2014-07-14
We integrate the all-electron electronic structure code FHI-aims into the general ChemShell package for solid-state embedding quantum and molecular mechanical (QM/MM) calculations. A major undertaking in this integration is the implementation of pseudopotential functionality into FHI-aims to describe cations at the QM/MM boundary through effective core potentials and therewith prevent spurious overpolarization of the electronic density. Based on numeric atomic orbital basis sets, FHI-aims offers particularly efficient access to exact exchange and second order perturbation theory, rendering the established QM/MM setup an ideal tool for hybrid and double-hybrid level density functional theory calculations of solid systems. We illustrate this capability by calculating the reduction potential of Fe in the Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for (photo-)catalytic water oxidation at TiO2(110).
Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework
Berger, Daniel; Logsdail, Andrew J.; Oberhofer, Harald; Farrow, Matthew R.; Catlow, C. Richard A.; Sherwood, Paul; Sokol, Alexey A.; Blum, Volker; Reuter, Karsten
2014-07-01
We integrate the all-electron electronic structure code FHI-aims into the general ChemShell package for solid-state embedding quantum and molecular mechanical (QM/MM) calculations. A major undertaking in this integration is the implementation of pseudopotential functionality into FHI-aims to describe cations at the QM/MM boundary through effective core potentials and therewith prevent spurious overpolarization of the electronic density. Based on numeric atomic orbital basis sets, FHI-aims offers particularly efficient access to exact exchange and second order perturbation theory, rendering the established QM/MM setup an ideal tool for hybrid and double-hybrid level density functional theory calculations of solid systems. We illustrate this capability by calculating the reduction potential of Fe in the Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for (photo-)catalytic water oxidation at TiO2(110).
Density functional calculations for a high energy density compound of formula C6H 6-n (NO 2) n.
Chi, Wei-Jie; Li, Lu-Lin; Li, Bu-Tong; Wu, Hai-Shun
2012-08-01
A series of polynitroprismanes, C(6)H(6-n )(NO(2))(n) (n = 1-6) intended for use as high energy density compounds (HEDCs) were designed computationally. Their electronic structures, heats of formation, interactions between nitro groups, specific enthalpies of combustion, bond dissociation energies, and explosive performances (detonation velocities and detonation pressures) were calculated using density functional theory (DFT) with the 6-311 G** basis set. The results showed that all of the polynitroprismanes had high positive heats of formation that increased with the number of substitutions for the prismane derivatives, while the specific enthalpy of combustion decreased as the number of nitro groups increased. In addition, the range of enthalpy of combustion reducing is getting smaller. Interactions between ortho (vicinal) groups deviate from the group additivity rule and decrease as the number of nitro groups increases. In terms of thermodynamic stability, all of the polynitroprismanes had higher bond dissociation energies (BDEs) than RDX and HMX. Detonation velocities and detonation pressures were estimated using modified Kamlet-Jacobs equations based on the heat of detonation (Q) and the theoretical density of the molecule (ρ). It was found that ρ, D, and P are strongly linearly related to the number of nitro groups. Taking both their energetic properties and thermal stabilities into account, pentanitroprismane and hexanitroprismane are potential candidate HEDCs.
On the thermal footsteps of neutralino relic gases
Cabral-Rosetti, L G [Departamento de Posgrado, Centro Interdisciplinario de Investigacion y Docencia en Educacion Tecnica (CIIDET), Av. Universidad 282 Pte., Col. Centro, A. Postal 752, C.P. 76000, Santiago de Queretaro, Qro. (Mexico); Sussman, R A [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico (ICN-UNAM). Apartado Postal 70-543, 04510 Mexico, D.F. (Mexico); Hernandez, X [Instituto de AstronomIa, Circuito de la Investigacion CientI.ca, C.U., Universidad Nacional Autnoma de Mexico (IA-UNAM). Apartado Postal 70-264, 04510 Mexico, D.F. (Mexico)
2006-05-15
Current literature suggests that neutralinos are the dominant cold dark matter particle species. Assuming the microcanonical definition of entropy, we examine the local entropy per particle produced between the 'freeze out' era to the present. An 'entropy consistency' criterion emerges by comparing this entropy with the entropy per particle of actual galactic structures given in terms of dynamical halo variables. We apply this criterion to the cases when neutralinos are mostly b-inos and mostly higgsinos, in conjunction with the usual 'abundance' criterion requiring that present neutralino relic density complies with 0.1 < {omega}{sub x-tilde{sup 0}{sub 1}} < 0.3 for h {approx_equal} 0.65. The joint application of both criteria reveals that a better fitting occurs for the b-ino channels, hence the latter seem to be favoured over the higgsino channels. The suggested methodology can be applied to test other annihilation channels of the neutralino, as well as other particle candidates of thermal gases relics.
On the thermal footsteps of Neutralino relic gases
Cabral-Rosetti, L G; Sussman, R A; Cabral-Rosetti, Luis G.; Hernández, Xabier; Sussman, Roberto A.
2006-01-01
Current literature suggests that neutralinos are the dominant cold dark matter particle species. Assuming the microcanonical definition of entropy, we examine the local entropy per particle produced between the ``freeze out'' era to the present. An ``entropy consistency'' criterion emerges by comparing this entropy with the entropy per particle of actual galactic structures given in terms of dynamical halo variables. We apply this criterion to the cases when neutralinos are mosly b-inos and mostly higgsinos, in conjunction with the usual ``abundance'' criterion requiring that present neutralino relic density complies with $0.1 < \\Omega_{\\chic{\\tilde\\chi^0_1}} < 0.3$ for $h\\simeq 0.65$. The joint application of both criteria reveals that a better fitting occurs for the b-ino channels, hence the latter seem to be favoured over the higgsino channels. The suggested methodology can be applied to test other annihilation channels of the neutralino, as well as other particle candidates of thermal gases relics.
Krykunov, Mykhaylo; Autschbach, Jochen
2007-01-14
We report implementations and results of time-dependent density functional calculations (i) of the frequency-dependent magnetic dipole-magnetic dipole polarizability, (ii) of the (observable) translationally invariant linear magnetic response, and (iii) of a linear intensity differential (LID) which includes the dynamic dipole magnetizability. The density functional calculations utilized density fitting. For achieving gauge-origin independence we have employed time-periodic magnetic-field-dependent basis functions as well as the dipole velocity gauge, and have included explicit density-fit related derivatives of the Coulomb potential. We present the results of calculations of static and dynamic magnetic dipole-magnetic dipole polarizabilities for a set of small molecules, the LID for the SF6 molecule, and dispersion curves for M-hexahelicene of the origin invariant linear magnetic response as well as of three dynamic polarizabilities: magnetic dipole-magnetic dipole, electric dipole-electric dipole, and electric dipole-magnetic dipole. We have also performed comparison of the linear magnetic response and magnetic dipole-magnetic dipole polarizability over a wide range of frequencies for H2O and SF6.
Excitation and ionization energies of substituted anilines calculated with density functional theory
Yuji Takahata
2010-06-01
Full Text Available Valence electron singlet excitation energies (VEExE, valence electron ionization energies (VEIE, core electron binding energies (CEBE, and non-resonant X-ray emission energies of substituted anilines and related molecules were calculated using density functional theory (DFT. The energy calculations were done with TZP basis set of Slater Type Orbitals. PW86x-PW91c, turned out to be the best XC functional among eight functionals tested for time dependent DFT (TDDFT calculation of the singlet excitation energies of the substituted anilines. Using the XC functional, average absolute deviation (AAD from experiment was 0.223 eV for eighteen cases with maximum absolute deviation of 0.932 eV. The valence electron ionization energies of the substituted benzenes were calculated by ΔSCF method with PW86x-PW91c. AAD from experiment was 0.21 eV. The CEBEs were calculated with the previously established method, named as scheme 2003. ΔCEBE(SMS,, sum of mono substituted (SMS CEBE shift, and mutual interference effect (MIE were defined and their values were calculated. Magnitude of MIE provides the degree of mutual interference between two substituents in a phenyl ring. Average absolute value of MIE was ca. 0.1 eV for the three isomers of phenetidine. Using the calculated valence electron ionization energies and the core electron binding energies of one of the phenetidines, some X-ray emission energies were calculated.
Bast, Radovan; Juselius, Jonas [Centre for Theoretical and Computational Chemistry (CTCC), Department of Chemistry, University of Tromso, N-9037 Tromso (Norway); Saue, Trond [Institut de Chimie de Strasbourg, CNRS et Universite Louis Pasteur, Laboratoire de Chimie Quantique, 4, rue Blaise Pascal, BP 1032, F-67070 Strasbourg (France)], E-mail: tsaue@chimie.u-strasbg.fr
2009-02-17
We present a 4-component relativistic implementation for calculating the magnetically induced current density within Hartree-Fock and Kohn-Sham linear response theory using a common gauge origin. We demonstrate how the current density can be decomposed into paramagnetic and diamagnetic contributions by calculating separately the contributions from rotations between positive-energy orbitals and contributions from rotations between the occupied positive-energy orbitals and the virtual negative-energy orbitals, respectively. This methodology is applied to the study of the magnetically induced current density in benzene and the group 15 heteroaromatic compounds C{sub 5}H{sub 5}E (E = N, P, As, Sb, Bi). Quantitative values for the magnetically induced ring currents are obtained by numerical integration over the current flow. We have found that the diatropic ring current is sustained for the entire series of the group 15 heteroaromatic compounds-the induced ring current susceptibility of bismabenzene being 76% of the benzene result. Having employed two hybrid and two nonhybrid generalized gradient approximation functionals, the results are found to be rather insensitive to the choice of the density functional approximation. The relativistic effect is relatively small, reaching its maximum of 8% for bismabenzene. The presented 4-component relativistic methodology opens up the possibility to visualize magnetically induced current densities of aromatic heavy-element systems with both scalar relativistic and spin-orbit effects included.
Ion Current Density Calculation of the Inductive Radio Frequency Ion Source
V.I. Voznyi
2012-10-01
Full Text Available A radio-frequency (RF inductive ion source at 27.12 MHz is investigated. With a global model of the argon discharge, plasma density, electron temperature and ion current density of the ion source is calculated in relation to absorbed RF power and gas pressure as a discharge chamber size changes. It is found that ion beam current density grows as the discharge chamber size decreases. Calculations show that in the RF source with a discharge chamber 30 mm in diameter and 35 mm long the ion current density is 40 mA/cm2 at 100 W of absorbed RF power and 7 mTorr of pressure, and agrees well with experimentally measured value of 43 mA/cm2. With decreasing discharge chamber diameter to 15 mm ion current density can reach 85 mA/cm2 at absorbed RF power of 100 W.
Rauhalahti, Markus; Taubert, Stefan; Sundholm, Dage; Liégeois, Vincent
2017-03-08
Magnetically induced current density susceptibilities and ring-current strengths have been calculated for neutral and doubly charged persubstituted benzenes C6X6 and C6X6(2+) with X = F, Cl, Br, I, At, SeH, SeMe, TeH, TeMe, and SbH2. The current densities have been calculated using the gauge-including magnetically induced current (GIMIC) method, which has been interfaced to the Gaussian electronic structure code rendering current density calculations using effective core potentials (ECP) feasible. Relativistic effects on the ring-current strengths have been assessed by employing ECP calculations of the current densities. Comparison of the ring-current strengths obtained in calculations on C6At6 and C6At6(2+) using relativistic and non-relativistic ECPs show that scalar relativistic effects have only a small influence on the ring-current strengths. Comparisons of the ring-current strengths and ring-current profiles show that the C6I6(2+), C6At6(2+), C6(SeH)6(2+), C6(SeMe)6(2+), C6(TeH)6(2+), C6(TeMe)6(2+), and C6(SbH2)6(2+) dications are doubly aromatic sustaining spatially separated ring currents in the carbon ring and in the exterior of the molecule. The C6I6(+) radical cation is also found to be doubly aromatic with a weaker ring current than obtained for the dication.
Standard hydrogen electrode and potential of zero charge in density functional calculations
Tripkovic, Vladimir; Björketun, Mårten; Skúlason, Egill
2011-01-01
Methods to explicitly account for half-cell electrode potentials have recently appeared within the framework of density functional theory. The potential of the electrode relative to the standard hydrogen electrode is typically determined by subtracting the experimental value of the absolute......) the calculated work function strongly depends on the structure of the water film covering the metal surface. In this paper, we first identify the most accurate experimental reference for the ASHEP by revisiting up-to-date literature, and validate the choice of electron reference level in single-electrode density...
SunYongsheng; MengXujun
1990-01-01
Schroedinger's wave equation is solved in Thomas-Fermi potential including the self-interaction modification of elctrons for arbitrary matter density and temperature,In order to describe relativistic effects,the mass-velocity correction,the Darwin correction and the spin-orbit coupling terms are included in the wave equation.Calculations are presented for the Fe26 and Rb37 atoms at a few temperatures and matter densities.Comparisons of present results with other more accurate one[9] are given in Table.The data obtained by the present method are not bad.
BAI Yu-Lin; CHENG Xiao-Hong; CHEN Xiang-Rong; YANG Xiang-Dong; ZHU Jun
2004-01-01
@@ The intermolecular interactions potentials for two configurations of CH4-Ne complex are calculated with local density approximation methods in the frame of density functional theory. It is found that the calculated potentials have two minima when the distance between the carbon atom of CH4 and the Ne atom takes R = 5.80 a.u.and 6.20a. u. for both the two configurations. For the edge configuration, the corresponding depth of the potential is 0.0669536 eV and 0.0671416 eV. For the face configuration, the corresponding depth of the potential is 0.0737956 eV and 0.0645506 eV. The global minimum occurs at R = 5.80 a.u. for the face configuration with a depth of the potential 0.0737956 eV. The depths of our calculation are in better agreement with the experimental data than the quantum chemical calculation approach, while the position of minimum potential for our calculation is underestimated.
Adhesion of oxide layer to metal-doped aluminum hydride surface: Density functional calculations
Takezawa, Tomoki; Itoi, Junichi; Kannan, Takashi
2017-07-01
The density functional theory (DFT) calculations were carried out to evaluate the adhesion energy of the oxide layer to the metal-doped surface of hydrogen storage material, aluminum hydride (alane, AlH3). The total energy calculations using slab model revealed that the surface doping of some metals to aluminum hydride weakens the adhesion strength of the oxide layer. The influence of titanium, iron, cobalt, and zirconium doping on adhesion strength were evaluated. Except for iron doping, the adhesion strength becomes weak by the doping.
Relic neutrino asymmetry evolution from first principles
Bell, Nicole F.; Volkas, Raymond R.; Wong, Yvonne Y. Y.
1998-01-01
The exact Quantum Kinetic Equations for a two-flavour active-sterile neutrino system are used to provide a systematic derivation of approximate evolution equations for the relic neutrino asymmetry. An extension of the adiabatic approximation for matter-affected neutrino oscillations is developed which incorporates decoherence due to collisions. Exact and approximate expressions for the decoherence and repopulation functions are discussed. A first pass is made over the exact treatment of multi...
Yu Wang
2002-01-01
Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.
Stochastic estimation of level density in nuclear shell-model calculations
Shimizu Noritaka
2016-01-01
Full Text Available An estimation method of the nuclear level density stochastically based on nuclear shell-model calculations is introduced. In order to count the number of the eigen-values of the shell-model Hamiltonian matrix, we perform the contour integral of the matrix element of a resolvent. The shifted block Krylov subspace method enables us its efficient computation. Utilizing this method, the contamination of center-of-mass motion is clearly removed.
Kullie, Ossama, E-mail: kullie@uni-kassel.de [Institute de Chimie de Strasbourg, CNRS et Université de Strasbourg, Laboratoire de Chimie Quantique, 4 rue Blaise Pascal, 67070 Strasbourg (France); Theoretical Physics, Institute for Physics, Department of Mathematics and Natural Science, University of Kassel (Germany)
2013-03-29
Highlights: ► The achievement of CAMB3LYP functional for excited states in framework of TD-DFT. ► Relativistic 4-components calculations for the excited states of the Cd{sub 2} dimer. ► Relativistic Spin-Free calculations for the excited states of Cd{sub 2} dimer. ► A comparison of the achievements of different types of DFT approximations upon Cd{sub 2}. - Abstract: In this paper we present a time-dependent density functional study for the ground-state as well the 20-lowest laying excited states of the cadmium dimer Cd{sub 2}, we analyze its spectrum obtained from all electrons calculations performed with time-depended density functional for the relativistic Dirac-Coulomb- and relativistic spin-free-Hamiltonian as implemented in DIRAC-PACKAGE. The calculations were obtained with different density functional approximations, and a comparison with the literature is given as far as available. Our result is very encouraging, especially for the lowest excited states of this dimer, and is expected to be enlightened for similar systems. The result shows that only long-range corrected functionals such as CAMB3LYP, gives the correct asymptotic behavior for the higher states. A comparable but less satisfactory results were obtained with B3LYP and PBE0 functionals. Spin-free-Hamiltonian is shown to be very efficient for systems containing heavy elements such as Cd{sub 2} in frameworks of (time-dependent) density functional without introducing large errors.
S SOMORENDRO SINGH; G SAXENA
2017-06-01
We calculate quark number density and susceptibility under one-loop correction in the mean-field potential. The calculation shows continuous increase in the number density and susceptibility up to the temperature $T = 0.4 \\rm{GeV}$. Then the values of number density and susceptibility approach the very weakly result with higher values of temperature. The result indicates that the calculated values fit well with increase in temperature to match the lattice QCD simulations of the same quantities.
Hwang, M.; Podloucky, R.; Gonis, A.; Freeman, A. J.
1986-01-01
Results of exact and analytic calculations of the electronic densities of states (DOS's) associated with semi-infinite substitutionally disordered chains are presented using the exact position-space renormalization-group (PSRG) method, the augmented-space (AS) formalism, and the embedded-cluster method (ECM). In addition to total DOS's, the PSRG method allows the calculation of exact partial DOS's associated with local atomic configurations in a disordered material. Comparisons with the exact results indicate that as in the case of infinite materials the ECM provides a reliable method for the calculation of single-particle properties, such as the DOS, of semi-infinite systems. Furthermore, the ECM is found to be much more accurate than the AS formalism, especially in the case of concentrated substitutionally disordered alloys.
Pisaturo, O; Pachoud, M; Bochud, F O; Moeckli, R
2012-07-21
The quantity of interest for high-energy photon beam therapy recommended by most dosimetric protocols is the absorbed dose to water. Thus, ionization chambers are calibrated in absorbed dose to water, which is the same quantity as what is calculated by most treatment planning systems (TPS). However, when measurements are performed in a low-density medium, the presence of the ionization chamber generates a perturbation at the level of the secondary particle range. Therefore, the measured quantity is close to the absorbed dose to a volume of water equivalent to the chamber volume. This quantity is not equivalent to the dose calculated by a TPS, which is the absorbed dose to an infinitesimally small volume of water. This phenomenon can lead to an overestimation of the absorbed dose measured with an ionization chamber of up to 40% in extreme cases. In this paper, we propose a method to calculate correction factors based on the Monte Carlo simulations. These correction factors are obtained by the ratio of the absorbed dose to water in a low-density medium □D(w,Q,V1)(low) averaged over a scoring volume V₁ for a geometry where V₁ is filled with the low-density medium and the absorbed dose to water □D(w,QV2)(low) averaged over a volume V₂ for a geometry where V₂ is filled with water. In the Monte Carlo simulations, □D(w,QV2)(low) is obtained by replacing the volume of the ionization chamber by an equivalent volume of water, according to the definition of the absorbed dose to water. The method is validated in two different configurations which allowed us to study the behavior of this correction factor as a function of depth in phantom, photon beam energy, phantom density and field size.
No Shock Across Part of a Radio Relic in the Merging Galaxy Cluster ZwCl 2341.1+0000?
Ogrean, G A; van Weeren, R J; Burgmeier, A; Simionescu, A
2014-01-01
The galaxy cluster ZwCl 2341.1+0000 is a merging system at z=0.27, which hosts two radio relics and a central, faint, filamentary radio structure. The two radio relics have unusually flat integrated spectral indices of -0.49 +/- 0.18 and -0.76 +/- 0.17, values that cannot be easily reconciled with the theory of standard diffusive shock acceleration of thermal particles at weak merger shocks. We present imaging results from XMM-Newton and Chandra observations of the cluster, aimed to detect and characterise density discontinuities in the ICM. As expected, we detect a density discontinuity near each of the radio relics. However, if these discontinuities are the shock fronts that fuelled the radio emission, then their Mach numbers are surprisingly low, both <=2. We studied the aperture of the density discontinuities, and found that while the NW discontinuity spans the whole length of the NW radio relic, the arc spanned by the SE discontinuity is shorter than the arc spanned by the SE relic. This startling res...
Qin, Mingpu; Zhang, Shiwei
2016-01-01
The vast majority of quantum Monte Carlo (QMC) calculations in interacting fermion systems require a constraint to control the sign problem. The constraint involves an input trial wave function which restricts the random walks. We introduce a systematically improvable constraint which relies on the fundamental role of the density or one-body density matrix. An independent-particle calculation is coupled to an auxiliary-field QMC calculation. The independent-particle solution is used as the constraint in QMC, which then produces the input density or density matrix for the next iteration. The constraint is optimized by the self-consistency between the many-body and independent-particle calculations. The approach is demonstrated in the two-dimensional Hubbard model by accurately determining the spin densities when collective modes separated by tiny energy scales are present in the magnetic and charge correlations. Our approach also provides an ab initio way to predict effective "U" parameters for independent-par...
Hoyer, Chad E; Gagliardi, Laura; Truhlar, Donald G
2015-11-05
Time-dependent Kohn-Sham density functional theory (TD-KS-DFT) is useful for calculating electronic excitation spectra of large systems, but the low-energy spectra are often complicated by artificially lowered higher-energy states. This affects even the lowest energy excited states. Here, by calculating the lowest energy spin-conserving excited state for atoms from H to K and for formaldehyde, we show that this problem does not occur in multiconfiguration pair-density functional theory (MC-PDFT). We use the tPBE on-top density functional, which is a translation of the PBE exchange-correlation functional. We compare to a robust multireference method, namely, complete active space second-order perturbation theory (CASPT2), and to TD-KS-DFT with two popular exchange-correlation functionals, PBE and PBE0. We find for atoms that the mean unsigned error (MUE) of MC-PDFT with the tPBE functional improves from 0.42 to 0.40 eV with a double set of diffuse functions, whereas the MUEs for PBE and PBE0 drastically increase from 0.74 to 2.49 eV and from 0.45 to 1.47 eV, respectively.
Thermal relics as hot, warm and cold dark matter in power-law $f(R)$ gravity
Tian, David Wenjie
2015-01-01
We investigate the thermal relics as hot, warm and cold dark matter in $\\mathscr{L}=\\varepsilon^{2-2\\beta}R^\\beta+{16\\pi}m_{\\text{Pl}}^{-2}\\mathscr{L}_m$ gravity, where $\\varepsilon$ is a constant balancing the dimension of the field equation, and $1<\\beta<(4+\\sqrt{6})/5$ for the positivity of energy density and temperature. If light neutrinos serve as hot/warm relics, the entropic number of statistical degrees of freedom $g_{*s}$ at freeze-out and thus the predicted fractional energy density $\\Omega_\\psi h^2$ are $\\beta-$dependent, which relaxes the standard mass bound $\\Sigma m_\
Liu, Yuan [Department of Physics, State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Ning, Chuangang, E-mail: ningcg@tsinghua.edu.cn [Department of Physics, State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)
2015-10-14
Recently, the development of photoelectron velocity map imaging makes it much easier to obtain the photoelectron angular distributions (PADs) experimentally. However, explanations of PADs are only qualitative in most cases, and very limited works have been reported on how to calculate PAD of anions. In the present work, we report a method using the density-functional-theory Kohn-Sham orbitals to calculate the photodetachment cross sections and the anisotropy parameter β. The spherical average over all random molecular orientation is calculated analytically. A program which can handle both the Gaussian type orbital and the Slater type orbital has been coded. The testing calculations on Li{sup −}, C{sup −}, O{sup −}, F{sup −}, CH{sup −}, OH{sup −}, NH{sub 2}{sup −}, O{sub 2}{sup −}, and S{sub 2}{sup −} show that our method is an efficient way to calculate the photodetachment cross section and anisotropy parameter β for anions, thus promising for large systems.
Density functional theory and evolution algorithm calculations of elastic properties of AlON
Batyrev, I. G.; Taylor, D. E.; Gazonas, G. A.; McCauley, J. W. [U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States)
2014-01-14
Different models for aluminum oxynitride (AlON) were calculated using density functional theory and optimized using an evolutionary algorithm. Evolutionary algorithm and density functional theory (DFT) calculations starting from several models of AlON with different Al or O vacancy locations and different positions for the N atoms relative to the vacancy were carried out. The results show that the constant anion model [McCauley et al., J. Eur. Ceram. Soc. 29(2), 223 (2009)] with a random distribution of N atoms not adjacent to the Al vacancy has the lowest energy configuration. The lowest energy structure is in a reasonable agreement with experimental X-ray diffraction spectra. The optimized structure of a 55 atom unit cell was used to construct 220 and 440 atom models for simulation cells using DFT with a Gaussian basis set. Cubic elastic constant predictions were found to approach the experimentally determined AlON single crystal elastic constants as the model size increased from 55 to 440 atoms. The pressure dependence of the elastic constants found from simulated stress-strain relations were in overall agreement with experimental measurements of polycrystalline and single crystal AlON. Calculated IR intensity and Raman spectra are compared with available experimental data.
McKechnie, Scott [Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Booth, George H. [Theory and Simulation of Condensed Matter, King’s College London, The Strand, London WC2R 2LS (United Kingdom); Cohen, Aron J. [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom); Cole, Jacqueline M., E-mail: jmc61@cam.ac.uk [Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Argonne National Laboratory, 9700 S Cass Avenue, Argonne, Illinois 60439 (United States)
2015-05-21
The best practice in computational methods for determining vertical ionization energies (VIEs) is assessed, via reference to experimentally determined VIEs that are corroborated by highly accurate coupled-cluster calculations. These reference values are used to benchmark the performance of density functional theory (DFT) and wave function methods: Hartree-Fock theory, second-order Møller-Plesset perturbation theory, and Electron Propagator Theory (EPT). The core test set consists of 147 small molecules. An extended set of six larger molecules, from benzene to hexacene, is also considered to investigate the dependence of the results on molecule size. The closest agreement with experiment is found for ionization energies obtained from total energy difference calculations. In particular, DFT calculations using exchange-correlation functionals with either a large amount of exact exchange or long-range correction perform best. The results from these functionals are also the least sensitive to an increase in molecule size. In general, ionization energies calculated directly from the orbital energies of the neutral species are less accurate and more sensitive to an increase in molecule size. For the single-calculation approach, the EPT calculations are in closest agreement for both sets of molecules. For the orbital energies from DFT functionals, only those with long-range correction give quantitative agreement with dramatic failing for all other functionals considered. The results offer a practical hierarchy of approximations for the calculation of vertical ionization energies. In addition, the experimental and computational reference values can be used as a standardized set of benchmarks, against which other approximate methods can be compared.
McKechnie, Scott; Booth, George H.; Cohen, Aron J.; Cole, Jacqueline M.
2015-05-01
The best practice in computational methods for determining vertical ionization energies (VIEs) is assessed, via reference to experimentally determined VIEs that are corroborated by highly accurate coupled-cluster calculations. These reference values are used to benchmark the performance of density functional theory (DFT) and wave function methods: Hartree-Fock theory, second-order Møller-Plesset perturbation theory, and Electron Propagator Theory (EPT). The core test set consists of 147 small molecules. An extended set of six larger molecules, from benzene to hexacene, is also considered to investigate the dependence of the results on molecule size. The closest agreement with experiment is found for ionization energies obtained from total energy difference calculations. In particular, DFT calculations using exchange-correlation functionals with either a large amount of exact exchange or long-range correction perform best. The results from these functionals are also the least sensitive to an increase in molecule size. In general, ionization energies calculated directly from the orbital energies of the neutral species are less accurate and more sensitive to an increase in molecule size. For the single-calculation approach, the EPT calculations are in closest agreement for both sets of molecules. For the orbital energies from DFT functionals, only those with long-range correction give quantitative agreement with dramatic failing for all other functionals considered. The results offer a practical hierarchy of approximations for the calculation of vertical ionization energies. In addition, the experimental and computational reference values can be used as a standardized set of benchmarks, against which other approximate methods can be compared.
The Radio Relics and Halo of El Gordo, a Massive $z=0.870$ Cluster Merger
Lindner, Robert R; Hughes, John P; Battaglia, Nick; Gupta, Neeraj; Knowles, Kenda; Marriage, Tobias A; Menanteau, Felipe; Moodley, Kavilan; Reese, Erik D; Srianand, Raghunathan
2013-01-01
We present 610 MHz and 2.1 GHz imaging of the massive SZE-selected z=0.870 cluster merger ACT-CL J0102-4915 (El Gordo), obtained with the GMRT and the ATCA, respectively. We detect two complexes of radio relics separated by 3.4' (1.6 Mpc) along the system's NW-to-SE collision axis that have high integrated polarizations (33%) and steep spectral indices, consistent with creation via Fermi acceleration by shocks in the ICM. From the spectral index of the relics, we compute a Mach number of 2.55 and shock speed of 4300^{+800}_{-500} km/s. With our ATCA data, we compute the Faraday rotation measure across the NW relic and find a mean value of 11 rad/m^2 and standard deviation of 6 rad/m^2. With the integrated line-of-sight gas density derived from new Chandra observations, our RM measurement implies B_parallel~0.01 \\mu G in the cluster outskirts. The extremely narrow shock widths in the relics (0.6. [abridged
A Zoo of Radio Relics: Cluster Cores to Filaments
Ruta Kale; K. S. Dwarakanath
2011-12-01
Radio relics in galaxy clusters can be electrons accelerated at cluster merger shocks or adiabatically compressed fossil radio cocoons or dying radio galaxies. The spectral evolution of radio relics is affected by the surrounding thermal plasma. We present a low frequency study of three radio relics representing environments of dense cluster core (A4038), cluster outskirts (A1664) and filaments (A786). The properties of the relics are found to be consistent with the effect of confinement by external medium if the effects of projection are ignored.
Christensen, Rune; Hansen, Heine Anton; Vegge, Tejs
2015-01-01
through first principle methods. Ensembles generated using a Bayesian error estimation functional, in this case the BEEF-vdW functional[6], are used for the error identification. The ensembles, which consist of perturbations of the main van der Waals density functional, can be generated at low......Density functional theory (DFT) calculations have greatly contributed to the atomic level understanding of electrochemical reactions. However, in some cases, the accuracy can be prohibitively low for a detailed understanding of, e.g. reaction mechanisms. Two cases are examined here, i...... that the systematic error is due to carbon-oxygen double bonds, as the change in number of carbon-oxygen double bonds in the reaction to methanol is two as compared to one for reaction to formic acid. This is subsequently confirmed by further comparisons of functional dependence and a significant source of systematic...
Edwin, Bismi; Hubert Joe, I
2012-11-01
Vibrational spectral analysis and quantum chemical computations based on density functional theory have been performed on the anti-neuro-degenerative drug Orphenadrine hydrochloride. The geometry, intermolecular hydrogen bond, and harmonic vibrational frequencies of the title molecule have been investigated with the help of B3LYP method. The calculated molecular geometry has been compared with the experimental data. The various intramolecular interactions have been exposed by natural bond orbital analysis. The distribution of Mulliken atomic charges and bending of natural hybrid orbitals also reflect the presence of intramolecular hydrogen bonding. The analysis of the electron density of HOMO and LUMO gives an idea of the delocalization and low value of energy gap indicates electron transport in the molecule and thereby bioactivity. Effective docking of the drug molecule with NMDA receptor subunit 3A also enhances its bioactive nature. Copyright © 2012 Elsevier B.V. All rights reserved.
Density functional calculation of many-electron systems in cartesian coordinate grid
Roy, Amlan K
2011-01-01
A recently developed density functional method, within Hohenberg-Kohn-Sham framework, is used for faithful description of atoms, molecules in Cartesian coordinate grid, by using an LCAO-MO ansatz. Classical Coulomb potential is obtained by means of a Fourier convolution technique. All two-body potentials (including exchange-correlation (XC)) are constructed directly on real grid, while their corresponding matrix elements are computed from numerical integration. Detailed systematic investigation is made for a representative set of atoms/molecules through a number of properties like total energies, component energies, ionization energies, orbital energies, etc. Two nonlocal XC functionals (FT97 and PBE) are considered for pseudopotential calculation of 35 species while preliminary all-electron results are reported for 6 atoms using the LDA XC density functional. Comparison with literature results, wherever possible, exhibits near-complete agreement. This offers a simple efficient route towards accurate reliable...
Pettigrew, John D; Manger, Paul R
2008-01-01
A single right retina from a black rhinoceros was whole mounted, stained and analyzed to determine the visual resolution of the rhinoceros, an animal with reputedly poor eyesight. A range of small (15-microm diameter) to large (100-microm diameter) ganglion cell types was seen across the retina. We observed two regions of high density of retinal ganglion cells at either end of a long, but thin, horizontal streak. The temporal specialization, which receives light from the anterior visual field, exhibited a ganglion cell density of approximately 2000/mm2, while the nasal specialization exhibited a density of approximately 1500/mm2. The retina exhibited a ganglion cell density bias toward the upper half, especially so, the upper temporal quadrant, indicating that the rhinoceros would be processing visual information from the visual field below the anterior horizon for the most part. Our calculations indicate that the rhinoceros has a visual resolution of 6 cycles/degree. While this resolution is one-tenth that of humans (60 cycles/deg) and less than that of the domestic cat (9 cycles/deg), it is comparable to that of the rabbit (6 cycles/deg), and exceeds that seen in a variety of other mammals including seals, dolphins, microbats, and rats. Thus, the reputation of the rhinoceros as a myopic, weakly visual animal is not supported by our observations of the retina. We calculate that the black rhinoceros could readily distinguish a 30 cm wide human at a distance of around 200 m given the appropriate visual background.
Nonmonotonic Recursive Polynomial Expansions for Linear Scaling Calculation of the Density Matrix.
Rubensson, Emanuel H
2011-05-10
As it stands, density matrix purification is a powerful tool for linear scaling electronic structure calculations. The convergence is rapid and depends only weakly on the band gap. However, as will be shown in this letter, there is room for improvements. The key is to allow for nonmonotonicity in the recursive polynomial expansion. On the basis of this idea, new purification schemes are proposed that require only half the number of matrix-matrix multiplications compared to previous schemes. The speedup is essentially independent of the location of the chemical potential and increases with decreasing band gap.
Quijada, M. [Departamento de Fisica de Materiales, Facultad de Quimicas UPV/EHU, Apartado 1072, 20080 San Sebastian (Spain); Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Borisov, A.G. [Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Universite Paris-Sud, Laboratoire des Collisions Atomiques et Moleculaires (France); CNRS, UMR 8625, Laboratoire des Collisions Atomiques et Moleculaires, LCAM, Batiment 351, UPS-11, Orsay, 91405 Orsay Cedex (France); Muino, R.D. [Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Centro de Fisica de Materiales, Centro Mixto CSIC-UPV/EHU, Edificio Korta, Avenida de Tolosa 72, 20018 San Sebastian (Spain)
2008-06-15
Time-dependent density functional theory is used to study the interaction between antiprotons and metallic nanoshells. The ground state electronic properties of the nanoshell are obtained in the jellium approximation. The energy lost by the antiproton during the collision is calculated and compared to that suffered by antiprotons traveling in metal clusters. The resulting energy loss per unit path length of material in thin nanoshells is larger than the corresponding quantity for clusters. It is shown that the collision process can be interpreted as the antiproton crossing of two nearly bi-dimensional independent metallic systems. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Seismic pattern treatment method through calculation of seismic density at grid nodes
无
2001-01-01
Analysis of seismic data and seismicity characteristics in China, we gave a method to deal with seismic patterns by calculating density at grid nodes. Number of earthquakes and epicenter distribution are considered comprehen-sively in this method. Effect of datum accuracy is stressed on parameter confirmation. Seismic patterns from this method are stable and can reflect seismic characteristics reliably. These seismic patterns are the base of quantita-tive analysis of seismicity. It can be applied in seismic tendency analysis and medium-long term earthquake pre-diction, earthquake countermeasure and risk mitigation.
Density functional theory calculations of the stress of oxidised (110) silicon surfaces
Melis, C; Colombo, L; Mana, G
2016-01-01
The measurement of the lattice-parameter of silicon by x-ray interferometry assumes the use of strain-free crystals. This might not be the case because surface relaxation, reconstruction, and oxidation cause strains without the application of any external force. In a previous work, this intrinsic strain was estimated by a finite element analysis, where the surface stress was modeled by an elastic membrane having a 1 N/m tensile strength. The present paper quantities the surface stress by a density functional theory calculation. We found a value exceeding the nominal value used, which potentially affects the measurement accuracy.
Calculation of the Nuclear Transition Charge Density in a Microscopic sdgIBM-1
ZHANG Zhan-Jun; SANG Jian-ping; LIU Yong
2000-01-01
Formulae of proton and neutron boson structure functions (BSF's) are deduced in terms of a microscopic approach of sdgIBM (namely, microscopic sdgIBM). For the nucleus 190Os, the value of BSF's is worked out. Due to the high similarity, the maximum F-spin truncation is made under the full-symmetry approximation. Thereafter, calculations of E2 and E4 transition charge densities (TCD's) are performed in the sdgIBM-1. It is found that the E2 and E4 TCD's can be reproduced quite satisfactorily in the uniform frame of microscopic sdgIBM-1.
Reducing Systematic Errors in Oxide Species with Density Functional Theory Calculations
Christensen, Rune; Hummelshøj, Jens S.; Hansen, Heine Anton
2015-01-01
Density functional theory calculations can be used to gain valuable insight into the fundamental reaction processes in metal−oxygen systems, e.g., metal−oxygen batteries. Here, the ability of a range of different exchange-correlation functionals to reproduce experimental enthalpies of formation...... for different types of alkali and alkaline earth metal oxide species has been examined. Most examined functionals result in significant overestimation of the stability of superoxide species compared to peroxides and monoxides, which can result in erroneous prediction of reaction pathways. We show that if metal...
Skulason, Egill; Tripkovic, Vladimir; Björketun, Mårten
2010-01-01
Density functional theory calculations have been performed for the three elementary steps―Tafel, Heyrovsky, and Volmer―involved in the hydrogen oxidation reaction (HOR) and its reverse, the hydrogen evolution reaction (HER). For the Pt(111) surface a detailed model consisting of a negatively...... charged Pt(111) slab and solvated protons in up to three water bilayers is considered and reaction energies and activation barriers are determined by using a newly developed computational scheme where the potential can be kept constant during a charge transfer reaction. We determine the rate limiting...
Polyoxomolybdate formation - A thermodynamic analysis from density functional/PCM calculations
Steffler, Fernando; de Lima, Guilherme Ferreira; Duarte, Hélio Anderson
2017-02-01
Polyoxomolybdates have been intensely investigated, but their mechanisms of formation are not completely understood. The complex equilibrium of different species is affected by concentration, pH, ionic strength and temperature. It is a challenging system to model using computational chemistry. In the present work, density functional calculations were carried out using the polarizable continuum method to include solvent effects in an effort to provide insight into the mechanism of polyoxomolybdate formation in aqueous solution. We establish a possible sequence of reactions for the formation of small polyoxomolybdates containing up to 8 Mo by addition of the monomeric unit [MoO4]2-.
Supergravity Inflation Free from Harmful Relics
Greene, P B; Murayama, H; Greene, Patrick B.; Kadota, Kenji; Murayama, Hitoshi
2003-01-01
We present a realistic supergravity inflation model which is free from the overproduction of potentially dangerous relics in cosmology, namely moduli and gravitinos which can lead to the inconsistencies with the predictions of baryon asymmetry and nucleosynthesis. The radiative correction turns out to play a crucial role in our analysis which raises the mass of supersymmetry breaking field to intermediate scale. We pay a particular attention to the non-thermal production of gravitinos using the non-minimal Kahler potential we obtained from loop correction. This non-thermal gravitino production however is diminished because of the relatively small scale of inflaton mass and small amplitudes of hidden sector fields.
Noises in Detecting Relic Gravitational Wave
LEE Zhi-Jun; WAN Zhen-Zhu
2006-01-01
We analyse the three basic kinds of noises in detecting the relic gravitational wave (GW), which are the noises caused by the thermal radiation in the detecting cavity and by the scattering of the Gaussian beam in the detecting cavity, and noise in the microwave radiometers. The analysis shows that a reasonable signal-to-noise ratio may be achieved for a detecting device with a suitable geometric structure only when the temperature of the environment is no more than T = 0.6 K, and the power of the radiation of the Gaussian beam is no less than P = 105W.
Using Density Functional Theory (DFT) for the Calculation of Atomization Energies
Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)
1995-01-01
The calculation of atomization energies using density functional theory (DFT), using the B3LYP hybrid functional, is reported. The sensitivity of the atomization energy to basis set is studied and compared with the coupled cluster singles and doubles approach with a perturbational estimate of the triples (CCSD(T)). Merging the B3LYP results with the G2(MP2) approach is also considered. It is found that replacing the geometry optimization and calculation of the zero-point energy by the analogous quantities computed using the B3LYP approach reduces the maximum error in the G2(MP2) approach. In addition to the 55 G2 atomization energies, some results for transition metal containing systems will also be presented.
Density functional theory calculations of tetracene on low index surfaces of copper crystal
Dou Wei-Dong; Zhang Han-Jie; Bao Shi-Ning
2009-01-01
This paper carries out the density functional theory calculations to study the adsorbate-substrate interaction between tetracene and Cu substrates (Cu (110) and Cu (100) surface). On each of the surfaces, two kinds of geometry are calculated, namely 'flat-lying' mode and 'upright standing' mode. For 'flat-lying' geometry, the molecule is found to be aligned with its longer molecular axis along close-packed direction of the substrata surfaces. For 'upright standing' geometry, the long axis of tetracene is found to be parallel to the surface normal of the substrate on Cu (110) surface. However, tetracene appears as 'tilted' mode on Cu (100) surface. Structures with 'flat-lying' mode have much larger adsorption energy and charge transfer upon adsorption than that with 'upright standing' mode, indicating the preference of 'flat-lying' geometry on both Cu (110) and Cu (100) surface.
Takaba, Hiromitsu; Kimura, Shou; Alam, Md. Khorshed
2017-03-01
Durability of organo-lead halide perovskite are important issue for its practical application in a solar cells. In this study, using density functional theory (DFT) and molecular dynamics, we theoretically investigated a crystal structure, electronic structure, and ionic diffusivity of the partially substituted cubic MA0.5X0.5PbI3 (MA = CH3NH3+, X = NH4+ or (NH2)2CH+ or Cs+). Our calculation results indicate that a partial substitution of MA induces a lattice distortion, resulting in preventing MA or X from the diffusion between A sites in the perovskite. DFT calculations show that electronic structures of the investigated partially substituted perovskites were similar with that of MAPbI3, while their bandgaps slightly decrease compared to that of MAPbI3. Our results mean that partial substitution in halide perovskite is effective technique to suppress diffusion of intrinsic ions and tune the band gap.
Xu, Hong-Guang; Zhang, Zeng-Guang; Feng, Yuan; Yuan, Jinyun; Zhao, Yuchao; Zheng, Weijun
2010-03-01
Vanadium-doped small silicon clusters, VSin- and VSin- ( n = 3-6), have been studied by anion photoelectron spectroscopy. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of these clusters were obtained from their photoelectron spectra. We have also conducted density-functional calculations of VSin- and VSin- clusters and determined their structures by comparison of theoretical calculations with experimental results. Our results show that two V atoms in VSin- clusters tend to form a strong V-V bond. VSi6- has D3d symmetry with the six Si atoms forming a chair like six-membered ring similar to the ring in cyclohexane and the two vanadium atoms are joined with a δ bond.
Endo, Kazunaka
2016-02-01
In the Auger electron spectra (AES) simulations, we define theoretical modified kinetic energies of AES in the density functional theory (DFT) calculations. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. This method is applied to simulate Auger electron spectra (AES) of 2nd periodic atom (Li, Be, B, C, N, O, F)-involving substances (LiF, beryllium, boron, graphite, GaN, SiO2, PTFE) by deMon DFT calculations using the model molecules of the unit cell. Experimental KVV (valence band electrons can fill K-shell core holes or be emitted during KVV-type transitions) AES of the (Li, O) atoms in the substances agree considerably well with simulation of AES obtained with the maximum kinetic energies of the atoms, while, for AES of LiF, and PTFE substance, the experimental F KVV AES is almost in accordance with the spectra from the transitionstate kinetic energy calculations.
Strain and Cohesive Energy of TiN Deposit on Al(001) Surface: Density Functional Calculation
Ren, Yuan; Liu, Xuejie
2016-07-01
To apply the high hardness of TiN film to soft and hard multilayer composite sheets, we constructed a new type of composite structural material with ultra-high strength. The strain of crystal and cohesive energy between the atoms in the eight structures of N atom, Ti atom, 2N2Ti island and TiN rock salt deposited on the Al(001) surface were calculated with the first-principle ultra-soft pseudopotential approach of the plane wave based on the density functional theory. The calculations of the cohesive energy showed that N atoms could be deposited in the face-centered-cubic vacancy position of the Al(001) surface and results in a cubic structure AlN surface. The TiN film could be deposited on the interface of β-AlN. The calculations of the strains showed that the strain in the TiN film deposited on the Al(001) surface was less than that in the 2N2Ti island deposited on the Al(001) surface. The diffusion behavior of interface atom N was investigated by a nudged elastic band method. Diffusion energy calculation showed that the N atom hardly diffused to the substrate Al layer.
Komorovsky, Stanislav; Repisky, Michal; Ruud, Kenneth; Malkina, Olga L; Malkin, Vladimir G
2013-12-27
A four-component relativistic method for the calculation of NMR shielding constants of paramagnetic doublet systems has been developed and implemented in the ReSpect program package. The method uses a Kramer unrestricted noncollinear formulation of density functional theory (DFT), providing the best DFT framework for property calculations of open-shell species. The evaluation of paramagnetic nuclear magnetic resonance (pNMR) tensors reduces to the calculation of electronic g tensors, hyperfine coupling tensors, and NMR shielding tensors. For all properties, modern four-component formulations were adopted. The use of both restricted kinetically and magnetically balanced basis sets along with gauge-including atomic orbitals ensures rapid basis-set convergence. These approaches are exact in the framework of the Dirac-Coulomb Hamiltonian, thus providing useful reference data for more approximate methods. Benchmark calculations on Ru(III) complexes demonstrate good performance of the method in reproducing experimental data and also its applicability to chemically relevant medium-sized systems. Decomposition of the temperature-dependent part of the pNMR tensor into the traditional contact and pseudocontact terms is proposed.
Density functional calculations of multiphonon capture cross sections at defects in semiconductors
Barmparis, Georgios D.; Puzyrev, Yevgeniy S.; Zhang, X.-G.; Pantelides, Sokrates T.
2014-03-01
The theory of electron capture cross sections by multiphonon processes in semiconductors has a long and controversial history. Here we present a comprehensive theory and describe its implementation for realistic calculations. The Born-Oppenheimer and the Frank-Condon approximations are employed. The transition probability of an incoming electron is written as a product of an instantaneous electronic transition in the initial defect configuration and the line shape function (LSF) that describes the multiphonon processes that lead to lattice relaxation. The electronic matrix elements are calculated using the Projector Augmented Wave (PAW) method which yields the true wave functions while still employing a plane-wave basis. The LSF is calculated by employing a Monte Carlo method and the real phonon modes of the defect, calculated using density functional theory in the PAW scheme. Initial results of the capture cross section for a prototype system, namely a triply hydrogenated vacancy in Si are presented. The results are relevant for modeling device degradation by hot electron effects. This work is supported in part by the Samsung Advanced Institute of Technology (SAIT)'s Global Research Outreach (GRO) Program and by the LDRD program at ORNL.
Fragment approach to constrained density functional theory calculations using Daubechies wavelets
Ratcliff, Laura E., E-mail: lratcliff@anl.gov [Argonne Leadership Computing Facility, Argonne National Laboratory, Lemont, Illinois 60439 (United States); Université de Grenoble Alpes, CEA, INAC-SP2M, L-Sim, F-38000 Grenoble (France); Genovese, Luigi; Mohr, Stephan; Deutsch, Thierry [Université de Grenoble Alpes, CEA, INAC-SP2M, L-Sim, F-38000 Grenoble (France)
2015-06-21
In a recent paper, we presented a linear scaling Kohn-Sham density functional theory (DFT) code based on Daubechies wavelets, where a minimal set of localized support functions are optimized in situ and therefore adapted to the chemical properties of the molecular system. Thanks to the systematically controllable accuracy of the underlying basis set, this approach is able to provide an optimal contracted basis for a given system: accuracies for ground state energies and atomic forces are of the same quality as an uncontracted, cubic scaling approach. This basis set offers, by construction, a natural subset where the density matrix of the system can be projected. In this paper, we demonstrate the flexibility of this minimal basis formalism in providing a basis set that can be reused as-is, i.e., without reoptimization, for charge-constrained DFT calculations within a fragment approach. Support functions, represented in the underlying wavelet grid, of the template fragments are roto-translated with high numerical precision to the required positions and used as projectors for the charge weight function. We demonstrate the interest of this approach to express highly precise and efficient calculations for preparing diabatic states and for the computational setup of systems in complex environments.
Khadraoui, Z.; Horchani-Naifer, K.; Ferhi, M.; Ferid, M.
2015-09-01
Single crystals of TbPO4 were grown by high temperature solid-state reaction and identified by means of X-ray diffraction, infrared and Raman spectroscopies analysis. The electronic properties of TbPO4 such as the energy band structures, density of states were carried out using density functional theory (DFT). We have employed the LDA+U functional to treat the exchange correlation potential by solving Kohn-Sham equation. The calculated total and partial density of states indicate that the top of valance band is mainly built upon O-2p states and the bottom of the conduction band mostly originates from Tb-5d states. The population analysis indicates that the P-O bond was mainly covalent and Tb-O bond was mainly ionic. The emission spectrum, color coordinates and decay curve were employed to reveal the luminescence properties of TbPO4. Moreover, the optical properties including the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum are investigated and analyzed. The results are discussed and compared with the available experimental data.
Fliegl, Heike; Jusélius, Jonas; Sundholm, Dage
2016-07-21
Gauge-origin independent current density susceptibility tensors have been computed using the gauge-including magnetically induced current (GIMIC) method. The anisotropy of the magnetically induced current density (ACID) functions constructed from the current density susceptibility tensors are therefore gauge-origin independent. The ability of the gauge-origin independent ACID function to provide quantitative information about the current flow along chemical bonds has been assessed by integrating the cross-section area of the ACID function in the middle of chemical bonds. Analogously, the current strength susceptibility passing a given plane through the molecule is obtained by numerical integration of the current flow parallel to the normal vector of the integration plane. The cross-section area of the ACID function is found to be strongly dependent on the exact location of the integration plane, which is in sheer contrast to the calculated ring-current strength susceptibilities that are practically independent of the chosen position of the integration plane. The gauge-origin independent ACID functions plotted for different isosurface values show that a visual assessment of the current flow and degree of aromaticity depends on the chosen isosurface. The present study shows that ACID functions are not an unambiguous means to estimate the degree of molecular aromaticity according to the magnetic criterion and to determine the current pathway of complex molecular rings.
Ruiz-Serrano, Álvaro; Skylaris, Chris-Kriton
2013-08-07
A new method for finite-temperature density functional theory calculations which significantly increases the number of atoms that can be simulated in metallic systems is presented. A self-consistent, direct minimization technique is used to obtain the Helmholtz free energy of the electronic system, described in terms of a set of non-orthogonal, localized functions which are optimized in situ using a periodic-sinc basis set, equivalent to plane waves. Most parts of the calculation, including the demanding operation of building the Hamiltonian matrix, have a computational cost that scales linearly with the number of atoms in the system. Also, this approach ensures that the Hamiltonian matrix has a minimal size, which reduces the computational overhead due to diagonalization, a cubic-scaling operation that is still required. Large basis set accuracy is retained via the optimization of the localized functions. This method allows accurate simulations of entire metallic nanostructures, demonstrated with calculations on a supercell of bulk copper with 500 atoms and on gold nanoparticles with up to 2057 atoms.
DENSITY-FUNCTIONAL CALCULATIONS FOR Ce, Th, AND Pu METALS AND ALLOYS
Landa, A; Soderlind, P
2004-04-05
The phase diagrams of Ce, Th, and Pu metals have been studied by means of density-functional theory (DFT). In addition to these metals, the phase stability of Ce-Th and Pu-Am alloys has been also investigated from first-principles calculations. Equation-of-state (EOS) for Ce, Th, and the Ce-Th alloys has been calculated up to 1 Mbar pressure in good comparison to experimental data. Present calculations shows that the Ce-Th alloys adopt a body-centeredtetragonal (bct) structure upon hydrostatic compression that is in excellent agreement with measurements. The ambient pressure phase diagram of Pu is shown to be very poorly described by traditional DFT but rather well modeled when including magnetic interactions. In particular, the anomalous {var_sigma} phase of Pu is shown to be stabilized by magnetic disorder at elevated temperatures. The Pu-Am system has also been studied in a similar fashion and it is shown that this system, for about 25% Am content, becomes antiferromagnetic below about 400 K that corroborate the recent discovery of a Curie-Weiss behavior in this system.
A-centers and isovalent impurities in germanium: Density functional theory calculations
Chroneos, A., E-mail: alexander.chroneos@imperial.ac.uk [Department of Materials, Imperial College London, London SW7 2BP (United Kingdom); Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ (United Kingdom); Londos, C.A. [University of Athens, Solid State Physics Section, Panepistimiopolis Zografos, Athens 157 84 (Greece); Bracht, H. [Institute of Materials Physics, University of Muenster, Wilhelm-Klemm-Strasse 10, D-48149 Muenster (Germany)
2011-03-25
In the present study density functional theory calculations have been used to calculate the binding energies of clusters formed between lattice vacancies, oxygen and isovalent atoms in germanium. In particular we concentrated on the prediction of binding energies of A-centers or oxygen interstitials that are at nearest and next nearest neighbor sites to isovalent impurities (carbon, silicon and tin) in germanium. The A-center is an oxygen interstitial atom near a lattice vacancy and is an important impurity-defect pair in germanium. In germanium doped with carbon or silicon, we calculated that most of the binding energy of the cluster formed between A-centers and the carbon or silicon atoms is due to the interaction between the oxygen interstitial atom and the carbon or silicon atoms. For tin-doped germanium most of the binding energy is due to the interaction of the oversized tin atom and the lattice vacancy, which essentially provide space for tin to relax. The nearest neighbor carbon-oxygen interstitial and the silicon-oxygen interstitial pairs are significantly bound, whereas the tin-oxygen interstitial pairs are not. The results are discussed in view of analogous investigations in isovalently doped silicon.
DENSITY-FUNCTIONAL CALCULATIONS FOR Ce, Th, AND Pu METALS AND ALLOYS
A.Landa
2004-01-01
Full Text Available The phase diagrams of Ce, Th, and Pu metals have been studied by means of density-functional theory (DFT. In addition to these metals, the phase stability of Ce-Th and Pu-Am alloys has been also investigated from first-principles calculations. Equation-of-state (EOS for Ce, Th, and the Ce-Th alloys has been calculated up to 1 Mbar pressure in good comparison to experimental data. Present calculations show that the Ce-Th alloys adopt a body-centered-tetragonal (bct structure upon hydrostatic compression which is in excellent agreement with measurements. The ambient pressure phase diagram of Pu is shown to be very poorly described by traditional DFT but rather well modelled when including magnetic interactions. In particular, the anomalous δ phase of Pu is shown to be stabilized by magnetic disorder at elevated temperatures. The Pu-Am system has also been studied in a similar fashion and it is shown that this system, for about 25% Am content, becomes antiferromagnetic below about 400 K which corroborates the recent discovery of a Curie-Weiss behavior in this system.
Relic neutrino decoupling with flavour oscillations revisited
Salas, Pablo F. de [Instituto de Física Corpuscular (CSIC-Universitat de València),Parc Científic UV, C/ Catedrático José Beltrán 2, E-46980 Paterna (Valencia) (Spain); Institute for Theoretical Particle Physics and Cosmology (TTK),RWTH Aachen University, D-52056 Aachen (Germany); Pastor, Sergio [Instituto de Física Corpuscular (CSIC-Universitat de València),Parc Científic UV, C/ Catedrático José Beltrán 2, E-46980 Paterna (Valencia) (Spain)
2016-07-28
We study the decoupling process of neutrinos in the early universe in the presence of three-flavour oscillations. The evolution of the neutrino spectra is found by solving the corresponding momentum-dependent kinetic equations for the neutrino density matrix, including for the first time the proper collision integrals for both diagonal and off-diagonal elements. This improved calculation modifies the evolution of the off-diagonal elements of the neutrino density matrix and changes the deviation from equilibrium of the frozen neutrino spectra. However, it does not vary the contribution of neutrinos to the cosmological energy density in the form of radiation, usually expressed in terms of the effective number of neutrinos, N{sub eff}. We find a value of N{sub eff}=3.045, in agreement with previous theoretical calculations and consistent with the latest analysis of Planck data. This result does not depend on the ordering of neutrino masses. We also consider the effect of non-standard neutrino-electron interactions (NSI), predicted in many theoretical models where neutrinos acquire mass. For two sets of NSI parameters allowed by present data, we find that N{sub eff} can be reduced down to 3.040 or enhanced up to 3.059.
Relic neutrino decoupling with flavour oscillations revisited
de Salas, Pablo F
2016-01-01
We study the decoupling process of neutrinos in the early universe in the presence of three-flavour oscillations. The evolution of the neutrino spectra is found by solving the corresponding momentum-dependent kinetic equations for the neutrino density matrix, including for the first time the proper collision integrals for both diagonal and off-diagonal elements. This improved calculation modifies the evolution of the off-diagonal elements of the neutrino density matrix and changes the deviation from equilibrium of the frozen neutrino spectra. However, it does not vary the contribution of neutrinos to the cosmological energy density in the form of radiation, usually expressed in terms of the effective number of neutrinos, N_eff. We find a value of N_eff=3.045, in agreement with previous theoretical calculations and consistent with the latest analysis of Planck data. This result does not depend on the ordering of neutrino masses. We also consider the effect of non-standard neutrino-electron interactions (NSI), ...
Kneur, J.L
2006-06-15
This document is divided into 2 parts. The first part describes a particular re-summation technique of perturbative series that can give a non-perturbative results in some cases. We detail some applications in field theory and in condensed matter like the calculation of the effective temperature of Bose-Einstein condensates. The second part deals with the minimal supersymmetric standard model. We present an accurate calculation of the mass spectrum of supersymmetric particles, a calculation of the relic density of supersymmetric black matter, and the constraints that we can infer from models.
Penfold, S; Miller, A [University of Adelaide, Adelaide, SA (Australia)
2015-06-15
Purpose: Stoichiometric calibration of Hounsfield Units (HUs) for conversion to proton relative stopping powers (RStPs) is vital for accurate dose calculation in proton therapy. However proton dose distributions are not only dependent on RStP, but also on relative scattering power (RScP) of patient tissues. RScP is approximated from material density but a stoichiometric calibration of HU-density tables is commonly neglected. The purpose of this work was to quantify the difference in calculated dose of a commercial TPS when using HU-density tables based on tissue substitute materials and stoichiometric calibrated ICRU tissues. Methods: Two HU-density calibration tables were generated based on scans of the CIRS electron density phantom. The first table was based directly on measured HU and manufacturer quoted density of tissue substitute materials. The second was based on the same CT scan of the CIRS phantom followed by a stoichiometric calibration of ICRU44 tissue materials. The research version of Pinnacle{sup 3} proton therapy was used to compute dose in a patient CT data set utilizing both HU-density tables. Results: The two HU-density tables showed significant differences for bone tissues; the difference increasing with increasing HU. Differences in density calibration table translated to a difference in calculated RScP of −2.5% for ICRU skeletal muscle and 9.2% for ICRU femur. Dose-volume histogram analysis of a parallel opposed proton therapy prostate plan showed that the difference in calculated dose was negligible when using the two different HU-density calibration tables. Conclusion: The impact of HU-density calibration technique on proton therapy dose calculation was assessed. While differences were found in the calculated RScP of bony tissues, the difference in dose distribution for realistic treatment scenarios was found to be insignificant.
Jacobsen, C.J.H.; Dahl, Søren; Boisen, A.
2002-01-01
For ammonia synthesis catalysts a volcano-type relationship has been found experimentally. We demonstrate that by combining density functional theory calculations with a microkinetic model the position of the maximum of the volcano curve is sensitive to the reaction conditions. The catalytic...... ammonia synthesis activity, to a first approximation, is a function only of the binding energy of nitrogen to the catalyst. Therefore, it is possible to evaluate which nitrogen binding energy is optimal under given reaction conditions. This leads to the concept of optimal catalyst curves, which illustrate...... the nitrogen binding energies of the optimal catalysts at different temperatures, pressures, and synthesis gas compositions. Using this concept together with the ability to prepare catalysts with desired binding energies it is possible to optimize the ammonia process. In this way a link between first...
Kanungo, Bikash
2016-01-01
We present a computationally efficient approach to perform large-scale all-electron density functional theory calculations by enriching the classical finite element basis with compactly supported atom-centered numerical basis functions that are constructed from the solution of the Kohn-Sham (KS) problem for single atoms. We term these numerical basis functions as enrichment functions, and the resultant basis as the enriched finite element basis. The enrichment functions are compactly supported through the use of smooth cutoff functions, which enhances the conditioning and maintains the locality of the basis. The integrals involved in the evaluation of the discrete KS Hamiltonian and overlap matrix in the enriched finite element basis are computed using an adaptive quadrature grid based on the characteristics of enrichment functions. Further, we propose an efficient scheme to invert the overlap matrix by using a block-wise matrix inversion in conjunction with special reduced-order quadrature rules to transform...
Gao, Haiyuan; Li, Meijiao; Guo, Zhendong; Chen, Hongshen; Jin, Zhonghe; Yu, Bin
2011-01-01
Electronic transport properties of monolayer graphene with extreme physical bending up to 90o angle are studied using ab Initio first-principle calculations. The importance of key structural parameters including step height, curvature radius and bending angle are discussed how they modify the transport properties of the deformed graphene sheet comparing to the corresponding flat ones. The local density of state reveals that energy state modification caused by the physical bending is highly localized. It is observed that the transport properties of bent graphene with a wide range of geometrical configurations are insensitive to the structural deformation in the low-energy transmission spectra, even in the extreme case of bending. The results support that graphene, with its superb electromechanical robustness, could serve as a viable material platform in a spectrum of applications such as photovoltaics, flexible electronics, OLED, and 3D electronic chips.
Density functional theory calculations on graphene/α-SiO2(0001) interface.
Ao, Zhimin; Jiang, Man; Wen, Zi; Li, Sean
2012-02-28
In this work, the graphene/α-SiO2(0001) interface is calculated using density functional theory. On the oxygen-terminated SiO2 surface, atomic structure reconstruction occurs at the graphene/SiO2 interface to eliminate the dangling bonds. The interface interaction is 77 meV/C atom, which indicates that van der Waals force dominates the interaction, but it is stronger than the force between the graphene layers in graphite. The distance between graphene and the SiO2 surface is 2.805 Å, which is smaller than the 3.4 Å interlayer distance of graphite. In addition, the SiO2 substrate induces p-type doping in graphene and opens a small gap of 0.13 eV at the Dirac point of graphene, which is desirable for electronic device applications.
Su Guo-Lin; Ren Xue-Guang; Zhang Shu-Feng; Ning Chuan-Gang; Zhou Hui; Li Bin; Li Gui-Qin; Deng Jing-Kang
2005-01-01
The first electronic structural study of the complete valence shell binding energy spectra of the antimicrobial agent diacetyl, encompassing both the outer and inner valence regions, is reported. The binding energy spectra as well as the individual orbital momentum profiles have been measured by using a high resolution (e, 2e) electron momentum spectrometer (EMS) at an impact energy of 1200eV plus the binding energy, and using symmetric noncoplanar kinematics.The experimental orbital electron momentum profiles are compared with self-consistent field (SCF) theoretical profiles calculated using the Hartree-Fock approximation and Density Functional theory predictions in the target Kohn-Sham approximation which includes some treatment of correlation via the exchange and correlation potentials with a range of basis sets. The pole strengths of the main ionization peaks from the inner valence orbitals are estimated.
Boll, Torben
2012-10-01
In this article the Cu-Au binding energy in Cu3Au is determined by comparing experimental atom probe tomography (APT) results to simulations. The resulting bonding energy is supported by density functional theory calculations. The APT simulations are based on the Müller-Schottky equation, which is modified to include different atomic neighborhoods and their characteristic bonds. The local environment is considered up to the fifth next nearest neighbors. To compare the experimental with simulated APT data, the AtomVicinity algorithm, which provides statistical information about the positions of the neighboring atoms, is applied. The quality of this information is influenced by the field evaporation behavior of the different species, which is connected to the bonding energies. © Microscopy Society of America 2012.
Andrade, Xavier; Botti, Silvana; Marques, Miguel A. L.; Rubio, Angel
2007-05-01
The authors present an efficient perturbative method to obtain both static and dynamic polarizabilities and hyperpolarizabilities of complex electronic systems. This approach is based on the solution of a frequency-dependent Sternheimer equation, within the formalism of time-dependent density functional theory, and allows the calculation of the response both in resonance and out of resonance. Furthermore, the excellent scaling with the number of atoms opens the way to the investigation of response properties of very large molecular systems. To demonstrate the capabilities of this method, they implemented it in a real-space (basis-set-free) code and applied it to benchmark molecules, namely, CO, H2O, and para-nitroaniline. Their results are in agreement with experimental and previous theoretical studies and fully validate their approach.
Sharma, S.; Pittalis, S.; Kurth, S.;
2007-01-01
The relative merits of current-spin-density- and spin-density-functional theory are investigated for solids treated within the exact-exchange-only approximation. Spin-orbit splittings and orbital magnetic moments are determined at zero external magnetic field. We find that for magnetic (Fe, Co...
Dimakis, Nicholas; Valdez, Danielle; Flor, Fernando Antonio; Salgado, Andres; Adjibi, Kolade; Vargas, Sarah; Saenz, Justin
2017-08-01
The adsorption of the alkali Li, K, and Na and the alkaline Ca on graphene is studied using periodic density functional theory (DFT) under various adatom coverages. The charge transfers between the adatom and the graphene sheet and the almost unchanged densities-of-states spectra in the energy region near and below the Fermi level support an ionic bond pattern between the adatom and the graphene atoms. However, the presence of small orbital overlap between the metal and the nearest graphene atom is indicative of small covalent bonding. Van der Waals interactions are examined through a semiempirical correction in the DFT functional and by comparing adatom-graphene calculations between 3% and 1.4% adatom coverages. Optimized adatom-graphene geometries identify the preferred adatom sites, whereas the adatom-graphene strength is correlated with the adsorption energy and the adatom distance from the graphene plane. Calculated electronic properties and structural parameters are obtained using hybrid functionals and a generalized gradient approximation functional paired with basis sets of various sizes. We found that due to long range electrostatic forces between the alkali/alkaline adatoms and the graphene monolayer, the adatom-graphene structural and electronic properties could be well-described by specific DFT functionals paired with high-quality adatom basis sets. For Li, K, and Na adsorbed on graphene, increased adatom surface coverage weakens the adatom-graphene interaction. However, this statement does not apply for Ca adsorbed on graphene. In this case, the Ca adsorption strength, which is stronger at higher coverages, is opposite to increases in the Ca-4s orbital population.
DGDFT: A Massively Parallel Method for Large Scale Density Functional Theory Calculations
Hu, Wei; Yang, Chao
2015-01-01
We describe a massively parallel implementation of the recently developed discontinuous Galerkin density functional theory (DGDFT) [J. Comput. Phys. 2012, 231, 2140] method, for efficient large-scale Kohn-Sham DFT based electronic structure calculations. The DGDFT method uses adaptive local basis (ALB) functions generated on-the-fly during the self-consistent field (SCF) iteration to represent the solution to the Kohn-Sham equations. The use of the ALB set provides a systematic way to improve the accuracy of the approximation. It minimizes the number of degrees of freedom required to represent the solution to the Kohn-Sham problem for a desired level of accuracy. In particular, DGDFT can reach the planewave accuracy with far fewer numbers of degrees of freedom. By using the pole expansion and selected inversion (PEXSI) technique to compute electron density, energy and atomic forces, we can make the computational complexity of DGDFT scale at most quadratically with respect to the number of electrons for both i...
DGDFT: A massively parallel method for large scale density functional theory calculations
Hu, Wei, E-mail: whu@lbl.gov; Yang, Chao, E-mail: cyang@lbl.gov [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Lin, Lin, E-mail: linlin@math.berkeley.edu [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Mathematics, University of California, Berkeley, California 94720 (United States)
2015-09-28
We describe a massively parallel implementation of the recently developed discontinuous Galerkin density functional theory (DGDFT) method, for efficient large-scale Kohn-Sham DFT based electronic structure calculations. The DGDFT method uses adaptive local basis (ALB) functions generated on-the-fly during the self-consistent field iteration to represent the solution to the Kohn-Sham equations. The use of the ALB set provides a systematic way to improve the accuracy of the approximation. By using the pole expansion and selected inversion technique to compute electron density, energy, and atomic forces, we can make the computational complexity of DGDFT scale at most quadratically with respect to the number of electrons for both insulating and metallic systems. We show that for the two-dimensional (2D) phosphorene systems studied here, using 37 basis functions per atom allows us to reach an accuracy level of 1.3 × 10{sup −4} Hartree/atom in terms of the error of energy and 6.2 × 10{sup −4} Hartree/bohr in terms of the error of atomic force, respectively. DGDFT can achieve 80% parallel efficiency on 128,000 high performance computing cores when it is used to study the electronic structure of 2D phosphorene systems with 3500-14 000 atoms. This high parallel efficiency results from a two-level parallelization scheme that we will describe in detail.
Density functional theory calculations of defect and fission gas properties in U-Si fuels
Andersson, Anders David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-02-03
Accident tolerant fuels (ATF) are being developed in response to the Fukushima Daiichi accident in Japan. One of the options being pursued is U-Si fuels, such as the U_{3}Si_{2} and U_{3}Si_{5} compounds, which benefit from high thermal conductivity (metallic) compared to the UO_{2} fuel (insulator or semi-conductor) used in current Light Water Reactors (LWRs). The U-Si fuels also have higher fissile density. In order to perform meaningful engineering scale nuclear fuel performance simulations, the material properties of the fuel, including the response to irradiation environments, must be known. Unfortunately, the data available for U-Si fuels are rather limited, in particular for the temperature range where LWRs would operate. The ATF HIP is using multi-scale modeling and simulations to address this knowledge gap. The present study investigates point defect and fission gas properties in U_{3}Si_{2}, which is one of the main fuel candidates, using density functional theory (DFT) calculations. Based on a few assumption regarding entropy contributions, defect and fission diffusivities are predicted. Even though uranium silicides have been shown to amorphize easily at low temperature, we assume that U_{3}Si_{2} remains crystalline under the conditions expected in Light Water Reactors (LWRs). The temperature and dose where amorphization occurs has not yet been well established.
Ansari, Reza; Ajori, Shahram; Malakpour, Sina
2016-04-01
The considerable demand for novel materials with specific properties has motivated the researchers to synthesize supramolecular nanostructures through different methods. Porous graphene is the first two-dimensional hydrocarbon synthesized quite recently. This investigation is aimed at studying the mechanical properties of atom-decorated (functionalized) porous graphene by employing density functional theory (DFT) calculation within both local density approximations (LDA) and generalized gradient approximations (GGA). The atoms are selected from period 3 of periodic table as well as Li and O atom from period 2. The results reveal that metallic atoms and noble gases are adsorbed physically on porous graphene and nonmetallic ones form chemical bonds with carbon atom in porous graphene structure. Also, it is shown that, in general, atom decoration reduces the values of mechanical properties such as Young's, bulk and shear moduli as well as Poisson's ratio, and this reduction is more considerable in the case of nonmetallic atoms (chemical adsorption), especially oxygen atoms, as compared to metallic atoms and noble gases (physical adsorption).
Detection relic gravitational waves in thermal case
Ghayour, Basem
2016-01-01
The thermal spectrum of relic gravitational waves causes the new amplitude that called `modified amplitude'. Our analysis shows that, there exist some chances for detection of the thermal spectrum in addition to the usual spectrum by Adv.LIGO and Dml detectors. The behaviour of the inflation and reheating stages are often known as power law expansion like $S(\\eta)\\propto \\eta^{1+\\beta}$, $S(\\eta)\\propto \\eta^{1+\\beta_s}$ respectively. The $\\beta$ and $\\beta_s$ have an unique effect on the shape of the spectrum. We find some upper bounds on the $\\beta$ and $\\beta_s$ by comparison the usual and thermal spectrum with the Adv.LIGO and Dml. As this result gives us more information about the nature of the evolution of inflation and reheating stages.
The refractive index of relic gravitons
Giovannini, Massimo
2016-01-01
The dynamical evolution of the refractive index of the tensor modes of the geometry produces a specific class of power spectra characterized by a blue (i.e. slightly increasing) slope which is directly determined by the competition of the slow-roll parameter and of the rate of variation of the refractive index. Throughout the conventional stages of the inflationary and post-inflationary evolution, the microwave background anisotropies measurements, the pulsar timing limits and the big-bang nucleosythesis constraints set stringent bounds on the refractive index and on its rate of variation. Within the physically allowed region of the parameter space the cosmic background of relic gravitons leads to a potentially large signal for the ground based detectors (in their advanced version) and for the proposed space-borne interferometers. Conversely, the lack of direct detection of the signal will set a qualitatively new bound on the dynamical variation of the refractive index.
Anomalous spectral lines and relic quantum nonequilibrium
Underwood, Nicolas G
2016-01-01
We describe general features that might be observed in the line spectra of relic cosmological particles should quantum nonequilibrium be preserved in their statistics. According to our arguments, these features would represent a significant departure from those of a conventional origin. Among other features, we find a possible spectral broadening (for incident photons) that is proportional to the energy resolution of the recording telescope (and so could be orders of magnitude larger than any intrinsic broadening). Notably, for a range of possible initial conditions we find the possibility of spectral line `narrowing' whereby a telescope could observe a spectral line which is narrower than it should conventionally be able to resolve. We briefly discuss implications for the indirect search for dark matter.
Diaconu, C V; Doll, J D; Freeman, D L; Diaconu, Cristian V.; Cho, Art E.; Freeman, David L.
2004-01-01
In the present work we investigate the adequacy of broken-symmetry (BS) unrestricted (U) density functional theory (DFT) for constructing the potential energy curve of nickel dimer and nickel hydride, as model for larger bare and hydrogenated nickel cluster calculations. We use three hybrid functionals: B3LYP, Becke98, and FSLYP (50% Hartree-Fock and 50% Slater exchange and LYP correlation functional) with two basis sets: all-electron (AE) Wachters+f basis set and Stuttgart RSC effective core potential (ECP) and basis set. We find that, overall, B3LYP functional with Wachters+f AE basis set performs best, with only 1.3% root-mean-square (RMS) deviation from experiment, followed by Becke98/AE and B3LYP/ECP, with RMS deviation from experimental value of 2.5% and 2.7%, respectively. We also find that for Ni dimer, the spin-projection for the broken-symmetry unrestricted singlet states changes the ordering of the states, but the splittings are less than 10 meV. All our calculations predict a (delta)(delta)-hole g...
Kuz'Min, Michael D.; Steinbeck, Lutz; Richter, Manuel
2002-02-01
A technique of determining the exchange field Bex on the 4f shell of Sm atoms in Sm-based magnets is proposed. It makes use of the 4f intermultiplet transition in Sm, observed in inelastic neutron scattering (INS) experiments. The method is used to analyze previously published data for a number of Sm-Fe and Sm-Co intermetallics, for all of which Bex is determined. Additional information on intramultiplet transitions in SmCo5 and Sm2Co17 makes it possible to obtain more accurate Bex values as well as to estimate the leading crystal field parameter (CFP) A02 for these compounds. For the same systems an independent determination of A02 is carried out using published magnetization curves and the Bex values found from the INS spectra. The two ``experimental'' values of A02 (INS and magnetization) agree well. For comparison, theoretical Sm-Co exchange fields and CFP for SmCo5 and Sm2Co17 are obtained from full-potential density-functional calculations. The theoretical A02 are shifted toward more negative values with respect to their experimental counterparts by a few millielectronvolts. The calculated Sm-Co exchange fields are in fair agreement with the experimentally determined values of the total exchange field on Sm, Bex, the weak Sm-Sm exchange interaction being accountable for the remaining small discrepancies.
Hafner, Jürgen
2010-09-29
During the last 20 years computer simulations based on a quantum-mechanical description of the interactions between electrons and atomic nuclei have developed an increasingly important impact on materials science, not only in promoting a deeper understanding of the fundamental physical phenomena, but also enabling the computer-assisted design of materials for future technologies. The backbone of atomic-scale computational materials science is density-functional theory (DFT) which allows us to cast the intractable complexity of electron-electron interactions into the form of an effective single-particle equation determined by the exchange-correlation functional. Progress in DFT-based calculations of the properties of materials and of simulations of processes in materials depends on: (1) the development of improved exchange-correlation functionals and advanced post-DFT methods and their implementation in highly efficient computer codes, (2) the development of methods allowing us to bridge the gaps in the temperature, pressure, time and length scales between the ab initio calculations and real-world experiments and (3) the extension of the functionality of these codes, permitting us to treat additional properties and new processes. In this paper we discuss the current status of techniques for performing quantum-based simulations on materials and present some illustrative examples of applications to complex quasiperiodic alloys, cluster-support interactions in microporous acid catalysts and magnetic nanostructures.
Jacob, D; Palacios, J J
2011-01-28
We study the performance of two different electrode models in quantum transport calculations based on density functional theory: parametrized Bethe lattices and quasi-one-dimensional wires or nanowires. A detailed account of implementation details in both the cases is given. From the systematic study of nanocontacts made of representative metallic elements, we can conclude that the parametrized electrode models represent an excellent compromise between computational cost and electronic structure definition as long as the aim is to compare with experiments where the precise atomic structure of the electrodes is not relevant or defined with precision. The results obtained using parametrized Bethe lattices are essentially similar to the ones obtained with quasi-one-dimensional electrodes for large enough cross-sections of these, adding a natural smearing to the transmission curves that mimics the true nature of polycrystalline electrodes. The latter are more demanding from the computational point of view, but present the advantage of expanding the range of applicability of transport calculations to situations where the electrodes have a well-defined atomic structure, as is the case for carbon nanotubes, graphene nanoribbons, or semiconducting nanowires. All the analysis is done with the help of codes developed by the authors which can be found in the quantum transport toolbox ALACANT and are publicly available.
Yu, Yingzhe; Sun, Xuanyu; Zhang, Minhua
2017-10-01
The mechanism of carbon deposition in acetic acid/palladium system is of great research significance in the catalytic field. In order to illustrate the plausible carbon formation routes, a systematic survey on the stepwise decomposition from adsorbed acetic acid to atomic carbon on Pd(100) was conducted via density functional theory calculations. A complex reaction network including Osbnd H bond scission reaction and various Csbnd H and Csbnd C bond scission reactions was built and the relevant structural and energetic properties were calculated. The results show that Osbnd H bond breaking is very possible for CH3COOH, that Csbnd C bond breaking is always more favorable than Csbnd H bond breaking for CHxCOO (x = 1-3), and the dehydrogenation of CHx (x = 1-3) is more likely to proceed than most of other reactions. The most possible pathway for the formation of carbon monomer was proposed based on the analysis of the reaction network and it features the decarbonation of CH3COO to CH3 as the rate-limiting step.
Effects of d-electrons in pseudopotential screened-exchange density functional calculations
Lee, Byounghak; Wang, Lin-Wang; Canning, Andrew
2008-06-01
We report a theoretical study on the role of shallow d states in the screened-exchange local density approximation (sX-LDA) band structure of binary semiconductor systems. We found that inaccurate pseudo-wave functions can lead to (1) an overestimation of the screened-exchange interaction between the localized d states and the delocalized higher energy s and p states, and (2) an underestimation of the screened-exchange interaction between the d states. The resulting sX-LDA band structures have substantially smaller band gaps compared with experiments. We correct the pseudo-wave functions of d states by including the semicore s and p states of the same shell in the valence states. The correction of pseudo-wave functions yields band gaps and d-state binding energies in good agreement with experiments and the full potential linearized augmented plane wave sX-LDA calculations. Compared with the quasiparticle GW method, our sX-LDA results shows not only similar quality on the band gaps but also much better d-state binding energies. Combined with its capability of ground-state structure calculation, the sX-LDA is expected to be a valuable theoretical tool for the II-VI and III-V (especially the III-N) bulk semiconductors and nanostructure studies.
van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J.
1998-12-01
In this paper we present time-dependent density functional calculations on frequency-dependent first (β) and second (γ) hyperpolarizabilities for the set of small molecules, N2, CO2, CS2, C2H4, NH3, CO, HF, H2O, and CH4, and compare them to Hartree-Fock and correlated ab initio calculations, as well as to experimental results. Both the static hyperpolarizabilities and the frequency dispersion are studied. Three approximations to the exchange-correlation (xc) potential are used: the widely used Local Density Approximation (LDA), the Becke-Lee-Yang-Parr (BLYP) Generalized Gradient Approximation (GGA), as well as the asymptotically correct Van Leeuwen-Baerends (LB94) potential. For the functional derivatives of the xc potential the Adiabatic Local Density Approximation (ALDA) is used. We have attempted to estimate the intrinsic quality of these methods by using large basis sets, augmented with several diffuse functions, yielding good agreement with recent numerical static LDA results. Contrary to claims which have appeared in the literature on the basis of smaller studies involving basis sets of lesser quality, we find that the static LDA results for β and γ are severely overestimated, and do not improve upon the (underestimated) Hartree-Fock results. No improvement is provided by the BLYP potential which suffers from the same incorrect asymptotic behavior as the LDA potential. The results are however clearly improved upon by the LB94 potential, which leads to underestimated results, slightly improving the Hartree-Fock results. The LDA and BLYP potentials overestimate the frequency dependence as well, which is once again improved by the LB94 potential. Future improvements are expected to come from improved models for asymptotically correct exchange-correlation potentials. Apart from the LB94 potential used in this work, several other asymptotically correct potentials have recently been suggested in the literature and can also be expected to improve considerably
Rudin, Sven P.; Bock, Nicolas; Wallace, Duane C.
2014-11-01
Density functional theory (DFT) calculations reliably aid in understanding the relative stability of different crystal phases as functions of pressure and temperature. Our purpose here is to employ DFT to analyze the character of the melting process, with an emphasis on comparing normal and anomalous melting. The normal-anomalous distinction is the absence or presence, respectively, of a significant electronic structure change between crystal and liquid. We study the normal melters Na and Cu, which are metallic in both phases, and the anomalous melter Ga, which has a partially covalent crystal and a nearly free-electron liquid. We calculate free energies from lattice dynamics for the crystal and from vibration-transit (V-T) theory for the liquid, where the liquid formulation is similar to that of the crystal but has an additional term representing the diffusive transits. Internal energies U and entropies S calculated for both phases of Na and Cu were previously shown to be in good agreement with experiment; here we find the same agreement for Ga. The dominant theoretical terms in the melting Δ U and Δ S are the structural potential energy, the vibrational entropy, and the purely liquid transit terms in both U and S . The melting changes in structural energy and vibrational entropy are much larger in Ga than in Na and Cu. This behavior arises from the change in electronic structure in Ga, and is the identifying characteristic of anomalous melting. We interpret our DFT results in terms of the physical effects of the relatively few covalent bonds in the otherwise metallic Ga crystal.
Introducing PROFESS: A new program for orbital-free density functional theory calculations
Ho, Gregory S.; Lignères, Vincent L.; Carter, Emily A.
2008-12-01
We present PROFESS (PRinceton Orbital-Free Electronic Structure Software), a new software package that performs orbital-free density functional theory (OF-DFT) calculations. OF-DFT is a first principles quantum mechanics method primarily for condensed matter that can be made to scale linearly with system size. We describe the implementation of energy, force, and stress functionals and the methods used to optimize the electron density under periodic boundary conditions. All electronic energy and potential terms scale linearly while terms involving the ions exhibit quadratic scaling in our code. Despite the latter scaling, the program can treat tens of thousands of atoms with quantum mechanics on a single processor, as we demonstrate here. Limitations of the method are also outlined, the most serious of which is the accuracy of state-of-the-art kinetic energy functionals, which limits the applicability of the method to main group elements at present. Program summaryProgram title: PROFESS Catalogue identifier: AEBN_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBN_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 35 933 No. of bytes in distributed program, including test data, etc.: 329 924 Distribution format: tar.gz Programming language: Fortran 90 Computer: Intel with ifort; AMD Opteron with pathf90 Operating system: Linux RAM: Problem dependent, but 2 GB is sufficient for up to 10,000 ions Classification: 7.3 External routines: FFTW ( http://www.fftw.org), MINPACK-2 Nature of problem: Given a set of coordinates describing the initial ion positions under periodic boundary conditions, recovers the ground state energy, electron density, ion positions, and cell lattice vectors predicted by orbital-free density functional theory. Except for computation of the
Density functional theory/B3LYP has been employed to optimize the conformations of selected 4-arylflavan-3-ols and their phenolic methyl ether 3-O-acetates. The electronic circular dichroism spectra of the major conformers have been calculated using time-dependent density functional theory to valida...
Model for Thermal Relic Dark Matter of Strongly Interacting Massive Particles.
Hochberg, Yonit; Kuflik, Eric; Murayama, Hitoshi; Volansky, Tomer; Wacker, Jay G
2015-07-10
A recent proposal is that dark matter could be a thermal relic of 3→2 scatterings in a strongly coupled hidden sector. We present explicit classes of strongly coupled gauge theories that admit this behavior. These are QCD-like theories of dynamical chiral symmetry breaking, where the pions play the role of dark matter. The number-changing 3→2 process, which sets the dark matter relic abundance, arises from the Wess-Zumino-Witten term. The theories give an explicit relationship between the 3→2 annihilation rate and the 2→2 self-scattering rate, which alters predictions for structure formation. This is a simple calculable realization of the strongly interacting massive-particle mechanism.
Kim, Leonard H.; Zhang Miao; Howell, Roger W.; Yue, Ning J.; Khan, Atif J. [Department of Radiation Oncology, University of Medicine and Dentistry of New Jersey: Robert Wood Johnson Medical School and Cancer Institute of New Jersey, New Brunswick, New Jersey 08903 (United States); Department of Radiology, University of Medicine and Dentistry of New Jersey: New Jersey Medical School, Newark, New Jersey 07103 (United States); Department of Radiation Oncology, University of Medicine and Dentistry of New Jersey: Robert Wood Johnson Medical School and Cancer Institute of New Jersey, New Brunswick, New Jersey 08903 (United States)
2013-01-15
Purpose: Recent recommendations by the American Association of Physicists in Medicine Task Group 186 emphasize the importance of understanding material properties and their effect on inhomogeneity-corrected dose calculation for brachytherapy. Radiographic contrast is normally injected into breast brachytherapy balloons. In this study, the authors independently estimate properties of contrast solution that were expected to be incorrectly specified in a commercial brachytherapy dose calculation algorithm. Methods: The mass density and atomic weight fractions of a clinical formulation of radiographic contrast solution were determined using manufacturers' data. The mass density was verified through measurement and compared with the density obtained by the treatment planning system's CT calibration. The atomic weight fractions were used to determine the photon interaction cross section of the contrast solution for a commercial high-dose-rate (HDR) brachytherapy source and compared with that of muscle. Results: The density of contrast solution was 10% less than that obtained from the CT calibration. The cross section of the contrast solution for the HDR source was 1.2% greater than that of muscle. Both errors could be addressed by overriding the density of the contrast solution in the treatment planning system. Conclusions: The authors estimate the error in mass density and cross section parameters used by a commercial brachytherapy dose calculation algorithm for radiographic contrast used in a clinical breast brachytherapy practice. This approach is adaptable to other clinics seeking to evaluate dose calculation errors and determine appropriate density override values if desired.
Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory
Zuniga-Gutierrez, Bernardo, E-mail: bzuniga.51@gmail.com [Departamento de Ciencias Computacionales, Universidad de Guadalajara, Blvd. Marcelino García Barragán 1421, C.P. 44430 Guadalajara, Jalisco (Mexico); Camacho-Gonzalez, Monica [Universidad Tecnológica de Tecámac, División A2, Procesos Industriales, Carretera Federal México Pachuca Km 37.5, Col. Sierra Hermosa, C.P. 55740 Tecámac, Estado de México (Mexico); Bendana-Castillo, Alfonso [Universidad Tecnológica de Tecámac, División A3, Tecnologías de la Información y Comunicaciones, Carretera Federal México Pachuca Km 37.5, Col. Sierra Hermosa, C.P. 55740 Tecámac, Estado de México (Mexico); Simon-Bastida, Patricia [Universidad Tecnlógica de Tulancingo, División Electromecánica, Camino a Ahuehuetitla No. 301, Col. Las Presas, C.P. 43642 Tulancingo, Hidalgo (Mexico); Calaminici, Patrizia; Köster, Andreas M. [Departamento de Química, CINVESTAV, Avenida Instituto Politécnico Nacional 2508, A.P. 14-740, México D.F. 07000 (Mexico)
2015-09-14
The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H{sup 12}C–{sup 12}CH–DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated.
Damas, Aurélie; Chamoreau, Lise-Marie; Cooksy, Andrew L; Jutand, Anny; Amouri, Hani
2013-02-04
The synthesis and X-ray molecular structure of the first metal-stabilized o-dithiobenzoquinone [Cp*Ir-o-(η(4)-C(6)H(4)S(2))] (2) are described. The presence of the metal stabilizes this elusive intermediate by π coordination and increases the nucleophilic character of the sulfur atoms. Indeed, the π-bonded dithiolene complex 2 was found to react with the organometallic solvated species [Cp*M(acetone)(3)][OTf](2) (M = Rh, Ir) to give a unique class of binuclear dithiolene compounds [Cp*Ir(C(6)H(4)S(2))MCp*][OTf](2) [M = Rh (3), Ir (4)] in which the elusive dithiolene η-C(6)H(4)S(2) acts as a bridging ligand toward the two Cp*M moieties. The electrochemical behavior of all complexes was investigated and provided us with valuable information about their redox properties. Density functional theory (DFT) calculations on the π-bonded dithiobenzoquinone ligand and related bimetallic systems show that the presence of Cp*M at the arene system of the dithiolene ligand increases the stability compared to the known monomeric species [Cp*Ir-o-(C(6)H(4)S(2)-κ(2)-S,S)] and enables these complexes Cp*Ir(C(6)H(4)S(2))MCp*][OTf](2) (3 and 4) to act as electron reservoirs. Time-dependent DFT calculations also predict the qualitative trends in the experimental UV-vis spectra and indicate that the strongest transitions arise from ligand-metal charge transfer involving primarily the HOMO-1 and LUMO. All of these compounds were fully characterized and identified by single-crystal X-ray crystallography. These results illustrate the first examples describing the coordination chemistry of the elusive o-dithiobenzoquinone to yield bimetallic complexes with an o-benzodithiolene ligand. These compounds might have important applications in the area of molecular materials.
Maeta, Takahiro [Graduate School of System Engineering, Okayama Prefectural University, 111 Kuboki, Soja, Okayama 719-1197 (Japan); GlobalWafers Japan Co., Ltd., Higashikou, Seirou-machi, Kitakanbara-gun, Niigata 957-0197 (Japan); Sueoka, Koji [Department of Communication Engineering, Okayama Prefectural University, 111 Kuboki, Soja, Okayama 719-1197 (Japan)
2014-08-21
Ge-based substrates are being developed for applications in advanced nano-electronic devices because of their higher intrinsic carrier mobility than Si. The stability and diffusion mechanism of impurity atoms in Ge are not well known in contrast to those of Si. Systematic studies of the stable sites of 2nd to 6th row element impurity atoms in Ge crystal were undertaken with density functional theory (DFT) and compared with those in Si crystal. It was found that most of the impurity atoms in Ge were stable at substitutional sites, while transition metals in Si were stable at interstitial sites and the other impurity atoms in Si were stable at substitutional sites. Furthermore, DFT calculations were carried out to clarify the mechanism responsible for the diffusion of impurity atoms in Ge crystals. The diffusion mechanism for 3d transition metals in Ge was found to be an interstitial-substitutional diffusion mechanism, while in Si this was an interstitial diffusion mechanism. The diffusion barriers in the proposed diffusion mechanisms in Ge and Si were quantitatively verified by comparing them to the experimental values in the literature.
Ling-hong YU; Geng-tao LIU; You-min SUN; Hong-yu ZHANG
2004-01-01
AIM: To investigate the effect of schisanhenol (Sal) on copper ion-induced oxidative modulation of human low density lipoprotein (LDL). METHODS: The antioxidative activity of eight schisandrins (DCL) on microsome lipid peroxidation induced by Vit C/NADPH system was first observed, and then, the effect of Sal on Cu2+-induced human LDL oxidation was studied. The generation of malondialdehyde (MDA), lipofuscin, reactive oxygen species (ROS), consumption of α-tocopherol as well as electrophoretic mobility of LDL were determined as criteria of LDL oxidation. Finally, the quantum chemical method was used to calculate the theoretical parameters of eight DCL for elucidating the difference of their antioxidant ability. RESULTS: Sal was shown to be the most active one among eight schizandrins in inhibiting microsome lipid oxidation induced by Vit C/NADPH. Sal 100, 50, and 10 μrnol/L inhibited production of MDA, lipofuscin and ROS as well as the consumption of α-tocopherol in Cu2+-induced oxidation of human LDL in a dose-dependent manner. Sal also reduced electrophoretic mobility of the oxidized human LDL. Further study of quantum chemistry found that Sal was the strongest one among eight DCL to scavenge O-2, R·, RO·, and ROO· radicals. CONCLUSION: Sal has antioxidative effect on human LDL oxidation.The mechanism of Sal against LDL oxidation may be through scavenging free radicals.
Yuan, H. K.; Chen, H., E-mail: chenh@swu.edu.cn; Tian, C. L.; Kuang, A. L.; Wang, J. Z. [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China)
2014-04-21
Gadolinium-oxide clusters in various sizes and stoichiometries have been systematically studied by employing the density functional theory with the generalized gradient approximation. The clusters in bulk stoichiometry are relatively more stable and their binding energies increase with the increasing size. Stoichiometric (Gd{sub 2}O{sub 3}){sub n} clusters of n = 1–3 prefer cage-like structures, whereas the clusters of n = 4–30 prefer compact structures layered by wedge-like units and exhibit a rough feature toward the bulk-like arrangement with small disorders of atomic positions. The polyhedral-cages analogous to carbon-fullerenes are stable isomers yet not the minimum energy configurations. Their stabilities can be improved by embedding one oxygen atom or a suitable cage to form core-shell configurations. The mostly favored antiferromagnetic couplings between adjacent Gd atoms are nearly degenerated in energy with their ferromagnetic couplings, resulting in super-paramagnetic characters of gadolinium-oxide clusters. The Ruderman-Kittel-Kasuya-Yosida (RKKY)-type mechanism together with the superexchange-type mechanism plays cooperation role for the magnetic interactions in clusters. We present, as a function of n, calculated binding energies, ionization potential, electron affinity, and electronic dipole moment.
The Density Matrix Renormalization Group Method and Large-Scale Nuclear Shell-Model Calculations
Dimitrova, S S; Pittel, S; Stoitsov, M V
2002-01-01
The particle-hole Density Matrix Renormalization Group (p-h DMRG) method is discussed as a possible new approach to large-scale nuclear shell-model calculations. Following a general description of the method, we apply it to a class of problems involving many identical nucleons constrained to move in a single large j-shell and to interact via a pairing plus quadrupole interaction. A single-particle term that splits the shell into degenerate doublets is included so as to accommodate the physics of a Fermi surface in the problem. We apply the p-h DMRG method to this test problem for two $j$ values, one for which the shell model can be solved exactly and one for which the size of the hamiltonian is much too large for exact treatment. In the former case, the method is able to reproduce the exact results for the ground state energy, the energies of low-lying excited states, and other observables with extreme precision. In the latter case, the results exhibit rapid exponential convergence, suggesting the great promi...
Jin, Yuanyuan; Lu, Shengjie; Hermann, Andreas; Kuang, Xiaoyu; Zhang, Chuanzhao; Lu, Cheng; Xu, Hongguang; Zheng, Weijun
2016-07-01
We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen- (n = 3-12), and their corresponding neutral species. Photoelectron spectra of RuGen- clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen-/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters.
Gauss-Bonnet gravity, relic coherent gravitons and optical chaos
Crowell, Lawrence B
2011-01-01
We discuss the production of massive relic coherent gravitons in Gauss-Bonnet gravity and their possible imprint in Cosmic Microwave Background. In fact, in the very early universe these relic gravitons could have acted as slow gravity waves. They may have then acted to focus the geodesics of radiation and matter. Therefore, their imprint on the later evolution of the universe could appear as filaments and domain wall in the Universe today. In that case, the effect on Cosmic Microwave Background should be analogous to the effect of water waves, which, in focusing light, create optical caustics which are commonly seen on the bottom of swimming pools. We analyze this important issue by showing how relic massive GWs perturb the trajectories of Cosmic Microwave Background photons (gravitational lensing by relic GWs). The consequence of the type of physics discussed is outlined by illustrating an amplification of what might be called optical chaos.
Filatov, M; Cremer, D
2005-01-01
It is demonstrated that the LYP correlation functional is not suited to be used for the calculation of electron spin resonance hyperfine structure (HFS) constants, nuclear magnetic resonance spin-spin coupling constants, magnetic, shieldings and other properties that require a balanced account of
Deep XMM-Newton Observations of the NW Radio Relic Region of Abell 3667
Sarazin, Craig L; Wik, Daniel R; Clarke, Tracy E
2016-01-01
The results of long XMM-Newton X-ray observations of the NW radio relic of Abell 3667 are presented. A shock is detected at the sharp outer edge of the radio relic, both in the X-ray surface brightness and the temperature profiles. The Mach number is M = 2.54^+0.80_-0.43. The temperature jump at the shock is larger than expected from the density jump, which may indicate that a dynamically important magnetic field aligned primarily parallel to the shock front is present. The gas temperature rises gradually over several arc minutes within the shock region. This could indicate that the shock energy is initially dissipated into some mix of thermal and nonthermal (e.g., turbulence) components, and that the nonthermal energy decays into heat in the post-shock region. The observed radio relic can be powered if ~0.2% of the energy dissipated in the shock goes into the (re)acceleration of relativistic electrons. We show that the observed steepening of the radio spectrum with distance behind the shock is consistent wit...
Relic abundance in a secluded dark matter scenario with a massive mediator
Okawa, Shohei; Tanabashi, Masaharu; Yamanaka, Masato
2017-01-01
The relic abundance of the dark matter (DM) particle d is studied in a secluded DM scenario, in which the d number decreasing process dominantly occurs not through the pair annihilation of d into the standard model particles, but via the d d →m m scattering process with a subsequently decaying mediator particle m . It is pointed out that the cosmologically observed relic abundance of DM can be accomplished even with a massive mediator having a mass mm non-negligibly heavy compared with the DM particle mass md. In the degenerated d -m case (md=mm), the DM relic abundance is realized by adjusting the d d →m m scattering amplitude large enough and by choosing an appropriate mediator particle lifetime. The DM evolution in the early universe exhibits characteristic "terrace" behavior, or two-step number density decreasing behavior, having a "fake" freeze-out at the first step. Based on these observations, a novel possibility of the DM model buildings is introduced in which the mediator particle m is unified with the DM particle d in an approximate dark symmetry multiplet. A pionic DM model is proposed to illustrate this idea in a renormalizable field theory framework.
Laurent Vial
2009-07-01
Full Text Available A number of small RNA sequences, located in different non-coding sequences and highly preserved across the tree of life, have been suggested to be molecular fossils, of ancient (and possibly primordial origin. On the other hand, recent years have revealed the existence of ubiquitous roles for small RNA sequences in modern organisms, in functions ranging from cell regulation to antiviral activity. We propose that a single thread can be followed from the beginning of life in RNA structures selected only for stability reasons through the RNA relics and up to the current coevolution of RNA sequences; such an understanding would shed light both on the history and on the present development of the RNA machinery and interactions. After presenting the evidence (by comparing their sequences that points toward a common thread, we discuss a scenario of genome coevolution (with emphasis on viral infectious processes and finally propose a plan for the reevaluation of the stereochemical theory of the genetic code; we claim that it may still be relevant, and not only for understanding the origin of life, but also for a comprehensive picture of regulation in present-day cells.
Stellar Relics from the Early Galaxy
T. Sivarani
2013-03-01
We reviewed the recent progress in the field of stellar/galactic archeology, which is a study of the relics from the early galaxy. The oldest and most pristine objects that can be observed in the galaxy are the low mass metal poor stars of the Milky Way. They were formed during the early phases, when the ISM might have been polluted only by the Pop-III supernovae. With the recent large spectroscopic surveys (e.g. HK survey by Beers and collaborators, the Hamburg-ESO survey by Christlieb and collaborators and Sloan Digital Sky Survey) it has been possible to get clues on the nature of the first stars that has contributed to the heavy elements. Most of these metal-poor low mass stars also retain their signature of the early dynamical evolution of the galaxy, which can be studied through their orbits around the galaxy and spatial distribution. Here, we discuss the connection between the chemical and the kinematical properties of metal-poor stars in order to probe the early galaxy formation. We also discuss about the globular clusters, the satellite galaxies around the Milky Way and its possible contribution to the formation of the galaxy halo.
RNA relics and origin of life.
Demongeot, Jacques; Glade, Nicolas; Moreira, Andrés; Vial, Laurent
2009-07-31
A number of small RNA sequences, located in different non-coding sequences and highly preserved across the tree of life, have been suggested to be molecular fossils, of ancient (and possibly primordial) origin. On the other hand, recent years have revealed the existence of ubiquitous roles for small RNA sequences in modern organisms, in functions ranging from cell regulation to antiviral activity. We propose that a single thread can be followed from the beginning of life in RNA structures selected only for stability reasons through the RNA relics and up to the current coevolution of RNA sequences; such an understanding would shed light both on the history and on the present development of the RNA machinery and interactions. After presenting the evidence (by comparing their sequences) that points toward a common thread, we discuss a scenario of genome coevolution (with emphasis on viral infectious processes) and finally propose a plan for the reevaluation of the stereochemical theory of the genetic code; we claim that it may still be relevant, and not only for understanding the origin of life, but also for a comprehensive picture of regulation in present-day cells.
Varini, Nicola; Ceresoli, Davide; Martin-Samos, Layla; Girotto, Ivan; Cavazzoni, Carlo
2013-08-01
One of the most promising techniques used for studying the electronic properties of materials is based on Density Functional Theory (DFT) approach and its extensions. DFT has been widely applied in traditional solid state physics problems where periodicity and symmetry play a crucial role in reducing the computational workload. With growing compute power capability and the development of improved DFT methods, the range of potential applications is now including other scientific areas such as Chemistry and Biology. However, cross disciplinary combinations of traditional Solid-State Physics, Chemistry and Biology drastically improve the system complexity while reducing the degree of periodicity and symmetry. Large simulation cells containing of hundreds or even thousands of atoms are needed to model these kind of physical systems. The treatment of those systems still remains a computational challenge even with modern supercomputers. In this paper we describe our work to improve the scalability of Quantum ESPRESSO (Giannozzi et al., 2009 [3]) for treating very large cells and huge numbers of electrons. To this end we have introduced an extra level of parallelism, over electronic bands, in three kernels for solving computationally expensive problems: the Sternheimer equation solver (Nuclear Magnetic Resonance, package QE-GIPAW), the Fock operator builder (electronic ground-state, package PWscf) and most of the Car-Parrinello routines (Car-Parrinello dynamics, package CP). Final benchmarks show our success in computing the Nuclear Magnetic Response (NMR) chemical shift of a large biological assembly, the electronic structure of defected amorphous silica with hybrid exchange-correlation functionals and the equilibrium atomic structure of height Porphyrins anchored to a Carbon Nanotube, on many thousands of CPU cores.
Itahana, Madoka; Takizawa, Motokazu; Akamatsu, Hiroki; Ohashi, Takaya; Ishisaki, Yoshitaka; Kawahara, Hajime; van Weeren, Reinout J.
2015-12-01
We present the results of Suzaku observations of the galaxy cluster 1RXS J0603.3+4214 with the "Toothbrush" radio relic. Although a shock with Mach number M ≃ 4 is expected at the outer edge of the relic from the radio observation, our temperature measurements of the intracluster medium indicate a weaker temperature difference than expected. The Mach number estimated from the temperature difference at the outer edge of the relic is M ≃ 1.5, which is significantly lower than the value estimated from the radio data even considering both statistical and systematic errors. This suggests that a diffusive shock acceleration theory in the linear test particle regime, which is commonly used to link the radio spectral index to the Mach number, is invalid for this relic. We also measured the temperature difference across the western part of the relic, where a shock with M ≃ 1.6 is suggested from the X-ray surface brightness analysis of the XMM-Newton data, and obtained consistent results in an independent way. We searched for the non-thermal inverse Compton component in the relic region and the resultant upper limit on the flux is 2.4 × 10-13 erg cm-2 s-1 in the 0.3-10 keV band. The lower limit of the magnetic field strength becomes 1.6 μG, which means that magnetic energy density could be more than a few percent of the thermal energy.
Density functional theory calculations on oxygen adsorption on the Cu{sub 2}O surfaces
Yu, Xiaohu [College of Physics and Electrical Engineering, Anyang Normal University, Anyang, Henan 455000 (China); State Key laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001 (China); Zhang, Xuemei [College of Physics and Electrical Engineering, Anyang Normal University, Anyang, Henan 455000 (China); Tian, Xinxin [State Key laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001 (China); Wang, Shengguang, E-mail: shengguang.wang@gmail.com [State Key laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001 (China); Synfuels China Co., Ltd., Huairou, Beijing 101407 (China); Feng, Gang, E-mail: fengg.sshy@sinopec.com [State Key laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001 (China); Shanghai Research Institute of Petrochemical Technology SINOPEC, Shanghai 201208 (China)
2015-01-01
Graphical abstract: - Highlights: • Atomic oxygen adsorption on Cu{sub 2}O(110) and Cu{sub 2}O(100) induces surface reconstruction. • Atomic O and molecular O{sub 2} adsorption on the Cu{sub 2}O(100) surface is stronger than on the Cu{sub 2}O(111) surface. • Dissociative adsorption was found to be energetically favorable. • Atomic O and molecular O{sub 2} adsorption on the Cu{sub 2}O(111) surface induces magnetism. - Abstract: In order to understand various surface properties such as corrosion and potential catalytic activity of Cu{sub 2}O surfaces in the presence of environmental gases, we report here spin-polarized density functional theory calculations of the adsorptions of atomic and molecular oxygen on three surface Cu{sub 2}O facets. Atomic oxygen adsorbs at the hollow site formed with copper atoms of Cu{sub 2}O(111), while its adsorption on the Cu{sub 2}O(110) and Cu{sub 2}O(100) induces surface reconstruction. Molecular oxygen adsorbs on one coordinated unsaturated surface copper atom and two coordinated saturated copper atoms of Cu{sub 2}O(111), on the top of two surface copper atoms of Cu{sub 2}O(110), and on four surface copper atoms on Cu{sub 2}O(100). It was found that atomic O and molecular O{sub 2} adsorption on the Cu{sub 2}O(100) surface is stronger than on the Cu{sub 2}O(111) surface. Atomic O and molecular O{sub 2} adsorption on the surface of Cu{sub 2}O(111) induces magnetism. This is different from other systems previously known to exhibit point defect ferromagnetism. On all three surfaces, dissociative adsorption was found to be energetically favorable.
Oishi Tomohiro
2016-01-01
We calculate the two-proton decay width of the 6 Be nucleus employing the schematic density-dependent contact potential for the proton-proton pairing interaction. The decay width is calculated with a time-dependent method, in which the two-proton emission is described as a time-evolution of a three-body meta-stable state. Model-dependence of the two-proton decay width has been shown by comparing the results obtained with the two different pairing models, schematic density-dependent contact and Minnesota interactions, which have zero and finite ranges, respectively.
Gao, Hongwei; Xia, FengYi; Huang, ChangJiang; Lin, Kuangfei
2011-04-01
A comparison of six density functional theory (DFT) methods and six basis sets for predicting the molecular structures and vibration spectra of cisplatin is reported. The theoretical results are discussed and compared with the experimental data. It is remarkable that LSDA/SDD level is clearly superior to all the remaining density functional methods (including mPW1PW) in predicting the structures of cisplatin. Mean deviation between the calculated harmonic and observed fundamental vibration frequencies for each method is also calculated. The results indicate that PBE1PBE/SDD is the best method to predict all frequencies on average for cisplatin molecule in DFT methods.
Taylor Series Trajectory Calculations Including Oblateness Effects and Variable Atmospheric Density
Scott, James R.
2011-01-01
Taylor series integration is implemented in NASA Glenn's Spacecraft N-body Analysis Program, and compared head-to-head with the code's existing 8th- order Runge-Kutta Fehlberg time integration scheme. This paper focuses on trajectory problems that include oblateness and/or variable atmospheric density. Taylor series is shown to be significantly faster and more accurate for oblateness problems up through a 4x4 field, with speedups ranging from a factor of 2 to 13. For problems with variable atmospheric density, speedups average 24 for atmospheric density alone, and average 1.6 to 8.2 when density and oblateness are combined.
杨忠志; 沈尔忠
1996-01-01
On the basis of a more precise expression of the atomic effective electronegativity deduced from the density functional theory and electronegativity equalization principle, a new scheme for calculating the group electronegativity and the atomic charges in a group is proposed and programed, and various parameters of electronegativity and hardness are given for some common atoms. Through calculation, analysis and comparison of more than one hundred groups, it is shown that the results from this scheme are reasonable and may be extended.
Hussain, Tanveer; Maark, Tuhina Adit; Pathak, Biswarup; Ahuja, Rajeev
2013-10-01
This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs) by means of hybrid density functional theory (PBE0). On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM's. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies.
Fourier Path Integral Monte Carlo Method for the Calculation of the Microcanonical Density of States
Freeman, D L; Freeman, David L.
1994-01-01
Using a Hubbard-Stratonovich transformation coupled with Fourier path integral methods, expressions are derived for the numerical evaluation of the microcanonical density of states for quantum particles obeying Boltzmann statistics. A numerical algorithmis suggested to evaluate the quantum density of states and illustrated on a one-dimensional model system.
Nabar, Rahul
Recent advances in theoretical techniques and computational hardware have made it possible to apply Density Functional Theory (DFT) methods to realistic problems in heterogeneous catalysis. Hydrocarbon processing is economically, and strategically, a very important industrial sector in today's world. In this thesis, we employ DFT methods to examine several important problems in hydrocarbon processing. Fischer Tropsch Synthesis (FTS) is a mature technology to convert synthesis gas derived from coal, natural-gas or biomass into liquid fuels, specifically diesel. Iron is an active FTS catalyst, but the absence of detailed reaction mechanisms make it difficult to maximize activity and optimize product distribution. We evaluate thermochemistry, kinetics and Rate Determining Steps (RDS) for Fischer Tropsch Synthesis on several models of Fe catalysts: Fe(110), Fe(211) and Pt promoted Fe(110). Our studies indicated that CO-dissociation is likely to be the RDS under most reaction conditions, but the DFT-calculated activation energy ( Ea) for direct CO dissociation was too large to explain the observed catalyst activity. Consequently we demonstrate that H-assisted CO-dissociation pathways are competitive with direct CO dissociation on both Co and Fe catalysts and could be responsible for a major fraction of the reaction flux (especially at high CO coverages). We then extend this alternative mechanistic model to closed-packed facets of nine transition metal catalysts (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt). H-assisted CO dissociation offers a kinetically easier route on each of the metals studied. DFT methods are also applied to another problem from the petroleum industry: discovery of poison-resistant, bimetallic, alloy catalysts (poisons: C, S, CI, P). Our systematic screening studies identify several Near Surface Alloys (NSAs) that are expected to be highly poison-resistant yet stable and avoiding adsorbate induced reconstruction. Adsorption trends are also correlated with
Ribeiro, M., E-mail: ribeiro.jr@oorbit.com.br [Office of Operational Research for Business Intelligence and Technology, Principal Office, Buffalo, Wyoming 82834 (United States)
2015-06-21
Ab initio calculations of hydrogen-passivated Si nanowires were performed using density functional theory within LDA-1/2, to account for the excited states properties. A range of diameters was calculated to draw conclusions about the ability of the method to correctly describe the main trends of bandgap, quantum confinement, and self-energy corrections versus the diameter of the nanowire. Bandgaps are predicted with excellent accuracy if compared with other theoretical results like GW, and with the experiment as well, but with a low computational cost.
Liu, Qing Zhong
1992-01-01
Unified analytical expressions have been derived for calculating the resonant frequencies, transimpedance and equivalent input noise current densities of the four most widely used tuned optical receiver front ends built with FETs and p-i-n diodes. A more accurate FET model has been used to improve...
Paidarová, Ivana; Sauer, Stephan P. A.
2012-01-01
We have compared the performance of density functional theory (DFT) using five different exchange-correlation functionals with four coupled cluster theory based wave function methods in the calculation of geometrical derivatives of the polarizability tensor of methane. The polarizability gradient...
Kadantsev, Eugene S.; Klooster, Rob; De Boeij, Paul L.; Ziegler, Tom
2007-01-01
Analytic energy gradients with respect to atomic coordinates for systems with translational invariance are formulated within the framework of Kohn-Sham Density Functional Theory. The energy gradients are implemented in the BAND program for periodic DFT calculations which directly employs a Bloch bas
Adsorption and Reaction of CO on (100) Surface of SrTiO3 by Density Function Theory Calculation
YUN Jiang-Ni; ZHANG Zhi-Yong; ZHANG Fu-Chun
2008-01-01
Adsorption and reaction of CO on two possible terminations of SrTi03 (100) surface are investigated by the first-principles calculation of plane wave ultrasoft pseudopotential based on the density function theory. The adsorption energy, Mulliken population analysis, density of states (DOS) and electronic density difference of CO on SrTi03 (100) surface, which have never been investigated before as far as we know are performed. The calculated results reveal that the Ti-CO orientation is the most stable configuration and the adsorption energy (0.449eV) is quite small. CO molecules adsorb weakly on the SrTiO3 (100) surface, there is predominantly electrostatic attraction between CO and the surface rather than a chemical bonding mechanism.
Saravanan, S. P.; Sankar, A.; Parimala, K.
2017-01-01
The complete structural and vibrational analysis of the 2,5-Difluoronitrobenzene (DNB) was carried out by Hartree-Fock (HF) and density functional theory (DFT) method (B3LYP) with 6-311++G (d,p) basis set. The fundamental vibrations are assigned on the basis of the potential energy distribution (PED) of the vibrational modes calculated with scaled quantum mechanics (SQM) method. Using the time-dependent density functional theory (TD-DFT) method, electronic absorption spectra of the title compound have been predicted and a good agreement with the experimental ones is determined. 13C and 1H NMR spectra were recorded and chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. The hyperconjugative interaction energy (E(2)) and electron densities of donor (i) and acceptor (j) bonds were calculated using natural bond orbital (NBO) analysis. In addition, molecular electrostatic potential (MEP) and atomic charges were calculated using B3LYP/6-311++G (d,p) level of theory. Moreover, thermodynamic properties (heat capacities, entropy, enthalpy and Gibb's free energy) of the title compound at different temperatures were calculated.
Kleis, Jesper; Schröder, Elsebeth; Hyldgaard, Per
2008-01-01
The dispersive interaction between nanotubes is investigated through ab initio theory calculations and in an analytical approximation. A van der Waals density functional (vdW-DF) [M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] is used to determine and compare the binding of a pair of nanotubes...... for the nanotube-crystal binding energy can be approximated by a sum of nanotube-pair interactions when these are calculated in vdW-DR This observation suggests a framework for an efficient implementation of quantum-physical modeling of the carbon nanotube bundling in more general nanotube bundles, including...... as well as in a nanotube crystal. To analyze the interaction and determine the importance of morphology, we further compare results of our ab initio calculations to a simple analytical result,that we obtain for a pair of well-separated nanotubes. In contrast to traditional density functional theory...
Buchman, Omri; Baer, Roi
2017-09-01
The one-body density matrix (OBDM) is a fundamental contraction of the Bose-Einstein condensate wave function, encapsulating its one-body properties. It serves as a major analysis tool with which the condensed component of the density can be identified. Despite its cardinal importance, calculating the ground-state OBDM of trapped interacting bosons is a challenge and to date OBDM calculations have been published only for homogeneous systems or for trapped weakly interacting bosons. In this paper we discuss an approach for computing the OBDM based on a double-walker diffusion Monte Carlo random walk coupled with a stochastic permanent calculation. We here describe the method and study some of its statistical convergence and properties applying it to some model systems.
Pande, Vikram
2016-01-01
Graphite is the most widely used and among the most widely-studied anode materials for lithium-ion batteries. Lithium intercalation into graphite has been extensively studied theoretically using density functional theory (DFT) calculations, complemented by experimental studies through X-ray diffraction, spectroscopy, optical imaging and other techniques. However, previous theoretical studies have not directly included van der Waals (vdW) interactions in their density functional theory calculations and vdW interactions play a crucial role in determining the stable phases. In this work, we present a first principles based model using DFT calculations, employing Bayesian Error Estimation Functional with van der Waals (BEEF-vdW) as the exchange correlation functional, and statistical thermodynamics to determine the phase transformations and subsequently, the thermodynamic intercalation potential diagram. We explore the entire configurational phase space by determining the important interactions and applying clust...
van Wüllen, Christoph
2009-10-29
Antiferromagnetic coupling in multinuclear transition metal complexes usually leads to electronic ground states that cannot be described by a single Slater determinant and that are therefore difficult to describe by Kohn-Sham density functional methods. Density functional calculations in such cases are usually converged to broken symmetry solutions which break spin and, in many cases, also spatial symmetry. While a procedure exists to extract isotropic Heisenberg (exchange) coupling constants from such calculations, no such approach is yet established for the calculation of magnetic anisotropy energies or zero field splitting parameters. This work proposes such a procedure. The broken symmetry solutions are not only used to extract the exchange couplings but also single-ion D tensors which are then used to construct a (phenomenological) spin Hamiltonian, from which the magnetic anisotropy and the zero-field energy levels can be computed. The procedure is demonstrated for a bi- and a trinuclear Mn(III) model compound.
Has inflation really solved the problems of flatness and absence of relics?
Lieu, Richard
2013-10-01
Among the three cosmological enigma solved by the theory of inflation, viz. (a) large-scale flatness, (b) absence of monopoles and strings and (c) structure formation, the first two are addressed from the viewpoint of the observed scales having originated from very small ones, on which the density fluctuations of the curvaton and relics are inevitably of the order of unity or larger. By analysing strictly classically (and in two different gauges to ensure consistency) the density evolution of the smoothest possible pre-inflationary component - thermal radiation - it is found that the O(1) statistical fluctuations on the thermal wavelength scale present formidable obstacles to the linear theory of amplitude growth by the end of inflation. Since this wavelength scale exited the horizon at an early stage of inflation, it severely limits the number of e-folds of perturbative inflation. With more e-folds than ≈60 there will be even larger fluctuations in the radiation density that ensures inflation keeps making `false starts'. The only `way out' is to invoke a super-homogeneous pre-inflationary fluid, at least on small scales, adding to the fine-tuning and preventing one from claiming that inflation simply `redshifts away' all the relic inhomogeneities; i.e. the theory actually provided no explanation of (a) or (b), merely a tautology.
Legler, C R; Brown, N R; Dunbar, R A; Harness, M D; Nguyen, K; Oyewole, O; Collier, W B
2015-06-15
The Scaled Quantum Mechanical (SQM) method of scaling calculated force constants to predict theoretically calculated vibrational frequencies is expanded to include a broad array of polarized and augmented basis sets based on the split valence 6-31G and 6-311G basis sets with the B3LYP density functional. Pulay's original choice of a single polarized 6-31G(d) basis coupled with a B3LYP functional remains the most computationally economical choice for scaled frequency calculations. But it can be improved upon with additional polarization functions and added diffuse functions for complex molecular systems. The new scale factors for the B3LYP density functional and the 6-31G, 6-31G(d), 6-31G(d,p), 6-31G+(d,p), 6-31G++(d,p), 6-311G, 6-311G(d), 6-311G(d,p), 6-311G+(d,p), 6-311G++(d,p), 6-311G(2d,p), 6-311G++(2d,p), 6-311G++(df,p) basis sets are shown. The double d polarized models did not perform as well and the source of the decreased accuracy was investigated. An alternate system of generating internal coordinates that uses the out-of plane wagging coordinate whenever it is possible; makes vibrational assignments via potential energy distributions more meaningful. Automated software to produce SQM scaled vibrational calculations from different molecular orbital packages is presented.
Jayatilaka, Dylan; Dittrich, Birger
2008-05-01
An approach is outlined for X-ray structure refinement using atomic density fragments obtained by Hirshfeld partitioning of quantum-mechanical density fragments. Results are presented for crystal structure refinements of urea and benzene using these 'Hirshfeld atoms'. Using this procedure, the quantum-mechanical non-spherical electron density is taken into account in the structural model based on the conformation found in the crystal. Contrary to current consensus in structure refinement, the anisotropic displacement parameters of H atoms can be reproduced from neutron diffraction measurements simply from a least-squares fit using the Hirshfeld atoms derived from the BLYP level of theory and including a simple point-charge model to treat the crystal environment.
Self-consistent density functional calculation of the image potential at a metal surface
Jung, J [Departamento de Fisica Fundamental, Universidad Nacional de Educacion a Distancia, Apartado 60141, 28080 Madrid (Spain); Alvarellos, J E [Departamento de Fisica Fundamental, Universidad Nacional de Educacion a Distancia, Apartado 60141, 28080 Madrid (Spain); Chacon, E [Instituto de Ciencias de Materiales de Madrid, Consejo Superior de Investigaciones CientIficas, E-28049 Madrid (Spain); GarcIa-Gonzalez, P [Departamento de Fisica Fundamental, Universidad Nacional de Educacion a Distancia, Apartado 60141, 28080 Madrid (Spain)
2007-07-04
It is well known that the exchange-correlation (XC) potential at a metal surface has an image-like asymptotic behaviour given by -1/4(z-z{sub 0}), where z is the coordinate perpendicular to the surface. Using a suitable fully non-local functional prescription, we evaluate self-consistently the XC potential with the correct image behaviour for simple jellium surfaces in the range of metallic densities. This allows a proper comparison between the corresponding image-plane position, z{sub 0}, and other related quantities such as the centroid of an induced charge by an external perturbation. As a by-product, we assess the routinely used local density approximation when evaluating electron density profiles, work functions, and surface energies by focusing on the XC effects included in the fully non-local description.
Projected gradient algorithms for Hartree-Fock and density matrix functional theory calculations
Cancès, Eric; Pernal, Katarzyna
2008-04-01
We present projected gradient algorithms designed for optimizing various functionals defined on the set of N-representable one-electron reduced density matrices. We show that projected gradient algorithms are efficient in minimizing the Hartree-Fock or the Müller-Buijse-Baerends functional. On the other hand, they converge very slowly when applied to the recently proposed BBk (k =1,2,3) functionals [O. Gritsenko et al., J. Chem. Phys. 122, 204102 (2005)]. This is due to the fact that the BBk functionals are not proper functionals of the density matrix.
Robust acceleration of self consistent field calculations for density functional theory.
Baarman, K; Eirola, T; Havu, V
2011-04-07
We show that the type 2 Broyden secant method is a robust general purpose mixer for self consistent field problems in density functional theory. The Broyden method gives reliable convergence for a large class of problems and parameter choices. We directly mix the approximation of the electronic density to provide a basis independent mixing scheme. In particular, we show that a single set of parameters can be chosen that give good results for a large range of problems. We also introduce a spin transformation to simplify treatment of spin polarized problems. The spin transformation allows us to treat these systems with the same formalism as regular fixed point iterations.
Kim, SeongMin; Ha, Jaewook; Kim, Jin-Baek
2016-11-01
We analytically calculated polarization and bound charge density inside the dielectric material in metal-to-dielectric-mode triboelectric nanogenerators (TENG) where the transferred charges are collected on the bottom metal via electrostatic induction from the triboelectric charges that are generated by frictional contact. This bound charge density is associated with the surface density of states (DOS), overline{Ns(E)}. Two cases are considered here: i) for overline{Ns(E)} ≫ 1, it is calculated that the bound charge density is proportional to the dielectric constant and the work function difference between the two materials, but inversely proportional to the thickness of the dielectric material (ɛ0(ɛ2-1) (E0-W)/e \\cdot d2); ii) for overline{Ns(E)} ≪ 1 with constant overline{Ns(E)}, the bound charge density is mostly proportional to the work function difference between the materials, and inversely proportional to the thickness of the dielectric material ((ɛ2-1)x/d_{2+\\varepsilon2\\cdot x} \\cdot Ns(E)\\cdot e\\cdot (E0-W)).
The radio relics and halo of El Gordo, a massive z = 0.870 cluster merger
Lindner, Robert R.; Baker, Andrew J.; Hughes, John P. [Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019 (United States); Battaglia, Nick [McWilliams Center for Cosmology, Wean Hall, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213 (United States); Gupta, Neeraj [ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo (Netherlands); Knowles, Kenda; Moodley, Kavilan [Astrophysics and Cosmology Research Unit, University of KwaZulu-Natal, Durban 4041 (South Africa); Marriage, Tobias A. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686 (United States); Menanteau, Felipe [National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 1205 W. Clark St., Urbana, IL 61801 (United States); Reese, Erik D. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, PA 19104 (United States); Srianand, Raghunathan, E-mail: rlindner@astro.wisc.edu [IUCAA, Ganeshkhind, Pune 411007 (India)
2014-05-01
We present 610 MHz and 2.1 GHz imaging of the massive Sunyaev-Zel'dovich Effect selected z = 0.870 cluster merger ACT-CL J0102–4915 ({sup E}l Gordo{sup )}, obtained with the Giant Metrewave Radio Telescope and the Australia Telescope Compact Array (ATCA), respectively. We detect two complexes of radio relics separated by 3.'4 (1.6 Mpc) along the system's northwest-to-southeast collision axis that have high integrated polarization fractions (33%) and steep spectral indices (α between 1 and 2; S {sub ν}∝ν{sup –α}), consistent with creation via Fermi acceleration by shocks in the intracluster medium triggered by the cluster collision. From the spectral index of the relics, we compute a Mach number M=2.5{sub −0.3}{sup +0.7} and shock speed of 2500{sub −300}{sup +400} km s{sup −1}. With our wide-bandwidth, full-polarization ATCA data, we compute the Faraday depth φ across the northwest relic and find a range of values spanning Δφ = 30 rad m{sup –2}, with a mean value of (φ) = 11 rad m{sup –2} and standard deviation σ{sub φ} = 6 rad m{sup –2}. With the integrated line-of-sight gas density derived from new Chandra X-ray observations, our Faraday depth measurement implies B {sub ∥} ∼ 0.01 μG in the cluster outskirts. The extremely narrow shock widths in the relics (d {sub shock} ≤ 23 kpc), caused by the short synchrotron cooling timescale of relativistic electrons at z = 0.870, prevent us from placing a meaningful constraint on the magnetic field strength B using cooling time arguments. In addition to the relics, we detect a large (r {sub H} ≅ 1.1 Mpc radius), powerful (log (L {sub 1.4}/W Hz{sup –1}) = 25.66 ± 0.12) radio halo with a shape similar to El Gordo's 'bullet'-like X-ray morphology. The spatially resolved spectral-index map of the halo shows the synchrotron spectrum is flattest near the relics, along the system's collision axis, and in regions of high T {sub gas}, all locations associated
Hirano, Toshiyuki; Sato, Fumitoshi
2014-07-28
We used grid-free modified Cholesky decomposition (CD) to develop a density-functional-theory (DFT)-based method for calculating the canonical molecular orbitals (CMOs) of large molecules. Our method can be used to calculate standard CMOs, analytically compute exchange-correlation terms, and maximise the capacity of next-generation supercomputers. Cholesky vectors were first analytically downscaled using low-rank pivoted CD and CD with adaptive metric (CDAM). The obtained Cholesky vectors were distributed and stored on each computer node in a parallel computer, and the Coulomb, Fock exchange, and pure exchange-correlation terms were calculated by multiplying the Cholesky vectors without evaluating molecular integrals in self-consistent field iterations. Our method enables DFT and massively distributed memory parallel computers to be used in order to very efficiently calculate the CMOs of large molecules.
Wu, Zhijian; Hao, Xianfeng; Liu, Xiaojuan; Meng, Jian
2007-02-01
The structure, elastic, and electronic properties of OsN2 at various space groups: cubic Fm-3m , Pa-3 , and orthorhombic Pnnm were studied by first-principles calculations based on density functional theory. Our calculation indicates that the structure in orthorhombic Pnnm phase is energetically more stable compared with cubic systems. It is metallic, mechanically stable and contains diatomic N-N units with the bond distance 1.418Å . These characters are consistent with experimental facts that OsN2 is orthorhombic and metallic. The calculated bulk modulus 394GPa is also the highest among the considered space groups, slightly larger than previous value 358GPa . The calculated elastic anisotropic factors and directional bulk modulus showed that OsN2 possess high elastic anisotropy.
Shamim, Md; Harbola, Manoj K, E-mail: sami@iitk.ac.i, E-mail: mkh@iitk.ac.i [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India)
2010-11-14
Transition energies of a new class of excited states (two-gap systems) of various atoms are calculated in time-independent density functional formalism by using a recently proposed local density approximation exchange energy functional for excited states. It is shown that the excitation energies calculated with this functional compare well with those calculated with exact exchange theories.
Linscheid, A; Sanna, A; Floris, A; Gross, E K U
2015-08-28
We show that the superconducting order parameter and condensation energy density of phonon-mediated superconductors can be calculated in real space from first principles density functional theory for superconductors. This method highlights the connection between the chemical bonding structure and the superconducting condensation and reveals new and interesting properties of superconducting materials. Understanding this connection is essential to describe nanostructured superconducting systems where the usual reciprocal space analysis hides the basic physical mechanism. In a first application we present results for MgB2, CaC6 and hole-doped graphane.
Bailey, William J.
1996-12-31
This Dr. ing. thesis covers a study of drilling hydraulics offshore. The purpose of drilling hydraulics is to provide information about downhole pressure, suitable surface pump rates, the quality of hole cleaning and optimum tripping speeds during drilling operations. Main fields covered are drilling hydraulics, fluid characterisation, pressure losses, and equivalent circulating density. 197 refs., 23 figs., 22 tabs.
The megaparsec radio relic in supercluster, Rood No. 27
Harris, D. E.; Stern, C. P.; Willis, A. G.; Dewdney, P. E.
1993-03-01
Observations of extended source of low surface brightness appear as a 'relic' of a currently inactive radio galaxy. The largest dimension is approximately 1.6 Mpc, the fractional polarization is high, and the magnetic field direction appears to be coherent over scales of at least several hundred kpc. Polarization and morphologies of relics are distinct from those of cluster halos, due to the different environment provided by cluster cores compared to that encountered in the outer fringes of the hot gas distribution which produces X-ray emission.
The megaparsec radio relic in supercluster, Rood No. 27
Harris, D. E.; Stern, C. P.; Willis, A. G.; Dewdney, P. E.
1993-01-01
Observations of extended source of low surface brightness appear as a 'relic' of a currently inactive radio galaxy. The largest dimension is approximately 1.6 Mpc, the fractional polarization is high, and the magnetic field direction appears to be coherent over scales of at least several hundred kpc. Polarization and morphologies of relics are distinct from those of cluster halos, due to the different environment provided by cluster cores compared to that encountered in the outer fringes of the hot gas distribution which produces X-ray emission.
Nanda, Sunil Kumar; Bharathy, M; Dinakaran, Asha; Ray, Lopamudra; Ravichandran, K
2017-01-01
Background: One of the risk factors for the development of coronary heart disease is high low-density lipoprotein (LDL) cholesterol levels. National Cholesterol Education Program ATP III guidelines suggest drug therapy to be considered at LDL-cholesterol levels >130 mg/dl. This makes accurate reporting of LDL cholesterol crucial in the management of Coronary heart disease. Estimation of LDL cholesterol by direct LDL method is accurate, but it is expensive. Hence, We compared Friedewald's calculated LDL values with direct LDL values. Aim: To evaluate the correlation of Friedewalds calculated LDL with direct LDL method. Materials and Methods: We compared LDL cholesterol measured by Friedewald's formula with direct LDL method in 248 samples between the age group of 20–70 years. Paired t-test was used to test the difference in LDL concentration obtained by a direct method and Friedewald's formula. The level of significance was taken as P values with Friedewald's formula. Results: There was no significant difference between the direct LDL values when compared to calculated LDL by Friedewalds formula (P = 0.140). Pearson correlation showed there exists good correlation between direct LDL versus Friedewalds formula (correlation coefficient = 0.98). The correlation between direct LDL versus Friedewalds calculated LDL was best at triglycerides values between 101 and 200 mg/dl. Conclusion: This study indicates calculated LDL by Friedewalds equation can be used instead of direct LDL in patients who cannot afford direct LDL method.
Nanda, Sunil Kumar; Bharathy, M; Dinakaran, Asha; Ray, Lopamudra; Ravichandran, K
2017-01-01
One of the risk factors for the development of coronary heart disease is high low-density lipoprotein (LDL) cholesterol levels. National Cholesterol Education Program ATP III guidelines suggest drug therapy to be considered at LDL-cholesterol levels >130 mg/dl. This makes accurate reporting of LDL cholesterol crucial in the management of Coronary heart disease. Estimation of LDL cholesterol by direct LDL method is accurate, but it is expensive. Hence, We compared Friedewald's calculated LDL values with direct LDL values. To evaluate the correlation of Friedewalds calculated LDL with direct LDL method. We compared LDL cholesterol measured by Friedewald's formula with direct LDL method in 248 samples between the age group of 20-70 years. Paired t-test was used to test the difference in LDL concentration obtained by a direct method and Friedewald's formula. The level of significance was taken as P correlation formula was used to test the correlation between direct LDL values with Friedewald's formula. There was no significant difference between the direct LDL values when compared to calculated LDL by Friedewalds formula (P = 0.140). Pearson correlation showed there exists good correlation between direct LDL versus Friedewalds formula (correlation coefficient = 0.98). The correlation between direct LDL versus Friedewalds calculated LDL was best at triglycerides values between 101 and 200 mg/dl. This study indicates calculated LDL by Friedewalds equation can be used instead of direct LDL in patients who cannot afford direct LDL method.
Investigation of the diffusion of atomic fission products in UC by density functional calculations
Bévillon, Émile, E-mail: emile.bevillon@yahoo.fr [IRSN, SEMIC, DPAM, LETR, Centre de Cadarache, 13115 Saint Paul Lez Durance (France); Ducher, Roland; Barrachin, Marc; Dubourg, Roland [IRSN, SEMIC, DPAM, LETR, Centre de Cadarache, 13115 Saint Paul Lez Durance (France)
2013-03-15
Activation energies of U and C atoms self-diffusion in UC, as well as activation energies of hetero-diffusion of fission products (FPs) are investigated by first-principles calculations. According to a previous study which showed a likely U site occupation was favoured for all the FPs, their diffusion is restricted to the uranium sublattice of UC in the present study. In this framework, long-range displacements are only possible through a concerted mechanism with a surrounding uranium vacancy. Using the apparent formation energies of the uranium vacancy defect calculated in our previous study and the classical approach used in UO{sub 2} by Andersson et al., the activation energies of the main fission products in the various stoichiometric domains have been calculated. The results are compared to those obtained with the five frequency model applied to two representative fission products, Xe and Zr. Interestingly, despite strong differences of formalism, both models provided similar activation energies.
Investigation of the diffusion of atomic fission products in UC by density functional calculations
Bévillon, Émile; Ducher, Roland; Barrachin, Marc; Dubourg, Roland
2013-03-01
Activation energies of U and C atoms self-diffusion in UC, as well as activation energies of hetero-diffusion of fission products (FPs) are investigated by first-principles calculations. According to a previous study which showed a likely U site occupation was favoured for all the FPs, their diffusion is restricted to the uranium sublattice of UC in the present study. In this framework, long-range displacements are only possible through a concerted mechanism with a surrounding uranium vacancy. Using the apparent formation energies of the uranium vacancy defect calculated in our previous study and the classical approach used in UO2 by Andersson et al., the activation energies of the main fission products in the various stoichiometric domains have been calculated. The results are compared to those obtained with the five frequency model applied to two representative fission products, Xe and Zr. Interestingly, despite strong differences of formalism, both models provided similar activation energies.
Jaroniec, Mietek; Kruk, Michal; Olivier, James
1995-11-01
Methods of calculating the fractal dimension (D) on the basis of single adsorption isotherms were critically tested by using argon composite adsorption isotherms for fractally porous solids. These isotherms were obtained from adsorption data for homogeneous slit-like pores calculated by employing the density functional theory (DFT). The composite adsorption isotherms were used to test the validity of the method based on the Frenkel-Halsey-Hill equation and so called "thermodynamic method" proposed by Neimark. The applicability of these methods was confirmed. However, our studies reveal new aspects of practical usage of both approaches, which need to be taken into consideration in analysis of experimental data.
Teale, Andrew M; Lutnæs, Ola B; Helgaker, Trygve; Tozer, David J; Gauss, Jürgen
2013-01-14
Accurate sets of benchmark nuclear-magnetic-resonance shielding constants and spin-rotation constants are calculated using coupled-cluster singles-doubles (CCSD) theory and coupled-cluster singles-doubles-perturbative-triples [CCSD(T)] theory, in a variety of basis sets consisting of (rotational) London atomic orbitals. The accuracy of the calculated coupled-cluster constants is established by a careful comparison with experimental data, taking into account zero-point vibrational corrections. Coupled-cluster basis-set convergence is analyzed and extrapolation techniques are employed to estimate basis-set-limit quantities, thereby establishing an accurate benchmark data set. Together with the set provided for rotational g-tensors and magnetizabilities in our previous work [O. B. Lutnæs, A. M. Teale, T. Helgaker, D. J. Tozer, K. Ruud, and J. Gauss, J. Chem. Phys. 131, 144104 (2009)], it provides a substantial source of consistently calculated high-accuracy data on second-order magnetic response properties. The utility of this benchmark data set is demonstrated by examining a wide variety of Kohn-Sham exchange-correlation functionals for the calculation of these properties. None of the existing approximate functionals provide an accuracy competitive with that provided by CCSD or CCSD(T) theory. The need for a careful consideration of vibrational effects is clearly illustrated. Finally, the pure coupled-cluster results are compared with the results of Kohn-Sham calculations constrained to give the same electronic density. Routes to future improvements are discussed in light of this comparison.
Avery, John Scales; Avery, James Emil; Aquilanti, Vincenzo;
2004-01-01
The generalized Sturmian method for atomic and molecular electronic structure calculations is a direct configuration interaction method in which the configurations are chosen to be isoenergetic solutions of an approximate N-electron Schrödinger equation with a weighted potential, $\\beta_\
Calculating the Lifetimes of Metastable States with Complex Density Functional Theory.
Zhou, Yongxi; Ernzerhof, Matthias
2012-07-19
Among other applications, complex absorbing potentials (CAPs) have proven to be useful tools in the theory of metastable states. They facilitate the conversion of unbound states of a finite lifetime into normalized bound states with a complex energy. Adding CAPs to a conventional Hamiltonian turns it into a non-Hermitian operator. Recently, we introduced a complex density functional theory (CODFT) that extends the Kohn-Sham method to the realm of non-Hermitian systems. Here, we combine CAPs with CODFT and present the first application of CODFT to metastable systems. In particular, we consider the negative ions of the beryllium atom and the nitrogen molecule. Using conventional exchange-correlation functionals as functionals of a complex density, the resonance positions and the resonance lifetimes are obtained, and they are in line with the findings of other studies.
A simple method to calculate first-passage time densities with arbitrary initial conditions
Nyberg, Markus; Ambjörnsson, Tobias; Lizana, Ludvig
2016-06-01
Numerous applications all the way from biology and physics to economics depend on the density of first crossings over a boundary. Motivated by the lack of general purpose analytical tools for computing first-passage time densities (FPTDs) for complex problems, we propose a new simple method based on the independent interval approximation (IIA). We generalise previous formulations of the IIA to include arbitrary initial conditions as well as to deal with discrete time and non-smooth continuous time processes. We derive a closed form expression for the FPTD in z and Laplace-transform space to a boundary in one dimension. Two classes of problems are analysed in detail: discrete time symmetric random walks (Markovian) and continuous time Gaussian stationary processes (Markovian and non-Markovian). Our results are in good agreement with Langevin dynamics simulations.
Fattebert, J
2008-07-29
We describe an iterative algorithm to solve electronic structure problems in Density Functional Theory. The approach is presented as a Subspace Accelerated Inexact Newton (SAIN) solver for the non-linear Kohn-Sham equations. It is related to a class of iterative algorithms known as RMM-DIIS in the electronic structure community. The method is illustrated with examples of real applications using a finite difference discretization and multigrid preconditioning.
Pseudopotential Density-Functional Calculations for Structures of Small Carbon Clusters CN (N = 2～8)
BAI Yu-Lin; CHEN Xiang-Rong; YANG Xiang-Dong; LU Peng-Fei
2004-01-01
We introduce a first-principles density-functional theory, i.e. the finite-difference pseudopotential densityfunctional theory in real space and the Langevin molecular dynamics annealing technique, to the descriptions of structures and some properties of small carbon clusters (CN, N = 2 ～ 8). It is shown that the odd-numbered clusters have linear structures and most of the even-numbered clusters prefer cyclic structures.
Meninno, Sara; Rizzo, Paola; Abbate, Sergio; Longhi, Giovanna; Mazzeo, Giuseppe; Monaco, Guglielmo; Lattanzi, Alessandra; Zanasi, Riccardo
2016-02-01
Density functional theory calculation of the vibrational circular dichroism spectrum was used to assign the absolute configuration of an all-carbon quaternary β-stereocenter of a γ-butyrolactone recently synthesized through an asymmetric organocatalytic tandem aldol/lactonization sequence. Comparison with the experimental spectrum is satisfactory, on account of the fact that spectroscopic features are weak due to the presence of multiple conformers. As a result, the (R) absolute configuration was assigned to the (+) optical isomer.
Weisman, Jennifer L.; Lee, Timothy J.; Salama, Farid; Gordon-Head, Martin; Kwak, Dochan (Technical Monitor)
2002-01-01
We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcoronene, the largest species containing more than 50 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.
1992-01-01
Unified analytical expressions have been derived for calculating the resonant frequencies, transimpedance and equivalent input noise current densities of the four most widely used tuned optical receiver front ends built with FETs and p-i-n diodes. A more accurate FET model has been used to improve the accuracy of the analysis. The Miller capacitance has been taken into account, and its impact on the performances of the tuned front ends has been demonstrated. The accuracy of the expressions ha...
Analysis of Vibration Mode for H2+F→HF+H Reaction Mechanism: Density functional Theory Calculation
无
2001-01-01
Three density functional theory methods (DFT) have been used to investigate the H2+F?HF+H reaction comparing with the Hartree-Fock method and Moller-Plesset (MP2) perturbation theory method. Through the analysis of the vibrational mode and vibrational frequency in the reaction process, the reaction mechanism has been discussed. The activation energy, the reorganization energy and rate constant of the ET reaction are calculated at semi-quantitative level.
Tanveer Hussain
2013-10-01
Full Text Available This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs by means of hybrid density functional theory (PBE0. On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM’s. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies.
Guang-Li Huang; Jian-Ping Li; Qi-Wu Song
2013-01-01
Based on Dulk and Marsh's approximate theory about nonthermal gyrosynchrotron radiation,one simple impulsive microwave burst with a loop-like structure is selected for radio diagnostics of the coronal magnetic field and column density of nonthermal electrons,which are calculated from the brightness temperature,polarization degree,and spectral index,as well as the turnover frequency,observed by using the Nobeyama Radioheliograph and the Nobeyama Radio Polarimeters,respectively.Very strong variations (up to one or two orders of magnitude) of the calculated transverse and longitudinal magnetic fields with respect to the line-of-sight,as well as the calculated electron column density,appear in the looptop and footpoint sources during the burst.The absolute magnitude and varied range of the transverse magnetic field are evidently larger than those of the longitudinal magnetic field.The time evolution of the transverse magnetic field is always anti-correlated with that of the longitudinal magnetic field,but positively correlated with that of the electron column density.These results strongly support the idea that quantifying the energy released in a flare depends on a reconstruction of the coronal magnetic field,especially for the transverse magnetic field,and they are basically consistent with the recent theoretical and observational studies on the photospheric magnetic field in solar flares.
Gu, Xuejun; Li, Jinsheng; Jia, Xun; Jiang, Steve B
2011-01-01
Targeting at developing an accurate and efficient dose calculation engine for online adaptive radiotherapy, we have implemented a finite size pencil beam (FSPB) algorithm with a 3D-density correction method on GPU. This new GPU-based dose engine is built on our previously published ultrafast FSPB computational framework [Gu et al. Phys. Med. Biol. 54 6287-97, 2009]. Dosimetric evaluations against MCSIM Monte Carlo dose calculations are conducted on 10 IMRT treatment plans with heterogeneous treatment regions (5 head-and-neck cases and 5 lung cases). For head and neck cases, when cavities exist near the target, the improvement with the 3D-density correction over the conventional FSPB algorithm is significant. However, when there are high-density dental filling materials in beam paths, the improvement is small and the accuracy of the new algorithm is still unsatisfactory. On the other hand, significant improvement of dose calculation accuracy is observed in all lung cases. Especially when the target is in the m...
Benkyi, Isaac; Fliegl, Heike; Valiev, Rashid R; Sundholm, Dage
2016-04-28
Magnetically induced current densities have been calculated and analyzed for a number of synthesized carbachlorins and carbaporphyrins using density functional theory and the gauge including magnetically induced current (GIMIC) method. Aromatic properties have been determined by using accurate numerical integration of the current flow yielding reliable current strengths and pathways that are related to the degree of aromaticity and the aromatic character of the studied molecules. All investigated compounds are found to be aromatic. However, the obtained aromatic pathways differ from those previously deduced from spectroscopic data and magnetic shielding calculations. For all studied compounds, the ring current divides into an outer and an inner branch at each pyrrolic subring, showing that all π-electrons of the pyrrolic rings take part in the delocalization pathway. The calculations do not support the common notion that the main share of the current takes the inner route at the pyrrolic rings without an inner hydrogen and follows an 18π aromatic pathway. The aromatic pathways of the investigated carbaporphyrins and carbachlorins are very similar, since the current strength via the Cβ[double bond, length as m-dash]Cβ' bond of the cyclopentadienyl ring of the carbaporphyrins is almost as weak as the current density passing the corresponding saturated Cβ-Cβ' bond of the carbachlorins.
Mastrolonardo, Giovanni; Francioso, Ornella; Carrari, Elisa; Brogi, Cristiana; Venturi, Martina; Certini, Giacomo
2017-04-01
Charcoal production in forests is one of the oldest human activities in Italy and the other European countries. Here, 3 thousand years ago civilizations were already used to convert wood into charcoal for energetic and metallurgic purposes. The technique for making charcoal remained substantially unchanged in time: wood piles covered with turf were built in appositely shaped emplacements, and then left to pyrolyse for days under controlled semi-anoxic conditions. This widespread activity lasted until a few decades ago, leaving as legacy a plethora of repeatedly used emplacements where soil shows a thick top layer very rich in charcoal. Despite the high frequency of relic charcoal kilns in the European forests, no studies aimed at accurately determining their C stock to assess their relevance as C sink in forest environment. In this work, we studied some relic charcoal kilns in a mixed oak forest at Marsiliana, Tuscany, central Italy, where charcoal production was enduring and massive at least since the Middle age. At Marsiliana, density of charcoal kiln sites was not uniform within the forest areas as it mostly depends on biomass availability. According to the aspect, northerly or southerly, we recognized two main forest areas where kiln sites density ranged between 2 and 3 sites per hectare. In general, the C content in the kiln soils was eight times the one in the surrounding soil, with just one third of the C in the form of pyrogenic C. Hence, natural organic carbon content was significantly higher in the kiln soils. Such a finding confirms that charcoal gives a substantial contribution to the C stock in the kilns but does not fully account for their particular richness in C. It has been thus hypothesized that charcoal is somehow able to stimulate the accumulation of native soil organic matter. At Marsiliana forest, relic charcoal kilns soils cover less than 0.5% of total surface. Nonetheless, their contribution to the total C stock in the top soil (30 cm
Christensen, Rune; Hansen, Heine Anton; Vegge, Tejs
2015-01-01
.e. the electrocatalytic reduction of CO2 and metal-air batteries. In theoretical studies of electrocatalytic CO2 reduction, calculated DFT-level enthalpies of reaction for CO2reduction to various products are significantly different from experimental values[1-3]. In theoretical studies of metal-air battery reactions......, systematic errors compared to experiments have also been found in calculation of enthalpies of formation for bulk metal oxide, peroxide and superoxide species[4,5]. It is here demonstrated how the errors, which depend explicitly on the choice of applied exchange-correlation functional, can be identified....... Errors can be significantly reduced by using metal chlorides as energy reference rather than pure metals. The mean absolute error per oxygen versus experiments for alkali metal peroxide and superoxide species will be 0.03 eV and 0.09 eV, respectively, using metal chlorides as reference, as compared to 0...
Skone, Jonathan; Govoni, Marco; Galli, Giulia
Dielectric-dependent hybrid [DDH] functionals have recently been shown to yield highly accurate energy gaps and dielectric constants for a wide variety of solids, at a computational cost considerably less than standard GW calculations. The fraction of exact exchange included in the definition of DDH functionals depends (self-consistently) on the dielectric constant of the material. In the present talk we introduce a range-separated (RS) version of DDH functionals where short and long-range components are matched using material dependent, non-empirical parameters. Comparing with state of the art GW calculations and experiment, we show that such RS hybrids yield accurate electronic properties of both molecules and solids, including energy gaps, photoelectron spectra and absolute ionization potentials. This work was supported by NSF-CCI Grant Number NSF-CHE-0802907 and DOE-BES.
Electron transport in a Pt-CO-Pt nanocontact: Density functional theory calculations
Strange, Mikkel; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel
2006-01-01
We have performed first-principles calculations for the mechanic and electric properties of pure Pt nanocontacts and a Pt contact with a single CO molecule adsorbed. For the pure Pt contacts we see a clear difference between point contacts and short chains in good agreement with experiments. We i...... of the transmission function for the Pt-CO-Pt contact, and show that the conductance is largely determined by the local d band at the Pt apex atoms....
2007-03-01
by Equation 42 exist, with the most successful based upon numerical fits to quantum mechanical Monte Carlo calculations on the ground state of a...mass with speed. The fifth term is known as the Darwin term, and is a result of zitterbewegung, or trembling motion. It is a result of the Heisenberg ...Benchmark Database. Technical Re- port, August 2005. NIST Standard Reference Database Number 101. 2. Adamo, Carlo and Vincenzo Barone. “Toward reliable
Defect properties of CuCrO2: A density functional theory calculation
Fang Zhi-Jie; Zhu Ji-Zhen; Zhou Jiang; Mo Man
2012-01-01
Using the first-principles methods,we study the formation energetics properties of intrinsic defects,and the charge doping properties of extrinsic defects in transparent conducting oxides CuCrO2.Intrinsic defects,some typical acceptortype,and donor-type extrinsic defects in their relevant charge state are considered.By systematically calculating the formation energies and transition energy,the results of calculation show that,Vcu,Oi,and OCu are the relevant intrinsic defects in CuCrO2; among these intrinsic defects,VCu is the most efficient acceptor in CuCrO2.It is found that all the donor-type extrinsic defects have difficulty in inducing n-conductivity in CuCrO2 because of their deep transition energy level.For all the acceptor-type extrinsic defects,substituting Mg for Cr is the most prominent doping acceptor with relative shallow transition energy levels in CuCrO2.Our calculation results are expected to be a guide for preparing promising n-type and p-type materials in CuCrO2.
Khan, Md Shahzad; Ratn, Rahul; Srivastava, Anurag
2017-07-01
Electronic and structural analysis of buckled antimonene has been performed using density functional theory-based ab-initio approach. Geometrical parameters such as bond length and bond angle are very close to the single ruffle layer of rhombohedral antimony. Phonon dispersion along the high symmetry point of the Brillouin zone does not signify any soft mode. Electronic indirect band gap of 1.61 eV is observed for the single-layer antimonene. However, the occurrence of bilayered quasi-2D sheet consequent to metallic behaviour is due to significant electronic charge dispersion between interlayer region.
MD SHAHZAD KHAN; RAHUL RATN; ANURAG SRIVASTAVA
2017-07-01
Electronic and structural analysis of buckled antimonene has been performed using density functional theory-based $\\it{ab-initio}$ approach. Geometrical parameters such as bond length and bond angle are very close to the single ruffle layer of rhombohedral antimony. Phonon dispersion along the high symmetry point of the Brillouin zone does not signify any soft mode. Electronic indirect band gap of 1.61 eV is observed for the single-layer antimonene. However, the occurrence of bilayered quasi-2D sheet consequent to metallic behaviour is due to significant electronic charge dispersion between interlayer region.
Nakatani, Naoki; Guo, Sheng
2017-03-01
This paper describes an interface between the density matrix renormalization group (DMRG) method and the complete active-space self-consistent field (CASSCF) method and its analytical gradient, as well as an extension to the second-order perturbation theory (CASPT2) method. This interfacing allows large active-space multi-reference computations to be easily performed. The interface and its extension are both implemented in terms of reduced density matrices (RDMs) which can be efficiently computed via the DMRG sweep algorithm. We also present benchmark results showing that, in practice, the DMRG-CASSCF calculations scale with active-space size in a polynomial manner in the case of quasi-1D systems. Geometry optimization of a binuclear iron-sulfur cluster using the DMRG-CASSCF analytical gradient is demonstrated, indicating that the inclusion of the valence p-orbitals of sulfur and double-shell d-orbitals of iron lead to non-negligible changes in the geometry compared to the results of small active-space calculations. With the exception of the selection of M values, many computational settings in these practical DMRG calculations have been tuned and black-boxed in our interface, and so the resulting DMRG-CASSCF and DMRG-CASPT2 calculations are now available to novice users as a common tool to compute strongly correlated electronic wavefunctions.
Dusty Relic to Shining Treasure: Embedded in a Multicultural Environment
Avery, Beth Fuseler; Batman, Cindy
2014-01-01
Far from being dusty old relics who are guardians of the book, embedded librarians need to be proactively leading students through the digital maze of the virtual library. Working with students more than 7,000 miles away changed perceptions of how to teach and learn, and how people interact online. We will share how as embedded librarians we…
ƒ(R Gravity, Relic Coherent Gravitons and Optical Chaos
Lawrence B. Crowell
2014-03-01
Full Text Available We discuss the production of massive relic coherent gravitons in a particular class of ƒ(R gravity, which arises from string theory, and their possible imprint in the Cosmic Microwave Background. In fact, in the very early Universe, these relic gravitons could have acted as slow gravity waves. They may have then acted to focus the geodesics of radiation and matter. Therefore, their imprint on the later evolution of the Universe could appear as filaments and a domain wall in the Universe today. In that case, the effect on the Cosmic Microwave Background should be analogous to the effect of water waves, which, in focusing light, create optical caustics, which are commonly seen on the bottom of swimming pools. We analyze this important issue by showing how relic massive gravity waves (GWs perturb the trajectories of the Cosmic Microwave Background photons (gravitational lensing by relic GWs. The consequence of the type of physics discussed is outlined by illustrating an amplification of what might be called optical chaos.
Spectral age modelling of the `Sausage' cluster radio relic
Stroe, Andra; Harwood, Jeremy J.; Hardcastle, Martin J.; Röttgering, Huub J. A.
2014-12-01
CIZA J2242.8+5301 is a post-core passage, binary merging cluster that hosts a large, thin, arc-like radio relic, nicknamed the `Sausage', tracing a relatively strong shock front. We perform spatially resolved spectral fitting to the available radio data for this radio relic, using a variety of spectral ageing models, with the aim of finding a consistent set of parameters for the shock and radio plasma. We determine an injection index of 0.77^{+0.03}_{-0.02} for the relic plasma, significantly steeper than was found before. Standard particle acceleration at the shock front implies a Mach number M=2.90^{+0.10}_{-0.13}, which now matches X-ray measurements. The shock advance speed is vshock ≈ 2500 km s-1, which places the core passage of the two subclusters 0.6-0.8 Gyr ago. We find a systematic spectral age increase from 0 at the northern side of the relic up to ˜60 Myr at ˜145 kpc into the downstream area, assuming a 0.6 nT magnetic field. Under the assumption of freely ageing electrons after acceleration by the `Sausage' shock, the spectral ages are hard to reconcile with the shock speed derived from X-ray and radio observations. Re-acceleration or unusually efficient transport of particle in the downstream area and line-of-sight mixing could help explain the systematically low spectral ages.
Spectral age modelling of the `Sausage' cluster radio relic
Stroe, Andra; Hardcastle, Martin J; Röttgering, Huub J A
2014-01-01
CIZA J2242.8+5301 is a post-core passage, binary merging cluster that hosts a large, thin, arc-like radio relic, nicknamed the `Sausage', tracing a relatively strong shock front. We perform spatially-resolved spectral fitting to the available radio data for this radio relic, using a variety of spectral ageing models, with the aim of finding a consistent set of parameters for the shock and radio plasma. We determine an injection index of $0.77^{+0.03}_{-0.02}$ for the relic plasma, significantly steeper than was found before. Standard particle acceleration at the shock front implies a Mach number $M=2.90^{+0.10}_{-0.13}$, which now matches X-ray measurements. The shock advance speed is $v_\\mathrm{shock}\\approx2500$ km s$^{-1}$, which places the core passage of the two subclusters $0.6-0.8$ Gyr ago. We find a systematic spectral age increase from $0$ at the northern side of the relic up to $\\sim60$ Myr at $\\sim145$ kpc into the downstream area, assuming a $0.6$ nT magnetic field. Under the assumption of freely-...
Pedesseau, L., E-mail: laurent.pedesseau@insa.rennes.fr [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France); Even, J. [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France); Katan, C. [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France); CNRS, Institut des Sciences Chimiques de Rennes, UMR 6226, 35042 Rennes (France); Raouafi, F. [Laboratoire de Physico-chimie des matériaux polymères, Institut Préparatoire aux Etudes Scientifiques et Techniques, BP51, 2070 La Marsa (Tunisia); Wei, Y.; Deleporte, E. [Laboratoire de Photonique Quantique et Moléculaire, Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94 235 Cachan Cedex (France); Jancu, J.-M. [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France)
2013-08-31
Density Functional Theory is used to study the vibrational properties of 2H-PbI{sub 2} semiconductor. The Born charge tensors are determined. Calculated phonon frequencies at the Brillouin zone center are compared to Raman scattering and IR absorption measurements. The computed Raman spectra show a good agreement with available experimental data. The simulated phonon dispersion curves are compared with triple-axis neutron scattering measurements. - Highlights: ► Symmetry properties of the optical phonons of the 2H-PbI{sub 2} crystal are analysed. ► Born charges and the dynamical matrix are calculated the Brillouin zone center. ► Raman spectra and Phonon dispersion have been compared with experimental results. ► Dielectric tensors are calculated and compared to measurements.
Frau, Juan; Glossman-Mitnik, Daniel
2017-01-01
Amino acids and peptides have the potential to perform as corrosion inhibitors. The chemical reactivity descriptors that arise from Conceptual DFT for the twenty natural amino acids have been calculated by using the latest Minnesota family of density functionals. In order to verify the validity of the calculation of the descriptors directly from the HOMO and LUMO, a comparison has been performed with those obtained through ΔSCF results. Moreover, the active sites for nucleophilic and electrophilic attacks have been identified through Fukui function indices, the dual descriptor Δf(r) and the electrophilic and nucleophilic Parr functions. The results could be of interest as a starting point for the study of large peptides where the calculation of the radical cation and anion of each system may be computationally harder and costly. PMID:28361050
Borges, P. D., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu; Scolfaro, L., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu [Department of Physics, Texas State University, San Marcos, Texas 78666 (United States)
2014-12-14
The thermoelectric properties of indium nitride in the most stable wurtzite phase (w-InN) as a function of electron and hole concentrations and temperature were studied by solving the semiclassical Boltzmann transport equations in conjunction with ab initio electronic structure calculations, within Density Functional Theory. Based on maximally localized Wannier function basis set and the ab initio band energies, results for the Seebeck coefficient are presented and compared with available experimental data for n-type as well as p-type systems. Also, theoretical results for electric conductivity and power factor are presented. Most cases showed good agreement between the calculated properties and experimental data for w-InN unintentionally and p-type doped with magnesium. Our predictions for temperature and concentration dependences of electrical conductivity and power factor revealed a promising use of InN for intermediate and high temperature thermoelectric applications. The rigid band approach and constant scattering time approximation were utilized in the calculations.
Frau, Juan; Glossman-Mitnik, Daniel
2017-01-01
Amino acids and peptides have the potential to perform as corrosion inhibitors. The chemical reactivity descriptors that arise from Conceptual DFT for the twenty natural amino acids have been calculated by using the latest Minnesota family of density functionals. In order to verify the validity of the calculation of the descriptors directly from the HOMO and LUMO, a comparison has been performed with those obtained through ΔSCF results. Moreover, the active sites for nucleophilic and electrophilic attacks have been identified through Fukui function indices, the dual descriptor Δf(r) and the electrophilic and nucleophilic Parr functions. The results could be of interest as a starting point for the study of large peptides where the calculation of the radical cation and anion of each system may be computationally harder and costly.
SU-E-T-496: A Study of Two Commercial Dose Calculation Algorithms in Low Density Phantom
Lim, S; Lovelock, D; Yorke, E; Kuo, L; LoSasso, T [Memorial Sloan- Kettering Cancer Center, NY, NY (United States)
2014-06-01
Purpose: Some lung cancer patients have very low lung density due to comorbidities. We investigate calculation accuracy of Eclipse AAA and Acuros(AXB) using a phantom that simulates this situation. Methods: A 2.5 x 5.0 x 5 cm (long) solid water inhomogeneity positioned 10 cm deep in a Balsa lung phantom (density 0.099 gm/cc) was irradiated with an off-center field such that the central axis was parallel to one side of the inhomogeneity. Radiochromic films were placed at 2.5cm(S1) and 5cm(S2) depths. After CT scanning, Hounsfield Units(HU) were converted to electron(ρe) and mass(ρm) density using in-house(IH) and vendor-supplied(V) calibration curves. IH electron densities were generated using a commercial electron density phantom. The phantom was exposed to 6 MV 3x3 and 20x20 fields. Dose distributions were calculated using the AAA and AXB algorithms. Results: The HU of BW is -910±40 which translates to ρe of 0.088±0.050(IH) and 0.090±0.050(V), and ρm of 0.101±0.045(IH) and 0.103±0.039(V). Both ρe(V) and ρm(V) are higher than ρe(IH) and ρm(IH) respectively by 1.4-5.3% and 0.5-12.3%. The average calculated dose inside the solid water ‘tumor’ are within 3.7% and 2.4% of measurements for both calibrations and field sizes using AAA and AXB. Within 10mm outside the ‘tumor’, AAA on average underestimates by 18.3% and 17.0% respectively for 3x3 using IH and V. AXB underestimates by 5.9%(S1)-6.6%(S2) and 13.1%(S1)-16.0%(S2) respectively using IH and V. For 20x20, AAA and AXB underestimate by 2.8%(S1)-4.4%(S2) and 0.3%(S1)-1.4%(S2) respectively with either calibration. Conclusion: The difference in the HU calibration between V and IH is not of clinical significance in normal field sizes. In the low density region of small fields, the calculations from both algorithms differ significantly from measurements. This may be attributed to the insufficient lateral electron transport modeled by two algorithms resulting in the over-estimation in penumbra
Autschbach, Jochen; Jorge, Francisco E; Ziegler, Tom
2003-05-05
Time-dependent density functional theory (TD-DFT) has for the first time been applied to the computation of circular dichroism (CD) spectra of transition metal complexes, and a detailed comparison with experimental spectra has been made. Absorption spectra are also reported. Various Co(III) complexes as well as [Rh(en)(3)](3+) are studied in this work. The resulting simulated CD spectra are generally in good agreement with experimental spectra after corrections for systematic errors in a few of the lowest excitation energies are applied. This allows for an interpretation and assignment of the spectra for the whole experimentally accessible energy range (UV/vis). Solvent effects on the excitations are estimated via inclusion of a continuum solvent model. This significantly improves the computed excitation energies for charge-transfer bands for complexes of charge +3, but has only a small effect on those for neutral or singly charged complexes. The energies of the weak d-to-d transitions of the Co complexes are systematically overestimated due to deficiencies of the density functionals. These errors are much smaller for the 4d metal complex. Taking these systematic errors and the effect of a solvent into consideration, TD-DFT computations are demonstrated to be a reliable tool in order to assist with the assignment and interpretation of CD spectra of chiral transition metal complexes.
István Bors
2015-09-01
Full Text Available Maize (Zea mays L. is often contaminated with Fusarium verticillioides. This harmful fungus produces fumonisins as secondary metabolites. These fumonisins can appear both free and hidden form in planta. The hidden form is usually bound covalently to cereal starch. From the hidden fumonisins, during enzymatic degradation, glycosides are formed, and the fumonisin is further decomposed during a de-esterification step. In this short communication some preliminary DFT calculated structural results which could be useful in the future to help to understand the van der Waals force controlled molecular interactions between these kinds of mycotoxin molecules and enzymes are demonstrated.
Ammonia synthesis over a Ru(0001) surface studied by density functional calculations
Logadottir, Ashildur; Nørskov, Jens Kehlet
2003-01-01
In this paper we present DFT studies of all the elementary steps in the synthesis of ammonia from gaseous hydrogen and nitrogen over a ruthenium crystal. The stability and configurations of intermediates in the ammonia synthesis over a Ru(0001) surface have been investigated, both over a flat...... surface and over a stepped surface. The calculations show that the step sites on the surface are much more reactive than the terrace sites. The DFT results are then used to study the mechanism of promotion by alkalies over the Ru(0001) and to determine the rate-determining step in the synthesis of ammonia...
Abtew, Tesfaye A; Drabold, D A [Department of Physics and Astronomy, Ohio University, Athens, OH 45701-2979 (United States)
2004-11-10
In this paper we study electron dynamics and transport in models of amorphous silicon and amorphous silicon hydride. By integrating the time-dependent Kohn-Sham equation, we compute the time evolution of electron states near the gap, and study the spatial and spectral diffusion of these states due to lattice motion. We perform these calculations with a view to developing ab initio hopping transport methods. The techniques are implemented with the ab initio local basis code SIESTA, and may be applicable to molecular, biomolecular and other condensed matter systems.
Nobre, G P A; Escher, J E; Thompson, I J; Dupuis, M; Terasaki, J; Engel, J
2010-01-01
A microscopic calculation of the reaction cross-section for nucleon-nucleus scattering has been performed by explicitly coupling the elastic channel to all particle-hole (p-h) excitation states in the target and to all one-nucleon pickup channels. The p-h states may be regarded as doorway states through which the flux flows to more complicated configurations, and subsequently to long-lived compound nucleus resonances. Target excitations for 40,48Ca, 58Ni, 90Zr and 144Sm were described in a QRPA framework using a Skyrme functional. Reaction cross sections calculated in this approach were compared to predictions of a fitted optical potential and to experimental data, reaching very good agreement. Couplings between inelastic states were found to be negligible, while the couplings to pickup channels contribute significantly. For the first time observed reaction cross-sections are completely accounted for by explicit channel coupling, for incident energies between 10 and 40 MeV.
Nonlocal energy density functionals for pairing and beyond-mean-field calculations
Bennaceur, K; Dobaczewski, J; Dobaczewski, P; Kortelainen, M; Raimondi, F
2016-01-01
We propose to use two-body regularized finite-range pseudopotential to generate nuclear energy density functional (EDF) in both particle-hole and particle-particle channels, which makes it free from self-interaction and self-pairing, and also free from singularities when used beyond mean field. We derive a sequence of pseudopotentials regularized up to next-to-leading order (NLO) and next-to-next-to-leading order (N2LO), which fairly well describe infinite-nuclear-matter properties and finite open-shell paired and/or deformed nuclei. Since pure two-body pseudopotentials cannot generate sufficiently large effective mass, the obtained solutions constitute a preliminary step towards future implementations, which will include, e.g., EDF terms generated by three-body pseudopotentials.
Wang Xiaowei; Wang Qiang, E-mail: qiangwang@cjlu.edu.cn [Department of Quality and Safety Engineering, China Jiliang University, Hangzhou, 310018 (China)
2011-02-01
In the room temperature and nitrogen conditions, we presented well-resolved absorption spectra and indexes of refraction of bactericide molecules in the far infrared radiation (FIR) spectral region recorded by terahertz time-domain spectroscopy (THz-TDS). As illustrative examples we discussed the absorption spectra of captan and folpet in THz region. The absorption coefficient and index of refraction of them were obtained. Meanwhile, density functional theory (DFT) with software package Gaussian 03 using B3LYP theory was employed for optimization and vibration analysis. With the help of Gaussian View 3.09, the distinct absorption peaks of those molecules were assigned with reliable accuracy. They were caused by intermolecular hydrogen-bonding, molecular torsion or vibration modes, absorption of water molecules, etc. As the absorption spectra are highly sensitive to the overall structure and configuration of the molecules, the THz-TDS procedure can provide a direct fingerprint of the molecular structure or conformational state of a compound.
ZIRAN CHEN; ZHANRONG HE; YOUHUI XU; WENHAO YU
2017-09-01
Charge transport rate is one of the key parameters determining the performance of organic electronic devices. In this paper, we used density functional theory (DFT) at the M06-2X/6−31+G(d) level to compute the charge transport rates of nine coronene topological structures. The results show that the energy gap of these nine coronene derivatives is in the range 2.90–3.30 eV, falling into the organic semiconductor category. The size of the conjugate ring has a large influence on the charge transport properties. Incorporation of methyl groupson the rigid core of tetrabenzocoronene and hexabenzocoronene is more conducive to the hole transport of the molecule than incorporating methoxyl groups. The derivatisation of a ‘long plate-like’ coronene with methoxylgroups facilitates both hole and electron transport. This class of molecules can thus be used in the design of ambipolar transport semiconductor materials.
Reimers, Jeffrey R; Cai, Zheng-Li; Bilić, Ante; Hush, Noel S
2003-12-01
As molecular electronics advances, efficient and reliable computation procedures are required for the simulation of the atomic structures of actual devices, as well as for the prediction of their electronic properties. Density-functional theory (DFT) has had widespread success throughout chemistry and solid-state physics, and it offers the possibility of fulfilling these roles. In its modern form it is an empirically parameterized approach that cannot be extended toward exact solutions in a prescribed way, ab initio. Thus, it is essential that the weaknesses of the method be identified and likely shortcomings anticipated in advance. We consider four known systematic failures of modern DFT: dispersion, charge transfer, extended pi conjugation, and bond cleavage. Their ramifications for molecular electronics applications are outlined and we suggest that great care is required when using modern DFT to partition charge flow across electrode-molecule junctions, screen applied electric fields, position molecular orbitals with respect to electrode Fermi energies, and in evaluating the distance dependence of through-molecule conductivity. The causes of these difficulties are traced to errors inherent in the types of density functionals in common use, associated with their inability to treat very long-range electron correlation effects. Heuristic enhancements of modern DFT designed to eliminate individual problems are outlined, as are three new schemes that each represent significant departures from modern DFT implementations designed to provide a priori improvements in at least one and possible all problem areas. Finally, fully semiempirical schemes based on both Hartree-Fock and Kohn-Sham theory are described that, in the short term, offer the means to avoid the inherent problems of modern DFT and, in the long term, offer competitive accuracy at dramatically reduced computational costs.
Adhesion and bonding of Pt/Ni and Pt/Co overlayers: Density functional calculations
Cabeza, Gabriela F.; Castellani, Norberto J.; Légaré, Pierre
2006-04-01
The electronic and energetic properties of bimetallic surfaces Pt/Ni(111) and Pt/Co(111) are examined using the FP-LAPW (Full-PotentialLinearized Augmented Plane Wave) method by means of spin-polarized and non-polarized calculations. We present both the results of the shifts in the d-band centers when one metal (Pt) is pseudomorfically deposited on another with smaller lattice constant (Ni, Co) and those corresponding to the surface and adhesion energies. The surface is modeled by a seven layer slab separated in z direction by a vacuum region of six substrate layers. The results obtained for pure Ni, Co and Pt surfaces are presented in order to compare with experimental and theoretical data reported in the literature
Zhou, Fei; Ozoliņš, Vidvuds
2012-02-01
Using a recently developed method combining a nonspherical self-interaction corrected LDA + U scheme and an on-site multibody Hamiltonian [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.83.085106 83, 085106 (2011)], we calculate the crystal field parameters and crystal field (CF) excitation levels of f-element dioxides in the fluorite structure with fn electronic configurations, including n=1 (PaO2, PrO2), n=2 (UO2), n=3 (NpO2), and n=4 (PuO2). It is shown that good agreement with experimental data (within approximately 10-20 meV) can be obtained in all cases. The properties of the multielectron CF ground states are analyzed.
Park, So Yeon; Park, Jong Min; Choi, Chang Heon; Chun, MinSoo; Han, Ji Hye; Cho, Jin Dong; Kim, Jung In [Dept. of Radiation Oncology, Seoul National University Hospital, Seoul (Korea, Republic of)
2017-03-15
The purpose of this study is to assign an appropriate density to virtual phantom for 2D diode array detector with different dose calculation algorithms to guarantee the accuracy of patient-specific QA. Ten VMAT plans with 6 MV photon beam and ten VMAT plans with 15 MV photon beam were selected retrospectively. The computed tomography (CT) images of MapCHECK2 with MapPHAN were acquired to design the virtual phantom images. For all plans, dose distributions were calculated for the virtual phantoms with four different materials by AAA and AXB algorithms. The four materials were polystyrene, 455 HU, Jursinic phantom, and PVC. Passing rates for several gamma criteria were calculated by comparing the measured dose distribution with calculated dose distributions of four materials. For validation of AXB modeling in clinic, the mean percentages of agreement in the cases of dose difference criteria of 1.0% and 2.0% for 6 MV were 97.2%±2.3%, and 99.4%±1.1%, respectively while those for 15 MV were 98.5%±0.85% and 99.8%±0.2%, respectively. In the case of 2%/2 mm, all mean passing rates were more than 96.0% and 97.2% for 6 MV and 15 MV, respectively, regardless of the virtual phantoms of different materials and dose calculation algorithms. The passing rates in all criteria slightly increased for AXB as well as AAA when using 455 HU rather than polystyrene. The virtual phantom which had a 455 HU values showed high passing rates for all gamma criteria. To guarantee the accuracy of patent-specific VMAT QA, each institution should fine-tune the mass density or HU values of this device.
Oberhofer, Harald; Blumberger, Jochen
2010-12-01
We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn-Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken-Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q-) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, ( { } )^{1/2} = 6.7 {mH}, is significantly higher than the value obtained for the minimum energy structure, | {H_ab } | = 3.8 {mH}. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q- in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.
McCammon, Catherine; Caracas, Razvan; Glazyrin, Konstantin; Potapkin, Vasily; Kantor, Anastasia; Sinmyo, Ryosuke; Prescher, Clemens; Kupenko, Ilya; Chumakov, Aleksandr; Dubrovinsky, Leonid
2016-12-01
Sound velocities of bridgmanite measured in the laboratory are a key to deciphering the composition of the lower mantle. Here, we report Debye sound velocities determined using nuclear inelastic scattering (NIS) for one majorite composition (Mg0.82Fe0.18SiO3) and five bridgmanite compositions (Mg0.82Fe0.18SiO3, Mg0.86Fe0.14Si0.98Al0.02O3, Mg0.88Fe0.12SiO3, Mg0.6Fe0.4Si0.63Al0.37O3, Mg0.83Fe0.15Si0.98Al0.04O3) measured in a diamond anvil cell at pressures up to 89 GPa at room temperature. Debye sound velocities for majorite determined from NIS are consistent with literature data from Brillouin scattering and ultrasonics, while Debye sound velocities for bridgmanite are significantly lower than literature values from the same methods. We calculated partial and total density of states (DOS) for MgSiO3 and FeSiO3 bridgmanite using density functional theory and demonstrate that Debye sound velocities calculated from the reduced DOS using the same approach as for the experimental data (i.e., the limit of D(E)/E2 as energy goes to zero) give the same sound velocities for each phase irrespective of which partial DOS is used. In addition, we show that Debye sound velocities calculated using this approach are consistent with values obtained from the calculation of the full elastic tensor. Comparison of the calculated DOS with the one obtained from NIS indicates that the experimental DOS has enhanced intensity at low energies that leads to a different slope of the DOS and hence a lower sound velocity. This effect is present in all of the bridgmanite samples examined in this study.
Skachkov, Dmitry; Krykunov, Mykhaylo; Kadantsev, Eugene; Ziegler, Tom
2010-05-11
We present here a method that can calculate NMR shielding tensors from first principles for systems with translational invariance. Our approach is based on Kohn-Sham density functional theory and gauge-including atomic orbitals. Our scheme determines the shielding tensor as the second derivative of the total electronic energy with respect to an external magnetic field and a nuclear magnetic moment. The induced current density due to a periodic perturbation from nuclear magnetic moments is obtained through numerical differentiation, whereas the influence of the responding perturbation in terms of the external magnetic field is evaluated analytically. The method is implemented into the periodic program BAND. It employs a Bloch basis set made up of Slater-type or numeric atomic orbitals and represents the Kohn-Sham potential fully without the use of effective core potentials. Results from calculations of NMR shielding constants based on the present approach are presented for isolated molecules as well as systems with one-, two- and three-dimensional periodicity. The reported values are compared to experiment and results from calculations on cluster models.
Sun, Y Y; Kim, Yong-Hyun; Lee, Kyuho; Zhang, S B
2008-10-21
Density functional theory (DFT) in the commonly used local density or generalized gradient approximation fails to describe van der Waals (vdW) interactions that are vital to organic, biological, and other molecular systems. Here, we propose a simple, efficient, yet accurate local atomic potential (LAP) approach, named DFT+LAP, for including vdW interactions in the framework of DFT. The LAPs for H, C, N, and O are generated by fitting the DFT+LAP potential energy curves of small molecule dimers to those obtained from coupled cluster calculations with single, double, and perturbatively treated triple excitations, CCSD(T). Excellent transferability of the LAPs is demonstrated by remarkable agreement with the JSCH-2005 benchmark database [P. Jurecka et al. Phys. Chem. Chem. Phys. 8, 1985 (2006)], which provides the interaction energies of CCSD(T) quality for 165 vdW and hydrogen-bonded complexes. For over 100 vdW dominant complexes in this database, our DFT+LAP calculations give a mean absolute deviation from the benchmark results less than 0.5 kcal/mol. The DFT+LAP approach involves no extra computational cost other than standard DFT calculations and no modification of existing DFT codes, which enables straightforward quantum simulations, such as ab initio molecular dynamics, on biomolecular systems, as well as on other organic systems.
CALCULATION AND COMPARISON OF NUTRIENT DENSITY/QUALITY SCORES FOR COMMONLY CONSUMED FRESH FRUIT
Gail RAMPERSAUD
2012-01-01
Full Text Available A number of methods have been developed to quantitatively describe the nutrient density/quality (ND/Q of foods and beverages. Seventeen commonly consumed fresh fruits were evaluated using six published ND/Q methods. Nutrient data for each fruit were obtained from the USDA National Nutrient Database for Standard Reference, Release 23. Numerical scores were produced and ranked for each fruit and method. The resulting ND/Q scores varied in range and magnitude but there was good to strong correlation among methods. The relative scores indicated that cantaloupe, strawberries, oranges, and grapefruit generally had the highest ND/Q scores across all methods. Further analysis indicated that vitamins C and A, nutrients common to all six methods, affected ND/Q scores substantially for some but not all fruits, suggesting that high values for specific nutrients may influence relative scoring and higher scores may not necessarily reflect a greater variety or balance of nutrients. Fresh fruits vary in their ND/Q as defined by several quantitative scoring systems. In this analysis, consistent results in how the fruits were ranked were obtained when using six different methods to quantify ND/Q for select fresh fruit.
Accurate variational electronic structure calculations with the density matrix renormalization group
Wouters, Sebastian
2014-01-01
During the past 15 years, the density matrix renormalization group (DMRG) has become increasingly important for ab initio quantum chemistry. The underlying matrix product state (MPS) ansatz is a low-rank decomposition of the full configuration interaction tensor. The virtual dimension of the MPS controls the size of the corner of the many-body Hilbert space that can be reached. Whereas the MPS ansatz will only yield an efficient description for noncritical one-dimensional systems, it can still be used as a variational ansatz for other finite-size systems. Rather large virtual dimensions are then required. The two most important aspects to reduce the corresponding computational cost are a proper choice and ordering of the active space orbitals, and the exploitation of the symmetry group of the Hamiltonian. By taking care of both aspects, DMRG becomes an efficient replacement for exact diagonalization in quantum chemistry. DMRG and Hartree-Fock theory have an analogous structure. The former can be interpreted a...
Guan Peng-Fei; Wang Chong-Yu; Yu Tao
2008-01-01
Local density functional is investigated by using the full-potential linearized augmented plane wave (FP-LAPW) method for ScN in the hexagonal structure and the rocksalt structure and for hexagonal structures linking a layered hexagonal phase with wurtzite structure along a homogeneous strain transition path. It is found that the wurtzite ScN is unstable and the layered hexagonal phase, labelled as ho, in which atoms are approximately fivefold coordinated,is metastable, and the rocksalt ScN is stable. The electronic structure, the physical properties of the intermediate structures and the energy band structure along the transition are presented. It is found that the band gaps change from 4.0 to 1.0eV continuously when c/a value varies from 1.68 to 1.26. It is noticeable that the study of ScN provides an opportunity to apply this kind of material (in wurtzite[h]-derived phase).
van de Streek, Jacco; Neumann, Marcus A
2010-10-01
This paper describes the validation of a dispersion-corrected density functional theory (d-DFT) method for the purpose of assessing the correctness of experimental organic crystal structures and enhancing the information content of purely experimental data. 241 experimental organic crystal structures from the August 2008 issue of Acta Cryst. Section E were energy-minimized in full, including unit-cell parameters. The differences between the experimental and the minimized crystal structures were subjected to statistical analysis. The r.m.s. Cartesian displacement excluding H atoms upon energy minimization with flexible unit-cell parameters is selected as a pertinent indicator of the correctness of a crystal structure. All 241 experimental crystal structures are reproduced very well: the average r.m.s. Cartesian displacement for the 241 crystal structures, including 16 disordered structures, is only 0.095 Å (0.084 Å for the 225 ordered structures). R.m.s. Cartesian displacements above 0.25 A either indicate incorrect experimental crystal structures or reveal interesting structural features such as exceptionally large temperature effects, incorrectly modelled disorder or symmetry breaking H atoms. After validation, the method is applied to nine examples that are known to be ambiguous or subtly incorrect.
Andrews, Lester
2004-02-20
Metal hydrides are of considerable importance in chemical synthesis as intermediates in catalytic hydrogenation reactions. Transition metal atoms react with dihydrogen to produce metal dihydrides or dihydrogen complexes and these may be trapped in solid matrix samples for infrared spectroscopic study. The MH(2) or M(H(2)) molecules so formed react further to form higher MH(4), (H(2))MH(2), or M(H(2))(2), and MH(6), (H(2))(2)MH(2), or M(H(2))(3) hydrides or complexes depending on the metal. In this critical review these transition metal and dihydrogen reaction products are surveyed for Groups 3 though 12 and the contrasting behaviour in Groups 6 and 10 is discussed. Minimum energy structures and vibrational frequencies predicted by Density Functional Theory agree with the experimental results, strongly supporting the identification of novel binary transition metal hydride species, which the matrix-isolation method is well-suited to investigate. 104 references are cited.
Eriksen, Troels K; Karlsen, Eva; Spanget-Larsen, Jens
2015-01-01
The title compounds were investigated by means of Linear Dichroism (LD) IR spectroscopy on samples partially aligned in uniaxially stretched low-density polyethylene and by density functional theory calculations. Satisfactory overall agreement between observed and calculated vibrational wavenumbe...... and IR intensities are obtained, allowing a fairly detailed assignment of the observed transitions in terms of individual nuclear motions....
Lee, Kwang Sung; Gill, Wonpyong
We have calculated the relative density and crossing time through the fitness barrier by switching on an asymmetric sharply-peaked landscape, from the initial state which is the quasispecies in a sharply-peaked landscape. It is found that the increment of the relative density with the reversal sequence is a linearly increasing function of time unless a new stationary state in an asymmetric sharply-peaked landscape is reached. It is also found that the relative density with the reversal sequence at the new stationary state X*L is in inverse proportion to the asymmetric parameter when the asymmetric parameter is greater than the saturation asymmetric parameter. We have derived the approximate formulae for the relaxation time, the saturation asymmetric parameter, and the relative density with the reversal sequence X*L, which nicely fit computer simulation results. It is found that the crossing time diverges at the critical fitness parameter in the asymmetric sharply-peaked landscape, in contrast with the symmetric sharply-peaked landscape where the crossing time scales as a power law in the fitness parameter. It is also found that the critical fitness parameter decreases as the asymmetric parameter and sequence length increase.
Di Valentin, Cristiana; Pacchioni, Gianfranco
2014-11-18
CONSPECTUS: Very rarely do researchers use metal oxides in their pure and fully stoichiometric form. In most of the countless applications of these compounds, ranging from catalysis to electronic devices, metal oxides are either doped or defective because the most interesting chemical, electronic, optical, and magnetic properties arise when foreign components or defects are introduced in the lattice. Similarly, many metal oxides are diamagnetic materials and do not show a response to specific spectroscopies such as electron paramagnetic resonance (EPR) spectroscopy. However, doped or defective oxides may exhibit an interesting and informative paramagnetic behavior. Doped and defective metal oxides offer an expanding range of applications in contemporary condensed matter science; therefore researchers have devoted enormous effort to the understanding their physical and chemical properties. The interplay between experiment and computation is particularly useful in this field, and contemporary simulation techniques have achieved high accuracies with these materials. In this Account, we show how the direct comparison between spectroscopic experimental and computational data for some selected and relevant materials provides ways to understand and control these complex systems. We focus on the EPR properties and electronic transitions that arise from the presence of dopants and defects in bulk metal oxide materials. We analyze and compare the effect of nitrogen doping in TiO2 and ZnO (two semiconducting oxides) and MgO (a wide gap insulator) and examine the effect of oxygen deficiency in the semiconducting properties of TiO2-x, ZnO1-x, and WO3-x materials. We chose these systems because of their relevance in applications including photocatalysis, touch screens, electrodes in magnetic random access memories, and smart glasses. Density functional theory (DFT) provides the general computational framework used to illustrate the electronic structure of these systems. However
Kuwahara, Riichi [Department of Physics, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan); Accelrys K. K., Kasumigaseki Tokyu Building 17F, 3-7-1 Kasumigaseki, Chiyoda-ku, Tokyo 100-0013 (Japan); Tadokoro, Yoichi; Ohno, Kaoru, E-mail: ohno@ynu.ac.jp [Department of Physics, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan)
2014-08-28
In this paper, we calculate kinetic and potential energy contributions to the electronic ground-state total energy of several isolated atoms (He, Be, Ne, Mg, Ar, and Ca) by using the local density approximation (LDA) in density functional theory, the Hartree–Fock approximation (HFA), and the self-consistent GW approximation (GWA). To this end, we have implemented self-consistent HFA and GWA routines in our all-electron mixed basis code, TOMBO. We confirm that virial theorem is fairly well satisfied in all of these approximations, although the resulting eigenvalue of the highest occupied molecular orbital level, i.e., the negative of the ionization potential, is in excellent agreement only in the case of the GWA. We find that the wave function of the lowest unoccupied molecular orbital level of noble gas atoms is a resonating virtual bound state, and that of the GWA spreads wider than that of the LDA and thinner than that of the HFA.
Kuwahara, Riichi; Tadokoro, Yoichi; Ohno, Kaoru
2014-08-28
In this paper, we calculate kinetic and potential energy contributions to the electronic ground-state total energy of several isolated atoms (He, Be, Ne, Mg, Ar, and Ca) by using the local density approximation (LDA) in density functional theory, the Hartree-Fock approximation (HFA), and the self-consistent GW approximation (GWA). To this end, we have implemented self-consistent HFA and GWA routines in our all-electron mixed basis code, TOMBO. We confirm that virial theorem is fairly well satisfied in all of these approximations, although the resulting eigenvalue of the highest occupied molecular orbital level, i.e., the negative of the ionization potential, is in excellent agreement only in the case of the GWA. We find that the wave function of the lowest unoccupied molecular orbital level of noble gas atoms is a resonating virtual bound state, and that of the GWA spreads wider than that of the LDA and thinner than that of the HFA.
Cosmic Neutrinos and Other Light Relics
Meyers, Joel
2016-01-01
Cosmological measurements of the radiation density in the early universe can be used as a sensitive probe of physics beyond the standard model. Observations of primordial light element abundances have long been used to place non-trivial constraints on models of new physics and to inform our understanding of the thermal history to the first few minutes of our present phase of expansion. Precision measurements of the angular power spectrum of the cosmic microwave background temperature and polarization will drastically improve our measurement of the cosmic radiation density over the next decade. These improved measurements will either uncover new physics or place much more stringent constraints on physics beyond the standard model, while pushing our understanding of the early universe to much earlier times.
Dutta, Alo, E-mail: alo_dutta@yahoo.com [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata, 700106 (India); Mukhopadhyay, P.K. [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata, 700106 (India); Sinha, T.P. [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata, 700 009 (India); Shannigrahi, Santiranjan [Institute of Materials Research and Engineering, Agency for Science Technology and Research, 3 Research Link, Singapore, 117602 (Singapore); Himanshu, A.K.; Sen, Pintu; Bandyopadhyay, S.K. [Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata, 700064 (India)
2016-08-15
The density functional theory (DFT) under the generalized gradient approximation (GGA) has been used to investigate the electronic structure of double perovskite oxide Sr{sub 2}SmNbO{sub 6} synthesized by the solid-state reaction technique. The Rietveld refinement of the X-ray diffraction pattern of the sample shows the monoclinic P2{sub 1}/n phase at room temperature. The X-ray photoemission spectrum (XPS) of the material is collected in the energy window of 0–1200 eV. The chemical shift of the constituent elements calculated from the core level XPS spectra is used to analyze the covalency between the O anion and Sm/Nb cations. The valence band (VB) XPS spectrum is compared with the calculated VB spectrum using partial density of states in a standard way. The Raman spectrum is employed to investigate the phonon modes of the material in the monoclinic phase. Lorentzian lines are used to fit the experimental Raman spectrum, which present 24 phonon modes corresponding to the stretching and banding of NbO{sub 6}/SmO{sub 6} octahedra and translational motion of Sr along the Sr−O bond. The discrepancy between the measured and calculated band gap values has been removed by applying modified Becke-Johnson (mBJ) potential in the DFT calculations. The experimental optical band gap obtained from the UV–visible reflectance spectrum is found to be 3.42 eV, which is well matched with the DFT calculated value of 3.2 eV, and suggests the semiconducting nature of the material. The real (ε′) and imaginary (ε″) parts of the optical dielectric constant as a function of energy along the x-, y- and z-polarization directions using mBJ potential are calculated. The collective vibrational modes of the atoms, the Born effective charge of the ions and their effect on the static dielectric constant of the material are studied using DFT. The calculated value of static dielectric constant for SSN is found to be 41.3. - Highlights: • Electronic structure and dynamical
Yun Jiang-Ni; Zhang Zhi-Yong
2009-01-01
This paper investigates the effect of Nb doping on the electronic structure and optical properties of by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory (DFT).The calculated results reveal that due to the electron doping, the Fermi level shifts into conduction bands(CBs) for Sr2NbxTi1-xO4 with x = 0.125 and the system shows n-type degenerate semiconductor features. Sr2TiO4 exhibits optical anisotropy in its main crystal axes, and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region. The optical transmittance is higher than 90% in the visible range for Sr2Nb0.125Ti0.875O4.
Powell, B J; Bernstein, N; Brake, K; McKenzie, Ross H; Meredith, P; Pederson, M R
2016-01-01
We report first principles density functional calculations for hydroquinone (HQ), indolequinone (IQ) and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of bio-macromolecules with important biological functions (including photoprotection) and with potential for certain bioengineering applications. We have used the DeltaSCF (difference of self consistent fields) method to study the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), Delta_HL. We show that Delta_HL is similar in IQ and SQ but approximately twice as large in HQ. This may have important implications for our understanding of the observed broad band optical absorption of the eumelanins. The possibility of using this difference in Delta_HL to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules ...
Genovese, Luigi; Ospici, Matthieu; Deutsch, Thierry; Méhaut, Jean-François; Neelov, Alexey; Goedecker, Stefan
2009-07-21
We present the implementation of a full electronic structure calculation code on a hybrid parallel architecture with graphic processing units (GPUs). This implementation is performed on a free software code based on Daubechies wavelets. Such code shows very good performances, systematic convergence properties, and an excellent efficiency on parallel computers. Our GPU-based acceleration fully preserves all these properties. In particular, the code is able to run on many cores which may or may not have a GPU associated, and thus on parallel and massive parallel hybrid machines. With double precision calculations, we may achieve considerable speedup, between a factor of 20 for some operations and a factor of 6 for the whole density functional theory code.
Farberow, Carrie A.; Dumesic, James A.; Mavrikakis, Manos
2014-10-03
Reaction pathways are explored for low temperature (e.g., 400 K) reduction of nitric oxide by hydrogen on Pt(111). First-principles electronic structure calculations based on periodic, self-consistent density functional theory(DFT-GGA, PW91) are employed to obtain thermodynamic and kinetic parameters for proposed reaction schemes on Pt(111). The surface of Pt(111) during NO reduction by H₂ at low temperatures is predicted to operate at a high NO coverage, and this environment is explicitly taken into account in the DFT calculations. Maximum rate analyses are performed to assess the most likely reaction mechanisms leading to formation of N₂O, the major product observed experimentally at low temperatures. The results of these analyses suggest that the reaction most likely proceeds via the addition of at least two H atoms to adsorbed NO, followed by cleavage of the N-O bond.
A novel hybrid FEM-BEM method for 3D eddy current field calculation using current density J
LIU; Zhizhen(刘志珍); WANG; Yanzhang(王衍章); JIA; Zhiping(贾智平); SUN; Yingming(孙英明)
2003-01-01
This paper introduces a novel hybrid FEM-BEM method for calculating 3D eddy current field. In the eddy current region, the eddy current density J is solved by the finite element method (FEM) which is discretized by brick finite element mesh, while in the eddy current free region, the magnetic field intensity H is solved by the boundary element method (BEM) which is discretized by rectangular boundary element mesh. Under the boundary conditions, an algebraic equation group is obtained that only includes J by eliminating H. This method has many advantages over traditional ones, such as fewer variables, more convenient coupling between the FEM and the BEM and wider application to multiply-connected regions. The calculated values of two models are in good agreement with experimental results. This shows the validity of our method.
Dark Matter Mass Constrained by the Relic Abundance, Direct Detections, and Colliders
Tsai, Ho-Chin
2013-01-01
We take into account a generic form of a Dirac fermionic dark matter (DM), which communicates with the Standard Model quarks via a scalar mediator, in a model-independent way. Four special interaction scenarios are investigated, where one is parity conserving and the other three are parity violating. Three of them result in the $v$ suppressed DM-nucleon cross sections, where $v \\sim 10^{-3} c$ is the velocity of the DM in the laboratory frame. We constrain the masses of the dark matter and mediator as well as the couplings from the thermal relic abundance, and the recent results of the XENON100 direct detection and collider experiments involving the two channels: (i) monojet plus large missing transverse energy, and (ii) dijet. The current monojet constraint is not stronger than that from the requirement of the correct relic density and the null result by the XENON100 direct detection. We find that the dijet resonance measurements can exclude a large portion of the parameter space $(m_\\chi, m_Y)$, where the c...
Poswal, H. K.; Sharma, Surinder M.; Sikka, S. K.
2010-03-01
High-pressure behaviour of superhydrous phase B (high temperature; HT) of Mg10Si3O14(OH)4 (Shy B) is investigated with the help of density functional theory-based first-principles calculations. In addition to the lattice parameters and equation of state, we use these calculations to determine the positional parameters of atoms as a function of pressure. Our results show that the compression induced structural changes involve cooperative distortions in the full geometry of the hydrogen bonds. The bond-bending mechanism proposed by Hofmeister et al. (Vibrational spectra of dense hydrous magnesium silicates at high pressure: Importance of the hydrogen bond angle, Am. Miner. 84 (1999), pp. 454-464) for hydrogen bonds to relieve the heightened repulsion due to short H- - -H contacts is not found to be effective in Shy B. The calculated O-H bond contraction is consistent with the observed blue shift in the stretching frequency of the hydrogen bond. These results establish that one can use first-principles calculations to obtain reliable insights into the pressure-induced bonding changes of complex minerals.
Balachandran, V.; Parimala, K.
This study is a comparative analysis of FT-IR and FT-Raman spectra of vanillin (3-methoxy-4-hydroxybenzaldehyde) and isovanillin (3-hydroxy-4-methoxybenzaldehyde). The molecular structure, vibrational wavenumbers, infrared intensities, Raman scattering activities were calculated for both molecules using the B3LYP density functional theory (DFT) with the standard 6-311++G∗∗ basis set. The computed values of frequencies are scaled using multiple scaling factors to yield good coherence with the observed values. The calculated harmonic vibrational frequencies are compared with experimental FT-IR and FT-Raman spectra. The geometrical parameters and total energies of vanillin and isovanillin were obtained for all the eight conformers (a-h) from DFT/B3LYP method with 6-311++G∗∗ basis set. The computational results identified the most stable conformer of vanillin and isovanillin as in the "a" form. Non-linear properties such as electric dipole moment (μ), polarizability (α), and hyperpolarizability (β) values of the investigated molecules have been computed using B3LYP quantum chemical calculation. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules.
Numerical Modeling of Exploitation Relics and Faults Influence on Rock Mass Deformations
Wesołowski, Marek
2016-12-01
This article presents numerical modeling results of fault planes and exploitation relics influenced by the size and distribution of rock mass and surface area deformations. Numerical calculations were performed using the finite difference program FLAC. To assess the changes taking place in a rock mass, an anisotropic elasto-plastic ubiquitous joint model was used, into which the Coulomb-Mohr strength (plasticity) condition was implemented. The article takes as an example the actual exploitation of the longwall 225 area in the seam 502wg of the "Pokój" coal mine. Computer simulations have shown that it is possible to determine the influence of fault planes and exploitation relics on the size and distribution of rock mass and its surface deformation. The main factor causing additional deformations of the area surface are the abandoned workings in the seam 502wd. These abandoned workings are the activation factor that caused additional subsidences and also, due to the significant dip, they are a layer on which the rock mass slides down in the direction of the extracted space. These factors are not taken into account by the geometrical and integral theories.
The scaling relations and the fundamental plane for radio halos and relics of galaxy clusters
Yuan, Z S; Wen, Z L
2015-01-01
Diffuse radio emission in galaxy clusters is known to be related to cluster mass and cluster dynamical state. We collect the observed fluxes of radio halos, relics and mini-halos for a sample of galaxy clusters from literature, and calculate their radio powers. We then obtain the values of cluster mass or mass proxies from previous observations, and also obtain the various dynamical parameters of these galaxy clusters from optical and X-ray data. The radio power of relics, halos and mini-halos are correlated with the cluster masses or mass proxies, as found by previous authors, with the correlations concerning giant radio halos being, in general, the strongest ones. We found that the inclusion of dynamical parameters as the third dimension can significantly reduce the data scatter for the scaling relations, especially for radio halos. We therefore conclude that the substructures in X-ray images of galaxy clusters and the irregular distributions of optical brightness of member galaxies can be used to quantitat...
Alipour, Mojtaba, E-mail: malipour@shirazu.ac.ir [Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of); Mohajeri, Afshan, E-mail: amohajeri@shirazu.ac.ir [Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)
2011-08-25
Graphical abstract: The electronic properties such as the static dipole polarizability, anisotropy of the polarizability, and dipole moment of yttrium bromide, YBr (X{sup 1}{Sigma}) have been theoretically studied. Highlights: {yields} Conventional ab initio and density functional theory methods were employed to study linear optical properties of YBr molecule. {yields} Properties derivatives and their level of theory dependence were studied. {yields} Electron correlation effects and rovibrational corrections have also been discussed. - Abstract: We have employed conventional ab initio and density functional theory methods to study the electronic properties such as the mean static dipole polarizability, {alpha}-bar, anisotropy of the polarizability, {Delta}{alpha}, and dipole moment, {mu}, of yttrium bromide. The bond length dependence of properties is determined at different levels of theory and appropriate expansions around experimental internuclear distance have been presented. Moreover, the first and second geometrical derivatives for each property are quantified and their level of theory dependence has been analyzed. To study the effect of molecular rotation and vibration on the electronic properties, the rovibrational corrections have also been carried out. It is found that these corrections are less pronounced for considered properties of YBr. In all calculations, the electron correlation effects have been considered and discussed. The obtained results show that the electron correlation is more significant in the calculation of the mean and the anisotropy of dipole polarizability.
Carli, Tancredi; Cooper-Sarkar, Amanda; Gwenlan, Claire; Salam, Gavin P; Siegert, Frank; Starovoitov, Pavel; Sutton, Mark
2010-01-01
A method to facilitate the consistent inclusion of cross-section measurements based on complex final-states from HERA, TEVATRON and the LHC in proton parton density function (PDF) fits has been developed. This can be used to increase the sensitivity of LHC data to deviations from Standard Model predictions. The method stores perturbative coefficients of NLO QCD calculations of final-state observables measured in hadron colliders in look-up tables. This allows the posteriori inclusion of parton density functions (PDFs), and of the strong coupling, as well as the a posteriori variation of the renormalisation and factorisation scales in cross-section calculations. The main novelties in comparison to original work on the subject are the use of higher-order interpolation, which substantially improves the trade-off between accuracy and memory use, and a CPU and computer memory optimised way to construct and store the look-up table using modern software tools. It is demonstrated that a sufficient accuracy on the cro...
Elgammal, Karim; Hugosson, Håkan W.; Smith, Anderson D.; Råsander, Mikael; Bergqvist, Lars; Delin, Anna
2017-09-01
We present dispersion-corrected density functional calculations of water and carbon dioxide molecules adsorption on graphene residing on silica and sapphire substrates. The equilibrium positions and bonding distances for the molecules are determined. Water is found to prefer the hollow site in the center of the graphene hexagon, whereas carbon dioxide prefers sites bridging carbon-carbon bonds as well as sites directly on top of carbon atoms. The energy differences between different sites are however minute - typically just a few tenths of a millielectronvolt. Overall, the molecule-graphene bonding distances are found to be in the range 3.1-3.3 Å. The carbon dioxide binding energy to graphene is found to be almost twice that of the water binding energy (around 0.17 eV compared to around 0.09 eV). The present results compare well with previous calculations, where available. Using charge density differences, we also qualitatively illustrate the effect of the different substrates and molecules on the electronic structure of the graphene sheet.
Aarup, Lasse Rye; Nahum, Alan E; Zacharatou, Christina
2009-01-01
and tumour have unit density). The lung tissue was assigned five densities (rho(lung)): 0.01, 0.1, 0.2, 0.4 and 1g/cm(3). Four-field treatment plans were calculated with 6- and 18 MV narrow beams for each value of rho(lung). We considered the Pencil Beam Convolution (PBC(Ecl)) and the Analytical Anisotropic...... Algorithm (AAA(Ecl)) from Varian Eclipse and the Pencil Beam Convolution (PBC(OMP)) and the Collapsed Cone Convolution (CCC(OMP)) algorithms from Oncentra MasterPlan. RESULTS: When changing rho(lung) from 0.4 to 0.1g/cm(3), the MC median target dose decreased from 89.2% to 74.9% for 6 MV and from 83...... Treatment Planning System (TPS) algorithms and one Monte Carlo (MC) system (EGSnrc). We compared the performance of the algorithms in calculating the target dose for different degrees of lung inflation. The phantoms had a cubic 'body' and 'lung' and a central 2-cm diameter spherical 'tumour' (the body...
Hair, Death, and Memory: The Making of an American Relic
Abigail Heiniger
2015-08-01
Full Text Available This article traces the transformation of hairworks in America during the mid-nineteenth-century. Harriet Beecher Stowe’s novel Uncle Tom’s Cabin transformed the meaning of hair and hairworks in the American cultural imaginary by endowing Little Evangeline St. Clare’s hair with sacred, moralizing power. Likewise, after the Emancipation Proclamation was issued in 1863, President Abraham Lincoln’s hair achieved nationwide, relic-like significance. The Abraham Lincoln Papers contains six hair requests; these letters demonstrate that the cultural meaning of Lincoln’s hair resembles the fictional power of Eva’s hair in Stowe’s novel. Analyzing this phenomena of relic-like hair modifies our understanding of the unprecedented sentimental reaction to Lincoln’s assassination and particularly the fascination with seeing and approaching the president’s body.
A shock front at the radio relic of Abell 2744
Eckert, D.; Jauzac, M.; Vazza, F.; Owers, M. S.; Kneib, J.-P.; Tchernin, C.; Intema, H.; Knowles, K.
2016-09-01
Radio relics are Mpc-scale diffuse radio sources at the peripheries of galaxy clusters which are thought to trace outgoing merger shocks. We present XMM-Newton and Suzaku observations of the galaxy cluster Abell 2744 (z = 0.306), which reveal the presence of a shock front 1.5 Mpc east of the cluster core. The surface-brightness jump coincides with the position of a known radio relic. Although the surface-brightness jump indicates a weak shock with a Mach number M=1.7_{-0.3}^{+0.5}, the plasma in the post-shock region has been heated to a very high temperature (˜13 keV) by the passage of the shock wave. The low-acceleration efficiency expected from such a weak shock suggests that mildly relativistic electrons have been re-accelerated by the passage of the shock front.
Tan, Chih-Shan; Huang, Michael H
2017-07-11
Density functional theory calculations have been performed on Si (100), (110), (111), and (112) planes with tunable number of planes for evaluation of their band structures and density of states profiles. The purpose is to see whether silicon can exhibit facet-dependent properties derived from the presence of a thin surface layer having different band structures. No changes have been observed for single to multiple layers of Si (100) and (110) planes with a consistent band gap between the valence band and the conduction band. However, for 1, 2, 4, and 5 Si (111) and (112) planes, metal-like band structures were obtained with continuous density of states going from the valence band to the conduction band. For 3, 6, and more Si (111) planes, as well as 3 and 6 Si (112) planes, the same band structure as that seen for Si (100) and (110) planes has been obtained. Thus, beyond a layer thickness of five Si (111) planes at ≈1.6 nm, normal semiconductor behavior can be expected. The emergence of metal-like band structures for the Si (111) and (112) planes are related to variation in Si-Si bond length and bond distortion plus 3s and 3p orbital electron contributions in the band structure. This work predicts possession of facet-dependent electrical properties of silicon with consequences in FinFET transistor design. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Holland, Jason P; Green, Jennifer C
2010-04-15
The electronic absorption spectra of a range of copper and zinc complexes have been simulated by using time-dependent density functional theory (TD-DFT) calculations implemented in Gaussian03. In total, 41 exchange-correlation (XC) functionals including first-, second-, and third-generation (meta-generalized gradient approximation) DFT methods were compared in their ability to predict the experimental electronic absorption spectra. Both pure and hybrid DFT methods were tested and differences between restricted and unrestricted calculations were also investigated by comparison of analogous neutral zinc(II) and copper(II) complexes. TD-DFT calculated spectra were optimized with respect to the experimental electronic absorption spectra by use of a Matlab script. Direct comparison of the performance of each XC functional was achieved both qualitatively and quantitatively by comparison of optimized half-band widths, root-mean-squared errors (RMSE), energy scaling factors (epsilon(SF)), and overall quality-of-fit (Q(F)) parameters. Hybrid DFT methods were found to outperform all pure DFT functionals with B1LYP, B97-2, B97-1, X3LYP, and B98 functionals providing the highest quantitative and qualitative accuracy in both restricted and unrestricted systems. Of the functionals tested, B1LYP gave the most accurate results with both average RMSE and overall Q(F) unity (>0.990) for the copper complexes. The XC functional performance in spin-restricted TD-DFT calculations on the zinc complexes was found to be slightly worse. PBE1PBE, mPW1PW91 and B1LYP gave the most accurate results with typical RMSE and Q(F) values between 5.3 and 7.3%, and epsilon(SF) around 0.930. These studies illustrate the power of modern TD-DFT calculations for exploring excited state transitions of metal complexes.
Roemelt, Michael
2015-07-01
Spin Orbit Coupling (SOC) is introduced to molecular ab initio density matrix renormalization group (DMRG) calculations. In the presented scheme, one first approximates the electronic ground state and a number of excited states of the Born-Oppenheimer (BO) Hamiltonian with the aid of the DMRG algorithm. Owing to the spin-adaptation of the algorithm, the total spin S is a good quantum number for these states. After the non-relativistic DMRG calculation is finished, all magnetic sublevels of the calculated states are constructed explicitly, and the SOC operator is expanded in the resulting basis. To this end, spin orbit coupled energies and wavefunctions are obtained as eigenvalues and eigenfunctions of the full Hamiltonian matrix which is composed of the SOC operator matrix and the BO Hamiltonian matrix. This treatment corresponds to a quasi-degenerate perturbation theory approach and can be regarded as the molecular equivalent to atomic Russell-Saunders coupling. For the evaluation of SOC matrix elements, the full Breit-Pauli SOC Hamiltonian is approximated by the widely used spin-orbit mean field operator. This operator allows for an efficient use of the second quantized triplet replacement operators that are readily generated during the non-relativistic DMRG algorithm, together with the Wigner-Eckart theorem. With a set of spin-orbit coupled wavefunctions at hand, the molecular g-tensors are calculated following the scheme proposed by Gerloch and McMeeking. It interprets the effective molecular g-values as the slope of the energy difference between the lowest Kramers pair with respect to the strength of the applied magnetic field. Test calculations on a chemically relevant Mo complex demonstrate the capabilities of the presented method.
Re-acceleration model for the "Toothbrush" Radio Relic
Kang, Hyesung
2016-01-01
The Toothbrush radio relic associated the merging cluster 1RXS J060303.3 is presumed to be produced by relativistic electrons accelerated at merger-driven shocks. Since the shock Mach number inferred from the observed radio spectral index, $M_{radio}\\approx 2.8$, is larger than that estimated from X-ray observations, $M_{X-ray}\\lesssim 1.5$, we consider the re-acceleration model in which a weak shock of $M_s\\approx 1.2-1.5$ sweeps through the intracluster plasma with a preshock population of relativistic electrons. We find the models with a power-law momentum spectrum with the slope, $s\\approx 4.6$, and the cutoff Lorentz factor, $\\gamma_{e,c}\\approx 7-8\\times 10^4$ can reproduce reasonably well the observed profiles of radio fluxes and integrated radio spectrum of the head portion of the Toothbrush relic. This study confirms the strong connection between the ubiquitous presence of fossil relativistic plasma originated from AGNs and the shock-acceleration model of radio relics in the intracluster medium.
Re-acceleration Model for Radio Relics with Spectral Curvature
Kang, Hyesung
2016-01-01
Most of the observed features of radio gischt relics such as spectral steepening across the relic width and power-law-like integrated spectrum can be adequately explained by diffusive shock acceleration (DSA) model, in which relativistic electrons are (re-)accelerated at shock waves induced in the intracluster medium. However, Kang & Ryu (2015) showed that the steep spectral curvature in the integrated spectrum above $\\sim 2$ GHz detected in the Sausage relic in cluster CIZA J2242.8+5301 may not be interpreted by simple radiative cooling of postshock electrons. In order to understand such steepening, we here consider a model in which a spherical shock sweeps through and then exits out of a finite-size cloud with fossil relativistic electrons. The ensuing integrated radio spectrum is expected to steepen much more than predicted for aging postshock electrons, since the re-acceleration stops after the cloud-crossing time. Using DSA simulations that are intended to reproduce radio observations of the Sausage ...
Re-Acceleration Model for the "Toothbrush" Radio Relic
Kang, Hyesung
2016-06-01
The Toothbrush radio relic associated with the merging cluster 1RXS J060303.3 is presumed to be produced by relativistic electrons accelerated at merger-driven shocks. Since the shock Mach number inferred from the observed radio spectral index, M_{radio}≈ 2.8, is larger than that estimated from X-ray observations, M_{X}≲ 1.5, we consider the re-acceleration model in which a weak shock of M_s≈ 1.2-1.5 sweeps through the intracluster plasma with a preshock population of relativistic electrons. We find the models with a power-law momentum spectrum with the slope, s≈ 4.6, and the cutoff Lorentz factor, γ_{e,c}≈ 7-8× 10^4 can reproduce reasonably well the observed profiles of radio fluxes and integrated radio spectrum of the head portion of the Toothbrush relic.This study confirms the strong connection between the ubiquitous presence of fossil relativistic plasma originated from AGNs and the shock-acceleration model of radio relics in the intracluster medium.
Simultaneous Generation of WIMP Miracle-like Densities of Baryons and Dark Matter
McDonald, John
2012-09-01
The observed density of dark matter is of the magnitude expected for a thermal relic weakly-interacting massive particle (WIMP). In addition, the observed baryon density is within an order of magnitude of the dark matter density. This suggests that the baryon density is physically related to a typical thermal relic WIMP dark matter density. We present a model which simultaneously generates thermal relic WIMP-like densities for both baryons and dark matter by modifying a large initial baryon asymmetry. Production of unstable scalars carrying baryon number at the LHC would be a clear signature of the model.
Generation of WIMP Miracle-like Densities of Baryons and Dark Matter
McDonald, John
2012-01-01
The observed density of dark matter is of the magnitude expected for a thermal relic weakly-interacting massive particle (WIMP). In addition, the observed baryon density is within an order of magnitude of the dark matter density. This suggests that the baryon density is physically related to a typical thermal relic WIMP dark matter density. We present a model which simultaneously generates thermal relic WIMP-like densities for both baryons and dark matter by modifying a large initial baryon asymmetry. Production of unstable scalars carrying baryon number at the LHC would be a clear signature of the model.
Merker, L.; Weichselbaum, A.; Costi, T. A.
2012-08-01
Recent developments in the numerical renormalization group (NRG) allow the construction of the full density matrix (FDM) of quantum impurity models [see A. Weichselbaum and J. von Delft, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.99.076402 99, 076402 (2007)] by using the completeness of the eliminated states introduced by F. B. Anders and A. Schiller [F. B. Anders and A. Schiller, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.95.196801 95, 196801 (2005)]. While these developments prove particularly useful in the calculation of transient response and finite-temperature Green's functions of quantum impurity models, they may also be used to calculate thermodynamic properties. In this paper, we assess the FDM approach to thermodynamic properties by applying it to the Anderson impurity model. We compare the results for the susceptibility and specific heat to both the conventional approach within NRG and to exact Bethe ansatz results. We also point out a subtlety in the calculation of the susceptibility (in a uniform field) within the FDM approach. Finally, we show numerically that for the Anderson model, the susceptibilities in response to a local and a uniform magnetic field coincide in the wide-band limit, in accordance with the Clogston-Anderson compensation theorem.
Yost, Dillon C.; Yao, Yi; Kanai, Yosuke
2017-09-01
In ion irradiation processes, electronic stopping power describes the energy transfer rate from the irradiating ion to the target material's electrons. Due to the scarcity and significant uncertainties in experimental electronic stopping power data for materials beyond simple solids, there has been growing interest in the use of first-principles theory for calculating electronic stopping power. In recent years, advances in high-performance computing have opened the door to fully first-principles nonequilibrium simulations based on real-time time-dependent density functional theory (RT-TDDFT). While it has been demonstrated that the RT-TDDFT approach is capable of predicting electronic stopping power for a wide range of condensed matter systems, there has yet to be an exhaustive examination of the physical and numerical approximations involved and their effects on the calculated stopping power. We discuss the results of such a study for crystalline silicon with protons as irradiating ions. We examine the influences of key approximations in RT-TDDFT nonequilibrium simulations on the calculated electronic stopping power, including approximations related to basis sets, finite size effects, exchange-correlation approximation, pseudopotentials, and more. Finally, we propose a simple and efficient correction scheme to account for the contribution from core-electron excitations to the stopping power, as it was found to be significant for large proton velocities.
Zhao, Zhengji
We study the reduced density matrix method, a variational approach for electronic structure calculations based on the two-body reduced density matrix. This method minimizes the ground state energy with respect to the two-body reduced density matrix subject to some conditions which it must satisfy, known as N-representability conditions. The resulting optimization problem is a semidefinite program, a convex optimization problem for which computational methods have greatly advanced during the past decade. Two significant advances are reported in this thesis. First, we formulate the reduced density matrix method using the dual formulation of semidefinite programming instead of the previously-used primal one; this results in substantial computational savings and makes it possible to study larger systems than was done previously. Second, in addition to the previously-used P, Q and G conditions we investigate a pair of positive semidefinite conditions that has a three-index form; we call them the T1 and T2 conditions. We find that the inclusion of the T1 and T2 conditions gives a significant improvement over results previously obtained using only the P, Q and G conditions; and provides in all cases we have studied (47 molecules) more accurate results than other more familiar methods: Hartree-Fork; 2nd order Moller-Plesset method (MP2), singly and doubly substituted configuration interaction (SDCI), quadratic configuration interaction including single and double substitutions (QCISD), Brueckner doubles (with triples) (BD(T)) and coupled cluster singles and doubles with perturbational treatment of triples (CCSD(T)).
Voufack, Ariste Bolivard; Claiser, Nicolas; Lecomte, Claude; Pillet, Sébastien; Pontillon, Yves; Gillon, Béatrice; Yan, Zeyin; Gillet, Jean Michel; Marazzi, Marco; Genoni, Alessandro; Souhassou, Mohamed
2017-08-01
Joint refinement of X-ray and polarized neutron diffraction data has been carried out in order to determine charge and spin density distributions simultaneously in the nitronyl nitroxide (NN) free radical Nit(SMe)Ph. For comparison purposes, density functional theory (DFT) and complete active-space self-consistent field (CASSCF) theoretical calculations were also performed. Experimentally derived charge and spin densities show significant differences between the two NO groups of the NN function that are not observed from DFT theoretical calculations. On the contrary, CASSCF calculations exhibit the same fine details as observed in spin-resolved joint refinement and a clear asymmetry between the two NO groups.
Lehtola, Susi; Head-Gordon, Martin; Jónsson, Hannes
2016-07-12
Implentation of seminumerical stability analysis for calculations using the Perdew-Zunger self-interaction correction is described. It is shown that real-valued solutions of the Perdew-Zunger equations for gas phase atoms are unstable with respect to imaginary orbital rotations, confirming that a proper implementation of the correction requires complex-valued orbitals. The orbital density dependence of the self-interaction corrected functional is found to lead to multiple local minima in the case of the acrylic acid, H6, and benzene molecules. In the case of benzene, symmetry breaking that results in incorrect ground state geometry is found to occur, erroneously leading to alternating bond lengths in the molecule.
Johnston, Karen; Verho, Tuukka; Puska, Martti J
2010-01-01
Several dissociated and two non-dissociated adsorption structures of the phenol molecule on the Si(001)-(2 \\times 1) surface are studied using density functional theory with various exchange and correlation functionals. The relaxed structures and adsorption energies are obtained and it is found that the dissociated structures are energetically more favourable than the non-dissociated structures. However, the ground state energies alone do not determine which structure is obtained experimentally. To elucidate the situation core level shift spectra for Si 2p and C 1s states are simulated and compared with experimentally measured spectra. Several transition barriers were calculated in order to determine which adsorption structures are kinetically accessible. Based on these results we conclude that the molecule undergoes the dissociation of two hydrogen atoms on adsorption.
Electronic structure of ScN and YN:density-functional theory LDA and GW approximation calculations
Lü Tie-Yu; Huang Mei-Chun
2007-01-01
The desirable physical properties of hardness, high temperature stability, and conductivity make the early transition metal nitrides important materials for various technological applications. To learn more about the nature of these materials, the local-density approximation(LDA) and GW approximation i.e. combination of the Green function G and the screened Coulomb interaction W, have been performed. This paper investigates the bulk electronic and physical properties of early transition metal mononitrides, ScN and YN in the rocksalt structure. In this paper, the semicore electrons are regarded as valance electrons. ScN appears to be a semimetal, and YN is semiconductor with band gap of0.142 eV within the LDA, but are in fact semiconductors with indirect band gaps of 1.244 and 0.544 eV respectively, as revealed by calculations performed using GW approximation.
Roman, Tanglaw; Groß, Axel
2013-04-12
Using periodic density-functional theory calculations, we address the work-function change induced by the adsorption of chlorine and iodine on Cu(111) which are shown to change the work function in opposite ways, contrary to what one may expect for these two electron acceptors. In contrast to previous studies, we demonstrate that substrate effects play only a minor role in work-function changes brought about by halogen adsorption on metals. Instead, polarization on the adsorbate not only explains the sign of the work-function change as a contributor to a positive surface dipole moment, but it is also the decisive factor in the dependence of adsorption-induced work-function changes on the coverage of halogens on metal surfaces.
Kanai, Y; Takeuchi, N
2009-10-14
We revisit the molecular line growth mechanism of styrene on the hydrogenated Si(001) 2x1 surface. In particular, we investigate the energetics of the radical chain reaction mechanism by means of diffusion quantum Monte Carlo (QMC) and density functional theory (DFT) calculations. For the exchange correlation (XC) functional we use the non-empirical generalized-gradient approximation (GGA) and meta-GGA. We find that the QMC result also predicts the intra dimer-row growth of the molecular line over the inter dimer-row growth, supporting the conclusion based on DFT results. However, the absolute magnitudes of the adsorption and reaction energies, and the heights of the energy barriers differ considerably between the QMC and DFT with the GGA/meta-GGA XC functionals.
Meštrić, H.; Eichel, R.-A.; Kloss, T.; Dinse, K.-P.; Laubach, So.; Laubach, St.; Schmidt, P. C.; Schönau, K. A.; Knapp, M.; Ehrenberg, H.
2005-04-01
The Fe3+ center in ferroelectric PbTiO3 together with an oxygen vacancy forms a charged defect associate, oriented along the crystallographic c axis. Its microscopic structure has been analyzed in detail comparing results from a semiempirical Newman superposition model analysis based on fine-structure data and from calculations using density functional theory. Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor center. The position of the iron ion in the ferroelectric phase is found to be similar to the B site in the paraelectric phase. Partial charge compensation is locally provided by a directly coordinated oxygen vacancy. Using high-resolution synchrotron powder diffraction, it was verified that lead titanate remains tetragonal down to 12K , exhibiting a c/a ratio of 1.0721.
Rak, Zs.; Rost, C. M.; Lim, M.; Sarker, P.; Toher, C.; Curtarolo, S.; Maria, J.-P.; Brenner, D. W.
2016-09-01
Density functional theory calculations were carried out for three entropic rocksalt oxides, (Mg0.1Co0.1Ni0.1Cu0.1Zn0.1)O0.5, termed J14, and J14 + Li and J14 + Sc, to understand the role of charge neutrality and electronic states on their properties, and to probe whether simple expressions may exist that predict stability. The calculations predict that the average lattice constants of the ternary structures provide good approximations to that of the random structures. For J14, Bader charges are transferable between the binary, ternary, and random structures. For J14 + Sc and J14 + Li, average Bader charges in the entropic structures can be estimated from the ternary compositions. Addition of Sc to J14 reduces the majority of Cu, which show large displacements from ideal lattice sites, along with reduction of a few Co and Ni cations. Addition of Li to J14 reduces the lattice constant, consistent with experiment, and oxidizes some of Co as well as some of Ni and Cu. The Bader charges and spin-resolved density of states (DOS) for Co+3 in J14 + Li are very different from Co+2, while for Cu and Ni the Bader charges form continuous distributions and the two DOS are similar for the two oxidation states. Experimental detection of different oxidation states may therefore be challenging for Cu and Ni compared to Co. Based on these results, empirical stability parameters for these entropic oxides may be more complicated than those for non-oxide entropic solids.
Ammar, H Y; Eid, Kh M
2013-10-01
The interactions of nitrogen dioxide molecule (NO2) on Au atom adsorbed on the surfaces of metal oxide MgO (100) on both anionic (O2-) and defect (F(s) and F(s)(+)-centers) sites have been studied using the Density Functional Theory (DFT) in combination with embedded cluster model. The adsorption energies of NO2 molecule (N-down as well as O-down) on O(-2), F(s) and F(s)(+)-sites were considered. Full optimization for the additive materials and partial optimization for MgO substrate surfaces have been done. The formation energies were evaluated for F(s) and F(s)(+) of MgO substrate surfaces. Some parameters, the Ionization Potential (IP) and electron Affinity (eA), for defect free and defect containing surfaces have been calculated. The interaction properties of NO2 have been analyzed in terms of the adsorption energy, the electron donation (basicity), the elongation of N-O bond length and the charge distribution by using Natural Bond Orbital (NBO) analysis. The adsorption properties were examined by calculation of the Density of State (DOS). The presence of the Au atom increases the surface chemistry of the anionic O(2-)-site of MgO substrate surfaces. On the other hand, the presence of the Au atom decreases the surface chemistry of the F(s) and F(s)(+)-sites of MgO substrate surfaces. Generally, the NO2 molecule is strongly adsorbed (chemisorption) on the MgO substrate surfaces containing F(s) and F(s)(+)-centers.
Rak, Zs.; Rost, C. M.; Lim, M.; Maria, J.-P.; Brenner, D. W. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907 (United States); Sarker, P.; Toher, C.; Curtarolo, S. [Department of Mechanical Engineering and Materials Science and Center for Materials Genomics, Duke University, Durham, North Carolina 27708 (United States)
2016-09-07
Density functional theory calculations were carried out for three entropic rocksalt oxides, (Mg{sub 0.1}Co{sub 0.1}Ni{sub 0.1}Cu{sub 0.1}Zn{sub 0.1})O{sub 0.5}, termed J14, and J14 + Li and J14 + Sc, to understand the role of charge neutrality and electronic states on their properties, and to probe whether simple expressions may exist that predict stability. The calculations predict that the average lattice constants of the ternary structures provide good approximations to that of the random structures. For J14, Bader charges are transferable between the binary, ternary, and random structures. For J14 + Sc and J14 + Li, average Bader charges in the entropic structures can be estimated from the ternary compositions. Addition of Sc to J14 reduces the majority of Cu, which show large displacements from ideal lattice sites, along with reduction of a few Co and Ni cations. Addition of Li to J14 reduces the lattice constant, consistent with experiment, and oxidizes some of Co as well as some of Ni and Cu. The Bader charges and spin-resolved density of states (DOS) for Co{sup +3} in J14 + Li are very different from Co{sup +2}, while for Cu and Ni the Bader charges form continuous distributions and the two DOS are similar for the two oxidation states. Experimental detection of different oxidation states may therefore be challenging for Cu and Ni compared to Co. Based on these results, empirical stability parameters for these entropic oxides may be more complicated than those for non-oxide entropic solids.
The widest-frequency radio relic spectra: observations from 150 MHz to 30 GHz
Stroe, Andra; Rumsey, Clare; van Weeren, Reinout; Kierdorf, Maja; Donnert, Julius; Jones, Thomas W; Röttgering, Huub J A; Hoeft, Matthias; Rodriguez-Gonzalvez, Carmen; Harwood, Jeremy J; Saunders, Richard D E
2015-01-01
Radio relics are patches of diffuse synchrotron radio emission that trace shock waves. Relics are thought to form when intra-cluster medium electrons are accelerated by cluster merger induced shock waves through the diffusive shock acceleration mechanism. In this paper, we present observations spanning 150 MHz to 30 GHz of the `Sausage' and `Toothbrush' relics from the Giant Metrewave and Westerbork telescopes, the Karl G. Jansky Very Large Array, the Effelsberg telescope, the Arcminute Microkelvin Imager and Combined Array for Research in Millimeter-wave Astronomy. We detect both relics at 30 GHz, where the previous highest frequency detection was at 16 GHz. The integrated radio spectra of both sources clearly steepen above 2 GHz, at the >6$\\sigma$ significance level, supports the spectral steepening previously found in the `Sausage' and the Abell 2256 relic. Our results challenge the widely adopted simple formation mechanism of radio relics and suggest more complicated models have to be developed that, for ...
Ding, Y. H.; Hu, S. X.
2017-06-01
Beryllium has been considered a superior ablator material for inertial confinement fusion (ICF) target designs. An accurate equation-of-state (EOS) of beryllium under extreme conditions is essential for reliable ICF designs. Based on density-functional theory (DFT) calculations, we have established a wide-range beryllium EOS table of density ρ = 0.001 to 500 g/cm3 and temperature T = 2000 to 108 K. Our first-principle equation-of-state (FPEOS) table is in better agreement with the widely used SESAME EOS table (SESAME 2023) than the average-atom INFERNO and Purgatorio models. For the principal Hugoniot, our FPEOS prediction shows ˜10% stiffer than the last two models in the maximum compression. Although the existing experimental data (only up to 17 Mbar) cannot distinguish these EOS models, we anticipate that high-pressure experiments at the maximum compression region should differentiate our FPEOS from INFERNO and Purgatorio models. Comparisons between FPEOS and SESAME EOS for off-Hugoniot conditions show that the differences in the pressure and internal energy are within ˜20%. By implementing the FPEOS table into the 1-D radiation-hydrodynamic code LILAC, we studied the EOS effects on beryllium-shell-target implosions. The FPEOS simulation predicts higher neutron yield (˜15%) compared to the simulation using the SESAME 2023 EOS table.
A guide for calculation of spot size to determine power density for free fiber irradiation of tissue
Tate, Lloyd P., Jr.; Blikslager, Anthony T.
2005-04-01
Transendoscopic laser treatment for upper airway disorders has been performed in the horse for over twenty years. Endoscopic laser transmission utilizing flexible fiber optics is limited to certain discreet wavelengths. Initially, the laser of choice was the Nd: YAG laser (1064nm), but in the early 1990's, diode lasers (810nm, 980nm) were introduced to veterinary medicine and are currently used in private practice and universities. Precise application of laser irradiation is dependent on the user knowing the laser's output as well as the amount of energy that is delivered to tissue. Knowledge of dosimetry is important to the veterinarian for keeping accurate medical records by being able to describe very specific treatment regimes. The applied energy is best described as power density or energy density. Calculation of this energy is dependent upon the users ability to determine the laser's spot size when irradiating tissue in a non-contact mode. The charts derived from this study provide the veterinarian the ability to estimate spot size for a number of commonly used lasers with the fiber positioned at various distances from the target.
Shi, Haifeng; Lan, Benyue; Zhang, Chengliang; Ye, Enjia; Nie, Yanguang; Bian, Baoan
2016-10-01
The influences of a series of anion doping on the electronic structures of sodium niobate (NaNbO3) have been systematically investigated by density functional theory (DFT) calculations with the hybrid B3LYP functional. As for B(C,P)-doped NaNbO3, the isolated B 2p (C 2p, P 3p) states were formed above the valence band maximum (VBM) of NaNbO3, which were too weak to mix with O 2p states and thus produced band gap narrowing. While the band gap of NaNbO3 was slightly narrowed after F doping. As for S-doped NaNbO3, the S 3p states mixed with O 2p states well and thus reduced the band gap energy. According to the calculation results, we tentatively put forward that S doping would be appropriate for single anion doping NaNbO3, while the B(C,P) elements would be suitable candidates for co-doping NaNbO3.
Lu, Deyu; Li, Yan; Rocca, Dario; Viet Nguyen, H.; Gygi, Francois; Galli, Giulia
2010-03-01
A recently developed technique to diagonalize iteratively dielectric matrices [1], is used to carry out efficient, ab-initio calculations of dispersion interactions, and excited state properties of nanostructures. In particular, we present results for the binding energies of weakly bonded molecular crystals [2], obtained at the EXX/RPA level of theory, and for absorption spectra of semiconducting clusters, obtained by an iterative solution of the Bethe-Salpeter equations [3]. We show that the ability to obtain the eigenmodes of dielectric matrices from Density Functional perturbation theory, without computing single particle excited states, greatly improves the efficiency of both EXX/RPA and many body perturbation theory [3,4] calculations and opens the way to large scale computations. [1] H. Wilson, F. Gygi and G. Galli, Phys. Rev. B , 78, 113303, 2008; and H. Wilson, D. Lu, F. Gygi and G. Galli, Phys. Rev. B, 79, 245106, 2009. [2] D. Lu, Y. Li, D. Rocca and G. Galli, Phys. Rev. Lett, 102, 206411, 2009; and Y. Li, D. Lu, V. Nguyen and G. Galli, J. Phys. Chem. C (submitted) [3] D. Rocca, D. Lu and G. Galli, submitted. [4] D. Lu, F. Gygi and G. Galli, Phys. Rev. Lett. 100, 147601, 2008. Work was funded by DOE/Scidac DE-FC02-06ER25794 and DOE/BES DE-FG02-06ER46262.
Greenebaum, Ben
2015-12-01
The prime goal of this work was to model essentially steady (DC) fields from electrodes, implanted in several ways, which have been suggested as possible means to encourage nerve fiber regrowth in spinal cord injuries. A simplified model of the human spinal cord in the lumbar region and the SEMCAD-X computer program were used to calculate electric field and current density patterns from electrodes outside vertebrae and those inserted extradurally within the spinal canal. DC electric fields guide nerve growth in developing organisms and in vitro. They also have been shown to encourage healing of injured peripheral nerves, and application of a longitudinal field has been used in attempts to bridge spinal cord injuries. When calculated results are scaled to the experimental level used in the literature, all modeled electrodes produced fields in the spinal cord below fields needed in the literature for stimulation of spinal as well as peripheral nerve growth in vitro, in dogs, and in a published clinical human trial. The highly-conducting cerebrospinal fluid appeared to provide effective shielding; there was also a very high degree of polarization at electrodes. © 2015 Wiley Periodicals, Inc.
Adsorption of CO on the LaCoO3 (0 0 1) surface by density functional theory calculation
Sun, Lihui; Li, Guoping; Chen, Wen; Luo, Fenghua; Hu, Jifan; Qin, Hongwei
2014-08-01
The adsorption of CO molecule on the LaCoO3 (0 0 1) surface has been investigated using density functional theory calculation. Calculation results show that the most suitable configuration is Cosbnd CO structure for the CoO-terminated LaCoO3 (0 0 1) surface. In the adsorption process electrons transfer from CO molecule to the surface. The Cosbnd C bond is mainly from the hybrid between the CO and Co-d orbital. When CO molecule adsorption on the LaO-terminated LaCoO3 (0 0 1) surface, the most suitable configuration is the Osbnd CO structure and the electrons transfer from the surface to the CO molecule in the adsorption process. The bond between the C atom and the surface O atom is mainly from the hybrid between the C-2p and O-2p orbital. The LaCoO3 could be used as the gas sensing material to detect CO gas.
Guo, Xiaojing; Huang, Liangliang; Li, Cheng; Hu, Jiangtao; Wu, Guozhong; Huai, Ping
2015-06-14
The polystyrene-supported primary amine -CH2NH2 has shown an at least 3-fold increase in uranyl capacity compared to a diamidoxime ligand on a polystyrene support. This study aims to understand the coordination of substitution complexes from UO2(CO3)3(4-) and amines using density functional theory calculations. Four kinds of amines (diethylamine (DEA), ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA)) were selected because they belong to different classes and have different chain lengths. The geometrical structures, electronic structures and the thermodynamic stabilities of various substitution complexes, as well as the trends in their calculated properties were investigated at equilibrium. In these optimized complexes, DEA groups bind to uranyl as monodentate ligands; EDA groups serve as monodentate and bidentate ligands; DETA groups act as monodentate and tridentate ligands; while TETA groups serve as monodentate, bidentate and tridentate ligands. The thermodynamic analysis confirmed that the primary amines coordinate to uranyl more strongly than does the secondary amine. The stabilities of substitution complexes with primary amines were calculated to decrease with increasing chain length of the amine, except for UO2(L2)(2+). Of the complexes analyzed, only UO2L(CO3)2(2-) (L = EDA and DETA) and UO2L2CO3 (L = EDA) were predicted to form from the substitution reactions with UO2(CO3)3(4-) and protonated amines as reactants in aqueous solution. Amines were calculated to be comparable to, or sometimes weaker than, amidoximate in replacing CO3(2-) in UO2(CO3)3(4-) to coordinate to uranium. Therefore, the coordination mechanism, in which amines replace carbonates to bind to uranyl, is not primarily responsible for the experimentally observed 3-fold or greater increase in uranyl capacity of primary amines compared to a diamidoxime ligand. Based on the results of our calculations, we believe that the cation exchange mechanism, in which the
Hybrid density functional calculations of the defect properties of ZnO:Rh and ZnO:Ir
Muñoz Ramo, David, E-mail: dm586@cam.ac.uk; Bristowe, Paul D., E-mail: pdb1000@cam.ac.uk
2014-03-31
We report density functional calculations of the atomic and electronic structure of the spinel phases ZnRh{sub 2}O{sub 4} and ZnIr{sub 2}O{sub 4} as well as crystalline ZnO lightly doped (1 at.%) with Rh and Ir ions using the B3LYP hybrid functional. Calculations for the spinels show band gaps (∼ 3 eV) and lattice parameters (∼ 2% difference) in reasonable agreement with experimental data. Incorporation of the transition metals into ZnO induces local distortions in the lattice and the appearance of metal d levels in the low gap region and near the conduction band minimum, with a d–d splitting of about 2 eV, which reduces the effective transparency of the material. Addition of a hole to the simulation cell of both spinels and doped ZnO leads to charge localization in the neighbourhood of Rh/Ir accompanied by local lattice deformations to form a small polaron which may lead to low hole mobility. We calculate polaron diffusion barriers in the spinels and obtain values around 0.02–0.03 eV. These very low barrier energies suggest that at high Rh/Ir concentrations polaron hopping is not going to be detected at room temperature. - Highlights: • Rh/Ir incorporation into ZnO at low doping induces local distortions in the lattice. • Localized levels appear in the gap of ZnO:Rh/ZnO:Ir near band edges. • Hole trapping is found in ZnO:Rh/ZnO:Ir and in the ZnRh{sub 2}O{sub 4}/ZnIr{sub 2}O{sub 4} spinels. • Hole diffusion barriers in the spinels are very small.
Solano Espinoza, Eduardo A; Vallejo Narváez, Wilmer E
2010-07-01
The potential energy profiles for the fragmentations that lead to [C(5)H(5)O](+) and [C(4)H(6)](+*) ions from the molecular ions [C(5)H(6)O](+*) of E-2,4-pentadienal were obtained from calculations at the UB3LYP/6-311G + + (3df,3pd)//UB3LYP/6-31G(d,p) level of theory. Kinetic barriers and harmonic frequencies obtained by the density functional method were then employed in Rice-Ramsperger-Kassel-Marcus calculations of individual rate coefficients for a large number of reaction steps. The pre-equilibrium and rate-controlling step approximations were applied to different regions of the complex potential energy surface, allowing the overall rate of decomposition to be calculated and discriminated between three rival pathways: C-H bond cleavage, decarbonylation and cyclization. These processes should have to compete for an equilibrated mixture of four conformers of the E-2,4-pentadienal ions. The direct dissociation, however, can only become important in the high-energy regime. In contrast, loss of CO and cyclization are observable processes in the metastable kinetic window. The former involves a slow 1,2-hydrogen shift from the carbonyl group that is immediately followed by the formation of an ion-neutral complex which, in turn, decomposes rapidly to the s-trans-1,3-butadiene ion [C(4)H(6)](+*). The predominating metastable channel is the second one, that is, a multi-step ring closure which starts with a rate-limiting cis-trans isomerization. This process yields a mixture of interconverting pyran ions that dissociates to the pyrylium ions [C(5)H(5)O](+). These results can be used to rationalize the CID mass spectrum of E-2,4-pentadienal in a low-energy regime.
Detecting Very-High-Frequency Relic Gravitational Waves by a Waveguide
Ming-Lei Tong; Yang Zhang
2008-01-01
The polarization vector (PV) of an electromagnetic wave (EW) will experience a rotation in a region of spacetime perturbed by gravitational waves (GWs). Based on this consideration, Cruise's group has built an annular waveguide to detect GWs. We give detailed calculations of the rotations of polarization vector of an EW caused by incident GWs from various directions and in various polarization states, and then analyze the accumulative effects on the polarization vector when the EW passes n cycles along the annular waveguide. We reexamine the feasibility and limitation of this method to detect GWs of high frequency around 100 MHz, in particular the relic gravitational waves (RGWs). By comparing the spectrum of RGWs in the accelerating universe with the detector sensitivity of the current waveguide, it is found that the amplitude of the RGWs is too low to be detected by the waveguide detectors currently operating. Possible ways of improvements on detection are suggested.
Initial Condition of Relic Gravitational Waves Constrained by LIGO S6 and Multiple Interferometers
Chen, Jie-Wen; Zhao, Wen; Tong, Ming-Lei
2014-01-01
The relic gravitational wave (RGW) generated during the inflation depends on the initial condition via the amplitude, the spectral index $n_t$ and the running index $\\alpha_t$. CMB observations so far have only constrained the tensor-scalar ratio $r$, but not $n_t$ nor $\\alpha_t$. Complementary to this, the ground-based interferometric detectors working at $\\sim 10^2$Hz are able to constrain the spectral indices that influence the spectrum sensitively at high frequencies. In this work we give a proper normalization of the analytical spectrum at the low frequency end, yielding a modification by a factor of $\\sim 1/50$ to the previous treatment. We calculate the signal-noise ratios (SNR) for various ($n_t,\\alpha_t$) at fixed $r=0.2$ by S6 of LIGO H-L, and obtain the observational upper limit on the running index $\\alpha_t0.01364$.
Another Shock for the Bullet Cluster, and the Source of Seed Electrons for Radio Relics
Shimwell, Timothy W,; Markevitch, Maxim; Brown, Shea; Feretti, Luigina; Gaensler, B. M.; Johnston-Hollitt, M.; Lage, Craig; Srinivasan, Raghav
2015-01-01
With Australia Telescope Compact Array observations, we detect a highly elongated Mpc-scale diffuse radio source on the eastern periphery of the Bullet cluster 1E 0657-55.8, which we argue has the positional, spectral and polarimetric characteristics of a radio relic. This powerful relic (2:30:11025 WHz(exp -1) consists of a bright northern bulb and a faint linear tail. The bulb emits 94% of the observed radio flux and has the highest surface brightness of any known relic. Exactly coincident with the linear tail we find a sharp X-ray surface brightness edge in the deep Chandra image of the cluster - a signature of a shock front in the hot intracluster medium (ICM), located on the opposite side of the cluster to the famous bow shock. This new example of an X-ray shock coincident with a relic further supports the hypothesis that shocks in the outer regions of clusters can form relics via diffusive shock (re- )acceleration. Intriguingly, our new relic suggests that seed electrons for reacceleration are coming from a local remnant of a radio galaxy, which we are lucky to catch before its complete disruption. If this scenario, in which a relic forms when a shock crosses a well-defined region of the ICM polluted with aged relativistic plasma - as opposed to the usual assumption that seeds are uniformly mixed in the ICM - is also the case for other relics, this may explain a number of peculiar properties of peripheral relics.
Linker, Gerrit-Jan; Loosdrecht , van Paul H.M.; van Duijnen, Piet Th.; Broer, Ria
2015-01-01
The insulating and conducting phases of (EDO-TTF)(2)PF6 were studied by all electron, periodic Hartre-Fock and hybrid density functional calculations. Electronic properties, such as the electronic band structure, the density of states and the Fermi surface are discussed in relation to the metal-insu
Relic keV sterile neutrinos and reionization.
Biermann, Peter L; Kusenko, Alexander
2006-03-10
A sterile neutrino with a mass of several keV can account for cosmological dark matter, as well as explain the observed velocities of pulsars. We show that x rays produced by the decays of these relic sterile neutrinos can boost the production of molecular hydrogen, which can speed up the cooling of gas and the early star formation, which can, in turn, lead to a reionization of the Universe at a high enough redshift to be consistent with the Wilkinson Microwave Anisotropy Probe results.
Robust Signatures of the Relic Neutrinos in CMB
Bashinsky, S V
2004-01-01
When the perturbations forming the acoustic peaks of the cosmic microwave background (CMB) reentered the horizon and interacted gravitationally with all the matter, neutrinos presumably comprised 41% of the universe energy. CMB experiments have reached a capacity to probe this background of relic neutrinos. I review the neutrino imprints on CMB anisotropy and polarization at the onset of the acoustic oscillations. The discussion addresses the underlying physics, robustness or degeneracy of the imprints with changes of free cosmological parameters, and non-minimal models for the unseen radiation sector with detectable signatures in CMB.
Supernova Relic Neutrino Search at Super-Kamiokande
Bays, K; Abe, K; Hayato, Y; Iyogi, K; Kameda, J; Koshio, Y; Marti, L; Miura, M; Moriyama, S; Nakahata, M; Nakayama, S; Obayashi, Y; Sekiya, H; Shiozawa, M; Suzuki, Y; Takeda, A; Takenaga, Y; Ueno, K; Kajita, K Ueshima S Yamada T Yokozawa H Kaji T; Kaneyuki, K; McLachlan, T; Okumura, K; Pik, L K; Martens, K; Vagins, M; Labarga, L; Kearns, E; Litos, M; Raaf, J L; Stone, J L; Sulak, L R; Kropp, W R; Mine, S; Regis, C; Renshaw, A; Smy, M B; Sobel, H W; Ganezer, K S; Hill, J; Keig, W E; Cho, S; Jang, J S; Kim, J Y; Lim, I T; Albert, J; Scholberg, K; Walter, C W; Wendell, R; Wongjirad, T; Ishizuka, T; Tasaka, S; Learned, J G; Matsuno, S; Smith, S; Hasegawa, T; Ishida, T; Ishii, T; Kobayashi, T; Nakadaira, T; Nakamura, K; Nishikawa, K; Oyama, Y; Sakashita, K; Sekiguchi, T; Tsukamoto, T; Suzuki, A T; Takeuchi, Y; Ikeda, M; Matsuoka, K; Minamino, A; Murakami, A; Nakaya, T; Fukuda, Y; Itow, Y; Mitsuka, G; Miyake, M; Tanaka, T; Hignight, J; Imber, J; Jung, C K; Taylor, I; Yanagisawa, C; Kibayashi, A; Ishino, H; Mino, S; Sakuda, M; Mori, T; Toyota, H; Kuno, Y; Kim, S B; Yang, B S; Okazawa, H; Choi, Y; Nishijima, K; Koshiba, M; Totsuka, Y; Yokoyama, M; Heng, Y; Chen, S; Zhang, H; Yang, Z; Mijakowski, P; Connolly, K; Dziomba, M; Wilkes, R J
2011-01-01
A new Super-Kamiokande (SK) search for Supernova Relic Neutrinos (SRNs) was conducted using 2853 live days of data. Sensitivity is now greatly improved compared to the 2003 SK result, which placed a flux limit near many theoretical predictions. This more detailed analysis includes a variety of improvements such as increased efficiency, a lower energy threshold, and an expanded data set. New combined upper limits on SRN flux are between 2.8 and 3.0 nu_e cm^-2 s^-1 > 16 MeV total positron energy (17.3 MeV E_nu).
Investigation of laser cleaning on bronze cultural relics
Ling, Xiulan; Wang, Gao; Zhang, Chen
2016-05-01
The effects of laser cleaning on the corrosion layers of bronze cultural relics were studied using a pulsed fiber laser. The laser cleaning threshold value of the corrosion layers was obtained. It was found that the corrosion layer was removed successfully by employing a laser fluence value of 0.32 J cm-2 and scanning for three times. To obtain experimental evidence, laser con-focal scanning microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), laser induced breakdown spectroscopy (LIBS) and laser Raman spectroscopy were employed to investigate the cleaning efficiency of corrosion layers on specimens.
A Search for supernova relic neutrinos at Super-Kamiokande
Iida, Takashi; Bays, Kirk, E-mail: iida@suketto.icrr.u-tokyo.ac.j [ICRR, University of Tokyo, Mozumi, Hida, Gifu (Japan)
2010-01-01
Supernova relic neutrinos (SRN) are the diffuse supernova neutrino background from all past supernovae. No experiment has succeeded in detecting SRN yet. Currently, the Super-Kamiokande experiment has the world's best flux upper limit of 1.2 {nu}-bar {sub e}/cm{sup 2}/sec for E{sub v} < 19.3 MeV. We have worked to improve this value by improving the data analysis. We have achieved better reduction efficiency and lowered the analysis energy threshold by developing a new spallation cut as well as optimizing other cuts.
Todorova, Teodora; Alexiev, Valentin; Weber, Thomas
2006-01-01
Hydrogen activation on the (100) surface of MoS[2] structures was investigated by means of density functional theory calculations. Linear and quadratic synchronous transit methods with a conjugate gradient refinement of the saddle point were used to localize transition states. The calculations include heterolytic and homolytic dissociation of…
Parsafar, G. A.; Shokouhi, M.
properties of the fluids at the zero density limit, including viscosity, thermal conductivity, and self-diffusion coefficients, are calculated using the same values of the potential parameters. Maximum percentage deviation of transport properties at the zero density limit is about 3% for viscosity (except for Ar, with 5%), about 2.5% for thermal conductivity (except for N2 and Ar, at 8 and 5%, respectively), and about 8% for the self-diffusion coefficient. In comparison with experimental data, the modified potential model gives more accurate results than those obtained from the hard-core and modified hard-core potential models, especially at high temperatures.
Brandenburg, Jan Gerit; Alessio, Maristella; Civalleri, Bartolomeo; Peintinger, Michael F; Bredow, Thomas; Grimme, Stefan
2013-09-26
We extend the previously developed geometrical correction for the inter- and intramolecular basis set superposition error (gCP) to periodic density functional theory (DFT) calculations. We report gCP results compared to those from the standard Boys-Bernardi counterpoise correction scheme and large basis set calculations. The applicability of the method to molecular crystals as the main target is tested for the benchmark set X23. It consists of 23 noncovalently bound crystals as introduced by Johnson et al. (J. Chem. Phys. 2012, 137, 054103) and refined by Tkatchenko et al. (J. Chem. Phys. 2013, 139, 024705). In order to accurately describe long-range electron correlation effects, we use the standard atom-pairwise dispersion correction scheme DFT-D3. We show that a combination of DFT energies with small atom-centered basis sets, the D3 dispersion correction, and the gCP correction can accurately describe van der Waals and hydrogen-bonded crystals. Mean absolute deviations of the X23 sublimation energies can be reduced by more than 70% and 80% for the standard functionals PBE and B3LYP, respectively, to small residual mean absolute deviations of about 2 kcal/mol (corresponding to 13% of the average sublimation energy). As a further test, we compute the interlayer interaction of graphite for varying distances and obtain a good equilibrium distance and interaction energy of 6.75 Å and -43.0 meV/atom at the PBE-D3-gCP/SVP level. We fit the gCP scheme for a recently developed pob-TZVP solid-state basis set and obtain reasonable results for the X23 benchmark set and the potential energy curve for water adsorption on a nickel (110) surface.
Neese, Frank
2007-10-28
The zero-field splitting (ZFS) (expressed in terms of the D tensor) is the leading spin-Hamiltonian parameter for systems with a ground state spin S>12. To first order in perturbation theory, the ZFS arises from the direct spin-spin dipole-dipole interaction. To second order, contributions arise from spin-orbit coupling (SOC). The latter contributions are difficult to treat since the SOC mixes states of different multiplicities. This is an aspect of dominant importance for the correct prediction of the D tensor. In this work, the theory of the D tensor is discussed from the point of view of analytic derivative theory. Starting from a general earlier perturbation treatment [F. Neese and E. I. Soloman, Inorg. Chem. 37, 6568 (1998)], straightforward response equations are derived that are readily transferred to the self-consistent field (SCF) Hartree-Fock (HF) or density functional theory (DFT) framework. The main additional effort in such calculations arises from the solution of nine sets of nonstandard coupled-perturbed SCF equations. These equations have been implemented together with the spin-orbit mean-field representation of the SOC operator and a mean-field treatment of the direct spin-spin interaction into the ORCA electronic structure program. A series of test calculations on diatomic molecules with accurately known zero-field splittings shows that the new approach corrects most of the shortcomings of previous DFT based methods and, on average, leads to predictions within 10% of the experimental values. The slope of the correlation line is essentially unity for the B3LYP and BLYP functionals compared to approximately 0.5 in previous treatments.
Lai, S. K.; Peng, W. P.; Wang, G. F.
2001-04-01
A realistic statistical-mechanics model is applied to describe the repulsive interaction between charged colloids. The latter, in combination with the long-range van der Waals attraction simulated under excess salt environment, gives rise to a total intercolloidal particle potential showing a clear second potential minimum. Differing from the usual Derjaguin-Landau-Verwey-Overbeek (DLVO) model, the present model is valid at any finite concentration of colloids and is thus an appropriate model for investigating the low- and high-density liquid phase transition. Employing this two-body colloid-colloid potential and in conjunction with the Weeks-Chandler-Andersen [J. D. Weeks, D. Chandler, and H. C. Andersen, J. Chem. Phys. 54, 5237 (1971)] thermodynamic perturbation theory, we derive analytical expressions for the pressure, chemical potential, and related thermodynamic functions. These thermodynamic quantities were used to calculate the phase diagrams of charged colloidal dispersions in terms of the critical parameters: temperature, volume fraction, and electrolyte concentration parameter kD. Compared with the DLVO model, we find the areas enclosed within the spinodal decomposition and also the liquid-liquid coexistence curves broader in the present model for an excess salt condition κ=kDσ0300, the disparities between the two models reduce. The same thermodynamic perturbation theory has been employed to study also the weak reversible coagulation whose physical origin is attributed to the presence of the second potential minimum. We examine various colloidal parameters that affect the structure of the latter and deduce from our analysis the conditions of colloidal stability. In comparison with the measured flocculation data for a binary mixture of polystyrene lattices and water, we find that our calculated results are generally reasonable, thus lending great credence to the presently used model.
Kumar, Chandan; Kjærgaard, Thomas; Helgaker, Trygve; Fliegl, Heike
2016-12-21
An atomic orbital density matrix based response formulation of the nuclei-selected approach of Beer, Kussmann, and Ochsenfeld [J. Chem. Phys. 134, 074102 (2011)] to calculate nuclear magnetic resonance (NMR) shielding tensors has been developed and implemented into LSDalton allowing for a simultaneous solution of the response equations, which significantly improves the performance. The response formulation to calculate nuclei-selected NMR shielding tensors can be used together with the density-fitting approximation that allows efficient calculation of Coulomb integrals. It is shown that using density-fitting does not lead to a significant loss in accuracy for both the nuclei-selected and the conventional ways to calculate NMR shielding constants and should thus be used for applications with LSDalton.
Re-Acceleration Model for the "Sausage" Radio Relic
Kang, Hyesung
2016-08-01
The Sausage radio relic is the arc-like radio structure in the cluster CIZA J2242.8+5301, whose observed properties can be best understood by synchrotron emission from relativistic electrons accelerated at a merger-driven shock.However, there remain a few puzzles that cannot be explained by the shock acceleration model with only in-situ injection. In particular, the Mach number inferred from the observed radio spectral index, M_{radio}≈ 4.6, while the Mach number estimated from X-ray observations, M_{X-ray}≈ 2.7. In an attempt to resolve such a discrepancy, here we consider the re-acceleration model in which a shock of M_s≈ 3 sweeps through the intracluster gas with a pre-existing population of relativistic electrons. We find that observed brightness profiles at multi frequencies provide strong constraints on the spectral shape of pre-existing electrons. The models with a power-law momentum spectrum with the slope, s≈ 4.1, and the cutoff Lorentz factor, γ_{e,c}≈ 3-5× 10^4, can reproduce reasonably well the observed spatial profiles of radio fluxes and integrated radio spectrum of the Sausage relic.The possible origins of such relativistic electrons in the intracluster medium remain to be investigated further.
Yingfeng Li
2013-05-01
Full Text Available The ways in which carbon atoms coalesce over the steps on copper (111 surface are ascertained by density functional theory (DFT calculations in the context of chemical vapor deposition (CVD growth of graphene. Two strategies, (1 by putting carbon atoms on and under the steps separately and (2 by importing additional carbon atoms between the ones separated by the steps, have been attempted to investigate if an over-step coalescence of carbon atoms could take place. Based on analyses about the optimized configurations and adsorption energies of carbon atoms nearby the steps, as well as the energy evolution curve of the system throughout the geometry optimizations process, we determined the main way in which graphene grows over the steps continuously: the carbon atoms, adsorbed additionally on the locations between the already existing ones which are separated by the steps, link them (these carbon atoms separated by the steps together. The direct over-step coalescence of the carbon atoms separated by the steps is very difficult, although the energy barrier preventing their coalescence can be weakened by importing carbon atoms on and under the steps gradually. Our results imply potential applications in directing the fabrication of graphene with particular structure by controlling the surface topography of copper substrate.
Elliott, S. D.; Dey, G.; Maimaiti, Y.
2017-02-01
Reaction cycles for the atomic layer deposition (ALD) of metals are presented, based on the incomplete data that exist about their chemical mechanisms, particularly from density functional theory (DFT) calculations. ALD requires self-limiting adsorption of each precursor, which results from exhaustion of adsorbates from previous ALD pulses and possibly from inactivation of the substrate through adsorption itself. Where the latter reaction does not take place, an "abbreviated cycle" still gives self-limiting ALD, but at a much reduced rate of deposition. Here, for example, ALD growth rates are estimated for abbreviated cycles in H2-based ALD of metals. A wide variety of other processes for the ALD of metals are also outlined and then classified according to which a reagent supplies electrons for reduction of the metal. Detailed results on computing the mechanism of copper ALD by transmetallation are summarized and shown to be consistent with experimental growth rates. Potential routes to the ALD of other transition metals by using complexes of non-innocent diazadienyl ligands as metal sources are also evaluated using DFT.
Elliott, S D; Dey, G; Maimaiti, Y
2017-02-07
Reaction cycles for the atomic layer deposition (ALD) of metals are presented, based on the incomplete data that exist about their chemical mechanisms, particularly from density functional theory (DFT) calculations. ALD requires self-limiting adsorption of each precursor, which results from exhaustion of adsorbates from previous ALD pulses and possibly from inactivation of the substrate through adsorption itself. Where the latter reaction does not take place, an "abbreviated cycle" still gives self-limiting ALD, but at a much reduced rate of deposition. Here, for example, ALD growth rates are estimated for abbreviated cycles in H2-based ALD of metals. A wide variety of other processes for the ALD of metals are also outlined and then classified according to which a reagent supplies electrons for reduction of the metal. Detailed results on computing the mechanism of copper ALD by transmetallation are summarized and shown to be consistent with experimental growth rates. Potential routes to the ALD of other transition metals by using complexes of non-innocent diazadienyl ligands as metal sources are also evaluated using DFT.
Jain, Anubhav
2017-04-01
Density functional theory (DFT) simulations solve for the electronic structure of materials starting from the Schrödinger equation. Many case studies have now demonstrated that researchers can often use DFT to design new compounds in the computer (e.g., for batteries, catalysts, and hydrogen storage) before synthesis and characterization in the lab. In this talk, I will focus on how DFT calculations can be executed on large supercomputing resources in order to generate very large data sets on new materials for functional applications. First, I will briefly describe the Materials Project, an effort at LBNL that has virtually characterized over 60,000 materials using DFT and has shared the results with over 17,000 registered users. Next, I will talk about how such data can help discover new materials, describing how preliminary computational screening led to the identification and confirmation of a new family of bulk AMX2 thermoelectric compounds with measured zT reaching 0.8. I will outline future plans for how such data-driven methods can be used to better understand the factors that control thermoelectric behavior, e.g., for the rational design of electronic band structures, in ways that are different from conventional approaches.
Xu, Jie; Wang, Lei; Liang, Guijie; Bai, Zikui; Wang, Luoxin; Xu, Weilin; Shen, Xiaolin
2011-01-01
The molecular structures and absorption spectra of triphenylamine dyes containing variable thiophene units as the spacers (TPA1-TPA3) were investigated by density functional theory (DFT) and time-dependent DFT. The calculated results indicate that the strong conjugation is formed in the dyes and the length of conjugate bridge increases gradually with the increased thiophene spacers. The interfacial charge transfer between the TiO2 electrode and TPA1-TPA3 are electron injection processes from the excited dyes to the semiconductor conduction band. The simulated absorption bands are assigned to π→π* transitions, which exhibit appreciable red-shift with respect to the experimental bands due to the lack of direct solute-solvent interaction and the inherent approximations in TD-DFT. The effect of thiophene spacers on the molecular structures, absorption spectra and photovoltaic performance were comparatively discussed and points out that the choice of appropriate conjugate bridge is very important for the design of new dyes with improved performance.
Rudin, Sven P.; Johnson, David C.
2015-04-01
Among composite materials that layer constituent substances of nanoscale thicknesses, [(SnSe) 1 +y]m(VSe2)n emerges as an example where the constituents retain incommensurate lattice structures. Perpendicular to the stacking direction, the system exhibits random translations and random rotations on average, i.e., turbostratic disorder, with local regions showing twelvefold diffraction patterns. Earlier theoretical work on these structures showed that combining density functional theory with an empirical treatment of the van der Waals interaction gave structural parameters in good agreement with experiment, but no attempt was made to examine the relative orientations. Here we approximate the extended system with one extended constituent and one finite constituent, which allows the treatment of all relative orientations on equal footing. The calculations show how the twelvefold periodicity follows from how the ions of the SnSe layer lock in with favored positions relative to the VSe2 layer, and the associated energy scale supports arguments for the overall turbostratic disorder. The success of this approximation in describing the structural parameters of the extended [(SnSe) 1 +y]m(VSe2)n system encourages its use for other properties and for other similar systems with other chemistries.
Xu, Xi-Ling; Deng, Xiao-Jiao; Xu, Hong-Guang; Zheng, Wei-Jun
2015-12-14
CnSm(-) (n = 2-7; m = 1, 2) clusters were investigated by using photoelectron spectroscopy combined with density functional theory calculations. We found that the vertical detachment energies of both CnS(-) and CnS2(-) (n = 2-7) clusters exhibit a strong odd-even alternation with an increasing number of carbon atoms: the VDEs of even-n clusters are higher than those of adjacent odd-n clusters. The most stable structures of the anionic and neutral CnS (n = 2-7) clusters are linear with the S atom locating at one end of the carbon chain except that the structure of C3S(-) is slightly bent. The ground state isomers of the anionic and neutral CnS2 (n = 2-7) clusters are all linear structures with two S atoms locating at two ends of the carbon chain. The electron affinities of the neutral CnS (n = 2, 4-7) and CnS2 (n = 2-7) clusters are determined based on the experimental adiabatic detachment energies of the corresponding anion species, because the most stable structures of the neutral clusters are similar to those of the corresponding anions.
Wu, D.; He, X. T.; Yu, W.; Fritzsche, S.
2017-02-01
A physical model based on a Monte Carlo approach is proposed to calculate the ionization dynamics of hot-solid-density plasmas within particle-in-cell (PIC) simulations, and where the impact (collision) ionization (CI), electron-ion recombination (RE), and ionization potential depression (IPD) by surrounding plasmas are taken into consideration self-consistently. When compared with other models, which are applied in the literature for plasmas near thermal equilibrium, the temporal relaxation of ionization dynamics can also be simulated by the proposed model. Besides, this model is general and can be applied for both single elements and alloys with quite different compositions. The proposed model is implemented into a PIC code, with (final) ionization equilibriums sustained by competitions between CI and its inverse process (i.e., RE). Comparisons between the full model and model without IPD or RE are performed. Our results indicate that for bulk aluminium at temperature of 1 to 1000 eV, (i) the averaged ionization degree increases by including IPD; while (ii) the averaged ionization degree is significantly over estimated when the RE is neglected. A direct comparison from the PIC code is made with the existing models for the dependence of averaged ionization degree on thermal equilibrium temperatures and shows good agreements with that generated from Saha-Boltzmann model and/or FLYCHK code.
Ben Gzaiel, M.; Oueslati, A.; Chaabane, I.; Gargouri, M.
2016-10-01
The molecular structure and vibrational spectra of bis-tetrapropyl-ammonium hexachloro-dizincate in the ground state have been investigated by density functional method (DFT) using the B3LYP method with the LanL2DZ and LanL2MB basis set. Infrared and Raman spectroscopes of the [N(C3H7)4]2Zn2Cl6 compound have been measured at room temperature in the frequencies range (3500-400 cm-1) and (3500-100 cm-1), respectively. The optimized geometric shows that the calculated values obtained by B3LYP/LanL2DZ basis are in much better agreement with the experimental data than those obtained by B3LYP/LanL2MB. Actually the theoretical vibrational spectra (B3LYP/LanL2DZ) of the title compound have been interpreted by means of potential energy distribution (PED) which is in good agreement with the experimental data. The comparison of the infrared spectrum of the tetrapropyl-ammonium chloride ligand with those of the bis-tetrapropyl-ammonium hexachloro-dizincate compound confirms an increase of the wavenumber in the [N(C3H7)4]2Zn2Cl6 compound. This can be explained by an increase of the electrostatic interactions of the [N(C3H7)4]Cl ligand.
Zhang, Feng; Tominaga, Keisuke, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp [Molecular Photoscience Research Center, Kobe University, Nada, Kobe 657-0013 (Japan); Hayashi, Michitoshi, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp; Wang, Houng-Wei [Center for Condensed Matter Sciences, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan (China); Kambara, Ohki; Sasaki, Tetsuo [Research Institute of Electronics, Shizuoka University, 3-5-1 Jyohoku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Nishizawa, Jun-ichi, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp [Jun-ichi Nishizawa Memorial Research Center, Tohoku University, 519-1176 Aoba, Aramaki, Aoba-ku, Sendai 980-0845 (Japan)
2014-05-07
The phonon modes of molecular crystals in the terahertz frequency region often feature delicately coupled inter- and intra-molecular vibrations. Recent advances in density functional theory such as DFT-D{sup *} have enabled accurate frequency calculation. However, the nature of normal modes has not been quantitatively discussed against experimental criteria such as isotope shift (IS) and correlation field splitting (CFS). Here, we report an analytical mode-decoupling method that allows for the decomposition of a normal mode of interest into intermolecular translation, libration, and intramolecular vibrational motions. We show an application of this method using the crystalline anthracene system as an example. The relationship between the experimentally obtained IS and the IS obtained by PBE-D{sup *} simulation indicates that two distinctive regions exist. Region I is associated with a pure intermolecular translation, whereas region II features coupled intramolecular vibrations that are further coupled by a weak intermolecular translation. We find that the PBE-D{sup *} data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D{sup *} produces significant deviations in IS in region I where strong coupling between inter- and intra-molecular vibrations contributes to normal modes. The result of this analysis is expected to facilitate future improvement of DFT-D{sup *}.
Hung, Linda; Huang, Chen; Shin, Ilgyou; Ho, Gregory S.; Lignères, Vincent L.; Carter, Emily A.
2010-12-01
: Intel with ifort; AMD Opteron with pathf90 Operating system: Linux Has the code been vectorized or parallelized?: Yes. Parallelization is implemented through domain composition using MPI. RAM: Problem dependent, but 2 GB is sufficient for up to 10,000 ions. Classification: 7.3 External routines: FFTW 2.1.5 ( http://www.fftw.org) Catalogue identifier of previous version: AEBN_v1_0 Journal reference of previous version: Comput. Phys. Comm. 179 (2008) 839 Does the new version supersede the previous version?: Yes Nature of problem: Given a set of coordinates describing the initial ion positions under periodic boundary conditions, recovers the ground state energy, electron density, ion positions, and cell lattice vectors predicted by orbital-free density functional theory. The computation of all terms is effectively linear scaling. Parallelization is implemented through domain decomposition, and up to ˜10,000 ions may be included in the calculation on just a single processor, limited by RAM. For example, when optimizing the geometry of ˜50,000 aluminum ions (plus vacuum) on 48 cores, a single iteration of conjugate gradient ion geometry optimization takes ˜40 minutes wall time. However, each CG geometry step requires two or more electron density optimizations, so step times will vary. Solution method: Computes energies as described in text; minimizes this energy with respect to the electron density, ion positions, and cell lattice vectors. Reasons for new version: To allow much larger systems to be simulated using PROFESS. Restrictions: PROFESS cannot use nonlocal (such as ultrasoft) pseudopotentials. A variety of local pseudopotential files are available at the Carter group website ( http://www.princeton.edu/mae/people/faculty/carter/homepage/research/localpseudopotentials/). Also, due to the current state of the kinetic energy functionals, PROFESS is only reliable for main group metals and some properties of semiconductors. Running time: Problem dependent: the test
SCRMS: An RFID and Sensor Web-Enabled Smart Cultural Relics Management System.
Xiao, Changjiang; Chen, Nengcheng; Li, Dandan; Lv, You; Gong, Jianya
2016-12-30
Cultural relics represent national or even global resources of inestimable value. How to efficiently manage and preserve these cultural relics is a vitally important issue. To achieve this goal, this study proposed, designed, and implemented an RFID and Sensor Web-enabled smart cultural relics management system (SCRMS). In this system, active photovoltaic subtle energy-powered Radio Frequency Identification (RFID) is used for long-range contactless identification and lifecycle management of cultural relics during their storage and circulation. In addition, different types of ambient sensors are integrated with the RFID tags and deployed around cultural relics to monitor their environmental parameters, helping to ensure that they remain in good condition. An Android-based smart mobile application, as middleware, is used in collaboration with RFID readers to collect information and provide convenient management for the circulation of cultural relics. Moreover, multiple sensing techniques are taken advantage of simultaneously for preservation of cultural relics. The proposed system was successfully applied to a museum in the Yongding District, Fujian Province, China, demonstrating its feasibility and advantages for smart and efficient management and preservation of cultural relics.
Double Relics in the Outskirts of A3376: Accretion Flows Meet Merger Shocks?
Ruta Kale; K. S. Dwarakanath; Joydeep Bagchi; Surajit Paul
2011-12-01
The case of spectacular ring-like double radio relics in the merging, rich galaxy cluster A3376 is of great interest to study non-thermal phenomena at cluster outskirts.We present the first low frequency (330 and 150 MHz) images of the double relics using the GMRT. With our GMRT 330 MHz map and the VLA 1400 MHz map (Bagchi et al. 2006), we have constructed and analyzed the distribution of spectral indices over the radio relics. We find flat spectral indices at the outer edges of both the relics and a gradual steepening of spectral indices toward the inner regions. This supports the model of outgoing merger shock waves. The eastern relic has a complex morphology and spectral index distribution toward the inner region. This will be discussed in the context of the effect of large-scale accretion flows on the outgoing merger shocks as reported in the recent simulations.
Development of ancestors' cultivation revealed in phytolith assemblages from Guangfulin relics
无
2003-01-01
Shanghai Museum has got great achievements in re-excavating Guangfulin relics. It is the first time that the cultural remains of Wangyoufang type is found above the Liangzhu cultural remains which comes from East Henan Province, providing previous materials for researching culture evolution around Taihu Lake. Samples were taken from the immature soil layer and cultural layers of Guangfulin relics for phytolith analysis. According to the systemic research for the archaeological remains and phytolith fossil, the phytoliths in Guangfulin relics can be divided into four zones. The development of rice agriculture and living condition of Guangfulin ancestors was discussed based on the existing rice fan-shaped phytolith, rice shell phytolith, diatom fossil and archaeology evidence in the same layer. The Guangfulin relics has gradually developed since a high sea level 5000 years ago, and the broad rice agriculture has simultaneously developed. The newly re-excavated relics provides valuable materials for the research of ancestors and ancient culture in Shanghai.
LI Fang-Yu; CHEN Zhen-Ya; YI Ying
2005-01-01
@@ It is shown that the coupling system between fractal membranes and a Gaussian beam passing through a static magnetic field has strong selection capability for the stochastic relic gravitational wave (GW) background. The relic G W components propagating along the positive direction of the symmetrical axis of the Gaussian beam might generate an optimal electromagnetic perturbation, while the perturbation produced by the relic GW components propagating along the negative and perpendicular directions to the symmetrical axis will be much less than the former, and the influence of the random fluctuation of the relic GWs to such effect can be neglected. The high-frequency relic GWs satisfying the parameters requirement (h ～ 10-31 or larger), frequency resonance and "direction coupling", in principle, would be selectable and measurable in seconds.
Primitive environment control for preservation of pit relics in archeology museums of China.
Gu, Zhaolin; Luo, Xilian; Meng, Xiangzhao; Wang, Zanshe; Ma, Tao; Yu, Chuck; Rong, Bo; Li, Ku; Li, Wenwu; Tan, Ying
2013-02-01
Immovable historical relics in some archeology museums of China suffer deterioration due to their improper preservation environment. The existing environmental control systems used in archeology museums are often designed for the amenities of visitors, and these manipulated environments are often inappropriate for the conservation of abiotic relics. This paper points out that the large open space of the existing archeology museum could be a cause of deterioration of the relics from the point of view of indoor air convective flow. The paper illustrates the need to introduce a local pit environmental control, which could reintegrate a pit primitive environment for the preservation of the historical relics by using an air curtain system, orientated to isolate the unearthed relics, semiexposed in pits to the large gallery open space of the exhibition hall.
Lattice calculation of composite dark matter form factors
Appelquist, T; Buchoff, M I; Cheng, M; Cohen, S D; Fleming, G T; Kiskis, J; Lin, M F; Neil, E T; Osborn, J C; Rebbi, C; Schaich, D; Schroeder, C; Syritsyn, S N; Voronov, G; Vranas, P; Wasem, J
2013-01-01
Composite dark matter candidates, which can arise from new strongly-coupled sectors, are well-motivated and phenomenologically interesting, particularly in the context of asymmetric generation of the relic density. In this work, we employ lattice calculations to study the electromagnetic form factors of electroweak-neutral dark-matter baryons for a three-color, QCD-like theory with Nf = 2 and 6 degenerate fermions in the fundamental representation. We calculate the (connected) charge radius and anomalous magnetic moment, both of which can play a significant role for direct detection of composite dark matter. We find minimal Nf dependence in these quantities. We generate mass-dependent cross-sections for dark matter-nucleon interactions and use them in conjunction with experimental results from XENON100, excluding dark matter candidates of this type with masses below 10 TeV.
CHEN Zhilong; ZHANG Ping; LI Juxi
2007-01-01
By analyzing the ten burials that have been unearthed at the Yang Emperor Mausoleum of the Han Dynasty, and China's first wholly underground protection and exhibition hall of relics that is under construction, the article expounds the importance of relic site protection through underground space. In particular, it discusses the preservation of historical and cultural relics, the harmonious relationship between architecture and nature, and the collection and security of cultural relics.
Gillet, Natacha; Berstis, Laura; Wu, Xiaojing; Gajdos, Fruzsina; Heck, Alexander; de la Lande, Aurelien; Blumberger, Jochen; Elstner, Marcus
2016-10-11
In this article, four methods to calculate charge transfer integrals in the context of bridge-mediated electron transfer are tested. These methods are based on density functional theory (DFT). We consider two perturbative Green's function effective Hamiltonian methods (first, at the DFT level of theory, using localized molecular orbitals; second, applying a tight-binding DFT approach, using fragment orbitals) and two constrained DFT implementations with either plane-wave or local basis sets. To assess the performance of the methods for through-bond (TB)-dominated or through-space (TS)-dominated transfer, different sets of molecules are considered. For through-bond electron transfer (ET), several molecules that were originally synthesized by Paddon-Row and co-workers for the deduction of electronic coupling values from photoemission and electron transmission spectroscopies, are analyzed. The tested methodologies prove to be successful in reproducing experimental data, the exponential distance decay constant and the superbridge effects arising from interference among ET pathways. For through-space ET, dedicated p-stacked systems with heterocyclopentadiene molecules were created and analyzed on the basis of electronic coupling dependence on donor-acceptor distance, structure of the bridge, and ET barrier height. The inexpensive fragment-orbital density functional tight binding (FODFTB) method gives similar results to constrained density functional theory (CDFT) and both reproduce the expected exponential decay of the coupling with donor-acceptor distances and the number of bridging units. These four approaches appear to give reliable results for both TB and TS ET and present a good alternative to expensive ab initio methodologies for large systems involving long-range charge transfers.
Gillet, Natacha; Berstis, Laura; Wu, Xiaojing; Gajdos, Fruzsina; Heck, Alexander; de la Lande, Aurélien; Blumberger, Jochen; Elstner, Marcus
2016-10-11
In this article, four methods to calculate charge transfer integrals in the context of bridge-mediated electron transfer are tested. These methods are based on density functional theory (DFT). We consider two perturbative Green's function effective Hamiltonian methods (first, at the DFT level of theory, using localized molecular orbitals; second, applying a tight-binding DFT approach, using fragment orbitals) and two constrained DFT implementations with either plane-wave or local basis sets. To assess the performance of the methods for through-bond (TB)-dominated or through-space (TS)-dominated transfer, different sets of molecules are considered. For through-bond electron transfer (ET), several molecules that were originally synthesized by Paddon-Row and co-workers for the deduction of electronic coupling values from photoemission and electron transmission spectroscopies, are analyzed. The tested methodologies prove to be successful in reproducing experimental data, the exponential distance decay constant and the superbridge effects arising from interference among ET pathways. For through-space ET, dedicated π-stacked systems with heterocyclopentadiene molecules were created and analyzed on the basis of electronic coupling dependence on donor-acceptor distance, structure of the bridge, and ET barrier height. The inexpensive fragment-orbital density functional tight binding (FODFTB) method gives similar results to constrained density functional theory (CDFT) and both reproduce the expected exponential decay of the coupling with donor-acceptor distances and the number of bridging units. These four approaches appear to give reliable results for both TB and TS ET and present a good alternative to expensive ab initio methodologies for large systems involving long-range charge transfers.
McMahan, A K
2005-03-30
This paper reports calculations for compressed Ce (4f{sup 1}), Pr (4f{sup 2}), and Nd (4f{sup 3}) using a combination of the local-density approximation (LDA) and dynamical mean field theory (DMFT), or LDA+DMFT. The 4f moment, spectra, and the total energy among other properties are examined as functions of volume and atomic number for an assumed face-centered cubic (fcc) structure. These materials are seen to be strongly localized at ambient pressure and for compressions up through the experimentally observed fcc phases ({gamma} phase for Ce), in the sense of having fully formed Hund's rules moments and little 4f spectral weight at the Fermi level. Subsequent compression for all three lanthanides brings about significant deviation of the moments from their Hund's rules values, a growing Kondo resonance at the fermi level, an associated softening in the total energy, and quenching of the spin orbit since the Kondo resonance is of mixed spin-orbit character while the lower Hubbard band is predominantly j = 5/2. while the most dramatic changes for Ce occur within the two-phase region of the {gamma}-{alpha} volume collapse transition, as found in earlier work, those for Pr and Nd occur within the volume range of the experimentally observed distorted fcc (dfcc) phase, which is therefore seen here as transitional and not part of the localized trivalent lanthanide sequence. The experimentally observed collapse to the {alpha}-U structure in Pr occurs only on further compression, and no such collapse is found in Nd. These lanthanides start closer to the localized limit for increasing atomic number, and so the theoretical signatures noted above are also offset to smaller volume as well, which is possibly related to the measured systematics of the size of the volume collapse being 15%, 9%, and none for Ce, Pr, and Nd, respectively.
Rüger, Robert; Heine, Thomas; Visscher, Lucas
2016-01-01
We propose a new method of calculating electronically excited states that combines a density functional theory (DFT) based ground state calculation with a linear response treatment that employs approximations used in the time-dependent density functional based tight binding (TD-DFTB) approach. The new method termed TD-DFT+TB does not rely on the DFTB parametrization and is therefore applicable to systems involving all combinations of elements. We show that the new method yields UV/Vis absorption spectra that are in excellent agreement with computationally much more expensive time-dependent density functional theory (TD-DFT) calculations. Errors in vertical excitation energies are reduced by a factor of two compared to TD-DFTB.
McWilliams, Sean F; Brennan-Wydra, Emma; MacLeod, K Cory; Holland, Patrick L
2017-06-30
The relative ease of Mössbauer spectroscopy and of density functional theory (DFT) calculations encourages the use of Mössbauer parameters as a validation method for calculations, and the use of calculations as a double check on crystallographic structures. A number of studies have proposed correlations between the computationally determined electron density at the iron nucleus and the observed isomer shift, but deviations from these correlations in low-valent iron β-diketiminate complexes encouraged us to determine a new correlation for these compounds. The use of B3LYP/def2-TZVP in the ORCA platform provides an excellent balance of accuracy and speed. We provide here not only this new correlation and a clear guide to its use but also a systematic analysis of the limitations of this approach. We also highlight the impact of crystallographic inaccuracies, DFT model truncation, and spin states, with intent to assist experimentalists to use Mössbauer spectroscopy and calculations together.
Imprints of relic gravitational waves on pulsar timing
Tong, Ming-Lei; Zhao, Cheng-Shi; Gao, Feng; Yan, Bao-Rong; Yang, Ting-Gao; Gao, Yu-Ping
2015-01-01
Relic gravitational waves (RGWs) , a background originated during inflation, would give imprints on the pulsar timing residuals. This makes RGWs be one of important sources for detection using the method of pulsar timing. In this paper, we discuss the effects of RGWs on the single pulsar timing, and give quantitively the timing residuals caused by RGWs with different model parameters. In principle, if the RGWs are strong enough today, they can be detected by timing a single millisecond pulsar with high precision after the intrinsic red noise in pulsar timing residuals were understood, even though observing simultaneously multiple millisecond pulsars is a more powerful technique in extracting gravitational wave signals. We corrected the normalization of RGWs using observations of the cosmic microwave background (CMB), which leads to the amplitudes of RGWs being reduced by two orders of magnitude or so compared to our previous works. We made new constraints on RGWs using the recent observations from the Parkes ...
Underground Searches for Cold Relics of the Early Universe
Baudis, L
2005-01-01
We have strong evidence on all cosmic scales, from galaxies to the largest structures ever observed, that there is more matter in the universe than we can see. Galaxies and clusters would fly apart unless they would be held together by material which we call dark, because it does not shine in photons. Although the amount of dark matter and its distribution are fairly well established, we are clueless regarding its composition. Leading candidates are Weakly Interacting Massive Particles (WIMPs), which are 'cold' thermal relics of the Big Bang, ie moving non-relativistically at the time of structure formation. These particles can be detected via their interaction with nuclei in deep-underground, low-background detectors. Experiments dedicated to observe WIMP interactions for the first time reach sensitivities allowing to probe the parameter space predicted by supersymmetric theories of particle physics. Current results of high sensitivity direct detection experiments are discussed and the most promising project...
Safarov, M. M.; Abdukhamidova, Z.
1995-09-01
We present the results from an experimental investigation of the density of the sunflower oil system as a function of the mass concentration of n-hexane in the ranges of temperatures T=290 520 K and pressures P=0.101 98.1 MPa. A method of hydrostatic weighing was used to measure the density of the solutions under study.
Yin, Shi; Bernstein, Elliot R
2016-10-21
A new magnetic-bottle time-of-flight photoelectron spectroscopy (PES) apparatus is constructed in our laboratory. The PES spectra of iron sulfide, hydrosulfide, and mixed sulfide/hydrosulfide [FeSm(SH)n(-); m, n = 0-3, 0 density functional theory. The most probable structures and ground state spin multiplicity for these cluster anions are tentatively assigned by comparing their theoretical first vertical detachment energies (VDEs) with their respective experiment values. The behavior of S and (SH) as ligands in these iron sulfide, hydrosulfide, and mixed sulfide/hydrosulfide cluster anions is investigated and compared. The experimental first VDEs for Fe(SH)1-3(-) cluster anions are lower than those found for their respective FeS1-3(-) cluster anions. The experimental first VDEs for FeS1-3(-) clusters are observed to increase for the first two S atoms bound to Fe(-); however, due to the formation of an S-S bond for the FeS3(-) cluster, its first VDE is found to be ∼0.41 eV lower than the first VDE for the FeS2(-) cluster. The first VDEs of Fe(SH)1-3(-) cluster anions are observed to increase with the increasing numbers of SH groups. The calculated partial charges of the Fe atom for ground state FeS1-3(-) and Fe(SH)1-3(-) clusters are apparently related to and correlated with their determined first VDEs. The higher first VDE is correlated with a higher, more positive partial charge for the Fe atom of these cluster anions. Iron sulfide/hydrosulfide mixed cluster anions are also explored in this work: the first VDE for FeS(SH)(-) is lower than that for FeS2(-), but higher than that for Fe(SH)2(-); the first VDEs for FeS2(SH)(-) and FeS(SH)2(-) are close to that for FeS3(-), but higher than that for Fe(SH)3(-). The first VDEs of general iron sulfide, hydrosulfide, and mixed sulfide/hydrosulfide clusters [FeSm(SH)n(-); m, n = 0-3, 0 number of hydrosulfide ligands in the cluster. The higher the partial charge on the Fe atom of these clusters, the larger the first VDE
Kanungo, Bikash; Gavini, Vikram
2017-01-01
We present a computationally efficient approach to perform large-scale all-electron density functional theory calculations by enriching the classical finite element basis with compactly supported atom-centered numerical basis functions that are constructed from the solution of the Kohn-Sham (KS) problem for single atoms. We term these numerical basis functions as enrichment functions, and the resultant basis as the enriched finite element basis. The compact support for the enrichment functions is obtained by using smooth cutoff functions, which enhances the conditioning and maintains the locality of the enriched finite element basis. The integrals involved in the evaluation of the discrete KS Hamiltonian and overlap matrix in the enriched finite element basis are computed using an adaptive quadrature grid that is constructed based on the characteristics of enrichment functions. Further, we propose an efficient scheme to invert the overlap matrix by using a blockwise matrix inversion in conjunction with special reduced-order quadrature rules, which is required to transform the discrete Kohn-Sham problem to a standard eigenvalue problem. Finally, we solve the resulting standard eigenvalue problem, in each self-consistent field iteration, by using a Chebyshev polynomial based filtering technique to compute the relevant eigenspectrum. We demonstrate the accuracy, efficiency, and parallel scalability of the proposed method on semiconducting and heavy-metallic systems of various sizes, with the largest system containing 8694 electrons. We obtain accuracies in the ground-state energies that are ˜1 mHa with reference ground-state energies employing classical finite element as well as Gaussian basis sets. Using the proposed formulation based on enriched finite element basis, for accuracies commensurate with chemical accuracy, we observe a staggering 50 -300 -fold reduction in the overall computational time when compared to classical finite element basis. Further, we find a
Background of relic gravitons in a perfect fluid in quantum cosmological models
Siffert, Beatriz B. [Centro Brasileiro de Pesquisas Fisicas (ICRA/CBPF), Rio de Janeiro, RJ (Brazil). Inst. de Cosmologia, Relatividade e Astrofisica; Bessada, Dennis [Instituto Nacional de Pesquisas Espaciais (INPE), SP (Brazil). Divisao de Astrofisica
2011-07-01
Full text: We studied the evolution of tensor cosmological perturbations of quantum origin in cosmological scenarios that predict a contracting phase prior to the present expansion phase. These bouncing models constitute a very plausible alternative to the current cosmological paradigm since they may be able to solve some of the cosmological puzzles present in the standard model, such as the horizon and flatness problems, without the requirement of an initial singularity or special initial conditions. While conventional inflationary models give rise to a relic background of gravitational waves that cannot be detected with present experiments, no such prediction had been made so far using quantum bouncing models. We have obtained analytically the graviton's energy density parameter as a function of time and frequency interval - which is the physical quantity to be confronted with observations - predicted by such models with a perfect fluid equation of state. To obtain the final spectrum, we numerically solved the expression for the density parameter for the time variable. The results can then be compared with the predictions from inflationary models and with the sensitivity curves of gravitational waves current detectors, such as the Virgo and Ligo interferometers, and upcoming detectors, like the LISA space mission, to determine the possibility of detection. (author)
Shock acceleration as origin of the radio relic in A521?
Giacintucci, S; Macario, G; Dallacasa, D; Brunetti, G; Markevitch, M; Cassano, R; Bardelli, S; Athreya, R
2008-01-01
We present new high sensitivity observations of the radio relic in A521 carried out with the Giant Metrewave Radio Telescope at 327 MHz and with the Very Large Array at 4.9 and 8.5 GHz. We imaged the relic at these frequencies and carried out a detailed spectral analysis, based on the integrated radio spectrum between 235 MHz and 4.9 GHz, and on the spectral index image in the frequency range 327-610 MHz. To this aim we used the new GMRT observations and other proprietary as well as archival data. We also searched for a possible shock front co-located with the relic on a short archival Chandra X-ray observation of the cluster. The integrated spectrum of the relic is consistent with a single power law; the spectral index image shows a clear trend of steepening going from the outer portion of the relic toward the cluster centre. We discuss the origin of the source in the light of the theoretical models for the formation of cluster radio relics. Our results on the spectral properties of the relic are consistent ...
AGN duty cycle and relic emission in the low frequency sky
Pandey-Pommier, M.; Intema, H.; Heald, G.
2016-12-01
Active Galactic Nuclei (AGNs) are amongst the brightest sources in the radio sky that deposit large amount of energy in the interstellar and intergalactic medium (ISM, IGM) via their jets. Recurrent flaring episodes in the AGN jets can terminate at large-scale faint diffuse 'relic' emission around them. These relic emissions are rare and represent the end stage of their life cycle. They show very steep spectrum giving insights of AGN duty cycle, their past activity history and surrounding environment properties. High sensitivity and arcsec scale observations at very low frequencies are needed to detect such rare relic emission and disentangle the details of their morphology. In this paper we highlight the important database provided by low frequency surveys to search for relic radio sources and discuss in particular the relic emission from the AGNs detected in the LOFAR Multi frequency Snapshot Sky Survey (MSSS) and TIFR GMRT Sky Survey (TGSS), both surveys performed with SKA pathfinder telescopes. The radio spectrum from 2 different types of relic radio galaxies (B2 0924+30 and 4C 35.06) are investigated and a correlation between the mean particle age of the relic emission and the central AGN properties is derived.
Glossman-Mitnik, Daniel
2014-07-01
The M06 family of density functionals has been assessed for the calculation of the molecular structure and properties of the Isonaringin flavonoid that can be an interesting material for dye-sensitized solar cells (DSSC). The chemical reactivity descriptors have been calculated through chemical reactivity theory within DFT (CR-DFT). The active sites for nucleophilic and electrophilic attacks have been chosen by relating them to the Fukui function indices and the dual descriptor f ((2))(r). A comparison between the descriptors calculated through vertical energy values and those arising from the Janak's theorem approximation have been performed in order to check for the validity of the last procedure.
Bates, Kevin R.; Daniels, Andrew D.; Scuseria, Gustavo E.
1998-01-01
We report a comparison of two linear-scaling methods which avoid the diagonalization bottleneck of traditional electronic structure algorithms. The Chebyshev expansion method (CEM) is implemented for carbon tight-binding calculations of large systems and its memory and timing requirements compared to those of our previously implemented conjugate gradient density matrix search (CG-DMS). Benchmark calculations are carried out on icosahedral fullerenes from C60 to C8640 and the linear scaling memory and CPU requirements of the CEM demonstrated. We show that the CPU requisites of the CEM and CG-DMS are similar for calculations with comparable accuracy.
Morisato, T.; Ohno, K.; Ohtsuki, T.; Hirose, K.; Sluiter, M.; Kawazoe, Y.
2008-01-01
Carrying out a first-principles calculation assuming linear relationship between the electron density at Be nucleus and the electron-capture (EC) decay rate, we explained why 7Be@C60 shows higher EC decay rate than 7Be crystal, which was originally found experimentally by Ohtsuki et al. [Phys. Rev.
Jisha Annie Abraham
2015-01-01
Full Text Available The electronic properties of magnetic cubic AuCu3 type GdX3 (X = In, Sn, Tl, and Pb have been studied using first principles calculations based on density functional theory. Because of the presence of strong on-site Coulomb repulsion between the highly localized 4f electrons of Gd atoms, we have used LSDA + U approach to get accurate results in the present study. The electronic band structures as well as density of states reveal that the studied compounds show metallic behavior under ambient conditions. The calculated density of states at the Fermi level N(EF shows good agreement with the available experimental results. The calculated electronic charge density plots show the presence of ionic bonding in all the compounds along with partial covalent bonding except in GdIn3. The complex optical dielectric function’s dispersion and the related optical properties such as refractive indices, reflectivity, and energy-loss function were calculated and discussed in detail.
Reshak, Ali H.; OUAHRANI, T.; Khenata, R.; A. Otero-de-la-Roza; Luana, V.; Baltache, H.
2011-01-01
An ab initio study of the band structure, density of states, topology of the electron density and the spectral features of the linear and non-linear optical properties of the Ga2AsSb chalcopyrite are presented. The lattice parameters (a, c), the internal structure parameter, u, describing the position of Ga atom and the (c/a) ratio are optimized. The covalent bonding character is predicted via analyzing the electron density at the equilibrium geometry. The linear optical properties namely the...
Zhang, Gaigong; Hu, Wei; Yang, Chao; Pask, John E
2015-01-01
Recently, we have proposed the adaptive local basis set for electronic structure calculations based on Kohn-Sham density functional theory in a pseudopotential framework. The adaptive local basis set is efficient and systematically improvable for total energy calculations. In this paper, we present the calculation of atomic forces, which can be used for a range of applications such as geometry optimization and molecular dynamics simulation. We demonstrate that, under mild assumptions, the computation of atomic forces can scale nearly linearly with the number of atoms in the system using the adaptive local basis set. We quantify the accuracy of the Hellmann-Feynman forces for a range of physical systems, benchmarked against converged planewave calculations, and find that the adaptive local basis set is efficient for both force and energy calculations, requiring at most a few tens of basis functions per atom to attain accuracy required in practice. Since the adaptive local basis set has implicit dependence on a...
Xiaoqi, J.
2015-08-01
As the popularization of cultural relics and the rapid development of cultural tourism industry, a large number of cultural relic tourism resources goes into public eyes. Activation of relics has became an important way for tourist to contact and understand culture relics. The way of how to properly interpret the historical sense and cultural uniqueness to the masses of tourists in order to achieve social service functions of relic resources has always been research focal point of site protection and utilization, so nowadays it has important significance to protection and utilization of heritage resources in our country. From the point of activation of relics and based on the analysis of resource characteristic, the paper in depth discuss ways of activation of relics of the Old Summer Palace, in order to provide reference for sustainable development of sites tourism in China.
O. B. Khokhlova
2017-01-01
Full Text Available The proposed method for calculation of the energy value of culture media is based on stoichiometric properties of biological oxidative reactions in the cell and allows for assessment of the nutritional value of organic substrates with consideration of their elemental composition. Three organogen elements (carbon, hydrogen and oxygen participate in the third stage of catabolism, which is the universal way of biological oxidation of organic nutritive substrate compounds. Their content in the composition of an organic compound (or food substrate allows for calculation of the amount of energy converted into work during cellular metabolism. The idea to calculate the energy value of a food substrate is based on the principle of energetic conjugation, according to which the useful energy of food substrates within the cell is accumulated in the energy-rich adenosine triphosphate (ATP bonds formed by biological oxidation of the substrate. Calculation of the energy values of organic substrate is traditionally based on the energy of the abiotic oxidation. The proportion of the useful energy converted into work is not considered in this case. The inherent problem of this approach is that the amount of ATP has been calculated only for several universal metabolites with known oxidative pathways, such as pyruvate and acetate. The proposed method is based on stoichiometric patterns and makes it possible to calculate the amount of ATP from the elemental composition of compounds and the mass fractions of carbon, hydrogen and oxygen. The results of calculation of biological oxidation energy obtained by this method coincide with the published data on biological oxidation metabolites in the citric acid cycle. The presented method, based on the composition of the compounds, allows for calculation of the energy value of any food substrate or culture medium containing a variety of organic compounds, including the case when their metabolic pathway of biological
2016-06-03
IR and UV-visible ranges. The absorption spectrum corresponding to excitation states of As-H2O complexes consisting of relatively small numbers of...complexes consisting of relatively small numbers of water molecules using DFT and TD- DFT. Calculation of excited state resonance structure using DFT and TD...absorption spectra. A significant aspect of using DFT and TD-DFT for the calculation of absorption spectra is that it adopts the perspective of computational
Kaplan, A., E-mail: abdullahkaplan@sdu.edu.tr [Süleyman Demirel Univesity, Faculty of Arts and Sciences, Department of Physics (Turkey); Sarpün, İ. H. [Afyon Kocatepe University, Faculty of Arts and Sciences, Department of Physics (Turkey); Aydın, A. [Kırıkkale University, Faculty of Arts and Sciences, Department of Physics (Turkey); Tel, E. [Osmaniye Korkut Ata University, Faculty of Arts and Sciences, Department of Physics (Turkey); Çapalı, V.; Özdoǧan, H. [Süleyman Demirel Univesity, Faculty of Arts and Sciences, Department of Physics (Turkey)
2015-01-15
There are several level density models that can be used to predict photo-neutron cross sections. Some of them are Constant Temperature + Fermi Gas Model (CTFGM), Back-Shifted Fermi Gas Model (BSFM), Generalized Superfluid Model (GSM), Hartree-Fock-Bogoliubov microscopic Model (HFBM). In this study, the theoretical photo-neutron cross sections produced by (γ, 2n) reactions for several eveneven lanthanide nuclei such as {sup 140,142}Ce, {sup 142,144,146,148,150}Nd, {sup 144,148,150,152,154}Sm, and {sup 160}Gd have been calculated on the different level density models as mentioned above by using TALYS 1.6 and EMPIRE 3.1 computer codes for incident photon energies up to 30 MeV. The obtained results have been compared with each other and available experimental data existing in the EXFOR database. Generally, at least one level density model cross-section calculations are in agreement with the experimental results for all reactions except {sup 144}Sm(γ, 2n){sup 142}Sm along the incident photon energy, TALYS 1.6 BSFM option for the level density model cross-section calculations can be chosen if the experimental data are not available or are improbable to be produced due to the experimental difficulty.
Tsai, Shan-Ho; Wang, Fugao; Landau, D P
2007-06-01
Using the Wang-Landau sampling method with a two-dimensional random walk we determine the density of states for an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. With an accurate density of states we were able to map out the phase diagram accurately and perform quantitative finite-size analyses at, and away from, the critical endpoint. We observe a clear divergence of the curvature of the spectator phase boundary and of the magnetization coexistence diameter derivative at the critical endpoint, and the exponents for both divergences agree well with previous theoretical predictions.
Tsai, Shan-Ho; Wang, Fugao; Landau, D. P.
2007-06-01
Using the Wang-Landau sampling method with a two-dimensional random walk we determine the density of states for an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. With an accurate density of states we were able to map out the phase diagram accurately and perform quantitative finite-size analyses at, and away from, the critical endpoint. We observe a clear divergence of the curvature of the spectator phase boundary and of the magnetization coexistence diameter derivative at the critical endpoint, and the exponents for both divergences agree well with previous theoretical predictions.
Abers, Geoffrey A.; Hacker, Bradley R.
2016-02-01
To interpret seismic images, rock seismic velocities need to be calculated at elevated pressure and temperature for arbitrary compositions. This technical report describes an algorithm, software, and data to make such calculations from the physical properties of minerals. It updates a previous compilation and Excel® spreadsheet and includes new MATLAB® tools for the calculations. The database of 60 mineral end-members includes all parameters needed to estimate density and elastic moduli for many crustal and mantle rocks at conditions relevant to the upper few hundreds of kilometers of Earth. The behavior of α and β quartz is treated as a special case, owing to its unusual Poisson's ratio and thermal expansion that vary rapidly near the α-β transition. The MATLAB tools allow integration of these calculations into a variety of modeling and data analysis projects.
无
2010-01-01
A density functional theory (DFT)-calculation scheme for constructing the modified embedded atom method (MEAM) potentials for face-centered cubic (fcc) metals is presented. The input quantities are carefully selected and a more reliable DFT approach for surface energy determination is introduced in the parameterization scheme, enabling MEAM to precisely predict the surface and nanoscale properties of metallic materials. Molecular dynamics simulations on Pt and Au crystals show that the parameterization employed leads to significantly improved accuracy of MEAM in calculating the surface and nanoscale properties, with the results agreeing well with both DFT calculations and experimental observations. The present study implies that rational DFT parameterization of MEAM may lead to a theoretical tool to bridge the gap between nanoscale theoretical simulations and DFT calculations.
Rodríguez, Juan I; Ayers, Paul W; Götz, Andreas W; Castillo-Alvarado, F L
2009-07-14
A new approach for computing the atom-in-molecule [quantum theory of atoms in molecule (QTAIM)] energies in Kohn-Sham density-functional theory is presented and tested by computing QTAIM energies for a set of representative molecules. In the new approach, the contribution for the correlation-kinetic energy (T(c)) is computed using the density-functional theory virial relation. Based on our calculations, it is shown that the conventional approach where atomic energies are computed using only the noninteracting part of the kinetic energy might be in error by hundreds of kJ/mol.
Mullins, J; Duan, X; Kruse, J; Herman, M [Mayo Clinic, Rochester, MN (United States); Bues, M [Mayo Clinic Arizona, Phoenix, AZ (United States)
2014-06-01
Purpose: To determine the suitability of dual-energy CT (DECT) to calculate relative electron density (RED) of tissues for accurate proton therapy dose calculation. Methods: DECT images of RED tissue surrogates were acquired at 80 and 140 kVp. Samples (RED=0.19−2.41) were imaged in a water-equivalent phantom in a variety of configurations. REDs were calculated using the DECT numbers and inputs of the high and low energy spectral weightings. DECT-derived RED was compared between geometric configurations and for variations in the spectral inputs to assess the sensitivity of RED accuracy versus expected values. Results: RED accuracy was dependent on accurate spectral input influenced by phantom thickness and radius from the phantom center. Material samples located at the center of the phantom generally showed the best agreement to reference RED values, but only when attenuation of the surrounding phantom thickness was accounted for in the calculation spectra. Calculated RED changed by up to 10% for some materials when the sample was located at an 11 cm radius from the phantom center. Calculated REDs under the best conditions still differed from reference values by up to 5% in bone and 14% in lung. Conclusion: DECT has previously been used to differentiate tissue types based on RED and Z for binary tissue-type segmentation. To improve upon the current standard of empirical conversion of CT number to RED for treatment planning dose calculation, DECT methods must be able to calculate RED to better than 3% accuracy throughout the image. The DECT method is sensitive to the accuracy of spectral inputs used for calculation, as well as to spatial position in the anatomy. Effort to address adjustments to the spectral calculation inputs based on position and phantom attenuation will be required before DECT-determined RED can achieve a consistent level of accuracy for application in dose calculation.
Wang, Dong-Gang; Chen, Jie-Wen
2015-01-01
The spectrum of relic gravitational wave (RGW) contains high-frequency divergences, which should be removed. We present a systematic study of the issue, based on the exact RGW solution that covers the five stages, from inflation to the acceleration, each being a power law expansion. We show that the present RGW consists of vacuum dominating at $f>10^{11}$Hz and graviton dominating at $f<10^{11}$Hz, respectively. The gravitons are produced by the four cosmic transitions, mostly by the inflation-reheating one. We perform adiabatic regularization to remove vacuum divergences in three schemes: at present, at the end of inflation, and at horizon-exit, to the 2-nd adiabatic order for the spectrum, and the 4-th order for energy density and pressure. In the first scheme a cutoff is needed to remove graviton divergences. We find that all three schemes yield the spectra of a similar profile, and the primordial spectrum defined far outside horizon during inflation is practically unaffected. We also regularize the gau...
Hint of relic gravitational waves in the Planck and WMAP data
Zhao, Wen; Huang, Qing-Guo
2014-01-01
Relic gravitational waves (RGWs) leave well-understood imprints on the anisotropies in the temperature and polarization of cosmic microwave background (CMB) radiation. In the TT and TE information channels, which have been well observed by WMAP and Planck missions, RGWs compete with density perturbations mainly at low multipoles. It is dangerous to include high-multipole CMB data in the search for gravitational waves, as the spectral indices may not be constants. In this paper, we repeat our previous work [W.Zhao & L.P.Grishchuk, Phys.Rev.D {\\bf 82}, 123008 (2010)] by utilizing the Planck TT and WMAP TE data in the low-multipole range $\\ell\\le100$. We find that our previous result is confirmed {with higher confidence}. The constraint on the tensor-to-scalar ratio from Planck TT and WMAP TE data is $r\\in [0.06,~0.60]$ (68% C.L.) with a peak around $r\\sim 0.2$. Correspondingly, the spectral index at the pivot wavenumber $k_*=0.002$Mpc$^{-1}$ is $n_s=1.13^{+0.07}_{-0.08}$, which is larger than 1 at more than...
A stellar relic from the early Milky Way
Christlieb, N; Beers, T C; Gustafsson, B; Korn, A J; Barklem, P S; Karlsson, T; Mizuno-Wiedner, M; Rossi, S; Christlieb, Norbert; Bessell, Michael S.; Beers, Timothy C.; Gustafsson, Bengt; Korn, Andreas; Barklem, Paul S.; Karlsson, Torgny; Mizuno-Wiedner, Michelle; Rossi, Silvia
2002-01-01
The chemical composition of the most metal-deficient stars reflects the composition of the gas from which they formed. These old stars provide crucial clues to the star formation history and the synthesis of chemical elements in the early Universe. They are the local relics of epochs otherwise observable only at very high redshifts; if totally metal-free (``population III'') stars could be found, this would allow the direct study of the pristine gas from the Big Bang. Earlier searches for such stars found none with an iron abundance less than 1/10,000 that of the Sun, leading to the suggestion that low-mass stars could only form from clouds above a critical iron abundance. Here we report the discovery of a low-mass star with an iron abundance as low as 1/200,000 of the solar value. This discovery suggests that population III stars could still exist, that is, that the first generation of stars also contained long-lived low-mass objects. The previous failure to find them may be an observational selection effect...
Re-acceleration model for the `Sausage' Radio Relic
Kang, Hyesung
2016-01-01
The Sausage radio relic is the arc-like radio structure in the cluster CIZA J2242.8+5301, whose observed properties can be best understood by synchrotron emission from relativistic electrons accelerated at a merger-driven shock. However, there remain a few puzzles that cannot be explained by the shock acceleration model with only in-situ injection. In particular, the Mach number inferred from the observed radio spectral index, $M_{\\rm radio}\\approx 4.6$, while the Mach number estimated from X-ray observations, $M_{\\rm X-ray}\\approx 2.7$. In an attempt to resolve such a discrepancy, here we consider the re-acceleration model in which a shock of $M_s\\approx 3$ sweeps through the intracluster gas with a pre-existing population of relativistic electrons. We find that observed brightness profiles at multi frequencies provide strong constraints on the spectral shape of pre-existing electrons. The models with a power-law momentum spectrum with the slope, $s\\approx 4.1$, and the cutoff Lorentz factor, $\\gamma_{e,c}\\a...
A double radio relic in the merging galaxy cluster ZwCl 0008.8+5215
van Weeren, R J; Rottgering, H J A; Bruggen, M; Intema, H T; van Velzen, S
2011-01-01
Some merging galaxy clusters host diffuse elongated radio sources, also called radio relics. It is proposed that these radio relics trace shock waves in the intracluster medium created during a cluster merger event. Within the shock waves particles are accelerated to relativistic energies, and in the presence of a magnetic field synchrotron radiation will be emitted. Here we present GMRT and WSRT observations of a new double relic in the galaxy cluster ZwCl 0008.8+5215. Optical V, R, and I band images of the cluster were taken with the INT. An optical spectrum, to determine the redshift of the cluster, was taken with the WHT. Our observations show the presence of a double radio relic in the galaxy cluster ZwCl 0008.8+5215, for which we find a spectroscopic redshift of z = 0.1032 \\pm 0.0018 from an optical spectrum of one of the cD galaxies. The spectral index of the two relics steepens inwards to the cluster center. For part of the relics, we measure a polarization fraction in the range ~ 5-25%. A ROSAT X-ray...
Another shock for the Bullet cluster, and the source of seed electrons for radio relics
Shimwell, Timothy W; Brown, Shea; Feretti, Luigina; Gaensler, B M; Johnston-Hollitt, M; Lage, Craig; Srinivasan, Raghav
2015-01-01
With Australia Telescope Compact Array observations, we detect a highly elongated Mpc-scale diffuse radio source on the eastern periphery of the Bullet cluster 1E0657-55.8, which we argue has the positional, spectral and polarimetric characteristics of a radio relic. This powerful relic (2.3+/-0.1 x 10^25 W Hz^-1) consists of a bright northern bulb and a faint linear tail. The bulb emits 94% of the observed radio flux and has the highest surface brightness of any known relic. Exactly coincident with the linear tail we find a sharp X-ray surface brightness edge in the deep Chandra image of the cluster -- a signature of a shock front in the hot intracluster medium (ICM), located on the opposite side of the cluster to the famous bow shock. This new example of an X-ray shock coincident with a relic further supports the hypothesis that shocks in the outer regions of clusters can form relics via diffusive shock (re-)acceleration. Intriguingly, our new relic suggests that seed electrons for reacceleration are coming...
M Talebian; E Talebian; A Abdi
2012-05-01
We obtained an approximation of the force ﬁeld of -quartz crystal using a new idea of applying density functional theory [J Purton, R Jones, C R A Catlow and M Leslie, Phys. Chem. Minerals 19, 392 (1993)]. Our calculations were based on B3LYP Hamiltonian [A N Lazarev and A P Mirgorodsky, Phys. Chem. Minerals 18, 231 (1991)] in 6−311+G(2d) basis set for H16Si7O6 cluster and included a unit cell of the lattice. The advantage of our method is the increase in the speed of calculations and the better adaption of simulation results with the experimental data.
Flower symbolism and the cult of relics in medieval Serbia
Popović Danica
2008-01-01
Full Text Available The Life of archbishop Eustathios I [Jevstatije] (1279-1286, deserving head of the medieval Serbian Church and a saint, is a very interesting source for studying the cult of relics with the Serbs. This is not surprising considering that the Life was penned by one of the most illustrious of Eustathios' successors on the church throne, Daniel II [Danilo], a learned Athonite and unquestionable master of the hagiographie literary genre. In his account of the life of his distinguished predecessor, Daniel describes extensively the events constituting the key stage in the glorification of a saint, namely Eustathios' death and posthumous occurrences at his grave. As most holy men, Eustathios foresaw his own death, and he departed from this world serenely. He was buried, with due honours, in the 'marble grave' he had prepared for himself in the cathedral church of Holy Saviour at Žiča. In keeping with the well-established saint-making process, a few years after the funeral 'extraordinary signs' began to occur at the archbishop's grave, in this particular case, candlelight and a multitude of murmuring voices followed by the miraculous cure of an incurably ill person. These occurrences preceded the great miracle which, to the best of my knowledge, is unparalleled in the medieval Serbian practice of relic veneration. Namely, 'one day they found growing from his marble grave three flowers endowed with wondrous beauty and impossible to liken to anything else. For, indeed, they were not of earthly humidity or of union with flowers that grow from earth; but, o wonder, how a dry stone standing for so long in the church could send forth fragrant flowers, to the renewal of the sanctified one's body'. Flower metaphors occur in the Service to the holy archbishop Eustathios, yet another piece penned by Daniel II, notably in his paraphrases of Psalm 92, 12-14 ('The righteous shall flourish like the palm tree: he shall grow like a cedar in Lebanon. These that be
Mitin, Alexander V; van Wüllen, Christoph
2006-02-14
A two-component quasirelativistic Hamiltonian based on spin-dependent effective core potentials is used to calculate ionization energies and electron affinities of the heavy halogen atom bromine through the superheavy element 117 (eka-astatine) as well as spectroscopic constants of the homonuclear dimers of these atoms. We describe a two-component Hartree-Fock and density-functional program that treats spin-orbit coupling self-consistently within the orbital optimization procedure. A comparison with results from high-order Douglas-Kroll calculations--for the superheavy systems also with zeroth-order regular approximation and four-component Dirac results--demonstrates the validity of the pseudopotential approximation. The density-functional (but not the Hartree-Fock) results show very satisfactory agreement with theoretical coupled cluster as well as experimental data where available, such that the theoretical results can serve as an estimate for the hitherto unknown properties of astatine, element 117, and their dimers.
Giesbertz, Klaas J H; Baerends, Evert Jan
2013-01-01
Recently, we have demonstrated that the problems finding a suitable adiabatic approximation in time-dependent one-body reduced density matrix functional theory can be remedied by introducing an additional degree of freedom to describe the system: the phase of the natural orbitals [Phys. Rev. Lett. 105, 013002 (2010), J. Chem. Phys. 133, 174119 (2010)]. In this article we will show in detail how the frequency-dependent response equations give the proper static limit ($\\omega\\to0$), including the perturbation in the chemical potential, which is required in static response theory to ensure the correct number of particles. Additionally we show results for the polarizability for H$_2$ and compare the performance of two different two-electron functionals: the phase-including L\\"owdin-Shull functional and the density matrix form of the L\\"owdin-Shull functional.
Zhang, Hong-ping; Luo, Xue-gang; Lin, Xiao-yang; Lu, Xiong; Leng, Yang; Song, Hong-tao
2013-10-01
Understanding the interaction mechanisms of CO, NO, SO2, and HCHO with graphene are important in developing graphene-based sensors for gas detection and removal. In this study, the effects of doped Ti or N atom on the interaction of these gases with graphene were investigated by density functional theory calculations. Analyses of adsorption energy, electron density difference, and density of states indicated that the doped Ti atom could greatly improve the interaction of gas molecules with graphene. The Ti-doped graphene sheet demonstrated selective gas absorption. The order of interaction between the gas molecules and the Ti-doped graphene sheet was as follows: SO2 > NO > HCHO > CO. By contrast, the N-doped graphene sheet did not exhibit apparent selective gas absorption. These results imply that the Ti-doped graphene sheet is more effective than the N-doped graphene sheet in detecting and removing gas molecules because of its high selectivity.
Foury-Leylekian, Pascale; Pouget, Jean-Paul; Lee, Young-Joo; Nieminen, Risto M.; Ordejón, Pablo; Canadell, Enric
2010-10-01
α-(BEDT-TTF)2KHg(SCN)4 develops a density wave ground state below 8 K whose origin is still debated. Here we report a combined x-ray diffuse scattering and first-principles density functional theory study supporting the charge density wave (CDW) scenario. In particular, we observe a triply incommensurate anharmonic lattice modulation with intralayer wave vector components which coincide within experimental errors to the maximum of the calculated Lindhard response function. A detailed study of the structural aspects of the modulation shows that the CDW instability in α-(BEDT-TTF)2KHg(SCN)4 is considerably more involved than those following a standard Peierls mechanism. We thus propose a microscopic mechanism where the CDW instability of the BEDT-TTF layer is triggered by the anion sublattice. Our mechanism also emphasizes the key role of the coupling of the BEDT-TTF and anion layers via the hydrogen bond network to set the global modulation.
Shang, Jin; Li, Gang; Singh, Ranjeet; Xiao, Penny; Danaci, David; Liu, Jefferson Z.; Webley, Paul A.
2014-02-01
The crucial role of dispersion force in correctly describing the adsorption of some typical small-size gas molecules (e.g., CO2, N2, and CH4) in ion-exchanged chabazites has been investigated at different levels of theory, including the standard density functional theory calculation using the Perdew, Burke, and Ernzerhof (PBE) exchange-correlation functional and van der Waals density functional theory (vdWDFT) calculations using different exchange-correlation models - vdW_DF2, optB86b, optB88, and optPBE. Our results show that the usage of different vdWDFT functionals does not significantly change the adsorption configuration or the profile of static charge rearrangement of the gas-chabazite complexes, in comparison with the results obtained using the PBE. The calculated values of adsorption enthalpy using different functionals are compared with our experimental results. We conclude that the incorporation of dispersion interaction is imperative to correctly predict the trend of adsorption enthalpy values, in terms of different gas molecules and Cs+ cation densities in the adsorbents, even though the absolute values of adsorption enthalpy are overestimated by approximate 10 kJ/mol compared with experiments.
Komorovsky, Stanislav; Repisky, Michal; Malkin, Elena; Demissie, Taye B; Ruud, Kenneth
2015-08-11
We present an implementation of the nuclear spin-rotation (SR) constants based on the relativistic four-component Dirac-Coulomb Hamiltonian. This formalism has been implemented in the framework of the Hartree-Fock and Kohn-Sham theory, allowing assessment of both pure and hybrid exchange-correlation functionals. In the density-functional theory (DFT) implementation of the response equations, a noncollinear generalized gradient approximation (GGA) has been used. The present approach enforces a restricted kinetic balance condition for the small-component basis at the integral level, leading to very efficient calculations of the property. We apply the methodology to study relativistic effects on the spin-rotation constants by performing calculations on XHn (n = 1-4) for all elements X in the p-block of the periodic table and comparing the effects of relativity on the nuclear SR tensors to that observed for the nuclear magnetic shielding tensors. Correlation effects as described by the density-functional theory are shown to be significant for the spin-rotation constants, whereas the differences between the use of GGA and hybrid density functionals are much smaller. Our calculated relativistic spin-rotation constants at the DFT level of theory are only in fair agreement with available experimental data. It is shown that the scaling of the relativistic effects for the spin-rotation constants (varying between Z(3.8) and Z(4.5)) is as strong as for the chemical shieldings but with a much smaller prefactor.
Kraisler, Eli; Kelson, Itzhak
2010-01-01
The total energies and the spin states for atoms and their first ions with Z = 1-86 are calculated within the the local spin-density approximation (LSDA) and the generalized-gradient approximation (GGA) to the exchange-correlation (xc) energy in density-functional theory. Atoms and ions for which the ground-state density is not pure-state v-representable, are treated as ensemble v- representable with fractional occupations of the Kohn-Sham system. A newly developed algorithm which searches over ensemble v-representable densities [E. Kraisler et al., Phys. Rev. A 80, 032115 (2009)] is employed in calculations. It is found that for many atoms the ionization energies obtained with the GGA are only modestly improved with respect to experimental data, as compared to the LSDA. However, even in those groups of atoms where the improvement is systematic, there remains a non-negligible difference with respect to the experiment. The ab-initio electronic configuration in the Kohn-Sham reference system does not always equ...
Kussmann, Jörg; Ochsenfeld, Christian
2007-11-28
A density matrix-based time-dependent self-consistent field (D-TDSCF) method for the calculation of dynamic polarizabilities and first hyperpolarizabilities using the Hartree-Fock and Kohn-Sham density functional theory approaches is presented. The D-TDSCF method allows us to reduce the asymptotic scaling behavior of the computational effort from cubic to linear for systems with a nonvanishing band gap. The linear scaling is achieved by combining a density matrix-based reformulation of the TDSCF equations with linear-scaling schemes for the formation of Fock- or Kohn-Sham-type matrices. In our reformulation only potentially linear-scaling matrices enter the formulation and efficient sparse algebra routines can be employed. Furthermore, the corresponding formulas for the first hyperpolarizabilities are given in terms of zeroth- and first-order one-particle reduced density matrices according to Wigner's (2n+1) rule. The scaling behavior of our method is illustrated for first exemplary calculations with systems of up to 1011 atoms and 8899 basis functions.
Desmarets, Christophe; Gontard, Geoffrey; Cooksy, Andrew L; Rager, Marie Noelle; Amouri, Hani
2014-05-05
A novel palladium-based metallacage was self-assembled. This nanocage displayed two complementary effects that operate in synergy for guest encapsulation. Indeed, a metal complex, [Pt(NO2)4](2-), was hosted inside the cavity, as demonstrated by solution NMR studies. Single-crystal X-ray diffraction shows that the guest adopts two different orientations, depending on the nature of the host-guest interactions involved. A density functional theory computational study is included to rationalize this type of host-guest interaction. These studies pave the way to a better comprehension of chemical interaction and transformation within confined nanospaces.
Vegge, Tejs
2004-01-01
The dissociation of molecular hydrogen on a Mgs0001d surface and the subsequent diffusion of atomic hydrogen into the magnesium substrate is investigated using Density Functional Theory (DFT) calculations and rate theory. The minimum energy path and corresponding transition states are located using...... the nudged elastic band method, and rates of the activated processes are calculated within the harmonic approximation to transition state rate theory, using both classical and quantum partition functions based atomic vibrational frequencies calculated by DFT. The dissociation/recombination of H2 is found...... to be rate-limiting for the ab- and desorption of hydrogen, respectively. Zero-point energy contributions are found to be substantial for the diffusion of atomic hydrogen, but classical rates are still found to be within an order of magnitude at room temperature....
Ucun, Fatih; Sağlam, Adnan; Güçlü, Vesile
2007-06-01
The molecular structures, vibrational frequencies and corresponding vibrational assignments of xanthine and its methyl derivatives (caffeine and theobromine) have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-31G(d, p) basis set level. The calculations were utilized to the CS symmetries of the molecules. The obtained vibrational frequencies and optimised geometric parameters (bond lengths and bond angles) were seen to be well agreement with the experimental data. The used scale factors which have been obtained the ratio of the frequency values of the strongest peaks in the calculated and experimental spectra seem to cause the gained vibrations well corresponding to the experimental ones. Theoretical infrared intensities and Raman activities are also reported.
Öner, Nazmiye; Tamer, Ömer; Başoǧlu, Adil; Avcı, Davut; Atalay, Yusuf
2017-02-01
In this paper, quantum chemical calculations of (2e)-3-(3-Bromo-4-methoxyphenyl) -1-(pyridin-2-yl)prop-2-en-1-one were performed by using B3LYP and CAMB3LYP levels of density functional theory (DFT) with 6-311++G(d, p) basis set. Geometric parameters of the title molecule in the ground state were found to be in good agreement with experimental data. 13C and 1H NMR chemical shifts were calculated within GIAO approach which is one of the most common approaches. The frontier molecular orbitals (HOMO and LUMO) were simulated by the same levels. Nonlinear optical parameters (NLO) were also evaluated by determining of dipole moment, polarizability and first hyperpolarizability. All of calculations were carried out Gaussian 09 package program.
杨忠志; 沈尔忠
1995-01-01
On the basis of electronegativity expressed in density functional theory and electronegativity equalization principle, a new scheme for calculating the atomic charges in a molecule has been proposed and designed, which gives a new scale of the atomic electronegativity and hardness in a certain molecular environment and takes the harmonic mean electronegativity as a reference value of the molecular electronegativity so that the multiple-regression and nonuniform parameters in the original method are avoided. This approach can be easily and widely applied to the calculation of atomic charges for a big molecule and quite good results of atomic charges in some illustrated molecules are obtained as compared with those from the ab initio STO-3G SCF calculations.