Density functional calculations for prediction of ultra-thin film structure and properties

Most of the published theoretical and calculational effort on unsupported, ordered, ultra-thin films (``UTF``) in vacuo has focused on the thickest computationally feasible systems as models for surface properties of semi-infinite slabs. Crystalline periodic length scales in two cartesian dimensions combined with molecular- scale thickness in the third, however, make UTF`s strong candidates for the occurrence of quantum interference effects. Many UTF properties were predicted first from jellium slab models. A noteworthy prediction was that there would be large oscillations in the work function as a function of layer number. Extensive calculations on a variety of N-layers (N = 1,2,3... atomic planes) using all-electron, full-potential, local-spin-density approximation techniques show that the work function oscillation is weaker than expected but that there are significant layer-number dependences in the equilibrium lattice parameters, inter-planar spacings, electronic structure, density of states, and electronic stopping power. This paper reviews our own calculations as well as some others. Our objectives include the discernment of systematics within UTF`s, systematics in relationship to their counterpart crystals, relationship with surface properties, and appraisal of challenges to current models and methods

Issues and Challenges in Orbital-free Density Functional Calculations

Solving the Euler equation which corresponds to the energy minimum of a density functional expressed in orbital-free form involves related but distinct computational challenges. One is the choice between all-electron and pseudo-potential calculations and, if the latter, construction of the pseudo-potential. Another is the stability, speed, and accuracy of solution algorithms. Underlying both is the fundamental issue of satisfactory quality of the approximate functionals (kinetic energy and exchange-correlation). We address both computational issues and illustrate them by some comparative performance testing of our recently developed modified-conjoint generalized gradient approximation kinetic energy functionals. Comparisons are given for atoms, diatomic molecules, and some simple solids.Comment: submitted to Computer Physics Communication

Quasiparticle Density-Matrix Representation of Nonlinear TDDFT Response Functions

The time-dependent density functional (TDDFT) equations may be written either for the Kohn-Sham orbitals in Hilbert space or for the single electron density matrix in Liouville space. A collective-oscillator, quasiparticle, representation of the density response of many-electron systems which explicitly reveals the relevant electronic coherence sizes is developed using the Liouville space representation of adiabatic TDDFT. Closed expressions for the nonlinear density-density response are derived, eliminating the need to solve nonlinear integral equations, as required in the Hilbert space formulation of the response.Comment: 24 page

Estimates of global, regional, and national incidence, prevalence, and mortality of HIV, 1980�2015: the Global Burden of Disease Study 2015

Background Timely assessment of the burden of HIV/AIDS is essential for policy setting and programme evaluation. In this report from the Global Burden of Disease Study 2015 (GBD 2015), we provide national estimates of levels and trends of HIV/AIDS incidence, prevalence, coverage of antiretroviral therapy (ART), and mortality for 195 countries and territories from 1980 to 2015. Methods For countries without high-quality vital registration data, we estimated prevalence and incidence with data from antenatal care clinics and population-based seroprevalence surveys, and with assumptions by age and sex on initial CD4 distribution at infection, CD4 progression rates (probability of progression from higher to lower CD4 cell-count category), on and off antiretroviral therapy (ART) mortality, and mortality from all other causes. Our estimation strategy links the GBD 2015 assessment of all-cause mortality and estimation of incidence and prevalence so that for each draw from the uncertainty distribution all assumptions used in each step are internally consistent. We estimated incidence, prevalence, and death with GBD versions of the Estimation and Projection Package (EPP) and Spectrum software originally developed by the Joint United Nations Programme on HIV/AIDS (UNAIDS). We used an open-source version of EPP and recoded Spectrum for speed, and used updated assumptions from systematic reviews of the literature and GBD demographic data. For countries with high-quality vital registration data, we developed the cohort incidence bias adjustment model to estimate HIV incidence and prevalence largely from the number of deaths caused by HIV recorded in cause-of-death statistics. We corrected these statistics for garbage coding and HIV misclassification. Findings Global HIV incidence reached its peak in 1997, at 3·3 million new infections (95 uncertainty interval UI 3·1�3·4 million). Annual incidence has stayed relatively constant at about 2·6 million per year (range 2·5�2·8 million) since 2005, after a period of fast decline between 1997 and 2005. The number of people living with HIV/AIDS has been steadily increasing and reached 38·8 million (95% UI 37·6�40·4 million) in 2015. At the same time, HIV/AIDS mortality has been declining at a steady pace, from a peak of 1·8 million deaths (95% UI 1·7�1·9 million) in 2005, to 1·2 million deaths (1·1�1·3 million) in 2015. We recorded substantial heterogeneity in the levels and trends of HIV/AIDS across countries. Although many countries have experienced decreases in HIV/AIDS mortality and in annual new infections, other countries have had slowdowns or increases in rates of change in annual new infections. Interpretation Scale-up of ART and prevention of mother-to-child transmission has been one of the great successes of global health in the past two decades. However, in the past decade, progress in reducing new infections has been slow, development assistance for health devoted to HIV has stagnated, and resources for health in low-income countries have grown slowly. Achievement of the new ambitious goals for HIV enshrined in Sustainable Development Goal 3 and the 90-90-90 UNAIDS targets will be challenging, and will need continued efforts from governments and international agencies in the next 15 years to end AIDS by 2030. Funding Bill & Melinda Gates Foundation, and National Institute of Mental Health and National Institute on Aging, National Institutes of Health. © 2016 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY licens

Fulminant properties of high explosives equation of state studies. Quarterly report, January--March 1964

This project consists of (1) essentially routine experimentation, including evaluation of detonation velocity, gap sensitivity testing, and drop weight-impact machine testing; and (2) an experimental program whose goal is the development of high precision one and two-dimensional hydrodynamic data for use in establishing empirical detonation product equations of state

Kubo–Greenwood electrical conductivity formulation and implementation for projector augmented wave datasets

As the foundation for a new computational implementation, we survey the calculation of the complex electrical conductivity tensor based on the Kubo-Greenwood (KG) formalism (Kubo, 1957; Greenwood, 1958), with emphasis on derivations and technical aspects pertinent to use of projector augmented wave datasets with plane wave basis sets (BIlichl, 1994). New analytical results and a full implementation of the KG approach in an open-source Fortran 90 post-processing code for use with Quantum Espresso (Giannozzi et al., 2009) are presented. Named KGEC ([K]ubo [G]reenwood [E]lectronic [C]onductivity), the code calculates the full complex conductivity tensor (not just the average trace). It supports use of either the original KG formula or the popular one approximated in terms of a Dirac delta function. It provides both Gaussian and Lorentzian representations of the Dirac delta function (though the Lorentzian is preferable on basic grounds). KGEC provides decomposition of the conductivity into intra- and inter band contributions as well as degenerate state contributions. It calculates the dc conductivity tensor directly. It is MPI parallelized over k-points, bands, and plane waves, with an option to recover the plane wave processes for their use in band parallelization as well. It is designed to provide rapid convergence with respect to k-point density. Examples of its use are given.U.S. Dept. of Energy [DE-SC0002139]Pre-print submitted, no embargo.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]