Density functional and electron correlated study offive linear birefringences --- Kerr, Cotton---Mouton, Buckingham,Jones and magnetoelectric ---in gaseous benzene

We present the results of an extended study of five birefringences—Kerr, Cotton–Mouton, Buckingham, Jones, and Magnetoelectric—on benzene in the gas phase. The relevant molecular quantities—first-order properties, linear, quadratic, and cubic response functions—are computed employing the density-functional theory ~DFT! response theory, with a choice of functionals. In some cases, different functionals are employed for the wave-function computational step and for the subsequent analytical response calculation to determine the combination yielding at the same time the optimal energy and energy derivative results. Augmented correlation consistent basis sets of double and triple zeta quality are used. The DFT results are compared to those obtained at the Hartree–Fock level and in some cases within a coupled cluster singles and doubles electronic structure model. The study tries to assess the ability of the DFT response theory to describe a wide range of properties in a system of rather large size and high complexity. The relative strength of the five birefringences for plausible experimental conditions is determined and, when possible, comparison is made with the results of the measurements

Electronic structure of copper phthalocyanine: An experimental and theoretical study of occupied and unoccupied levels RID G-7348-2011

An experimental and theoretical study of the electronic structure of copper phthalocyanine (CuPc) molecule is presented. We performed x-ray photoemission spectroscopy (XPS) and photoabsorption [x-ray absorption near-edge structure (XANES)] gas phase experiments and we compared the results with self-consistent field, density functional theory (DFT), and static-exchange theoretical calculations. In addition, ultraviolet photoelectron spectra (UPS) allowed disentangling several outer molecular orbitals. A detailed study of the two highest occupied orbitals (having a(1u) and b(1g) symmetries) is presented: the high energy resolution available for UPS measurements allowed resolving an extra feature assigned to vibrational stretching in the pyrrole rings. This observation, together with the computed DFT electron density distributions of the outer valence orbitals, suggests that the a(1u) orbital (the highest occupied molecular orbital) is mainly localized on the carbon atoms of pyrrole rings and it is doubly occupied, while the b(1g) orbital, singly occupied, is mainly localized on the Cu atom. Ab initio calculations of XPS and XANES spectra at carbon K-edge of CuPc are also presented. The comparison between experiment and theory revealed that, in spite of being formally not equivalent, carbon atoms of the benzene rings experience a similar electronic environment. Carbon K-edge absorption spectra were interpreted in terms of different contributions coming from chemically shifted C 1s orbitals of the nonequivalent carbon atoms on the inner ring of the molecule formed by the sequence of CN bonds and on the benzene rings, respectively, and also in terms of different electronic distributions of the excited lowest unoccupied molecular orbital (LUMO) and LUMO+1. In particular, the degenerate LUMO appears to be mostly localized on the inner pyrrole ring

Impact Of Particle Agglomeration On Accumulation Rates In The Glass Discharge Riser Of HLW Melter

The major factor limiting waste loading in continuous high-level radioactive waste (HLW) melters is an accumulation of particles in the glass discharge riser during a frequent and periodic idling of more than 20 days. An excessive accumulation can produce robust layers a few centimeters thick, which may clog the riser, preventing molten glass from being poured into canisters. Since the accumulation rate is driven by the size of particles we investigated with x-ray microtomography, scanning electron microscopy, and image analysis the impact of spinel forming components, noble metals, and alumina on the size, concentration, and spatial distribution of particles, and on the accumulation rate. Increased concentrations of Fe and Ni in the baseline glass resulted in the formation of large agglomerates that grew over the time to an average size of ~185+-155 {mu}m, and produced >3 mm thick layer after 120 h at 850 deg C. The noble metals decreased the particle size, and therefore significantly slowed down the accumulation rate. Addition of alumina resulted in the formation of a network of spinel dendrites which prevented accumulation of particles into compact layers

Density functional theory study of electric and magnetic properties of hexafluorobenzene in the vapor phase

A series of electric and magnetic properties of hexafluorobenzene have been calculated, including the electric dipole polarizability, magnetizability, electric quadrupole moment, and nonlinear mixed electric dipole-magnetic dipole-electric quadrupole hyperpolarizabilities needed to obtain estimates of the Kerr, Cotton-Mouton, Buckingham, Jones, and magnetoelectric birefringences in the vapor phase. Time-dependent density-functional theory was employed for the calculation of linear-, quadratic, and cubic response functions. A number of density functionals have been considered, along with Sadlej’s triple-z basis set and the augmented correlation-consistent polarized valence double zeta and augmented correlation-consistent polarized valence triple zeta basis sets. Comparisons have been made with experiment where possible. The analysis of results allows for an assessment of the capability of time-dependent density-functional theory for high-order electromagnetic properties of an electron-rich system such as hexafluorobenzene

Linear-scaling implementation of molecular response theory in self-consistent field electronic-structure theory.

A linear-scaling implementation of Hartree-Fock and Kohn-Sham self-consistent field theories forthe calculation of frequency-dependent molecular response properties and excitation energies ispresented, based on a nonredundant exponential parametrization of the one-electron density matrixin the atomic-orbital basis, avoiding the use of canonical orbitals. The response equations are solvediteratively, by an atomic-orbital subspace method equivalent to that of molecular-orbital theory.Important features of the subspace method are the use of paired trial vectors to preserve thealgebraic structure of the response equations, a nondiagonal preconditioner for rapid convergence,and the generation of good initial guesses for robust solution. As a result, the performance of theiterative method is the same as in canonical molecular-orbital theory, with five to ten iterationsneeded for convergence. As in traditional direct Hartree-Fock and Kohn-Sham theories, thecalculations are dominated by the construction of the effective Fock/Kohn-Sham matrix, once ineach iteration. Linear complexity is achieved by using sparse-matrix algebra, as illustrated incalculations of excitation energies and frequency-dependent polarizabilities of polyalanine peptidescontaining up to 1400 atoms