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.The theoretical description of the optical properties of materials by first principles calculations is one of the classical issues in solid state physics. After photon absorption, the excitonic effects, driven by the electron and hole (e-h) interactions, are principal actors, rendering the ab initio computational description demanding. The most successful approach is, so far, based on ManyBody Perturbation theory: the GW self energy accounts for electron-electron (e-e) many-body effects in the band structure calculations, whereas the Bethe-Salpeter Equation is solved to introduce e-h interactions [1]. This accurate method has a limited applicability to large systems due to its high computational cost.Time-Dependent Density-Functional Theory (TD-DFT) is another theory for the exact treatment of excited states. Similarly to ground state DFT, its main drawback is to properly approximate the unknown dynamic exchange-correlation (xc) kernel f xc , which should account for both e-e and e-h interactions. From the very first attempt, the Homogeneous Electron Gas (HEG) model system had been employed in construction of xc kernels [2,3], and one of the most used approach was derived from local density approximation (LDA) xc potential v xc in the static regime, Adiabatic LDA (ALDA) [2]. ALDA has been successfully applied to molecules and clusters, but it usually becomes inappropriate in solids where the improvements with respect to the Random Phase Approximation (RPA) (with the trivial f xc = 0) are negligible. The introduction of shortrange non-locality, like in a generalized-gradient approximation (GGA) [4] or in a non-LDA (NLDA) [5] approach, does not improve with respect to LDA or RPA optical spectra. Main reason for this failure resides in the missed ultra-long range behaviour, 1/|r−r ′ | or 1/q 2 in reciprocal space, absent in HEG and HEG-based kernels. On the other hand, the introduced empirical long range contribution (LRC) kernel, f xc = α/q 2 [6-8], with α found related to the screening, correctly reproduces e-h excitonic effects but it is limited to semiconductors and small gap insulators. Very recently, renewed interest in this issue has been boosted by two new approaches. In the first one, the Bootstrap kernel [9] extends the LRC kernel to a matricial form and proposes a heuristic form for the LRC weight in terms of the screening which has to be calculated self-consistently. This method has been successfully applied to a wide range of bulk materials. In the second work [10], starting from the meta-GGA xc functiona...

We study the compatibility between the PBEsol exchange-correlation energy functional of Phys. Rev. Lett. 100, 136406 (2008) and the rVV10 van der Waals nonlocal correlation functional of Phys. Rev. B 87, 041108 (2013). By applying a density-gradient dependence in the expression of rVV10, we develop a new functional: The PBEsol + rVV10s functional, which is remarkably accurate for layered solids, rare-gas crystals, densely packed bulk solids, and the adsorption of noble-gas atoms on metal surfaces, and is also competitive for noncovalent interactions between molecular complexes as well as for potential-energy curves of noble-gas dimers. The capacity of this dispersion-corrected functional to describe various interactions in solids makes it useful for electronic-structure calculations in solid-state physics and materials science.

Using the semiclassical neutral atom theory, we extend to fourth order the modified gradient expansion of the exchange energy of density functional theory. This expansion can be applied both to large atoms and solid-state problems. Moreover, we show that it can be employed to construct a simple and non-empirical generalized gradient approximation (GGA) exchange-correlation functional competitive with state-of-the-art GGAs for solids, but also reasonably accurate for large atoms and ordinary chemistry.Comment: 10 pages, 7 figure

We investigate the interfacial electronic structure of the dipolar organic semiconductor vanadyl naphthalocyanine on Au(111) in a combined computational and experimental approach to understand the role of the permanent molecular dipole moment on energy-level alignment at this interface. First-principles Density Functional Theory (DFT) calculations on such large systems are challenging, due to the large computational cost and the need to accurately consider dispersion interactions. Our DFT results with dispersion correction show a molecular deformation upon adsorption but no strong chemical bond formation. Ultraviolet photoelectron spectroscopy measurements show a considerable workfunction change of −0.73(2) eV upon growth of the first monolayer, which is well reproduced by the DFT calculations. This shift originates from a large electron density “push-back” effect at the gold surface, whereas the large out-of-plane vanadyl dipole moment plays only a minor role.

Abstract:We extend the SG4 generalized gradient approximation, developed for covalent and ionic solids with a nonlocal van der Waals functional. The resulting SG4-rVV10m functional is tested, considering two possible parameterizations, for various kinds of bulk solids including layered materials and molecular crystals as well as regular bulk materials. The results are compared to those of similar methods, PBE + rVV10L and rVV10. In most cases, SG4-rVV10m yields a quite good description of systems (from iono-covalent to hydrogen-bond and dispersion interactions), being competitive with PBE + rVV10L and rVV10 for dispersion-dominated systems and slightly superior for iono-covalent ones. Thus, it shows a promising applicability for solid-state applications. In a few cases, however, overbinding is observed. This is analysed in terms of gradient contributions to the functional.