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

Green's function calculation of Ballistic Electron Emission Microscopy currents (BEEM v2.1)

The Green function method for the two-surface problem

Surface states in (111) covalent faces are obtained as a function of the alkali coverage of the surface. The theoretical results are in good agreement with the available experimental evidence.

Alkali adsorbates and surface states in (111) covalent faces

A theoretical analysis of the metal-superconductor currents in the scanning tunneling microscope is presented. In our approach we use a tight-binding method and relate the metal-superconductor coupling to the Bardeen tunneling currents between the tip and the sample orbitals. The total tunneling intensity is calculated using the Keldish method; our expressions give the normal currents and the supercurrents as a function of the different tip and sample Green's functions, and their densities of states. We present calculations for different geometries simulating a planar-planar interface and the three-dimensional tip-sample interface of the microscope. Our results show that the effect of the small size associated with the tip is to reduce the supercurrents in the microscope.

Metal-superconductor supercurrents in the scanning tunneling microscope

In the conventional DFT+U approach, the mean field solution of the Hubbard Hamiltonian associated with the d or f (i σ) electrons of a transition metal atom is used to define the DFT+U potential acting on the i σ-electrons. In this work, by means of a many-body Density Functional solution of a Kanamori Hamiltonian (an extension of the atomic Hubbard Hamiltonian), that takes as independent variables of its DF-solution the orbital occupancies, niσ, of the atomic orbitals, we calculate in a first step the electronic properties for a transition metal atom connected to different channels representing an environment. Then, we use this analysis to introduce a DFT+U potential extending previous proposals to materials with arbitrarily high correlation. In particular, we find that this potential mainly screens the conventional mean field potential contribution, and also yields new terms associated with the number of atomic electrons. Our results show that the atomic correlation effects enhance the role played by the intra-atomic exchange interaction and favor the formation of magnetic solutions.

Fernando Flores

Papers

Green's function calculation of Ballistic Electron Emission Microscopy currents (BEEM v2.1)

The Green function method for the two-surface problem

Alkali adsorbates and surface states in (111) covalent faces

Metal-superconductor supercurrents in the scanning tunneling microscope

A local-orbital density functional formalism for a many-body atomic Hamiltonian: Hubbard-Hund's coupling and DFT + U functional.