Metafunction Research Articles

Structure and electronic spectral property of coumarin–chalcone hybrids: A comparative study using conventional and long-range corrected hybrid functionals

The structures and electronic absorption spectra of a series of coumarin–chalcone hybrids have been investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT). Standard hybrid (PBE1PBE and BHHLYP), hybrid meta (BMK, M06, M06-2X and M06-HF) and long-range corrected hybrid (CAM-B3LYP) functionals have been chosen for calculations. The relative performance of the seven exchange–correlation functionals has been discussed and it turns out that, within the selected TDDFT framework, BMK emerges as the most efficient hybrid functional for coumarin–chalcone hybrids with a mean absolute error (MAE) of 0.16 eV (21.0 nm). Based on BMK results, the structure-spectra relationship and the effects of substituent, solvent and elongation of the conjugate chain on electronic spectra have been discussed. The experimentally observed substitution and solvent effects are well reproduced by calculation. The results reveal that the lowest energy transitions should be of intramolecular charge transfer (ICT) nature, which predominantly correspond to the π → π * transitions from HOMO to LUMO.

Harmonic vibrational frequencies: Scale factors for pure, hybrid, hybrid meta, and double‐hybrid functionals in conjunction with correlation consistent basis sets

Scale factors for (a) low (<1000 cm(-1)) and high harmonic vibrational frequencies, (b) thermal contributions to enthalpy and entropy, and (c) zero-point vibrational energies have been determined for five hybrid functionals (B3P86, B3PW91, PBE1PBE, BH&HLYP, MPW1K), five pure functionals (BLYP, BPW91, PBEPBE, HCTH93, and BP86), four hybrid meta functionals (M05, M05-2X, M06, and M06-2X) and one double-hybrid functional (B2GP-PLYP) in combination with the correlation consistent basis sets [cc-pVnZ and aug-cc-pVnZ, n = D(2),T(3),Q(4)]. Calculations for vibrational frequencies were carried out on 41 organic molecules and an additional set of 22 small molecules was used for the zero-point vibrational energy scale factors. Before scaling, approximately 25% of the calculated frequencies were within 3% of experimental frequencies. Upon application of the derived scale factors, nearly 90% of the calculated frequencies deviated less than 3% from the experimental frequencies for all of the functionals when the augmented correlation consistent basis sets were used.

Theoretical insights into the catalytic mechanism of β-hexosaminidase

The enzyme (β-Hex) has a specific role in the degradation of a particular type of glycolipid, the GM2 ganglioside. This specificity is also manifested by its unusual mechanism of substrate-assisted catalysis, which is considered to be an alternative pathway for the breakage of glycosidic bonds. We have studied its catalytic mechanism using a small model of the enzyme: substrate Michaelis complex with DFT and MP2/MP3 methods. The results reflect the intrinsic chemical reactivity of the active site, decoupled from the long-range enzyme electrostatic field. The mechanism supports, and adds further atomic detail, on the earlier mechanistic suggestions based on experimental data. Moreover, we also have compared the geometry and full potential energy surface obtained with nine different exchange–correlation functionals. It was surprising that the B3LYP activation energies were lower than the ones from some of the hybrid meta functionals (known by their excellent performance on kinetics) by as much as 10 kcal/mol and lower than the MP2 energies by more than 12 kcal/mol. It is known that B3LYP underestimates barriers but underestimations of this extent are unusual and surprising. The effect of the theoretical method on the geometry, usually supposed to be less significant, had in some cases a relevant influence in the mechanism. Therefore, a more thoughtful choice should be made when choosing a methodology for geometry optimization.

Density Functional Theory for Reaction Energies: Test of Meta and Hybrid Meta Functionals, Range-Separated Functionals, and Other High-Performance Functionals

The present study compares the accuracy of 30 density functionals for four databases of reaction energies studied recently by Grimme and co-workers. For 20 of the density functionals, the calculations are new, and the calculations are compared to previous work for the other 10. We present the results in detail for 11 of the functionals and as mean unsigned errors for the others. The results presented in detail are for the seven most recent Minnesota functionals (M05-2X, M06-L, M06-HF, M06, M06-2X, M08-HX, and M08-SO), three range-separated functionals (HSE, LC-ωPBE, and ωB97X-D), and one dispersion-corrected global hybrid generalized gradient approximation (B97-D); the other functionals include five dispersion-corrected functionals and their uncorrected analogs, eight high-performing functionals on a recent catalytic-energies test, and the TPSSh functional because it is of special interest to compare its performance to that of M08-SO. Three of the four databases contain a total of 21 rearrangement reaction energies and 13 diverse dissociation or association energies, and the fourth contains three dissociation reaction energies of alkali metal clusters and three dissociation reaction energies of alkali-metal-cation−benzene complexes. The results are especially promising for the Minnesota hybrid meta-GGA functionals and the ωB97X-D, B2PLYP-D, and HSE functionals.

Density Functional and Spin−Orbit Ab Initio Study of CF3Br: Molecular Properties and Electronic Curve Crossing

Quantum chemical calculations of CF(3)Br and the CF(3) radical are performed using density functional theory (DFT) and time-dependent DFT (TDDFT). Molecular structures, vibrational frequencies, dipole moment, bond dissociation energy, and vertical excitation energies of CF(3)Br are calculated and compared with available experimental results. The performance of six hybrid and five hybrid meta functionals in DFT and TDDFT calculations are evaluated. The ωB97X, B3PW91, and M05-2X functionals give very good results for molecular structures, vibrational frequencies, and vertical excitation energies, respectively. The ωB97X functional calculates well the dipole moment of CF(3)Br. B3LYP, one of the most widely used functionals, does not perform well for calculations of the C-Br bond length, bond dissociation energy, and vertical excitation energies. Potential energy curves of the low-lying excited states of CF(3)Br are obtained using the multiconfigurational spin-orbit ab initio method. The crossing point between 2A(1) and 3E states is located near the C-Br bond length of 2.45 Å. Comparison with CH(3)Br shows that fluorination does not alter the location of the crossing point. The relation between the calculated potential energy curves and recent experimental result is briefly discussed.

π Interactions Studied with Electronic Structure Methods: The Ethyne Methyl Isocyanide Complex and Thioanisole.

Two molecular systems for which previous studies had found qualitative differences in the results from calculations with the B3LYP and MP2 methods are investigated with a range of different electronic structure methods, including meta and double hybrid density functionals and DFT-D (DFT augmented with an empirical dispersion term). The performance of the different methods is assessed by comparison to estimated CCSD(T)/CBS (complete basis set) results. The first molecular system studied is the ethyne methyl isocyanide complex (CH3NC-C2H2), which exhibits π hydrogen bonds involving the C≡C and N≡C triple bonds. Earlier work on this system had shown that B3LYP predicts significantly longer hydrogen-bond distances than MP2. Here, we show that this is likely due to missing dispersion in the B3LYP calculations. On the basis of the CCSD(T) results, the ethyne methyl isocyanide interaction energy is estimated to be 12 ± 1 kJ/mol. B3LYP significantly underestimates the stability of the complex, whereas MP2 slightly overestimates. M05-2X, B3LYP-D, and (CP-corrected) mPW2-PLYP-D give results in close proximity to the CCSD(T) reference values. The second molecule investigated is thioanisole (C6H6SCH3), which can adopt two different conformations (thiomethyl group either planar or perpendicular with respect to the benzene ring). Potential energy curves for rotation around the C(sp(2))-S bond are computed and compared to the estimated CCSD(T)/CBS curve. CCSD(T) predicts the planar conformation to be the global minimum, with a plateau region near the perpendicular conformation (∼4 kJ/mol higher in energy than the planar conformation). The shape of the curve, and location of minima and barriers, is very dependent on the method and basis set employed. MP2, B3LYP, M05-2X, mPW2-PLYP, and mPW2-PLYP-D (employing basis sets of double- or triple-ζ quality) give results in reasonable agreement with the CCSD(T) results, whereas B3LYP-D and M06-L give vastly overestimated barriers at the perpendicular conformation.

Absorption Spectra of Riboflavin—A Difficult Case for Computational Chemistry

Computing accurate absorption spectra of riboflavin (RBF) has proven a difficult task for computational chemistry. Time-dependent density functional theory have herein been employed using a wide range of recent range-separated and hybrid meta functionals to investigate ultraviolet and visible spectra of RBF to determine if any progress has been made through recent developments. It is concluded that B3LYP and PBE0 perform the best throughout the entire test set. However, since all methods deviate from experimental results by at least 40 nm when computing the spectra in vacuum, two approaches to describe aqueous solution are implemented together with the MPWB1K, B3LYP, and PBE0 functionals: implicitly using integral equation formulation of the polarized continuum model (minor improvement) and explicitly through molecular dynamics (MD) simulations of the molecule embedded in a water cluster whereafter snapshots of RBF-water clusters are extracted and time-dependent density functional theory calculations performed. The resulting averaged spectra from the MD-simulated clusters show a constant blue-shift for all peaks by ∼20 nm compared to experimental data at the TD-B3LYP/6-31+G(d,p) level.

The far side: the meta functions of humanitarianism in a globalised world

This paper explores the meta functions of humanitarianism--that is, the functions that, as an ideology, a movement and a profession, it performs, wittingly or unwittingly, in the early twenty-first century. The term humanitarianism is used as shorthand to encompass a complex set of currents of thought, actions and institutions of which the boundaries are unclear. The focus is on mainstream humanitarianism, the dominant Northern/Western enterprise. The paper first discusses the relationship between humanitarianism and globalised power. It goes on to examine three types of functions that humanitarianism and humanitarian action perform: 'macro' functions--the deep undercurrents, power relations and values that humanitarianism articulates and transmits; 'meso' functions--those that relate to the political economy of humanitarian action and to the mechanics (rather than to the ideology) of globalisation; and 'micro' functions that relate to the motivations of the individuals who devote their energies to humanitarianism.

Density functional theory for transition metals and transition metal chemistry

We introduce density functional theory and review recent progress in its application to transition metal chemistry. Topics covered include local, meta, hybrid, hybrid meta, and range-separated functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including molecules, clusters, nanoparticles, surfaces, and solids.

Assessment of New Meta and Hybrid Meta Density Functionals for Predicting the Geometry and Binding Energy of a Challenging System: The Dimer of H2S and Benzene

Noncovalent interactions of a hydrogen bond donor with an aromatic pi system present a challenge for density functional theory, and most density functionals do not perform well for this kind of interaction. Here we test seven recent density functionals from our research group, along with the popular B3LYP functional, for the dimer of H 2S with benzene. The functionals considered include the four new meta and hybrid meta density functionals of the M06 suite, three slightly older hybrid meta functionals, and the B3LYP hybrid functional, and they were tested for their abilities to predict the dissociation energies of three conformations of the H 2S-benzene dimer and to reproduce the key geometric parameters of the equilibrium conformation of this dimer. All of the functionals tested except B3LYP correctly predict which of the three conformations of the dimer is the most stable. The functionals that are best able to reproduce the geometry of the equilibrium conformation of the dimer with a polarized triple-zeta basis set are M06-L, PWB6K, and MPWB1K, each having a mean unsigned relative error across the two experimentally verifiable geometric parameters of only 8%. The success of M06-L is very encouraging because it is a local functional, which reduces the cost for large simulations. The M05-2X functional yields the most accurate binding energy of a conformation of the dimer for which a binding energy calculated at the CCSD(T) level of theory is available; M05-2X gives a binding energy for the system with a difference of merely 0.02 kcal/mol from that obtained by the CCSD(T) calculation. The M06 functional performs well in both categories by yielding a good representation of the geometry of the equilibrium structure and by giving a binding energy that is only 0.19 kcal/mol different from that calculated by CCSD(T). We conclude that the new generation of density functionals should be useful for a variety of problems in biochemistry and materials where aromatic functional groups can serve as hydrogen bond acceptors.

Theoretical Comparison of Ketene Dimerization in the Gas and Liquid Phase

We present the first theoretical comparison between ketene dimerization in gas phase and ketene dimerization in solution. Density functional theory (DFT) calculations on the ketene dimerization were carried out considering the following product dimers: diketene (d-I), 1,3-cyclobutanedione (d-II), 2,4-dimethylene-1,3-dioxetane (d-III), and 2-methyleneoxetan-3-one (d-IV). All structures were optimized at the PW86x+PBEc/DZP level of theory. Based on these geometries, a total of 58 meta and hybrid functionals were used to evaluate the heat of dimerization. The MPW1K functional was found to fit the experimental data best and subsequently used in the final analyses for all energy calculations. It was found on both kinetic and thermodynamic grounds that only d-I and d-II are formed during ketene dimerization in gas phase and solution. In gas phase, d-I is favored over d-II by 2 kcal/mol. However, the dimerization barrier for d-I is 1 kcal/mol higher than for d-II. Solvation makes dimerization more favorable. On the enthalpic surface this is due to a favorable interaction between the dimer dipole moment and solvent molecules. The dimer is stabilized further on the Gibbs energy surface by an increase of the dimerization entropy in solution compared to gas phase. The species d-I remains the most stable dimer in solution by 1 kcal/mol. Kinetically, the dimerization barriers for the relevant species d-I and d-II are cut in half by solvation, due to both favorable dimer-dipole/solvent interactions (DeltaH++, DeltaG++) and an increase in the activation entropies (DeltaS++). While the dimerization barrier for d-II is lowest for the gas phase and toluene, the barrier for d-I formation becomes lowest for the more polar solvent acetone by 1 kcal/mol as d-I dimerization has the most polar transition state.

Computational Electrochemistry: The Aqueous Ru3+|Ru2+ Reduction Potential

We present results of density functional calculations for the standard reduction potential of the Ru3+|Ru2+ couple in aqueous solution. The metal cations are modeled as [Ru(H2O)n]q+ surrounded by continuum solvent (q = 2, 3; n = 6, 18). The continuum model includes bulk electrostatic polarization as well as atomic surface tensions accounting for the deviation of the second or third hydration shell from the bulk. After consideration of 37 density functionals with 5 different basis sets, it has been found that hybrid and hybrid meta functionals provide the most accurate predictions for the [Ru(H2O)n]q+ geometries and for the corresponding reduction potential in comparison with available experimental data. The gas-phase ionization potentials of [Ru(H2O)n]2+ calculated by density functional theory are also compared to results of ab initio computations using second-order Møller−Plesset perturbation theory. The difference in solvation free energies of Ru3+ and Ru2+ varies from −10.56 to −10.99 eV for n = 6 and from −6.83 to −7.45 eV for n = 18 depending on the density functional and basis set quality. The aqueous standard reduction potential is overestimated when only the first solvation shell is treated explicitly and is underestimated when the first and second solvation shells are treated explicitly.

Embedding machining features in function blocks for distributed process planning

IEC 61499 function blocks, being emerging industrial process measurement and control standards, are chosen as data processing and execution control elements within the context of a distributed process planning (DPP) system. A two-layer structure, consisting of supervisory planning (SP) and operation planning (OP), is identified to separate the generic process data from those machine-specific ones. Within DPP, function blocks are used for data encapsulation, machining parameter optimization, process monitoring, scheduling integration, and CNC control. From SP to OP, a function block evolves from meta function block, through object function block, to execution function block. The detailed design of a meta function block is depicted in this paper. A function block designer has been developed to help process planners define basic function block types and generate composite function block networks. It is expected that the function block-enabled DPP approach and the associated algorithms can largely improve the dynamism of process plans as well as the flexibility and productivity of job shop operations in a changing environment.

Language Switches in L3 Production: Implications for a Polyglot Speaking Model

In general, discussion of cross-linguistic influence has focussed almost exclusively on the role of L1 in L2 production, both in the form of cross-linguistic influence on the learner's interlanguage and in the form of language switches to the L1 during L2 production. As yet, there has been little work done on the influence of a learner's other previously learned L2s in the acquisition of a new language (L3). The few studies that have been been carried out on the role of L2 in L3 production however show that L2 does play an important role in L3 acquisition. This paper presents the results of ongoing research on non-adapted language switches, using data from a two-year longitudinal case study of an adult learner of L3 Swedish with L1 English and L2 German. Our study is based on 844 non-adapted language switches. We identified four main types of switch, three of which had pragmatic purpose, namely: (i) EDIT (marking self-repair, beginning of turntake etc.), (ii) META (used for asides, to comment on L3 performance or ask for help) and (iii) INSERT (use of non-L3 items to overcome lexical problems in L3), and the last of which we refer to as Without Identified Pragmatic Purpose (WIPP switch; cf. 'non-intentional switches', Poulisse and Bongaerts 1994). We found that while L1 English prevailed in EDIT, META and INSERT functions, almost only L2 German occurred in WIPP switches. Most of these WIPP switches were function words. We also noticed that a number of the English utterances used in INSERT function appeared to show German influence, although this was not the case when English was used in META function. Our results show that in this case study of L3 acquisition, L1 and L2 play different roles. We suggest that L2 German, which was shown to be the non-L3 language predominantly used to supply material for lexical construction attempts in the L3 (Williams and Hammarberg 1994), is activated in parallel to the L3 interlanguage, underlying L3 production and even L1 producti

The Application of Meta Functions to the Quasi-Static Analysis of Workpiece Displacement Within a Machining Fixture

Spherical-tipped locators and clamps are often used for the restraint of workpieces during machining. For structurally rigid fixtures and workpieces, contact region deformation, slip, and lift-off are the predominant modes of workpiece displacement during clamp actuation and machining. This paper presents a general model for the quasi-static analysis of workpiece displacement. It also shows how meta functions can be applied to simplify the modeling of contact forces. Through the use of meta functions, the general model can be formulated and solved quickly. This paper concludes with a description of an experimental study used to validate this model.

ChemInform Abstract: Inert Carbon Free Radicals. Part 13. New Free Radicals of PTM ( Perchlorotriphenylmethyl) Series with meta Functionalization

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Inert carbon free radicals. 13. New free radicals of PTM (perchlorotriphenylmethyl) series with meta functionalization

The synthesis of new organic free radicals of the PTM (perchlorotriphenylmethyl) series with different substituents in the 3- and 5-positions of one phenyl ring and their α- H precursors are described. All these radicals are stable red solids with high melting points. Their electron spin resonance spectra in solution and their magnetic susceptibilities in solid are reported and commented upon. Electrochemical behavior of radical 5 by means of cyclic voltammetry is also presented.

Formal semantics of the unified modeling language [formula omitted

A formal semantics is an essential element of language design because it supports comparison of language designs, provides implementation guidelines, and enables properties about a language to be proved. However, in the field of model management, there has been a lack of attention to the formal semantics of modeling languages. In this paper, the philosophy and formal semantics of the Unified Modeling Language ( L U ) are presented. The L U supports integrated modeling environments with a large number of models from diverse domains and management science paradigms. We discuss the philosophy of the L U in which logical deduction about empirical worlds is combined with efficient computations about mathematical worlds. We argue that measurement theory stressing homomorphic mappings from empirical to mathematical worlds is an ideal foundation for integrated modeling environments. A denotational semantics is given for the L U including the semantic domain, meta functions, and semantic equations. The L U is unique because measurement theory plays a salient role in its underlying denotational semantics. In particular, the semantic domain of the L U includes explicit homomorphic mappings from empirical to mathematical worlds and semantic equations define conditions, based on homomorphisms, that must be satisfied by valid models.

Une voie de synthese simple et rapide de phenols meta acyles

A new method for the meta acylation of anisole and its para-methyl or fluoro derivatives, is described. Addition of two trimethysilyl groups in the 2 and 5 positions (relative to the methoxy group), followed by hydrolysis affords the corresponding 5-trimethylsilyl-3-Cyclohexenones. Electrophilic substitution of the silyl group using RCOCl/2AlCl 3 at low temperature provides, after final aromatisation promoted by Pd/C or CuBr 2/LiBr, the expected meta acylated products. This mode of meta functionalization has been successfully applied to an original synthesis of ketoprofen starting from anisole.

Extending Petri nets for specifying man–machine dialogues

The requirements of man-machine dialogue-specification techniques are examined. Petri nets are identified as possible candidates for a modelling technique for dialogues on the basis of their applicability to concurrent, asynchronous systems. Labelled Petri nets are extended to nested Petri nets, allowing transitions to invoke subnets. It is shown that this extension allows nested Petri nets to generate at least the set of context-free languages. Further extensions are made to simplify the modelling of input and output in the user interface, resulting in input-output nets. Transitions labelled by error conditions and meta functions on nets are introduced to increase the usability of the model. Finally, the use of the model is demonstrated by modelling a small hypothetical command language.