Arthur J Freeman

Bio: Arthur J Freeman is an academic researcher from Northwestern University. The author has contributed to research in topics: Electronic band structure & Electronic structure. The author has an hindex of 96, co-authored 915 publications receiving 39210 citations. Previous affiliations of Arthur J Freeman include University of Paris & Northwest University (United States).

Full-potential self-consistent linearized-augmented-plane-wave method for calculating the electronic structure of molecules and surfaces: O 2 molecule

Abstract: The linearized-augmented-plane-wave (LAPW) method for thin films is generalized by removing the remaining shape approximation to the potential inside the atomic spheres. A new technique for solving Poisson's equation for a general charge density and potential is described and implemented in the film LAPW method. In the resulting full-potential LAPW method (FLAPW), all contributions to the potential are completely taken into account in the Hamiltonian matrix elements. The accuracy of the method---already well known for clean metal surfaces---is demonstrated for the case of a nearly free (noninteracting) ${\mathrm{O}}_{2}$ molecule which is a severe test case of the method because of its large anisotropic charge distribution. Detailed comparisons show that the accuracy of the FLAPW results for ${\mathrm{O}}_{2}$ exceeds that of existing state-of-the-art local-density linear-combination-of-atomic-orbitals (LCAO)-type calculations, and that taking the full potential LAPW results as a reference, the LCAO basis can be improved by adding off-site functions. Thus the full-potential LAPW is a unified method which is ideally suited to test not only molecular adsorption on surfaces, but also the components of the same system separately, i.e., the extreme limits of the molecule and the clean surface.

Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection

Abstract: The synthesis, crystal growth, and structural and optoelectronic characterization has been carried out for the perovskite compound CsPbBr3. This compound is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photoconductivity response, with detector resolution comparable to that of commercial, state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temperature does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approximately equal. The μτ product for electrons is comparable to cadmium zinc telluride (CZT) and that for holes is 10 times higher than CZT.

CsSnI3: Semiconductor or Metal? High Electrical Conductivity and Strong Near-Infrared Photoluminescence from a Single Material. High Hole Mobility and Phase-Transitions

Abstract: CsSnI3 is an unusual perovskite that undergoes complex displacive and reconstructive phase transitions and exhibits near-infrared emission at room temperature. Experimental and theoretical studies of CsSnI3 have been limited by the lack of detailed crystal structure characterization and chemical instability. Here we describe the synthesis of pure polymorphic crystals, the preparation of large crack-/bubble-free ingots, the refined single-crystal structures, and temperature-dependent charge transport and optical properties of CsSnI3, coupled with ab initio first-principles density functional theory (DFT) calculations. In situ temperature-dependent single-crystal and synchrotron powder X-ray diffraction studies reveal the origin of polymorphous phase transitions of CsSnI3. The black orthorhombic form of CsSnI3 demonstrates one of the largest volumetric thermal expansion coefficients for inorganic solids. Electrical conductivity, Hall effect, and thermopower measurements on it show p-type metallic behavior w...

Theoretical Investigation of Some Magnetic and Spectroscopic Properties of Rare-Earth Ions

Abstract: Investigations of some magnetic and spectroscopic properties of rare-earth ions based on approximate Hartree-Fock calculations are reported. First, a set of conventional, nonrelativistic Hartree-Fock wave functions were obtained for ${\mathrm{Ce}}^{3+}$, ${\mathrm{Pr}}^{3+}$, ${\mathrm{Nd}}^{3+}$, ${\mathrm{Sm}}^{3+}$, ${\mathrm{Eu}}^{2+}$, ${\mathrm{Gd}}^{3+}$, ${\mathrm{Dy}}^{3+}$, ${\mathrm{Er}}^{3+}$, and ${\mathrm{Yb}}^{3+}$; second, calculations for ${\mathrm{Ce}}^{3+}$ were carried out in which spin-orbit coupling was directly included in the conventional Hartree-Fock equations in order to obtain some estimate of wave-function dependence on $J$ and the resulting effects on experimental quantities. These results are then used to discuss spin-orbit splittings, hyperfine interactions, and the determination of nuclear magnetic moments, the Slater ${F}^{k}(4f, 4f)$ integrals, and the crystal-field parameters, ${{V}_{n}}^{m}={{A}_{n}}^{m}〈{r}^{n}〉$, all of which depend fairly critically on the precise form of the $4f$ wave functions. Comparisons are made with experiment and with the result of previous theoretical investigations which relied on either Hartree or modified hydrogenic wave functions or on semiempirical parametrizations. The usual spin-orbit formula, $〈\frac{{r}^{\ensuremath{-}1}\mathrm{dV}}{\mathrm{dr}}〉$, is found not to give agreement with experiment; the reasons for this are discussed, and some evidence is described which indicates the importance of including spin-orbit exchange terms between the $4f$ electrons and the core. The implications of this result for efforts to relate $〈{r}^{\ensuremath{-}3}〉$ integrals to experimentally observed spin-orbit coupling parameters are discussed, as is the relation (and use) of $〈{r}^{\ensuremath{-}3}〉$ integrals to the determination of nuclear magnetic moments. Our $〈{r}^{\ensuremath{-}3}〉$ values agree very closely (i.e., to within 5%) with Bleaney's parametrized values, and, hence, so do our estimates for the hyperfine interactions. A sampling of estimated rare-earth nuclear magnetic moments, based on the conventional Hartree-Fock $〈{r}^{\ensuremath{-}3}〉$ data, is given; comparison with previous estimates are made; and several causes of the uncertainty in these and all other estimates are discussed. The spectroscopic properties of these ions in a crystalline field are interpreted on the basis of the simple crystal-field theory. The $〈{r}^{n}〉$ integrals are found to be in good agreement for $n=2, 4, \mathrm{and} 6$ with the Elliott and Stevens parametrization formula, but the assumption of the constancy with $Z$ of the ${{A}_{n}}^{m}$ is not valid, as is shown by analysis of the available trichloride and ethyl-sulfate data. Systematic discrepancies between experimental and theoretical ${F}^{k}(4f, 4f)$ have been found which are similar to but greater than what has been previously observed for smaller ions. Finally, the role of spin polarization and aspherical distortions (of the closed shells and the $4f$ electrons) is indicated, particularly from the "unrestricted" Hartree-Fock point of view, and an estimate of the field due to polarization of the core electrons is given for all the ions. Results for smaller ions and their implications for the interpretation of observed rare-earth magnetic and spectroscopic properties are sketched.

Self-interaction correction to density-functional approximations for many-electron systems

Abstract: The exact density functional for the ground-state energy is strictly self-interaction-free (i.e., orbitals demonstrably do not self-interact), but many approximations to it, including the local-spin-density (LSD) approximation for exchange and correlation, are not. We present two related methods for the self-interaction correction (SIC) of any density functional for the energy; correction of the self-consistent one-electron potenial follows naturally from the variational principle. Both methods are sanctioned by the Hohenberg-Kohn theorem. Although the first method introduces an orbital-dependent single-particle potential, the second involves a local potential as in the Kohn-Sham scheme. We apply the first method to LSD and show that it properly conserves the number content of the exchange-correlation hole, while substantially improving the description of its shape. We apply this method to a number of physical problems, where the uncorrected LSD approach produces systematic errors. We find systematic improvements, qualitative as well as quantitative, from this simple correction. Benefits of SIC in atomic calculations include (i) improved values for the total energy and for the separate exchange and correlation pieces of it, (ii) accurate binding energies of negative ions, which are wrongly unstable in LSD, (iii) more accurate electron densities, (iv) orbital eigenvalues that closely approximate physical removal energies, including relaxation, and (v) correct longrange behavior of the potential and density. It appears that SIC can also remedy the LSD underestimate of the band gaps in insulators (as shown by numerical calculations for the rare-gas solids and CuCl), and the LSD overestimate of the cohesive energies of transition metals. The LSD spin splitting in atomic Ni and $s\ensuremath{-}d$ interconfigurational energies of transition elements are almost unchanged by SIC. We also discuss the admissibility of fractional occupation numbers, and present a parametrization of the electron-gas correlation energy at any density, based on the recent results of Ceperley and Alder.

Toward reliable density functional methods without adjustable parameters: The PBE0 model

Abstract: We present an analysis of the performances of a parameter free density functional model (PBE0) obtained combining the so called PBE generalized gradient functional with a predefined amount of exact exchange. The results obtained for structural, thermodynamic, kinetic and spectroscopic (magnetic, infrared and electronic) properties are satisfactory and not far from those delivered by the most reliable functionals including heavy parameterization. The way in which the functional is derived and the lack of empirical parameters fitted to specific properties make the PBE0 model a widely applicable method for both quantum chemistry and condensed matter physics.

Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides

Abstract: To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.

An all‐electron numerical method for solving the local density functional for polyatomic molecules

Abstract: A method for accurate and efficient local density functional calculations (LDF) on molecules is described and presented with results The method, Dmol for short, uses fast convergent three‐dimensional numerical integrations to calculate the matrix elements occurring in the Ritz variation method The flexibility of the integration technique opens the way to use the most efficient variational basis sets A practical choice of numerical basis sets is shown with a built‐in capability to reach the LDF dissociation limit exactly Dmol includes also an efficient, exact approach for calculating the electrostatic potential Results on small molecules illustrate present accuracy and error properties of the method Computational effort for this method grows to leading order with the cube of the molecule size Except for the solution of an algebraic eigenvalue problem the method can be refined to quadratic growth for large molecules