Hydrogen bond symmetrization and elastic constants under pressure of δ-AlOOH.

The elastic constants of δ-AlOOH have been calculated for applied pressures in the range 0-40 GPa using three exchange-correlation functionals, i.e. PBEsol, TCAsol and PBE.

Stability of the different AlOOH phases under pressure.

The pressure effects on three different AlOOH structures (α, γ, and δ phases) are systematically analyzed by density functional theory with different exchange and correlation energy functional approximations, namely two local, two generalized-gradient approximation (GGA), and two GGA for solids (GGAsol). Phase stability, compressibility and hydrogen bond evolution are studied in a range of pressures from 0 to 30 GPa. In general, the use of GGAsol functionals is mandatory in order to have the correct phase stability order, a good description of the hydrogen bonds, and a close agreement with the experimental lattice parameters at the various pressures.

Global hybrids from the semiclassical atom theory satisfying the local density linear response.

We propose global hybrid approximations of the exchange-correlation (XC) energy functional which reproduce well the modified fourth-order gradient expansion of the exchange energy in the semiclassical limit of many-electron neutral atoms and recover the full local density approximation (LDA) linear response. These XC functionals represent the hybrid versions of the APBE functional [Phys. Rev.

Classical to quantum transition of heat transfer between two silica clusters.

Heat transfer between two silica clusters is investigated by using the nonequilibrium Green's function method. In the gap range between 4 Å and 3 times the cluster size, the thermal conductance decreases as predicted by the surface charge-charge interaction. Above 5 times the cluster size, the volume dipole-dipole interaction predominates.

Effective electron displacements: a tool for time-dependent density functional theory computational spectroscopy.

We extend our previous definition of the metric Δr for electronic excitations in the framework of the time-dependent density functional theory [C. A. Guido, P.

On the Metric of Charge Transfer Molecular Excitations: A Simple Chemical Descriptor.

A new index is defined with the aim of further exploring the metric of excited electronic states in the framework of the time-dependent density functional theory. This descriptor, called Δr, is based on the charge centroids of the orbitals involved in the excitations and can be interpreted in term of the hole-electron distance. The tests carried out on a set of molecules characterized by a significant number of charge-transfer excitations well illustrate its ability in discriminating between short (Δr ≤ 1.

Communication: one third: a new recipe for the PBE0 paradigm.

We analyze the performances of the parameter-free hybrid density functional PBE0-1/3 obtained combining the PBE generalized-gradient functional with a predefined amount of exact exchange of 1/3, as recently discussed by Cortona [J. Chem. Phys.

Assessing modern GGA functionals for solids.

We present periodic calculations carried out with Gaussian-type basis sets on a test set of 21 solids with nine exchange-correlation functionals, extending previous works performed with two parameter-free correlation functionals (TCA and revTCA) which showed promising results for molecules in terms of key structural and energetic properties. Two LDAs and seven GGAs were considered for the prediction of equilibrium lattice constants, bulk moduli, and cohesive energies, using the same test set for all properties when possible. The effect of combining the TCA correlation with exchange potentials other than the PBE form originally used is also addressed.

Density-functional calculations for large systems: can GGA functionals be competitive with hybrid functionals?

Two recently proposed correlation functionals, TCA and RevTCA, belonging to the generalized-gradient approximation (GGA) class, are briefly presented and their performances are discussed. The emphasis is put on the comparison with hybrid functionals, which are often the preferred ones for applications to molecular (but not to solid-state) systems. We show that the TCA and RevTCA performances are not far from those of hybrid functionals such as B3LYP or PBE0 when standard tests are performed and can be even better when less standard systems are considered.

Toward a combined DFT/QTAIM description of agostic bonds: the critical case of a Nb(III) complex.

A detailed analysis concerning the effect of the exchange-correlation functional on a prototypical agostic niobium complex has been carried out, with particular attention to a fundamental property of the functional, namely, the recovering of the uniform electron gas limit. The obtained results allow for revisiting the role of this limit for a proper description of the beta-H agostic interaction. Starting from these results, a new criterion for the bond analysis based on the electron density behavior is proposed.

A new parameter-free correlation functional based on an average atomic reduced density gradient analysis.

A new parameter-free correlation functional based on the local Ragot-Cortona approach [J. Chem. Phys.

Correlation energy of many-electron systems: a modified Colle-Salvetti approach.

The Colle and Salvetti approach [Theo. Chim. Acta 37, 329 (1975)] to the calculation of the correlation energy of a system is modified in order to explicitly include into the theory the kinetic contribution to the correlation energy.