Publications (339)1342.71 Total impact

Article: Benchmarking Nuclear Fission Theory
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ABSTRACT: We suggest a small set of fission observables to be used as test cases for validation of theoretical calculations. The purpose is to provide common data to facilitate the comparison of different fission theories and models. The proposed observables are chosen from fission barriers, spontaneous fission lifetimes, fission yield characteristics, and fission isomer excitation energies.Journal of Physics G Nuclear and Particle Physics 02/2015; 42(7). DOI:10.1088/09543899/42/7/077001 · 2.84 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the energy deposition by very short laser pulses in SiO_2 (alphaquartz) with a view to establishing systematics for predicting damage and nanoparticle production. The theoretical framework is timedependent density functional theory, implemented by the realtime method in a multiscale representation. For the most realistic simulations we employ a metaGGA KohnSham potential similar to that of Becke and Johnson. We find that the deposited energy in the medium can be accurately modeled as a function of the local electromagnetic pulse fluence. The energydeposition function can in turn be quite well fitted to the strongfield Keldysh formula for a range of intensities from below the melting threshold to well beyond the ablation threshold. We find reasonable agreement between the damage threshold and the energy required to melt the substrate. The ablation threshold estimated by the energy to convert the substrate to an atomic fluid is higher than the measurement, indicating significance of nonthermal nature of the process. A fair agreement is found for the depth of the ablation.  [Show abstract] [Hide abstract]
ABSTRACT: The ground state octupole correlations energies obtained with the D1M variant of the Gogny force are analyzed in detail. First we consider the correlation energy gained at the mean field level by allowing reflection symmetry breaking. Next we consider the energy gain coming from symmetry (parity) restoration and finally we analyze the ground state correlation energy after configuration mixing with axially symmetric octupole states. We find that these correlations do not significantly affect the trends of binding energies and systematics near closed shells. In particular, the toolarge shell gaps predicted by selfconsistent mean field models are not altered by the correlations.  [Show abstract] [Hide abstract]
ABSTRACT: Deformation, a key concept in our understanding of heavy nuclei, is based on a meanfield description that breaks the rotational invariance of the nuclear manybody Hamiltonian. We present a method to analyze nuclear deformations at finite temperature in a framework that preserves rotational invariance. The auxiliaryfield MonteCarlo method is used to generate the statistical ensemble and calculate the probability distribution associated with the quadrupole operator. Applying the technique to nuclei in the rareearth region, we identify modelindependent signatures of deformation and find that deformation effects persist to higher temperatures than the sphericaltodeformed shape phasetransition temperature of meanfield theory.Physical Review Letters 08/2014; 113(26). DOI:10.1103/PhysRevLett.113.262503 · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We derive equations of motion for calculating the nearedge xray absorption spectrum in molecules and condensed matter, based on a twodeterminant approximation and Dirac's variational principle. The theory provides an exact solution for the linear response when the Hamiltonian or energy functional has only diagonal interactions in some basis. We numerically solve the equations to compare with the MahanNozièresDe Dominicis theory of the edge singularity in metallic conductors. Our extracted powerlaw exponents are similar to those of the analytic theory, but are not in quantitative agreement. The calculational method can be readily generalized to treat KohnSham Hamiltonians with electronelectron interactions derived from correlationexchange potentials.Physical Review B 01/2014; 89(7). DOI:10.1103/PhysRevB.89.075135 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the dielectric response of crystalline silicon following irradiation by a highintensity laser pulse, modeling the dynamics by the timedependent KohnSham equations in the presence of the laser field. Pumpprobe measurements of the response are numerically simulated by including both pump and probe externals fields in the simulation. As expected, the excited silicon shows features of an electronhole plasma of nonequilibrium phase in its response, characterized by a negative divergence in the real part of the dielectric function at small frequencies. The response to the probe pulse depends on the polarization of the pump pulse. We also find that the imaginary part of the dielectric function can be negative, particularly for the parallel polarization of pump and probe fields. We compare the calculated response with a simple Drude model. The real part of the dielectric function is well fitted by the model, treating the effective mass as a fitting parameter while taking electron density from the calculation. The fitted effective masses are consistent with carrierband dispersions.Physical Review B 01/2014; 89(6). DOI:10.1103/PhysRevB.89.064304 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Levels densities of independentparticle Hamiltonians can be calculated easily by using the realtime representation of the evolution operator together with the fast Fourier transform. We describe the method and implement it with a set of Python programs. Examples are provided for the total and partial levels densities of a heavy deformed nucleus (Dy164). The partial level densities that may be calculated are the projected ones on neutron number, proton number, azimuthal angular momentum, and parity.Computer Physics Communications 01/2014; DOI:10.1016/j.cpc.2014.08.012 · 2.41 Impact Factor 
Conference Paper: Abinitio theoretical approach to coherent phonon generation in solids
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ABSTRACT: We investigate mechanisms of coherent phonon generation in timedependent densityfunctional theory. It provides intuitive understanding of the generation mechanism as well as its change depending on electric field frequency.International Conference on Ultrafast Phenomena; 01/2014  [Show abstract] [Hide abstract]
ABSTRACT: The GallagherMoszkowski rule in the spectroscopy of oddodd nuclei imposes a new spin constraint on the energy functionals for selfconsistent mean field theory. The commonly used parameterization of the effective threebody interaction in the Gogny and Skyrme families of energy functionals is illsuited to satisfy the spin constraint. In particular, the Gogny parameterization of the threebody interaction has the opposite spin dependence to that required by the observed spectra. The twobody part has a correct sign, but in combination the rule is violated as often as not. We conclude that a new functional form is needed for the effective threebody interaction that can take into better account the different spinisospin channels of the interaction.Physical Review C 10/2013; 89(2). DOI:10.1103/PhysRevC.89.021303 · 3.88 Impact Factor 
Dataset: JChemPhys.134.144106
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ABSTRACT: We derive a timedependent density functional theory appropriate for calculating the nearedge Xray absorption spectrum in molecules and condensed matter. The basic assumption is to increase the space of manybody wave functions from one Slater determinant to two. The equations of motion derived from Dirac's variational principle provide an exact solution for the linear response when the interaction Hamiltonian has only a coreelectron field. The equations can be solved numerically nearly as easily as the ordinary realtime timedependent KohnSham equations. We carry out the solution under conditions that permit comparison with the expected powerlaw behavior. Our extracted powerlaw exponents are similar to those derived by Nozieres and DeDominicis, but are not in quantitative agreement. We argue that our calculational method can be readily generalized to density functionals that take into account the more general electronelectron interactions that are needed for treating dynamic effects such as plasmon excitations. 
Dataset: JChemPhys.134.144106
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ABSTRACT: We have been developing a theoretical framework to describe electron dynamics in a crystalline solid under an ultrashort laser pulse. We rely upon the timedependent density functional theory, solving the timedependent KohnSham equation in realtime and realspace. Using our method, it is possible to describe both linear and nonlinear lightmatter interactions in a unified way. In my presentation, I will focus on the application to coherent phonon generation, a coherent atomic oscillation over a macroscopic volume. I will show applications to two material, semiconductor Si and semimetal Sb. For Si, we have found that the TDDFT is capable of describe two distinct mechanisms of the coherent phonon generation. When the laser frequency is below the direct bandgap, virtual electronic excitation induces impulsive force to atoms. When the laser frequency is above the gap, real electronic excitation causes the atomic motion. For Sb, we study the frequency dependence of the coherent phonon generation and compare our results with phenomenological theories. 
Article: Erratum: "Nonadiabatic generation of coherent phonons" [J. Chem. Phys. 137, 22A527 (2012)].
The Journal of Chemical Physics 01/2013; 138(2):029903. DOI:10.1063/1.4776755 · 3.12 Impact Factor 
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ABSTRACT: As part of a program to study oddA nuclei in the HartreeFockBogoliubov (HFB) theory, we have developed a new calculational tool to find the HFB minima of oddA nuclei based on the gradient method and using interactions of Gogny's form. The HFB minimization includes both timeeven and timeodd fields in the energy functional, avoiding the commonly used "filling approximation". Here we apply the method to calculate neutron pairing gaps in some representative isotope chains of spherical and deformed nuclei, namely the Z=8,50 and 82 spherical chains and the Z=62 and 92 deformed chains. We find that the gradient method is quite robust, permitting us to carry out systematic surveys involving many nuclei. We find that the timeodd field does not have large effect on the pairing gaps calculated with the Gogny D1S interaction. Typically, adding the Todd field as a perturbation increases the pairing gap by ~100 keV, but the reminimization brings the gap back down. This outcome is very similar to results reported for the Skyrme family of nuclear energy density functionals. Comparing the calculated gaps with the experimental ones, we find that the theoretical errors have both signs implying that the D1S interaction has a reasonable overall strength. However, we find some systematic deficiencies comparing spherical and deformed chains and comparing the lighter chains with the heavier ones. The gaps for heavy spherical nuclei are too high, while those for deformed nuclei tend to be too low. The calculated gaps of spherical nuclei show hardly any Adependence, contrary to the data. Inclusion of the Todd component of the interaction does not change these qualitative findings.Physical Review C 10/2012; 86(6). DOI:10.1103/PhysRevC.86.064313 · 3.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The timedependent density functional theory (TDDFT) is the leading computationally feasible theory to treat excitations by strong electromagnetic fields. Here the theory is applied to coherent optical phonon generation produced by intense laser pulses. We examine the process in the crystalline semimetal antimony (Sb), where nonadiabatic coupling is very important. This material is of particular interest because it exhibits strong phonon coupling and optical phonons of different symmetries can be observed. The TDDFT is able to account for a number of qualitative features of the observed coherent phonons, despite its unsatisfactory performance on reproducing the observed dielectric functions of Sb. A simple dielectric model for nonadiabatic coherent phonon generation is also examined and compared with the TDDFT calculations.The Journal of Chemical Physics 08/2012; 137(22):22A527. DOI:10.1063/1.4739844 · 3.12 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Spectroscopic observables such as electromagnetic transitions strengths can be related to the properties of the intrinsic meanfield wave function when the latter are strongly deformed, but the standard rotational formulas break down when the deformation decreases. Nevertheless there is a welldefined, nonzero, spherical limit that can be evaluated in terms of overlaps of meanfield intrinsic deformed wave functions. We examine the transition between the spherical limit and strongly deformed one for a range of nuclei comparing the two limiting formulas with exact projection results. We find a simple criterion for the validity of the rotational formula depending on $<\Delta \vec{J}^2>$, the mean square fluctuation in the angular momentum of the intrinsic state. We also propose an interpolation formula which describes the transition strengths over the entire range of deformations, reducing to the two simple expressions in the appropriate limits.Physical Review C 06/2012; 86(5). DOI:10.1103/PhysRevC.86.054306 · 3.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The HartreeFockBogoliubov approximation is very useful for treating both long and shortrange correlations in finite quantum fermion systems, but it must be extended in order to describe detailed spectroscopic properties. One problem is the symmetrybreaking character of the HFB approximation. We present a general and systematic way to restore symmetries and to extend the configuration space using pfaffian formulas for the manybody matrix elements. The advantage of those formulas is that the sign of the matrix elements is unambiguously determined. It is also helpful to extend the space of configurations by constraining the HFB solutions in some way. A powerful method for finding these constrained solutions is the gradient method, based on the generalized Thouless transformation. The gradient method also preserves the number parity of the Bogoliubov transformation, which facilitates the application of the theory to systems with odd particle number.  [Show abstract] [Hide abstract]
ABSTRACT: We show that longrange correlations for nuclear masses have a significant effect on the synthesis of heavy elements by the rprocess. As calculated by Delaroche et al. [1], these correlations suppress magic number effects associated with minor shells. This impacts the calculated abundances before the third rprocess peak (at mass number A~195), where the abundances are low and form a trough. This trough and the position of the third abundance peak are strongly affected by the masses of nuclei in the transition region between deformed and spherical. Based on different astrophysical environments, our results demonstrate that a microscopic theory of nuclear masses including correlations naturally smoothens the separation energies, thus reducing the trough and improving the agreement with observed solar system abundances.Physical Review Letters 04/2012; 108(15):151101. DOI:10.1103/PhysRevLett.108.151101 · 7.73 Impact Factor
Publication Stats
14k  Citations  
1,342.71  Total Impact Points  
Top Journals
 Physical Review C (103)
 Physics Letters B (32)
 Nuclear Physics A (31)
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Institutions

1994–2015

University of Washington Seattle
 • Institute for Nuclear Theory
 • Department of Physics
Seattle, Washington, United States


1974–1998

Michigan State University
 Department of Physics and Astronomy
East Lansing, MI, United States


1987–1988

McGill University
 Department of Physics
Montréal, Quebec, Canada


1985–1986

The University of Tennessee Medical Center at Knoxville
Knoxville, Tennessee, United States 
University of Tennessee
Knoxville, Tennessee, United States 
Oak Ridge National Laboratory
 Physics Division
Oak Ridge, Florida, United States 
Joint Institute for Heavy Ion Research
Oak Ridge, Tennessee, United States


1981–1986

State of Michigan
Lansing, Michigan, United States


1982

University of California, Santa Barbara
Santa Barbara, California, United States


1977

Lawrence Berkeley National Laboratory
Berkeley, California, United States
