Generalized generalized gradient approximation: An improved density-functional theory for accurate orbital eigenvalues

The generalized gradient approximation (GGA) for the exchange functional in conjunction with accurate expressions for the correlation functional have led to numerous applications in which density-functional theory (DFT) provides structures, bond energies, and reaction activation energies in excellent agreement with the most accurate ab initio calculations and with the experiment. However, the orbital energies that arise from the Kohn-Sham auxiliary equations of DFT may differ by a factor of 2 from the ionization potentials, indicating that excitation energies and properties involving sums over excited states (nonlinear-optical properties, van der Waals attraction) may be in serious error.mWe propose herein a generalization of the GGA in which the changes in the functionals due to virtual changes in the orbitals are allowed to differ from the functional used to map the exact density onto the exact energy. Using the simplest version of this generalized GGA we show that orbital energies are within ∼5% of the correct values and the long-range behavior has the correct form

Lancifodilactone G : insights about an unusually stable enol

From quantum mechanics calculations we confirm that the naturally occurring enol lancifodilactone G is stable over the keto form (by 2.6 kcal/mol in water), the only known stable aliphatic enol (devoid of conjugated or bulky aromatics and lacking a 1,3-diketone structural motif known to stabilize enols). We determine architectural elements responsible for the enol stabilization and find a mechanism for keto-enol conversion in solution. In addition, we correct previously reported computational results that were performed on the misinterpreted structure demonstrating that the enol form of this natural product is more stable than previously thought

The electronic structure of pyrazine. Configuration interaction calculations using an extended basis

Extensive ab initio double zeta basis set configuration interaction calculations have been carried out on the nπ^∗ and ππ^∗ states of pyrazine as well as on the low‐lying n and π cations. The calculations corroborate the validity of the valence bond (VB) model for the interaction of lone pair excitations proposed earlier by Wadt and Goddard. Good agreement (errors of ∼0.2 eV) with experiment is obtained (except for the higher‐lying 1ππ∗ states that possess significant ionic character). The calculations indicate that the order of increasing ionization potentials is ^2A_g(n), 2B_(1g)(π), 2B_(1u)(n), and ^2B_(2g)(π). The forbidden 1 ^1B_(2g)(nπ^∗) state is predicted to be 1.30 eV above the allowed 1^ 1B_(3u)(nπ^∗) state. Finally, the calculations indicate that the adiabatic excitation energies to the 1^ 3B_1(nπ^∗) and 1^ 3A_1(ππ^∗) states in pyridine should be nearly degenerate at ∼3.6 eV

Molecular mechanics and molecular dynamics analysis of Drexler-Merkle gears and neon pump

Over the past two years at the Materials and Process Simulation Center, we have been developing simulation approaches for studying the molecular nanomachine designs pioneered by Drexler and Merkle. These nanomachine designs, such as planetary gears and neon pump, are described with atomistic details and involve up to 10 000 atoms. With the Dreiding and universal force fields, we have optimized the structures of the two planetary gear designs and the neon pump. At the Fourth Foresight conference, we reported rotational impulse dynamics studies of the first and second generation designs of planetary gears undergoing very high-frequency rotational motions. We will explore stability of these designs in the lower frequency regimes which require long time simulations. We will report the molecular mechanics and molecular dynamics simulations performed on these model systems. We explore the following modes in these studies: (1) impulse mode; (2) constant angular velocity - perpetual rotation; (3) constant torque - acceleration from rest

Attitudes Towards and Satisfaction with Credit Unions in Alberta. A Regression and Scale Analysis.

Credit unions have played an important historical role in the Canadian economy. However, recent changes in the financial, agricultural and agri-food industry are posing great challenges to Credit unions in Western Canada. Much attention has been given to the impact of competitive rates and the environment offered by banks on credit union performance to the neglect of issues relating to member satisfaction and commitment which may be adding to other problems in the credit union sector. Studies by Feinberg (2001), Sibbald, et al (1999), Loser et. al (1999) , Fried, et. al (1999), Karels and McClatchey (1999) and Tokle, and Tokle (2001) among others have identified key issues relating to the competitive financial roles of credit unions in small financial services, in comparative analysis studies as well as merger related issues. However many of these studies have focused on the financial aspects of credit unions, and have not dealt with broader issues of whether or not the public understands the nature of credit unions, why people stop or intend to continue being members of credit unions. A mailed questionnaire, designed to elicit understanding of and attitudes towards credit unions was sent out to 1500 Alberta residents. In spite of the fact that the survey was complex with no reminder notice sent, the response rate was 12%. Analysis was conducted with a series of scale and logit regression analyses based on the Theory of Planned Behaviour (TpB) (Ajzen and Fishbein 1975, 1980 and Ajzen (2001) to elicit respondents´ beliefs, satisfaction and attitudes towards credit unions, and to measure the factors affecting their intention to patronize credit unions. Results indicate 78% of respondents were familiar with and understood the concept of credit unions. The majority (58%) was male, and 71% were aged 45 or older. Respondents who are active members of a credit union generally held positive attitudes towards their credit unions, and 89% rated their credit unions as performing well under a set of six performance categories. Analysis from the logit models found credit unions involvement with the local community and customer service to be the major reasons for credit union patronage. Elicitation of respondents´ intentions to patronize a credit union from the TpB analysis show that among the three attributes (attitude, subjective norm, and perceived behavior control), respondents´ subjective norm (siblings influence) and perceived behavioral control significantly explained patronization intentions. Results suggest that a 22 percentage of the public is unaware of credit unions, a further 30 percentage was once and is no longer a member of a credit union. For the 58% of the population that remain committed to credit union, there are still significant issues around member involvement in decision making, communication and provision of education/training to them.Agricultural Finance,

Attitudes Towards and Satisfaction with Cooperatives in Alberta: A Survey Analysis

The purpose of the study is to assess the attitude towards, and satisfaction of residents of Alberta to their cooperatives. A mailed questionnaire to 1500 Alberta residents, with a 16% response rate is analyzed using Likert scales and the theory of planned behavior. The majority of the respondents are males, aged 45 or older, and earn incomes of $49,000 or less. They are reasonably educated with a high school, college or university degrees. Results of the analysis also show a population that has a general positive attitude towards and is satisfied with their cooperatives as is reflected in assessing the performance of their cooperatives as good. Further analysis using the theory of planned behaviour show that respondents' attitude towards their cooperatives is the single most important and significant predictor of their patronization behaviour. However, there are still issues of concern to be addressed for current and past members. These include the inability of management to include members in the decision making process as well as issues of member training and education for the current members, and for the former members who left because they found the experience not rewarding or unable to use the services of their cooperatives when they moved.Institutional and Behavioral Economics,

Mechanisms of Auger-induced chemistry derived from wave packet dynamics

To understand how core ionization and subsequent Auger decay lead to bond breaking in large systems, we simulate the wave packet dynamics of electrons in the hydrogenated diamond nanoparticle C_(197)H_(112). We find that surface core ionizations cause emission of carbon fragments and protons through a direct Auger mechanism, whereas deeper core ionizations cause hydrides to be emitted from the surface via remote heating, consistent with results from photon-stimulated desorption experiments [Hoffman A, Laikhtman A, (2006) J Phys Condens Mater 18:S1517–S1546]. This demonstrates that it is feasible to study the chemistry of highly excited large-scale systems using simulation and analysis tools comparable in simplicity to those used for classical molecular dynamics

Predictions of structural elements for the binding of Hin recombinase with the hix site of DNA

Molecular dynamics simulations were coupled with experimental data from biochemistry and genetics to generate a theoretical structure for the binding domain of Hin recombinase complexed with the hix site of DNA. The theoretical model explains the observed sequence specificity of Hin recombinase and leads to a number of testable predictions concerning altered sequence selectivity for various mutants of protein and DNA. Combining molecular dynamics simulations with constraints based on current knowledge of protein structure leads to a theoretical structure of the binding domain of Hin recombinase with the hix site of DNA. The model offers a mechanistic explanation of the presently known characteristics of Hin and predicts the effects of specific mutations of both protein and DNA. The predictions can be tested by currently feasible experiments that should lead to refinements in and improvements on the current theoretical model. Because current experimental and theoretical methods are all limited to providing only partial information about protein-DNA interactions, we believe that this approach of basing molecular simulations on experimental knowledge and using the results of these simulations to design new, more precise experimental tests will be of general utility. These results provide additional evidence for the generality of the helix-turn-helix motif in DNA recognition and stabilization of proteins on DNA

The Predicted Binding Site and Dynamics of Peptide Inhibitors to the Methuselah GPCR from Drosophila melanogaster

Peptide inhibitors of Methuselah (Mth), a G protein-coupled receptor (GPCR), were reported that can extend the life span of Drosophila melanogaster. Mth is a class B GPCR, which is characterized by a large, N-terminal ectodomain that is often involved with ligand recognition. The crystal structure of the Mth ectodomain, which binds to the peptide inhibitors with high affinity, was previously determined. Here we report the predicted structures for RWR motif peptides in complex with the Mth ectodomain. We studied representatives of both Pro-class and Arg-class RWR motif peptides and identified ectodomain residues Asp139, Phe130, Asp127, and Asp78 as critical in ligand binding. To validate these structures, we predicted the effects of various ligand mutations on the structure and binding to Mth. The binding of five mutant peptides to Mth was characterized experimentally by surface plasmon resonance, revealing measured affinities that are consistent with predictions. The electron density map calculated from our MD structure compares well with the experimental map of a previously determined peptide/Mth crystal structure and could be useful in refining the current low-resolution data. The elucidation of the ligand binding site may be useful in analyzing likely binding sites in other class B GPCRs

Shock-induced consolidation and spallation of Cu nanopowders

A useful synthesis technique, shock synthesis of bulk nanomaterials from nanopowders, is explored here with molecular dynamics simulations. We choose nanoporous Cu (∼11 nm in grain size and 6% porosity) as a representative system, and perform consolidation and spallation simulations. The spallation simulations characterize the consolidated nanopowders in terms of spall strength and damage mechanisms. The impactor is full density Cu, and the impact velocity (u_i) ranges from 0.2 to 2 km s^(−1). We present detailed analysis of consolidation and spallation processes, including atomic-level structure and wave propagation features. The critical values of u_i are identified for the onset plasticity at the contact points (0.2 km s^(−1)) and complete void collapse (0.5 km s^(−1)). Void collapse involves dislocations, lattice rotation, shearing/friction, heating, and microkinetic energy. Plasticity initiated at the contact points and its propagation play a key role in void collapse at low u_i, while the pronounced, grain-wise deformation may contribute as well at high u_i. The grain structure gives rise to nonplanar shock response at nanometer scales. Bulk nanomaterials from ultrafine nanopowders (∼10 nm) can be synthesized with shock waves. For spallation, grain boundary (GB) or GB triple junction damage prevails, while we also observe intragranular voids as a result of GB plasticity