Correlated dynamics in aqueous proton diffusion.

The aqueous proton displays an anomalously large diffusion coefficient that is up to 7 times that of similarly sized cations. There is general consensus that the proton achieves its high diffusion through the Grotthuss mechanism, whereby protons hop from one molecule to the next. A main assumption concerning the extraction of the timescale of the Grotthuss mechanism from experimental results has been that, on average, there is an equal probability for the proton to hop to any of its neighboring water molecules.

Orbital angular momentum eigenfunctions for fast and numerically stable evaluations of closed-form pseudopotential matrix elements.

The computation of s-type Gaussian pseudopotential matrix elements involving low powers of the distance from the pseudopotential center using Gaussian orbitals can be reduced to familiar integrals. They may be directly expressed as either simple three-center overlap integrals for even powers of the radial distance from the pseudopotential center or related to the three-center nuclear integrals of a Gaussian charge distribution for odd powers. Orbital angular momentum about each atom is added to these integrals by solid-harmonic differentiation with respect to its center.

Sb@Ni@Sb and Sb@Pd@Sb Cluster Anions, Where n = +1, -1, -3, -4: Multi-Oxidation-State Clusters of Interpenetrating Platonic Solids.

KSb and KSb Zintl ion precursors react with Pd(PPh) in ethylenediamine/toluene/PBu solutions to give crystals of Sb@Pd@Sb/PBu salts, where n = 3, 4. The clusters are structurally identical in the two charge states, with nearly perfect I point symmetry, and can be viewed as an Sb@Pd icosahedron centered inside of an Sb dodecahedron. The metric parameters suggest very weak Sb-Sb and Pd-Pd interactions with strong radial Sb-Pd bonds between the Sb and Pd shells.

Density perturbation theory.

Despite the fundamental importance of electron density in density functional theory, perturbations are still usually dealt with using Hartree-Fock-like orbital equations known as coupled-perturbed Kohn-Sham (CPKS). As an alternative, we develop a perturbation theory that solves for the perturbed density directly, removing the need for CPKS. This replaces CPKS with a true Hohenberg-Kohn density perturbation theory.

Thermodynamic and kinetic stabilities of CO2 oligomers.

Density-functional and coupled cluster calculations suggest that the stability, against unimolecular dissociation, of the cyclic D(3h) trimer of CO2, 1,3,5-trioxetanetrione, is greater than all but one other chemically bound oligomer of CO2. It requires far less energy to produce, on a per CO2 basis, than the low-symmetry cyclic 1,2 dioxetanedione dimer, but its kinetic stability against unimolecular dissociation is much lower. The extreme stability of the dimer, which makes it an excellent intermediate in chemiluminescence, is caused by an extreme range of geometric change to its transition state leading to a trapezoidal potential energy surface.

Shattering dissociation in high-energy molecular collisions between nitrate esters.

We present ab initio molecular dynamics simulations of head-on collisions between ethyl nitrate molecules at collisional energies from 200 to 1200 kJ/mol. Above a threshold energy, an increasing fraction of the collisions led to rapid dissociation on impact--"shattering." The probability of the shattering dissociation was derived from the quasiclassical trajectories sampling the initial vibrational motion at T(vib) = 300 K.

Molecular dynamics simulation of yttria-stabilized zirconia (YSZ) crystalline and amorphous solids.

An empirically fitted atomic potential allows a classical molecular dynamics study of the static and dynamic properties of both crystalline and amorphous yttria-stabilized zirconia (YSZ) with typical dilute Y(2)O(3) concentrations (i.e. 3.

Self-consistent, constrained linear-combination-of-atomic-potentials approach to quantum mechanics.

Variational fitting gives a stationary linear-combination of atomic potentials (LCAP) approximation to the Kohn-Sham (KS) potential, V. That potential is central to density-functional theory because it generates all orbitals, occupied as well as virtual. Perturbation theory links two self-consistent field (SCF) calculations that differ by the perturbation.

Optical excitation energies, Stokes shift, and spin-splitting of C24H72Si14.

As an initial step toward the synthesis and characterization of sila-diamondoids, such as sila-adamantane (Si(10)H(16),T(d)), the synthesis of a fourfold silylated sila-adamantane molecule (C(24)H(72)Si(14),T(d)) has been reported in literature [Fischer et al., Science 310, 825 (2005)]. We present the electronic structure, ionization energies, quasiparticle gap, and the excitation energies for the Si(14)(CH(3))(24) and the exact silicon analog of adamantane Si(10)H(16) obtained at the all-electron level using the delta-self-consistent-field and transitional state methods within two different density functional models: (i) Perdew-Burke-Ernzerhof generalized gradient approximation and (ii) fully analytic density functional (ADFT) implementation with atom dependent potential.

Electronic structure and molecular dynamics of breaking the RO-NO2 bond.

Decomposition of energetic molecules such as pentaerythritol tetranitrate is accompanied by extensive changes in their electronic configuration and thus is challenging for ab initio Born-Oppenheimer molecular dynamics simulations. The performance of single-determinant methods (in particular, density-functional theory) is validated on electronic structure and molecular dynamics simulations of RO-NO(2) bond dissociation in a smaller nitric ester, ethyl nitrate. Accurate description of dissociating molecule requires using unrestricted, spin-symmetry-broken orbitals.

Lattice dielectric and thermodynamic properties of yttria stabilized zirconia solids.

A study of lattice dielectric and thermodynamic properties of yttria stabilized zirconia (YSZ) crystals as a function of yttria concentration is reported. This study is based on density functional perturbation theory, using ABINIT. Within the local density approximation and the harmonic approximation, we find excellent agreement between calculated and low temperature experimental specific heat and dielectric constants.

Variational, V-representable, and variable-occupation-number perturbation theories.

Density-functional perturbation theory with variationally fitted Kohn-Sham (KS) potentials is described. Requiring the Fock matrix and density matrix to commute through each order of perturbation theory determines the off-diagonal elements of the density matrix, and thus the effect of changing occupation numbers in density-functional perturbation theory. At each order of perturbation theory, the change in occupation numbers at that order enters only the diagonal part of the density matrix.

Dipole moments from atomic-number-dependent potentials in analytic density-functional theory.

Molecular dipole moments of analytic density-functional theory are investigated. The effect of element-dependent exchange potentials on these moments are examined by comparison with conventional quantum-chemical methods and experiment for the subset of the extended G2 set of molecules that have nonzero dipole moment. Fitting the Kohn-Sham [Phys.

The limitations of Slater's element-dependent exchange functional from analytic density-functional theory.

Our recent formulation of the analytic and variational Slater-Roothaan (SR) method, which uses Gaussian basis sets to variationally express the molecular orbitals, electron density, and the one-body effective potential of density-functional theory, is reviewed. Variational fitting can be extended to the resolution of identity method, where variationality then refers to the error in each two-electron integral and not to the total energy. However, a Taylor-series analysis shows that all analytic ab initio energies calculated with variational fits to two-electron integrals are stationary.

Slater's Exchange Parameters α for Analytic and Variational Xα Calculations.

Recently, we formulated a fully analytical and variational implementation of a subset of density functional theory using Gaussian basis sets to express orbital and the one-body effective potential. The implementation, called the Slater-Roothaan (SR) method, is an extension of Slater's Xα method, which allows arbitrary scaling of the exchange potential around each type of atom in a heteroatomic system. The scaling parameter is Slater's exchange parameter, α, which can be determined for each type of atom by choosing various criteria depending on the nature of problem undertaken.