Active site structure of NO decomposition on perovskite(-like) oxides: An investigation from experiment and density functional theory

Active site structure for NO decomposition carried out on perovskite-like oxides were discussed based on the N-2 yield measured from LaSrNi1-x,AlxO4 with different B-site cations and from La2-ySryCuO4 with different crystal phases. Results show that the active site contains two oxygen vacancies, two transition metals, and one lattice-oxygen, with the oxygen vacancy locating on the apex of MO6 octahedron, and the lattice oxygen locating between the two transition metals (i.e., M-O-M plane). Density functional theory (DFT) analysis to the structure shows that this new active site is the most active structure for NO adsorbing, and hence, for NO decomposition. The similar trend of the relative energies that are required for the formation of oxygen vacancies with f form (calculated from DFT), the amount of oxygen vacancies, and the activities (N-2 yield) certifies this result further.

Electronic structures of MCO (M = Nb, Ta, Rh, Ir, Pd, Pt) molecules by density functional theory

Equilibrium geometries, vibrational frequencies, and dissociation energies of the transition metal carbonyls MCO (M = Nb, Ta, Rh, Ir, Pd, Pt) were studied by use of diverse density functional methods B3LYP, BLYP, B3P86, B3PW91, BHLYP, BP86, and PBE1PBE. It was found that the ground electronic state is (6)Sigma(+) for NbCO and TaCO, (2)Sigma(+) for RhCO,(2)Delta for IrCO, and (1)Sigma(+) for PdCO and PtCO, in agreement with previous theoretical studies. The calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy. For most of the molecules, the predicted bond distance is in agreement with experiments and previous theoretical results. BHLYP is the worst method in reproducing the experimental results compared with the other density functional methods for the title molecules.

Electronic structures of hafnium dimer and trimer by density functional theory

Equilibrium geometries, vibrational frequencies and dissociation energies of hafnium dimer and trimer were studied by density functional methods B3LYP, BLYP, B3PW91, BHLYP, BP86, B3P86, mPW1PW91 and PBE1PBE. The results indicate that singlet is the ground state both for hafnium dimer and for trimer. For hafnium dimer, the calculated bond distance is less sensitive to the methods used. Except at BHLYP level, the calculated vibrational frequency is comparable to the experimental value. For hafnium trimer, equilateral triangle with D-3h symmetry is slightly favored compared with isosceles triangle with C-2v, symmetry except at BHLYP level. This conclusion is in agreement with experiment in which the ground state of Hf-3 is fluxional and low-spin or closed shell is preferred.

Electron affinities and ionization potentials of 4d and 5d transition metal atoms by CCSD(T), MP2 and density functional theory

The electron affinities and ionization potentials of 4d and 5d transition metal atoms were studied by CCSD(T), MP2 and density functional methods. The calculated results indicate that density functional method B3LYP has the best overall performance in predicting both electron affinity and ionization potential. SVWN gives largest IP and EA for 4d and 5d atoms. For the two basis sets used in this study, LANL2DZ and SDD, the performance of B3LYP/SDD combination is better than B3LYP/LANL2DZ, in particular for electron affinity calculation.

Self-assembly of star block copolymers by dynamic density functional theory

The dynamic mean-field density functional method, driven from the generalized time-dependent Ginzburg-Landau equation, was applied to the mesoscopic dynamics of the multi-arms star block copolymer melts in two-dimensional lattice model. The implicit Gaussian density functional expression of a multi-arms star block copolymer chain for the intrinsic chemical potentials was constructed for the first time. Extension of this calculation strategy to more complex systems, such as hyperbranched copolymer or dendrimer, should be straightforward. The original application of this method to 3-arms block copolymer melts in our present works led to some novel ordered microphase patterns, such as hexagonal (HEX) honeycomb lattice, core-shell HEX lattice, knitting pattern, etc. The observed core-shell HEX lattice ordered structure is qualitatively in agreement with the experiment of Thomas [Macromolecules 31, 5272 (1998)].

Theoretical investigation of LaC3n+ (n = 0, 1, 2) clusters by density functional theory

LaC3n+ (n = 0, 1, 2) clusters have been studied using B3LYP (Becke 3-parameter-Lee-Yang-Parr) density functional method. The basis set is Dunning/ Huzinaga valence double zeta for carbon and [2s2p2d] for lanthanum, denoted LANL1DZ. Four isomers are presented for each cluster; two of them are edge binding isomers with C-2 upsilon symmetry, the other two are Linear chains with C-infinity upsilon symmetry. Meanwhile, two spin states for each isomer, that is, singlet and triplet for LaC3+, doublet and quartet for LaC3 and LaC32+, respectively, are also considered. Geometries, vibrational frequencies, infrared intensities, and other quantities are reported and discussed. The results indicate that at some spin states; the C-2 upsilon symmetry isomers are the dominant structures, while for the other spin states, linear isomers are energetically favored. (C) 1998 John Wiley & Sons, Inc.

空间及言语工作记忆任务的情绪效应：来自ERP/ fMRI的证据

In the present study, based on processing efficiency theory, we used the event-related potentials (ERP) and functional magnetic resonance image (fMRI) techniques to explore the underlying neutral mechanism of influences of negative emotion on three subsystems of working memory, phonological loop、 visuospatial sketh pad and the central executive. The modified DSMT (delayed matching-to-sample task) and n-back tasks were adopted and IAPS (International Affective Picture System) pictures were employed to induce the expected emotional state of subjects. The main results and conclusions obtained in the series of experiments are as the following: 1. In DSM tasks, we found P200 and P300 were reduced by negative emotion in both spatial and verbal tasks, however the increased negative slow wave were only observed in spatial tasks, not in verbal tasks. 2. In n-back tasks, the updating function of WM associated P300 was affected by negative emotion only in spatial tasks, not in verbal tasks. Current density analysis revealed strong current density in the fronto-parietal cortex only in the spatial tasks as well. 3. We adopted fMRI-block design and ROIs analysis, and found significant emotion and task effects in spatial WM-associated right superior parietal cortex; only emotion effect in verbal WM-associated Broca’s area; the interaction effect in attention-associated medial prefrontal area and bilateral inferior parietal cortex. These results implied the negative emotion mainly disturbed the spatial WM-related areas, and the attention control system play a key role in the interaction of spatial WM and negative emotion. 4. to further examine the effects of positive、negative and neutral emotion on tasks with different cognitive loads, the selective effect of emotion on the ERP components of spatial WM was only found in 2-back tasks, not in visual searching tasks. So, firstly the positive emotion as well as negative emotion selectively disturbed on spatial WM in light of the attention resource competition mechanism. Secondly, the selective influences based on the different WM systems, not the properties of spatial and verbal information. At last, the manner of the interaction of emotion and cognition is correlated with the cognitive load.

Atomic layer deposition of copper – study through density functional theory

The wonder of the last century has been the rapid development in technology. One of the sectors that it has touched immensely is the electronic industry. There has been exponential development in the field and scientists are pushing new horizons. There is an increased dependence in technology for every individual from different strata in the society. Atomic Layer Deposition (ALD) is a unique technique for growing thin films. It is widely used in the semiconductor industry. Films as thin as few nanometers can be deposited using this technique. Although this process has been explored for a variety of oxides, sulphides and nitrides, a proper method for deposition of many metals is missing. Metals are often used in the semiconductor industry and hence are of significant importance. A deficiency in understanding the basic chemistry at the nanoscale for possible reactions has delayed the improvement in metal ALD. In this thesis, we study the intrinsic chemistry involved for Cu ALD. This work reports computational study using Density Functional Theory as implemented in TURBOMOLE program. Both the gas phase and surface reactions are studied in most of the cases. The merits and demerits of a promising transmetallation reaction have been evaluated at the beginning of the study. Further improvements in the structure of precursors and coreagent have been proposed. This has led to the proposal of metallocenes as co-reagents and Cu(I) carbene compounds as new set of precursors. A three step process for Cu ALD that generates ligand free Cu layer after every ALD pulse has also been studied. Although the chemistry has been studied under the umbrella of Cu ALD the basic principles hold true for ALD of other metals (e.g. Co, Ni, Fe ) and also for other branches of science like thin film deposition other than ALD, electrochemical reactions, etc.

Reformulating time-dependent density functional theory with non-orthogonal localized molecular orbitals.

Time-dependent density functional theory (TDDFT) has broad application in the study of electronic response, excitation and transport. To extend such application to large and complex systems, we develop a reformulation of TDDFT equations in terms of non-orthogonal localized molecular orbitals (NOLMOs). NOLMO is the most localized representation of electronic degrees of freedom and has been used in ground state calculations. In atomic orbital (AO) representation, the sparsity of NOLMO is transferred to the coefficient matrix of molecular orbitals (MOs). Its novel use in TDDFT here leads to a very simple form of time propagation equations which can be solved with linear-scaling effort. We have tested the method for several long-chain saturated and conjugated molecular systems within the self-consistent charge density-functional tight-binding method (SCC-DFTB) and demonstrated its accuracy. This opens up pathways for TDDFT applications to large bio- and nano-systems.

Less wiring, more firing: low-performing older adults compensate for impaired white matter with greater neural activity.

The reliable neuroimaging finding that older adults often show greater activity (over-recruitment) than younger adults is typically attributed to compensation. Yet, the neural mechanisms of over-recruitment in older adults (OAs) are largely unknown. Rodent electrophysiology studies have shown that as number of afferent fibers within a circuit decreases with age, the fibers that remain show higher synaptic field potentials (less wiring, more firing). Extrapolating to system-level measures in humans, we proposed and tested the hypothesis that greater activity in OAs compensates for impaired white-matter connectivity. Using a neuropsychological test battery, we measured individual differences in executive functions associated with the prefrontal cortex (PFC) and memory functions associated with the medial temporal lobes (MTLs). Using event-related functional magnetic resonance imaging, we compared activity for successful versus unsuccessful trials during a source memory task. Finally, we measured white-matter integrity using diffusion tensor imaging. The study yielded 3 main findings. First, low-executive OAs showed greater success-related activity in the PFC, whereas low-memory OAs showed greater success-related activity in the MTLs. Second, low-executive OAs displayed white-matter deficits in the PFC, whereas low-memory OAs displayed white-matter deficits in the MTLs. Finally, in both prefrontal and MTL regions, white-matter decline and success-related activations occurred in close proximity and were negatively correlated. This finding supports the less-wiring-more-firing hypothesis, which provides a testable account of compensatory over-recruitment in OAs.

Experimental and density functional theory study of the vibrational properties of 2-mercaptobenzimidazole in interaction with gold

The vibrational properties of the 2-mercaptobenzimidazole (MBI) molecule in interaction with gold were examined by a combined approach of FTIR measurements and density functional theory (DFT). A complete assignment of the 42 normal modes of MBI has been performed on the basis of DFT calculations at the B3PW91 level in complement to the Raman and FTIR spectra. Calculations demonstrated that, on the deprotonated MBI molecule, the negative charge is localized on the sulfur atom, favoring the formation of a gold-sulfur bond upon reaction of MBI with gold. This was confirmed by the very good agreement between the calculated spectrum and the experimental spectra of different gold-MBI compounds, indicating that the vibrational properties of adsorbed MBI are chiefly determined by the coordination through the sulfur atom. © 2006 American Chemical Society.

Can density functional theory (DFT) be used as an aid to a deeper understanding of tandem mass spectrometric fragmentation pathways?

Prediction of tandem mass spectrometric (MS/MS) fragmentation for non-peptidic molecules based on structure is of immense interest to the mass spectrometrist. If a reliable approach to MS/MS prediction could be achieved its impact within the pharmaceutical industry could be immense. Many publications have stressed that the fragmentation of a molecular ion or protonated molecule is a complex process that depends on many parameters, making prediction difficult. Commercial prediction software relies on a collection of general heuristic rules of fragmentation, which involve cleaving every bond in the structure to produce a list of 'expected' masses which can be compared with the experimental data. These approaches do not take into account the thermodynamic or molecular orbital effects that impact on the molecule at the point of protonation which could influence the potential sites of bond cleavage based on the structural motif. A series of compounds have been studied by examining the experimentally derived high-resolution MS/MS data and comparing it with the in silico modelling of the neutral and protonated structures. The effect that protonation at specific sites can have on the bond lengths has also been determined. We have calculated the thermodynamically most stable protonated species and have observed how that information can help predict the cleavage site for that ion. The data have shown that this use of in silico techniques could be a possible way to predict MS/MS spectra. Copyright (C) 2009 John Wiley & Sons, Ltd.