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A tuple of commuting Hilbert space operators (S 1 , … , S n - 1 , P) having the closed symmetrized polydisc Γ n = ∑ i = 1 n z i , ∑ 1 ≤ i < j ≤ n z i z j , … , ∏ i = 1 n z i : | z i | ≤ 1 , 1 ≤ i ≤ n - 1 as a spectral set is called a Γ n -contraction. From the literature we have that a point (s 1 , … , s n - 1 , p) in Γ n can be represented as s i = c i + p c n - i for some (c 1 , … , c n - 1 ) ∈ Γ n - 1 . We construct a minimal Γ n -isometric dilation for a particular class of c.n.u. Γ n -contractions (S 1 , … , S n - 1 , P) and obtain a functional model for them. With the help of this model we express each S i as S i = C i + P C n - i , which is an operator theoretic analogue of the scalar result. We also produce an abstract model for a different class of c.n.u. Γ n -contractions satisfying S i ∗ P = P S i ∗ for each i. By exhibiting a counter example we show that such abstract model may not exist if we drop the hypothesis that S i ∗ P = P S i ∗ . We apply this abstract model to achieve a complete unitary invariant for such c.n.u. Γ n -contractions. Additionally, we present different necessary conditions for dilation and a sufficient condition under which a commuting tuple (S 1 , … , S n - 1 , P) becomes a Γ n -contraction. The entire program goes parallel to the operator theoretic program developed by Sz.-Nagy and Foias for a c.n.u. contraction. [ABSTRACT FROM AUTHOR]

The symmetrization map π : C 2 → C 2 is defined by π (z 1 , z 2) = (z 1 + z 2 , z 1 z 2). The closed symmetrized bidisc Γ is the symmetrization of the closed unit bidisc D 2 ¯ , that is, Γ = π ( D 2 ¯) = { (z 1 + z 2 , z 1 z 2) : | z i | ≤ 1 , i = 1 , 2 }. A pair of commuting Hilbert space operators (S, P) for which Γ is a spectral set is called a Γ -contraction. Unlike the scalars in Γ , a Γ -contraction may not arise as a symmetrization of a pair of commuting contractions, even not as a symmetrization of a pair of commuting bounded operators. We characterize all Γ -contractions which are symmetrization of pairs of commuting contractions. We show by constructing a family of examples that even if a Γ -contraction (S , P) = (T 1 + T 2 , T 1 T 2) for a pair of commuting bounded operators T 1 , T 2 , no real number less than 2 can be a bound for the set { ‖ T 1 ‖ , ‖ T 2 ‖ } in general. Then we prove that every Γ -contraction (S, P) is the restriction of a Γ -contraction (S ~ , P ~) to a common reducing subspace of S ~ , P ~ and that (S ~ , P ~) = (A 1 + A 2 , A 1 A 2) for a pair of commuting operators A 1 , A 2 with max { ‖ A 1 ‖ , ‖ A 2 ‖ } ≤ 2 . We find new characterizations for the Γ -unitaries and describe the distinguished boundary of Γ in a different way. We also show some interplay between the fundamental operators of two Γ -contractions (S, P) and (S 1 , P) . [ABSTRACT FROM AUTHOR]

More than 47,000 articles have been published in the area of Metal-Organic Framework since its seminal discovery in 1995, exemplifying the intense research carried out in this short span of time. Among other applications, gas adsorption and storage are perceived as central to the MOFs research, and more than 10,000 MOFs structures are reported to date to utilize them for various gas storage/separation applications. Molecular modeling, particularly based on density functional theory, played a key role in (i) understanding the nature of interactions between the gas and the MOFs geometry (ii) establishing various binding pockets and relative binding energies, and (iii) offering design clues to improve the gas uptake capacity of existing MOF architectures. In this review, we have looked at various MOFs that are studied thoroughly using DFT/periodic DFT (pDFT) methods for CO2, H2, O2, and CH4 gases to provide a birds-eye-view on how various exchange-correlation functionals perform in estimating the binding energy for various gases and how factors such as nature of the (i) metal ion, (ii) linkers, (iii) ligand, (iv) spin state and (v) spin-couplings play a role in this process with selected examples. While there is still room for improvement, the rewards offered by the molecular modelling of MOFs were already substantial that we advocate experimental and theoretical studies to go hand-in-hand to undercut the trial-and-error approach that is often perceived in the selection of MOFs and gas partners in this area. The importance of density functional theory-based molecular modeling studies in offering design clues to improve the gas adsorption and storage capacity of existing MOF architectures is discussed here. The use of DFT-based investigation in conjunction with experimental synthesis is an imperative tool in designing new-generation MOFs with enhanced uptake capacity. [ABSTRACT FROM AUTHOR]

The soft function in non-abelian gauge theories exponentiate, and their logarithms can be organised in terms of the collections of Feynman diagrams called Cwebs. The colour factors that appear in the logarithm are controlled by the web mixing matrices. Direct construction of the diagonal blocks of Cwebs using the new concepts of Normal ordering, basis Cweb and Fused-Web was recently carried out in [1]. In this article we establish correspondence between the boomerang webs introduced in [2] and non-boomerang Cwebs. We use this correspondence together with Uniqueness theorem and Fused web formalism introduced in [1] to obtain the diagonal blocks of four general classes of Cwebs to all orders in perturbation theory which also cover all the four loop Boomerang Cwebs connecting four Wilson lines. We also fully construct the mixing matrix of a special Cweb to all orders in perturbation theory. [ABSTRACT FROM AUTHOR]

SrF, being a laser-coolable molecule, can be an interesting system for spectroscopic tests of fundamental physics. We present an electronic structure study of this molecule within the four-component relativistic coupled-cluster singles and doubles (RCCSD) framework and employ the RCCSD-based methods to compute its molecular-frame dipole moment and core properties such as hyperfine structure coupling constant and molecular P, T-odd electronic structure parameters that are of great importance for the high-precision tests of fundamental physics. The impact of basis set size, Hamiltonian and nuclear model on the property calculation of SrF is also investigated. The computed results are in good agreement with the available experimental values. The present study shows that the SrF molecule could be useful for high-precision molecular experiments to explore physics beyond the Standard Model of elementary particles. [ABSTRACT FROM AUTHOR]

A commuting triple of Hilbert space operators (A, B, P) for which the closure of the tetrablock E , where E = { (x 1 , x 2 , x 3) ∈ C 3 : | x 3 | < 1 & x 1 = c 1 + x 3 c ¯ 2 , x 2 = c 2 + x 3 c ¯ 1 , c 1 , c 2 ∈ C with | c 1 | + | c 2 | < 1 } , is a spectral set is called a tetrablock contraction or an E -contraction. To every E -contraction (A, B, P), there are unique operators F 1 , F 2 ∈ B (D P) , which are called the fundamental operators of (A, B, P), satisfying A - B ∗ P = D P F 1 D P , B - A ∗ P = D P F 2 D P. An E -contraction (A, B, P) admits a canonical decomposition (A 1 ⊕ A 2 , B 1 ⊕ B 2 , P 1 ⊕ P 2) into an E -unitary (A 1 , B 1 , P 1) and a completely non-unitary (c.n.u.) E -contraction (A 2 , B 2 , P 2) . As there already exists an easily understood model for an E -unitary in the literature, it suffices to restrict attention to the c.n.u. E -contraction part. Here we construct an explicit minimal E -isometric dilation for a c.n.u. E -contraction whose fundamental operators satisfy (1.1) below (a class for which it is known that such dilation exists). As a consequence of this explicit dilation, we obtain a functional model for the same class of E -contractions. With the help of this functional model we express an E -contraction (A, B, P) as A = C 1 + P C 2 ∗ , B = C 2 + P C 1 ∗ for some operators C 1 , C 2 and this representation is operator theoretic analogue of the representation of the points in E . We also construct a different functional model, which is not necessarily commutative, for a c.n.u. E -contraction (A, B, P) when A, B commute with P ∗ . This functional model is obtained even without having an E -isometric dilation exhibited in the model. We show by an example that such a model may not be possessed by (A, B, P) if the condition that A, B commute with P ∗ , is dropped from the hypothesis. A complete unitary invariant is achieved for a c.n.u. E -contraction (A, B, P) when A, B commute with P ∗ . The fundamental operators play the central role in all these constructions. Also, we produce a new characterization for an E -unitary. [ABSTRACT FROM AUTHOR]

We make some sharp estimates to obtain a Schwarz lemma for the symmetrized polydisc G n , a family of domains naturally associated with the spectral interpolation, defined by G n : = ∑ 1 ≤ i ≤ n z i , ∑ 1 ≤ i < j ≤ n z i z j … , ∏ i = 1 n z i : | z i | < 1 , i = 1 , … , n. We first make a few estimates for the the extended symmetrized polydisc G ~ n , a family of domains introduced in [35] and defined in the following way: G ~ n : = { (y 1 , … , y n - 1 , q) ∈ C n : q ∈ D , y j = β j + β ¯ n - j q , β j ∈ C and | β j | + | β n - j | < n j for j = 1 , … , n - 1 }. We then show that these estimates are sharp and provide a Schwarz lemma for G ~ n . It is easy to verify that G n = G ~ n for n = 1 , 2 and that G n ⊊ G ~ n for n ≥ 3 . As a consequence of the estimates for G n ~ , we have analogous estimates for G n . Since for a point (s 1 , … , s n - 1 , p) ∈ G n , n i is the least upper bound for | s i | , which is same for | y i | for any (y 1 , … , y n - 1 , q) ∈ G n ~ , 1 ≤ i ≤ n - 1 , the estimates become sharp for G n too. We show that these conditions are necessary and sufficient for G n ~ when n = 1 , 2 , 3 . In particular for n = 2 , our results add a few new necessary and sufficient conditions to the existing Schwarz lemma for the symmetrized bidisc. [ABSTRACT FROM AUTHOR]

The correlators of Wilson-line operators in non-abelian gauge theories are known to exponentiate, and their logarithms can be organised in terms of the collections of Feynman diagrams called Cwebs. The colour factors that appear in the logarithm correspond to completely connected diagrams and are determined by the web mixing matrices. In this article we introduce several new concepts: (a) Normal ordering of the diagrams of a Cweb, (b) Fused-Webs (c) Basis and Family of Cwebs. We use these ideas together with a Uniqueness theorem that we prove to arrive at an understanding of the diagonal blocks, and several null matrices that appear in the mixing matrices. We demonstrate using our formalism that, once the basis Cwebs present upto order α s n are determined, the number of exponentiated colour factors for several classes of Cwebs starting at order α s n + 1 can be predicted. We further provide complete results for the mixing matrices, to all orders in perturbation theory, for two special classes of Cwebs using our framework. [ABSTRACT FROM AUTHOR]

Correlators of Wilson-line operators in non-abelian gauge theories are known to exponentiate, and their logarithms can be organised in terms of collections of Feynman diagrams called webs. In [1] we introduced the concept of Cweb, or correlator web, which is a set of skeleton diagrams built with connected gluon correlators, and we computed the mixing matrices for all Cwebs connecting four or five Wilson lines at four loops. Here we complete the evaluation of four-loop mixing matrices, presenting the results for all Cwebs connecting two and three Wilson lines. We observe that the conjuctured column sum rule is obeyed by all the mixing matrices that appear at four-loops. We also show how low-dimensional mixing matrices can be uniquely determined from their known combinatorial properties, and provide some all-order results for selected classes of mixing matrices. Our results complete the required colour building blocks for the calculation of the soft anomalous dimension matrix at four-loop order. [ABSTRACT FROM AUTHOR]

Event shapes are classical tools for the determination of the strong coupling and for the study of hadronization effects in electron-positron annihilation. In the context of analytical studies, hadronization corrections take the form of power-suppressed contributions to the cross section, which can be extracted from the perturbative ambiguity of Borel-resummed distributions. We propose a simplified version of the well-established method of Dressed Gluon Exponentiation (DGE), which we call Eikonal DGE (EDGE), which determines all dominant power corrections to event shapes by means of strikingly elementary calculations. We believe our method can be generalized to hadronic event shapes and jet shapes of relevance for LHC physics. [ABSTRACT FROM AUTHOR]

The automorphisms of the symmetrized polydisc G n are well-known and are given in the coordinates of the polydisc in Edigarian and Zwonek (Arch. Math.84 (2005) 364–374). We find an explicit formula for the automorphisms of G n in its own coordinates. If τ is an automorphism of G n , then τ (S 1 , ⋯ , S n - 1 , P) is a Γ n -contraction, where a Γ n -contraction is a commuting n-tuple of Hilbert space operators for which the closed symmetrized polydisc Γ n is a spectral set. Corresponding to every Γ n -contraction (S 1 , ⋯ , S n - 1 , P) , there exist n - 1 unique operators A 1 , ⋯ , A n - 1 such that S i - S n - i ∗ P = D P A i D P , D P = (I - P ∗ P) 1 / 2 , for i = 1 , ⋯ , n - 1 . This unique (n - 1) -tuple (A 1 , ⋯ , A n - 1) , which is called the fundamental operator tuple or F O -tuple of (S 1 , ⋯ , S n - 1 , P) in the literature, plays central role in every section of operator theory on Γ n . We find an explicit form of the F O -tuple of τ (S 1 , ⋯ , S n - 1 , P) when n = 3 . We show by an example that a Γ n -contraction may not have commuting F O -tuple. Also, we obtain a necessary and sufficient condition under which two Γ n -contractions are unitarily equivalent. [ABSTRACT FROM AUTHOR]

Correlators of Wilson-line operators are fundamental ingredients for the study of the infrared properties of non-abelian gauge theories. In perturbation theory, they are known to exponentiate, and their logarithm can be organised in terms of collections of Feynman diagrams called webs. We study the classification of webs to high perturbative orders, proposing a set of tools to generate them recursively: in particular, we introduce the concept of Cweb, or correlator web, which is a set of skeleton diagrams built with connected gluon correlators, instead of individual Feynman diagrams. As an application, we enumerate all Cwebs entering the soft anomalous dimension matrix for multi-parton scattering amplitudes at four loops, and we compute the mixing matrices for all Cwebs connecting four or five Wilson lines at that loop order, verifying that they obey sum rules that were derived or conjectured in the literature. Our results provide the colour building blocks for the calculation of the soft anomalous dimension matrix at four-loop order. [ABSTRACT FROM AUTHOR]

A tuple of commuting operators (S1,⋯,Sn-1,P) for which the closed symmetrized polydisc Γn is a spectral set is called a Γn-contraction. We show that every Γn-contraction admits a decomposition into a Γn-unitary and a completely non-unitary Γn-contraction. This decomposition is an analogue to the canonical decomposition of a contraction into a unitary and a completely non-unitary contraction. We also find new characterizations for the set Γn and Γn-contractions. [ABSTRACT FROM AUTHOR]

ZnO is one of the most promising candidate for photoelectrochemical splitting of water for hydrogen production. To increase the efficiency of ZnO based photoelectrochemical cell, its band-gap and band edges should be tailored to match visible light spectra and water redox potential respectively. In this paper, First-principles density functional theory calculations have been performed to evaluate the effect of non-metal dopants on electronic properties of ZnO. The model structures of X-doped ZnO were constructed using 32-atom 2 × 2 × 2 supercell of wurtzite ZnO with one O atom replaced with X (carbon C, phosphorus P). With respect to the electronic band structure, C (2 p), P (3 p) states are located above the valence band maximum of ZnO and mixing of these states is feeble to produce significant band gap narrowing. Doping of these non-metals dopants helps in the creation of isolated states which enhances visible light absorption of ZnO. Our theoretical calculations are consistent with the experimental results of C (P) doped ZnO and fully explains its visible light activity on non-metal doping. [ABSTRACT FROM AUTHOR]

The Z-vector method in the relativistic coupled-cluster framework is employed to calculate the parallel and perpendicular components of the magnetic hyperfine structure constant of a few small alkaline earth hydrides (BeH, MgH, and CaH) and fluorides (MgF and CaF). We have compared our Z-vector results with the values calculated by the extended coupled-cluster (ECC) method reported in Phys. Rev. A 91 022512 (2015). All these results are compared with the available experimental values. The Z-vector results are found to be in better agreement with the experimental values than those of the ECC values. [ABSTRACT FROM AUTHOR]

The C–X [X = Cl, Br] bond dissociation is a challenging problem due to its high activation barrier. Many transition metal-based clusters, acting as catalysts, are known to dissociate this bond. We have carried out DFT-based calculation and found that small-sized aluminum clusters can break these bonds quite effectively with a high rate constant. Our analysis gives a detailed description of thermodynamics and kinetics of the reaction. Fukui functions and NBO calculation provide an insight into the reactivity and mechanism. Hence nanoaluminum clusters can dissociate C–X bond with a lower activation barrier compared to the known gold or platinum catalysts. [ABSTRACT FROM AUTHOR]

Catalysis of molecular activation of small molecules through scission of strong chemical bonds is one of the major challenges faced by chemists. More specifically, activation of the strong C–H and O–H bonds of various alcohols, especially methanol, is one of the various important intermediate steps of key organic reactions. Our present work explores a suitable metal cluster catalyst towards methanol dissociation. In particular, we have examined the effect of ruthenium doping (Rh:Ru = 2:1) on the catalytic activity of Rh6 cluster towards methanol dissociation. Density functional theory-based calculations illustrate two competitive pathways for methanol dissociation, which are via O–H and C–H bond breaking. Both the pathways are found to be energetically favourable in the presence of bimetallic and mono-metallic clusters. Importantly, energy barrier for O–H bond dissociation reduces considerably in doped cluster as compared to pure Rh6 cluster and is smaller than the values reported for a number of other small metallic clusters. [ABSTRACT FROM AUTHOR]

In this paper, we study the reactivity of diimines like 2, 2-bipyridine, 1, l0-phenanthroline and 1, 2, 4-triazines using density-based reactivity descriptors. We discuss the enhancement or diminution in the reactivity of these ligands as a function of two substituent groups, namely methyl (-CH) group and phenyl (-CH) group. The global reactivity descriptors explain the global affinity and philicity of these ligands, whereas the local softness depicts the particular site selectivity. The inter-molecular reactivity trends for the same systems are analysed through the philicity and group philicity indices. The σ-donor character of these ligands is quantified with the help of electron density profile. In addition, the possible strength of interaction of these ligands with metal ions is supported with actual reaction energies of Ru-L complexes. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this article, different reactivity descriptors have been reviewed. Con-ceptual density functional theory is an important area where a lot of interesting developments in terms of descriptors and molecule interactions have taken place in recent years. This review will highlight our own work on such development of descriptors and their applications to characterise stability and reactivity in molecule systems. [ABSTRACT FROM AUTHOR]

The role of exchange-correlation is well known for accurate calculations of electric response properties. The exchange-correlation functional in density functional theory (DFT) has been well studied for ground state equilibrium geometry. However, the behaviour of these functional in stretched geometries, where static correlation play an important role, has not been studied systematically, particularly for response electric properties. Thus, we present here the rigorous calculation of electric response properties at distorted geometries of the molecules. We have considered dipole polarizability and dipole-quadrupole polarizability for description of role of static and dynamic correlation for electric response properties. The calculations are performed with our new approach, non-iterative approximation to coupled-perturbed Kohn-Sham method. These DFT results are compared with higher level ab initio such as coupled perturbed singles and doubles and fully correlated full CI. We have studied single, double and triple-bonded systems at different inter-nuclear separation. We report here the dipole polarizability and dipole-quadrupole polarizability of HF, BH, HCO, CO and NO. We also present the effect of basis and functional on polarizability and dipole-quadrupole polarizability. [ABSTRACT FROM AUTHOR]

Dipole moment calculations of SF and ClO radicals have been carried out using the recently developed partial triples correction to Fock-space multi-reference coupled cluster method. Theoretical calculation of the doublet SF and ClO radicals is useful due to their importance in atmospheric chemistry. The dipole moments of these radicals are extremely sensitive to correlation effects. A brief insight to the way the triples correction has been implemented is presented. We compare the results obtained from our analytic response treatment with that of restricted open Hartree-Fock (ROHF) calculations. Results are presented for both relaxed and non-relaxed approach in the ROHF method. Results suggest the importance of triples corrections. The effects of orbital relaxation are also analysed from the results. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In the present article, we study the influence of external electric field on the density-based global and local reactivity descriptors using examples of some planar nonlinear polyatomic molecules with C 2 V point group symmetry. The study mainly involves the application of weak electric field in a direction along the principal axis and along its perpendicular direction. We also discuss the strength of the electric field studied in this work in terms of the strength of the molecular interaction. The work is expected to throw light on the effect of interactions within the above range on reactivity descriptors. Results are presented for a few prototype molecules. [ABSTRACT FROM AUTHOR]

In this paper, we study the reactivity of diimines like 2,2'-bipyridine and its analogues using reactivity descriptors. We discuss evaluation of local descriptors using relaxed as well as frozen approximation and characterize the σ/π acceptance/donor characteristics of the above ligands. The intermolecular reactivity sequence for the same systems is examined by the global and local philicity index. In addition, electron density analysis has been carried out to highlight the possible strengths of interaction of the bipyridine and its analogues with metal ions. [ABSTRACT FROM AUTHOR]

The size-dependence of different local reactivity descriptors of dimer A and AB type of systems is discussed. We derive analytic results of these descriptors calculated using finite difference approximation. In particular, we studied Fukui functions, relative electrophilicity and relative nucleophilicity, local softness and local philicity. The results are explained using the example of the dimer of BHNH. [ABSTRACT FROM AUTHOR]

Molecular orbital calculations (EHMO) have been performed on five ruthenium carbonyl clusters considered to be involved in the reductive carbonylation of nitrobenzene. The bonding in the isocyanate cluster, [HRu(CO)(HNCO)], is shown to arise mainly from the interaction between the LUMO of HNCO and HOMO of the [HRu(CO)] fragment. The relative stabilities of this cluster, two of its isomers and the CO-eliminated cluster [HRu(CO)(HN)], are also commented upon. The calculated results are in accordance with empirical kinetic data. [ABSTRACT FROM AUTHOR]

We have demonstrated an application of a stationary coupled cluster response approach for molecular properties using an Euler functional. This involves terms which are of cubic power in cluster amplitudes. We have shown that these are important terms and have also discussed the convergence properties of the functional for higher order properties. [ABSTRACT FROM AUTHOR]

Low temperature oxidation of CO to CO2 is an important process for the environment. Similarly adsorption of CO from the releasing sources is also of major concern today. Whereas the potential of gold and silver clusters is well proven for the catalysis of the above mentioned reaction, the potential of aluminum (Al) clusters remains unexplored. The present study proves that, similar to the transition metals, Al clusters can also be used for adsorption of gases. We first tested the potential of Al cluster as adsorbents for CO. The high binding energy (BE) values prove that Al clusters can be used for adsorbing both CO and O2. Since oxygen binding is more facile, we adsorbed oxygen on Al and then checked the effect of this O2 on the BE of CO. The results were obtained by DFT calculations at M062X/TZVP level of theory.Activation of carbon monoxide (CO) on oxygen-adsorbed aluminum (Al) cluster [ABSTRACT FROM AUTHOR]

A foreword to the special issue of the "Journal of Chemical Sciences" is presented.