Optical spectra of solids obtained by time-dependent density-functional theory with the jellium-with-gap model exchange-correlation kernel

Within the framework of ab initio time-dependent density-functional theory (TD-DFT), we propose a static approximation to the exchange-correlation kernel based on the jellium-with-gap model. This kernel accounts for electron-hole interactions and it is able to address both strongly bound excitons and weak excitonic effects. TD-DFT absorption spectra of several bulk materials (both semiconductor and insulators) are reproduced in very good agreement with the experiments and with a low computational cost.Comment: 5 pages, 3 figures, 1 tabl

High-Level Correlated Approach to the Jellium Surface Energy, Without Uniform-Electron-Gas Input

We resolve the long-standing controversy over the surface energy of simple metals: Density functional methods that require uniform-electron-gas input agree with each other at many levels of sophistication, but not with high-level correlated calculations like Fermi Hypernetted Chain and Diffusion Monte Carlo (DMC) that predict the uniform-gas correlation energy. Here we apply a very high-level correlated approach, the inhomogeneous Singwi-Tosi-Land-Sj\"olander (ISTLS) method, and find that the density functionals are indeed reliable (because the surface energy is "bulk-like"). ISTLS values are close to recently-revised DMC values. Our work also vindicates the previously-disputed use of uniform-gas-based nonlocal kernels in time-dependent density functional theory.Comment: 4 pages, 1 figur

Dimensional crossover of the exchange-correlation energy at the semilocal level

Commonly used semilocal density functional approximations for the exchange-correlation energy fail badly when the true two dimensional limit is approached. We show, using a quasi-two-dimensional uniform electron gas in the infinite barrier model, that the semilocal level can correctly recover the exchange-correlation energy of the two-dimensional uniform electron gas. We derive new exact constraints at the semilocal level for the dimensional crossover of the exchange-correlation energy and we propose a method to incorporate them in any exchange-correlation density functional approximation.Comment: 6 pages, 5 figure

Towards adiabatic-connection interpolation model with broader applicability

The Adiabatic Connection Integrand Interpolation (ACII) method represents a general path for calculating correlation energies in electronic systems within the Den sity Functional Theory. ACII functionals include both exact-exchange and the second-order correlation energy, as well as an interpolating function toward the strictly-correlated electron (SCE) regime. Several interpolating functions have been proposed in the last years targeting different properties, yet an accurate ACII approach with broad applicability is sti ll missing. Recently, we have proposed an ACII functional that was made accurate for the three-dimensional (3D) uniform electron gas as well as for model metal clusters. In this work we present an ACII functional (named genISI2) which is very accurate for both three-dimensional (3D) and two-dimensional (2D) uniform electron gases and for the q uasi-2D infinite barrier model, where most of the exchange-correlation functionals fail badly, as well as for strongly correlated two-electrons systems. Using the exact-exchange Kohn-Sham orbitals, we have also assessed the genISI2 for various molecular systems, showing a superior performance with respect to the o ther ACII methods for total energies, atomization energies, and ionization potentials. The genISI2 functional can thus find application in a broad range of systems and properties

Simple and accurate screening parameters for dielectric-dependent hybrids

A simple effective screening parameter for screened range-separated hybrid is constructed from the compressibility sum rule in the context of linear-response time-dependent Density Functional Theory. When applied to the dielectric-dependent hybrid (DDH), it becomes remarkably accurate for bulk solids compared to those obtained from fitting with the model dielectric function or depending on the valence electron density of materials. The present construction of the screening parameter is simple and realistic. The screening parameter developed in this way is physically appealing and practically useful as it is straightforward to obtain using the average over the unit cell volume of the bulk solid, bypassing high-level calculations of the dielectric function depending on random-phase approximation. Furthermore, we have obtained a very good accuracy for energy band gaps, positions of the occupied d-bands, ionization potentials, optical properties of semiconductors and insulators, and geometries of bulk solids (equilibrium lattice constants and bulk moduli) from the constructed DDH.Comment: 13 page

Ionization potentials in the limit of large atomic number

By extrapolating the energies of non-relativistic atoms and their ions with up to 3000 electrons within Kohn-Sham density functional theory, we find that the ionization potential remains finite and increases across a row, even as $Z\rightarrow\infty$. The local density approximation becomes chemically accurate (and possibly exact) in some cases. Extended Thomas-Fermi theory matches the shell-average of both the ionization potential and density change. Exact results are given in the limit of weak electron-electron repulsion.Comment: 4 pages, 5 figure