Assessment of exchange-correlation functionals for the calculation of dynamical properties of small clusters in time-dependent density functional theory (original) (raw)
Related papers
An extensive benchmarking of exchange-correlation functionals, pseudopotentials, and basis sets on real X-ray resolved nanoclusters has been carried out and reported here for the first time. The systems investigated and used for the tests are two undecagold and one Au + 24 -based nanoparticles stabilized by thiol and phosphine ligands. Time-dependent density-functional calculations have been performed for comparing results with experimental data on optical gaps. It has been observed that GGA functionals employing PBE-like correlation (viz. PBE itself, BPBE, BP86, and BPW91) coupled with an improved version of the LANL2DZ pseudopotential and basis set provide fairly accurate results for both structure and optical gaps of gold nanoparticles, at a reasonable computational cost. Good geometries have been also obtained using some global hybrid (e.g. PBE0, B3P86, B3PW91) and range separated hybrid (e.g. HSE06, LC-BLYP) functionals, even though they yield optical gaps that constantly overestimate the experimental findings. To probe the effect of the stabilizing organic ligands on the structural and electronic properties of the metal core, we have simulated the full metalorganic nanoparticles (whose diameter exceed the 2 nm threshold) with an ONIOM QM/QM' approach and at the density-functional level of theory. This work represents a first step toward the simulations of structural and opto-electronic properties of larger metal-organic particles suitable for a wide range of nanotechnological applications.
Theoretical Chemistry Accounts, 2016
Here we have investigated the structural and optical properties of five monolayer-protected gold nanoclusters with a combination of exchange-correlation functionals, namely B-PBE for the geometry relaxation and CAM-B3LYP for the time-dependent calculations. We have tested the accuracy of five different basis sets in reproducing the experimental structures of these nanoclusters, and we have found that even a rather small basis set (single zeta) can outperform a significantly larger one (double zeta) if some selected atoms are treated with polarization functions. Namely, the sulfur and phosphorous atoms of the capping thiols and phosphines usually are hypervalent when bonded to the gold inner core, therefore polarization functions allow them significantly more structural flexibility. With the two best performing basis sets we carried out optical calculations and found that the resulting UV-Vis profiles are largely similar, in particular for low energy transitions. In particular, the energy and orbital contributions of the optical gaps are very close. The results support the use of the small basis set proposed here to investigate larger nanoclusters with hybrid and range-corrected functionals.
The journal of physical chemistry. A, 2014
An extensive benchmark of exchange-correlation functionals on the structure of the X-ray resolved phosphine and thiolate-protected Ag14-based nanocluster, named XMC1, is reported. Calculations were performed both on simplified model systems, with the complexity of the ligands greatly reduced, and on the complete XMC1 particle. Most of the density functionals that yielded good relaxed structures on analogous calculations on gold nanoclusters (viz. those employing the generalized gradient approximation) significantly deform the structure of XMC1. On the contrary, some of the exchange-correlation functionals including part of the exact Hartree-Fock exchange (hybrid functionals) reproduce the experimental geometry with minimal errors. In particular, the widely adopted B3LYP yields fairly accurate structures for XMC1, whereas it is outperformed by many other functionals (both hybrids and generalized gradient corrected) in similar calculations on analogous gold-based systems. Time-depende...
Electronic structure calculations for nanomolecular systems
2005
The electronic structure constitutes the fundamentals on which a reliable quantitative knowledge of the electrical properties of materials should be based. Here, we first present an overview of the methods employed to elucidate the ground-state electronic properties, with an emphasis on the results of Density Functional Theory (DFT) calculations on selected cases of (bio)molecular nanostructures that are currently exploited as potential candidates for devices. In particular, we show applications to carbon nanotubes and assemblies of DNA-based homoguanine stacks. Then, to move ahead from the electronic properties to the computation of measurable features in the operation of nanodevices (e.g., transport characteristics, optical yield ), we proceed along two different lines to address two non-negligible issues: the role of excitations and the role of contacts. On one hand, for an accurate simulation of charge transport, as well as of optoelectronic features, the ground state is not sufficient and one needs to take into account the excited states of the system: to this aim, we introduce Time-Dependent DFT (TDDFT), we describe the TDDFT frameworks and their relation to the optical properties of materials. We present the application of TDDFT to compute the optical absorption spectra of fluorescent proteins and of DNA bases. On the other hand, the details of the conductor-leads interfaces are of crucial importance to determine the current under applied voltage, and one should compute the transport properties for a device geometry that mimics the experimental setup: to this aim, we introduce a novel development based on Wannier functions. The method, which is a framework for both an in-depth analysis of the electronic states and the plug-in of tight-binding parameters into the Green's function, is described with the aid of examples on nanostructures potentially relevant for device applications.
HAL (Le Centre pour la Communication Scientifique Directe), 2012
Understanding the charging kinetics of electric double layers is of fundamental importance for the design and development of novel electrochemical devices such as supercapacitors and field-effect transistors. In this work, we study the dynamic behavior of room-temperature ionic liquids using a classical time-dependent density functional theory that accounts for the molecular excluded volume effects, the electrostatic correlations, and the dispersion forces. While the conventional models predict a monotonic increase of the surface charge with time upon application of an electrode voltage, our results show that dispersion between ions results in a non-monotonic increase of the surface charge with the duration of charging. Furthermore, we investigate the effects of van der Waals attraction between electrode/ionic-liquid interactions on the charging processes.
Journal of Physics: Condensed Matter, 2014
The realization of metal–molecule junctions for future electronic devices relies on our ability to assemble these heterogeneous objects at a molecular level and understand their structure and the behavior of the electronic states at the interface. Delocalized interface states near the metal Fermi level are a key ingredient for tailoring charge injection, and such a delocalization depends on a large number of chemical, structural and morphological parameters, all influencing the spatial extension of the electron wavefunctions. Our large-scale dynamical simulations, combined with experiments, show that a double-decker organometallic compound (ferrocene) can be deposited on a Cu(111) surface, providing an ideal system to investigate the adsorption, the interface states and localized spin states at a metal–organometallic interface. Adsorbed ferrocene is shown to have a peculiar pattern and realizes a 2D-like interface state strongly resembling Shockley's surface state of Cu. By a subsequent deposition of single metal atoms on the adsorbed ferrocene, we analyze the sensitivity of the interface state to local modifications of the interface potential. This provides an insight into adsorption, spin configuration and charge redistribution processes, showing how to tune the electron behavior at a metal–molecule interface.
Benchmark Many-Body GW and Bethe–Salpeter Calculations for Small Transition Metal Molecules
Journal of Chemical Theory and Computation, 2014
We study the electronic and optical properties of 39 small molecules containing transition metal atoms and 7 others related to quantumdots for photovoltaics. We explore in particular the merits of the many-body GW formalism, as compared to the ΔSCF approach within density functional theory, in the description of the ionization energy and electronic affinity. Mean average errors of 0.2−0.3 eV with respect to experiment are found when using the PBE0 functional for ΔSCF and as a starting point for GW. The effect of partial self-consistency at the GW level is explored. Further, for optical excitations, the Bethe−Salpeter formalism is found to offer similar accuracy as time-dependent DFT-based methods with the hybrid PBE0 functional, with mean average discrepancies of about 0.3 and 0.2 eV, respectively, as compared to available experimental data. Our calculations validate the accuracy of the parameter-free GW and Bethe−Salpeter formalisms for this class of systems, opening the way to the study of large clusters containing transition metal atoms of interest for photovoltaic applications.
The electronic structure of the metal–organic interface of isolated ligand coated gold nanoparticles
Nanoscale advances, 2022
Light induced electron transfer reactions of molecules on the surface of noble metal nanoparticles (NPs) depend significantly on the electronic properties of the metal-organic interface. Hybridized metalmolecule states and dipoles at the interface alter the work function and facilitate or hinder electron transfer between the NPs and ligand. X-ray photoelectron spectroscopy (XPS) measurements of isolated AuNPs coated with thiolated ligands in a vacuum have been performed as a function of photon energy, and the depth dependent information of the metal-organic interface has been obtained. The role of surface dipoles in the XPS measurements of isolated ligand coated NPs is discussed and the binding energy of the Au 4f states is shifted by around 0.8 eV in the outer atomic layers of 4-nitrothiophenol coated AuNPs, facilitating electron transport towards the molecules. Moreover, the influence of the interface dipole depends significantly on the adsorbed ligand molecules. The present study paves the way towards the engineering of the electronic properties of the nanoparticle surface, which is of utmost importance for the application of plasmonic nanoparticles in the fields of heterogeneous catalysis and solar energy conversion.