The limitations of Slater's element-dependent exchange functional from analytic density functional theory

Our recent formulation of the analytic and variational Slater-Roothaan (SR) method, which uses Gaussian basis sets to variationally express the molecular orbitals, electron density and the one body effective potential of density functional theory, is reviewed. Variational fitting can be extended to the resolution of identity method,where variationality then refers to the error in each two electron integral and not to the total energy. It is proposed that the appropriate fitting functions be charge neutral and that all ab initio energies be evaluated using two-center fits of the two-electron integrals. The SR method has its root in the Slater's Xalpha method and permits an arbitrary scaling of the Slater-Gaspar-Kohn-Sham exchange-correlation potential around each atom in the system. Of several ways of choosing the scaling factors (Slater's exchange parameters), two most obvious are the Hartree-Fock (HF), alpha_HF, values and the exact atomic, alpha_EA, values. The performance of this simple analytic model with both sets for atomization energies of G2 set of 148 molecules is better than the local density approximation or the HF theory, although the errors in atomization energy are larger than the target chemical accuracy. To improve peformance for atomization energies, the SR method is reparametrized to give atomization energies of 148 molecules to be comparbale to those obtained by one of the most widely used generalized gradient approximations. The mean absolute error in ionization potentials of 49 atoms and molecules is about 0.5 eV and that in bond distances of 27 molecules is about 0.02 Angstrom. The overall good performance of the computationally efficient SR method using any reasonable set of alpha values makes it a promising method for study of large systems.Comment: 33 pages, Uses RevTex, to appear in The Journal of Chemical Physic

Accurate molecular energies by extrapolation of atomic energies using an analytic quantum mechanical model

Using a new analytic quantum mechanical method based on Slater's Xalpha method, we show that a fairly accurate estimate of the total energy of a molecule can be obtained from the exact energies of its constituent atoms. The mean absolute error in the total energies thus determined for the G2 set of 56 molecules is about 16 kcal/mol, comparable to or better than some popular pure and hybrid density functional models.Comment: 5 pages, REVTE

Energetic disorder at the metal/organic semiconductor interface

The physics of organic semiconductors is dominated by the effects of energetic disorder. We show that image forces reduce the electrostatic component of the total energetic disorder near an interface with a metal electrode. Typically, the variance of energetic disorder is dramatically reduced at the first few layers of organic semiconductor molecules adjacent to the metal electrode. Implications for charge injection into organic semiconductors are discussed.Comment: 9 pages, 2 figure

Evaluating the Mode of Inheritance in Tetraploid Alfalfa by Means of Genetic Intra-class Correlation

Observed segregation ratios for qualitative traits in tetraploid alfalfa have been interpreted on both disomic and tetrasomic modes of inheritance. In fact, some tetrasomic ratios cannot be distinguished from disomic ones (13) without intensive analysis. For quantitative traits, arbitrarily established segregation ratios in themselves are incapable of interpretation with respect to mode of inheritance. Progressive change and fitness in species depend upon continuous variation; analogously, it may be reasonably inferred that artificial plant improvement too, rests upon the exploitation of continuous variation. The alfalfa breeder, in particular, to complement his art with science, must be able to select superior plants with a minimum of error and then to combine such plants in the most effective numbers, and in the most efficient manner. He must then be able to predict the behavior of given combinations in advanced generations. Application of the methods of biometrical genetics to the solution of these problems depends first upon a knowledge of the mode of inheritance. The main objective of this thesis was to determine the mode of inheritance of quantitative traits in tetraploid alfalfa. Continuous variation, however, can only be studied through the statistical properties of the population. For purposes of this investigation, therefore, a statistic was required that would be amenable to both theoretical and experimental determination. It needed to be one to which some test of significance could be applied. A final requirement was that it be a statistic with theoretically different values dependent upon mode of inheritance. These three requirements, rigorously adhered to, set the course of the investigation. The genetic intra-class correlation was found to fulfill these requirements satisfactorily in the analysis of first generation selfed (S1) families. In this thesis, therefore, we have sought to evaluate the mode of inheritance, whether disomic or tetrasomic, by means of the genetic intra-class correlation

Distribution of averages in a correlated Gaussian medium as a tool for the estimation of the cluster distribution on size

Calculation of the distribution of the average value of a Gaussian random field in a finite domain is carried out for different cases. The results of the calculation demonstrate a strong dependence of the width of the distribution on the spatial correlations of the field. Comparison with the simulation results for the distribution of the size of the cluster indicates that the distribution of an average field could serve as a useful tool for the estimation of the asymptotic behavior of the distribution of the size of the clusters for "deep" clusters where value of the field on each site is much greater than the rms disorder.Comment: 15 pages, 6 figures, RevTe

Theoretical infra-red, Raman, and Optical spectra of the B36N36 cage

The B36N36 fullerene-like cage structure was proposed as candidate structure for the single-shell boron-nitride cages observed in electron-beam irradiation experiment. We have performed all electron density functional calculations, with large polarized Gaussian basis sets, on the B36N36 cage. We show that the cage is energetically and vibrationally stable. The infra-red, Raman and optical spectra are calculated. The predicted spectra, in combination with experimentally measured spectra, will be useful in conclusive assignment of the proposed B36N36 cage. The vertical and adiabatic ionization potentials as well as static dipole polarizability are also reported.Comment: RevTex, 4 pages, 4 figures (TO appear in Physical Review A (Breif Report)

The Lived Experience of Welfare Reform in Drug-Using Welfare-Needy Households in Inner-City New York

Welfare reform has transformed a needs-based family income support into temporary assistance for persons entering the workforce. This paper uses observations from an ethnographic study covering the period from 1995- 2001 to examine the impact on drug-using welfare-needy households in inner-city New York. The analysis suggests that studies may underestimate the extent to which substance use is associated with welfare problems. Nearly all of these already distressed households lost their AFDC/TANF benefits, had difficulty with work programs, and were having more difficulty covering expenses. The conclusion highlights ways to better study this population and policy initiatives that could help them reform their impoverished lives for themselves and their children

The Severely-Distressed African American Family in the Crack Era: Empowerment is not Enough

Numerous African American families have struggled for generations with persistent poverty, especially in the inner city. These conditions were further strained during the 1980s and 1990s by the widespread use of crack cocaine. For many, crack use became an obsession, dominated their lives, and superseded family responsibilities. This behavior placed additional pressure on already stressed kin support networks. This paper explores the processes prevailing in two households during this period. In the 2000s, children born to members of the Crack Generation are avoiding use of crack but face major deficits from their difficult childhoods. This presents both challenges and opportunities. The discussion considers initiatives from both a social problems and a strengths perspective that could help these families and help these families help themselves to advance their economic circumstances

Electronic and magnetic properties of some rare-earth dihydrides and dideuterides

Mössbauer spectroscopy has been used to study the electronic and magnetic properties of a number of rare-earth dihydrides and dideuterides. In stoichiometric ErH2 and DyH2, magnetic transitions and crystal field ground states have been established. In non-stoichiometric compounds DyH2+x and (Er)HoH2+x changes of the rare-earth point symmetry due to distributions in hydrogen site occupations are seen. This results in increases in the magnetic transition temperatures and distributions in the magnetic moments