A new density functional (DF) of the generalized gradient approximation (GGA) type for general chemistry applications termed B97-D is proposed. It is based on Becke's power-series ansatz from 1997 and is explicitly parameterized by including damped atom-pairwise dispersion corrections of the form C(6) x R(-6). A general computational scheme for the parameters used in this correction has been established and parameters for elements up to xenon and a scaling factor for the dispersion part for several common density functionals (BLYP, PBE, TPSS, B3LYP) are reported. The new functional is tested in comparison with other GGAs and the B3LYP hybrid functional on standard thermochemical benchmark sets, for 40 noncovalently bound complexes, including large stacked aromatic molecules and group II element clusters, and for the computation of molecular geometries. Further cross-validation tests were performed for organometallic reactions and other difficult problems for standard functionals. In summary, it is found that B97-D belongs to one of the most accurate general purpose GGAs, reaching, for example for the G97/2 set of heat of formations, a mean absolute deviation of only 3.8 kcal mol(-1). The performance for noncovalently bound systems including many pure van der Waals complexes is exceptionally good, reaching on the average CCSD(T) accuracy. The basic strategy in the development to restrict the density functional description to shorter electron correlation lengths scales and to describe situations with medium to large interatomic distances by damped C(6) x R(-6) terms seems to be very successful, as demonstrated for some notoriously difficult reactions. As an example, for the isomerization of larger branched to linear alkanes, B97-D is the only DF available that yields the right sign for the energy difference. From a practical point of view, the new functional seems to be quite robust and it is thus suggested as an efficient and accurate quantum chemical method for large systems where dispersion forces are of general importance.

Semiempirical GGA-type density functional constructed with a long-range dispersion correction.

The reduction of graphene oxide

Mechanical properties of nanocrystalline materials

Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

In this contribution we address the theoretical understanding of weak chemical interactions and of the van der Waals forces, in conjunction with the last developments in this area and selected applications to nanostructures. In the first section, we highlight the importance of these interactions, in physics and chemistry and also in biology, and we recall early treatments of these issues, as those by van der Waals and London. After a brief review of the existing methods to treat such interactions, we present a model based on DFT (for each van der Waals-interacting independent system) and an intermolecular perturbation theory that uses a localized orbitals basis set. We will first detail a weak overlap expansion (LCAO-S 2 )a s a perturbation treatment to determine the weak chemical interaction. Then we will show how to implement the van der Waals interaction in the DFT solution, from the dipolar approximation in a perturbation theory. We apply this model to a reference system for weak interactions, i.e., the interaction between two planes of graphene. In the framework of a minimal basis set that describes each independent system and the weak chemical repulsion, we show that it is necessary to take into account atomic dipole transitions involving high excited states like 3d orbitals to properly describe the van der Waals interaction. We demonstrate how the delicate balance between chemical repulsion and van der Waals attractive interaction gives the equi- librium geometry and the binding energy of the system. Moreover, as an extension of this work, we obtain the adsorption energy of a carbon nanotube on graphene, the adsorption energy of a C60 molecule on a carbon nanotube, and the energy of a C60 molecule encapsulated in a carbon nanotube. This gives us the opportunity to discuss

https://www.springer.com/cda/content/document/cda_downloaddocument/9783642046490-c1.pdf?SGWID=0-0-45-855869-p173925309

Weak Chemical Interaction and van der Waals Forces: A Combined Density Functional and Intermolecular Perturbation Theory – Application to Graphite and Graphitic Systems

Ga adsorption on the Si(112) surface results in the formation of pseudomorphic Ga atom chains. Compressive strain in these atom chains is relieved via creation of adatom vacancies and their self-organization into meandering vacancy lines. The average spacing between these line defects can be controlled, within limits, by adjusting the chemical potential $\ensuremath{\mu}$ of the Ga adatoms. We derive a lattice model that quantitatively connects density functional theory (DFT) calculations for perfectly ordered structures with the fluctuating disorder seen in experiment and the experimental control parameter $\ensuremath{\mu}$. This hybrid approach of lattice modeling and DFT can be applied to other examples of line defects in heteroepitaxy.

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Controlled Self-Organization of Atom Vacancies in Monatomic Gallium Layers

Two-dimensional melting is one of the most fascinating and poorly understood phase transitions in nature. Theoretical investigations often point to a two-step melting scenario involving unbinding of topological defects at two distinct temperatures. Here, we report on a novel melting transition of a charge-ordered K-Sn alloy monolayer on a silicon substrate. Melting starts with short-range positional fluctuations in the K sublattice while maintaining long-range order, followed by longer-range K diffusion over small domains, and ultimately resulting in a molten sublattice. Concomitantly, the charge order of the Sn host lattice collapses in a multistep process with both displacive and order-disorder transition characteristics. Our combined experimental and theoretical analysis provides a rare insight into the atomistic processes of a multistep melting transition of a two-dimensional materials system.

Coupled Sublattice Melting and Charge-Order Transition in Two Dimensions.

Tunneling experiments in metal‐oxide superconductor have shown the existence of ‘‘leakage’’ currents for applied voltages V smaller than one‐half of the superconductor gap Δ. These currents are independent of temperature T. Recently experiments with scanning tunneling microscopy (STM) and squeezable tunnel junctions have shown that the observation of the superconductor gap depends strongly on the resistance in the junction. In fact only for resistances larger than ∼106 Ω the gap is clearly observable. These experiments have been explained in terms of the perturbative Hamiltonian formalism of Bardeen. However, it may happen that this theory while applicable for very large resistances may not be so for small tunnel resistances. We present here a nonperturbative theory in all orders of the transmitivity ‖To‖2 and show the existence of supercurrents for values of V<Δ at T=0. This is done by performing a matching in the junction between the superconductor Bogolubov wave functions for Copper pairs and the elect...

Theory of tunneling in metal-superconductor devices: Supercurrents in the superconductor gap at zero temperature

The electronic properties of H and He embedded in a uniform electron gas are studied from an atomic point of view abandoning the local density formalism. The effect of the electron gas on the bound states of the proton is analysed: (i) by using a linear dielectric response in which the free electrons are described by orthogonalised plane waves instead of plane wave states; (ii) by including the exchange and correlation effects between the orthogonalised plane waves and bound states. The electronic bound states are then determined by means of a variational procedure. By using many-body techniques, the quasiparticle spectrum is also determined. The authors results are in reasonable agreement with those obtained in the local density formalism.

Fernando Flores

Papers

Weak Chemical Interaction and van der Waals Forces: A Combined Density Functional and Intermolecular Perturbation Theory – Application to Graphite and Graphitic Systems

Controlled Self-Organization of Atom Vacancies in Monatomic Gallium Layers

Coupled Sublattice Melting and Charge-Order Transition in Two Dimensions.

Theory of tunneling in metal-superconductor devices: Supercurrents in the superconductor gap at zero temperature

Light impurities in a uniform electron gas