Interference patterns in the scattering of positrons and electrons by diatomic homonuclear molecules are ab initio calculated. Our results are compared to model potential calculations with incident particles in twisted and plane wave states. All calculations are obtained in the first Born approximation framework. The comparison of the elastic differential cross sections shows how an ab initio description of the electronic molecular structure influence the interference minima structure. The origin of such patterns are also discussed.
The Fourier transform of Cartesian Gaussian functions product is presented in the light of positron scattering. The calculation of this class of integrals is crucial in order to obtain the scattering amplitude in the first Born approximation framework for an _ab initio_ method recently proposed. A general solution to the scattering amplitude is given to a molecular target with no restriction due to symmetry. Moreover, symmetry relations are presented with the purpose of identifying terms that do not contribute to the calculation for the molecules in the D∞h point group optimizing the computational effort. KEYWORDS — Positron and electron scattering, Fourier transform of the Gaussian product theorem, McMurchie-Davidson procedure, Obara-Saika procedure, linear molecules .
Cyclohexyl radicals are crucial primary intermediates in combustion of fossil and alternative fuels. They would present the inherent conformation feature, i.e. diverse conformers retained in inversion-topomerization pathways, jointly controlled by the varying radical site and specific spatial positions of alkyl side chains on “easy-distortion” cyclic ring. These conformers for one radical have different energies and thermodynamics, and are highly expected to influence their subsequent decomposition reactions in terms of energetics and kinetics. To reveal such impact, all conformational structures and their interconversion mechanisms for trans-1,2-dimethylcyclohexyl isomers were explored by employing quantum chemical calculations coupled with transition state theory. Originated from distinct conformers, all accessible transition states were explicitly identified in different reaction paths for each type of intramolecular H-transfer or β-scission, and then were carefully used in computing rate coefficients. The kinetic predictions demonstrate that the fairly speedy equilibrium among conformers would be established for one isomer via conformation before they proceed the initial decomposition over 300-2500 K. This allows thoroughly evaluating the contribution of various conformers to the kinetics for multiple paths in one reaction regarding to their thermodynamic properties. Moreover, conformational analysis elucidates that H-transfers exhibit strong structure dependence. Note that the most favorable 1,5 H-transfer is only feasible for one twist-boat with radical site in axial side chain accompanied by one isoclinal methyl group. The results for β-scissions are affected by steric energies and substituent effects remained in conformational structures. These findings facilitate to finally suggest the proper kinetic parameters for each decomposition reaction with the aim of their potential implication in kinetic modelling.
Perovskite materials are considered the mainstay of PV manufacturing asoutstandingto notable optoelectronic properties. In this work the act of Pb-free FASnI3 based PSC, TiO2 as ETL, and Cu2O as HTL and Ag,Au, Pt,are the different metal contact is simulated using SCAPS software. Here we focused on the impactparameters of device such as the thickness of the Ab-Layer, doping level ofperovskite layer and different working temperature. Additionally, we investigated the effect of different metal contact and their work function. The simulated results show that a perovskite layer thickness of 350nm for good perovskite solar cell. For optimizing parameters, efficiency 18.10%, FF 78.14, Jsc 29.61, and Voc 0.7821 have been achieved for Cu2O and TiO2 respectively. The thermal study shows that device configurations for this present work at 300k it is stable for this entire work.
In a recent experimental investigation, the chlorination of the highly efficient Y6 fluorinated molecule improved up to 16.5 \% the power conversion efficiency of an organic solar cell. To understand the better performance of BTP-4Cl:PBDB-TF acceptor-donor combination in comparison with BTP-4F:PBDB -TF in the newly reported organic solar cell, DFT calculations were performed in order to obtain a diversity of parameters related to molecular proper ties, such as electroacceptance, electron energy levels, absorption spectrum, charge mobility, and kinetics in exciton dissociation/recombination processes. Interestingly, chlorination improves charge mobility and the capacity to accept electrons. The binding energy is lower for the chlorinated than the fluorinated molecule, revealing an easier exciton cleavage in the former. Absorption spectra are in line with experimental ones, suggesting an ex cellent donor-acceptor complementarity. Additionally, novel molecules were proposed taking into account synthesized compounds, and the same parameters were analyzed. Results showed exciting behavior for the theoretically suggested compounds. Many properties were improved with the proposed molecules, which can also be exploited in solar photocells. Although it is a challenge to simulate/model a complete photoactive layer of an organic solar cell, it is proved through electronic structure calculations that the properties of the materials involved in the photovoltaic device can be obtained. In this way, give some light on the power conversion efficiency comparison and propose new compounds.
We investigate the presence of helical character and chirality using a vector-based charge density perspective instead of energetic or structural measures. The vector-based perspective of the chemical bonding, constructed using the most preferred direction of charge density accumulation, finds the presence of induced symmetry-breaking for α,ω-disubstituted cumulenes as the end groups are torsioned. The stress tensor trajectories Tσ(s) are used to provide the additional symmetry-breaking required to quantify the degree and nature of the chirality and helical character. We find an absence of chirality for cumulene but a very significant degree of axiality as demonstrated by the purely axial form of the Tσ(s) indicating a lack of helical character. The S-1,5-dimethyl-cumulene contains a very low degree of chiral character but significant axiality(helicity) resulting in a weakly helical morphology of the corresponding Tσ(s). The (-)S(-), (+)S(-) and (+)S(+) conformations of S-1,5-diamino-cumulene contain very significant degrees of both chirality and helical character resulting in helical morphology of the corresponding Tσ(s). The chirality assignments are in agreement with the Cahn–Ingold–Prelog (CIP) classifications for the (-)S(-), (+)S(-) and (+)S(+) conformations of S-1,5-diamino-cumulene. We discuss the consequences for the Tσ(s) in locating chiral character in these molecules in future experiment investigations.
Spin projected wave functions are known as generalizations of the Hartree-Fock wave function. Among them, the Half-Projected Hartree-Fock (HPHF) model represents a good compromise between the restricted (RHF) and unrestricted (UHF) Hartree-Fock methods. The HPHF wave function is a nearly pure wave function of spin and recovers a small part of the spin correlation energy. This paper reviews the history of the HPHF theory, not only from the conceptual point of view but also providing a compilation of the publications of this method over the years until now. In addition, the extension of the HPHF method to the calculation of non-orthogonal excited states to the ground state will be treated. The variational collapse during the calculation of singlet excited states with the same symmetry as the ground state is avoided by orthogonalizing the excited orbital to the corresponding occupied orbital. As an example, the potential energy surface of the S0 ground and 1S1(n, π∗) first excited state of the formic acid HCOOH are calculated. Formic acid exhibits complex energy surfaces with respect two large amplitude motions, the torsional rotation of the O-H group and the waving out-of-plane angle of the H atom. In the excited state, the molecule adopts a pyramidal structure. The obtained energy results are fitted to curves that can be used for the calculation of the theoretical spectrum.
A mechanism for the reaction of diformylhydrazine with o- and p-aminophenols has been studied by quantum-chemical calculations within the framework of electron density functional theory using the B3LYP/6-311++G (d,p)//B2PLYP/6-311++G (d, p) basis sets. It is shown that the first stage of this reaction involves nucleophilic addition of the aminophenol nitrogen to one of the carbonyl groups of diformylhydrazine to afford an unstable geminal amino alcohol, which can be further dehydrated to iminohydrazide or hydrazonamide. The prototropic imino-amine rearrangement occurring in the iminohydrazide delivers hydrazonamide, The latter, owing to nucleophilic attack of the nitrogen atom at the second carbonyl group, is converted into a cyclic amino alcohol, dehydration of which produces the target 1,2,4-triazole. The obtained results have been compared with the data NMR spectroscopy.
Structures, stabilities, and interactions of AuX (X = C - Pb) series are theoretically investigated at CCSD(T) and B3LYP levels with extend basis sets. Natural bond orbital analysis shows that the Au-X interaction is resulted by the overlap of sp hybrid on X and 6s5d hybrid on Au atom. Laplacian and total electronic energy density values at BCP shows the “intermediate type” of Au-X (X = Si, Ge, Sn, Pb) interactions and covalent type of Au-C interaction. Moreover, analysis of electron density deformation shows pronounced charge accumulation in the middle of the region between lighter X and Au, suggesting obvious covalent character of interaction. ELF shows increased covalency from X = Pb to X = C. Energy decomposition analysis shows positive steric contribution and negative quantum contributions to the Au-X interactions. Comparing the interaction energy of AuC with other AuX series, the decrease of interaction strength between them is caused by the positive contribution of steric effect and the negative contribution of quantum and electrostatic effects. Steric charge distribution shows interaction type causes effects to distribution of steric charge. And steric energy is correlated positively with the total interaction energy and correlated positively with the steric charge deformation at BCP.
Compounds with (NHC)→E coordination bond are being generated and their chemistry is being explored over the past 15 years (NHC= N-heterocyclic carbenes, E = main group elements). Many examples of species with N-heterocyclic olefins (NHOs) are known, which exhibit umpolung chemistry. Increasing number of chemical species, which carry NHC as a functional unit, are being reported. There is a need to understand their electronic structure. Alkylated imidazole oximes (cationic, found useful in medicinal chemistry) ((NHC)-C(H)=N-OH(+)) carry NHC unit as a functional group. Similarly, the corresponding nitroso-N-heterocyclic olefins ((NHC)=C(R)-N=O) also carry NHC as a functional unit. It is important to establish the interaction between the NHC unit and the rest part of the molecule in these species. Density functional (DFT) study has been carried out to explore the electronic structure details of a few oximes and nitroso NHOs. The results indicate that a structure with NHC→C coordination interaction can be considered as one of the resonance structures of these species.
Herein an assessment of several Long Range Corrected (LRC) Density Functional Theory (DFT) methods for the calculation of reduction potentials of the ([Ni(X2C2H2)2]n/[Ni(X2C2H2)2]n-1), and ([Ni(X2C2H2)(N2C2H4)]n/[Ni(X2C2H2)(N2C2H4)]n-1) and (where X= S or Se and n = 0, or -1) redox couples was done. From the results the values of ω that provide best agreement with CCSD(T) for the tested LRC DFT methods are 0.05 bohr-1, 0.15 bohr-1, 0.05 bohr-1, and 0.20 bohr-1 for ω-B97XD, LC-BLYP, CAM-B3LYP, and ω-B97, respectively. With these values the unsigned average in error was 0.12 V with a standard deviation of 0.13 V for ω-B97XD. For LC-BLYP, CAM-B3LYP, and ω-B97 the unsigned averages in relative errors were 0.12 V, 0.11 V, and 0.13 V, respectively, with respective standard deviations of 0.11 V, 0.12 V and 0.13 V.
The relativistic properties of Hydrogen-like atoms (HLAs) are here investigated in the Heisenberg picture for the first time. The relativistic vibrational Hamiltonian (RVH) is first defined as a power series of harmonic oscillator Hamiltonian by using the relativistic energy eigenvalue . By applying the first-order RVH (proportional to ) to the Heisenberg equation, a pair of coupled equations is turned out for the relativistic motion of the electron’s position and linear momentum. A simple comparison of the first-order relativistic and nonrelativistic equations reveals this reality that the natural (fundamental) frequency of HLA (like entropy) is slowly raised by increasing the atomic number from . The second-order RVH (proportional to ) has then been implemented to determine an exact expression for the electron relativistic frequency in the different atomic energy levels. In general, the physical role of RVH is fundamental because it not only specifies the temporal relativistic variations of position, velocity, and linear momentum of the oscillating electron, but also identifies the corresponding relativistic potential, kinetic, and mechanical energies. The results will finally be testified by demonstrating energy conservation.
Is a classical description of nuclear motion sufficient when describing chemical reactions? The present paper investigates some phenomena that were previously attributed to nuclear quantum effects. The aim is to show that these phenomena can be modelled with traditional Car-Parrinello molecular dynamics, that is, with a method which treats nuclear motion classically. We find that no additional paradigm is needed for describing chemical reactions. The special reactivity observed for carbenes can be attributed to the special environment represented by a noble gas matrix. Also the infrared spectrum of porphycene is perfectly modelled by traditional Car-Parrinello molecular dynamics. If no more convincing examples are produced, one will stick to deterministic quantum mechanics, as it is the simpler theory which, in addition, is free of paradoxa.
A series of 8-hydroxyquinoline derivatives were characterized and tested as potential antennas in a set of designed lanthanide complexes. The molecular structure and ligand localized nature of the excited states were studied in the framework of the multiconfigurational methods CASSCF/NEVPT2 combined with TDDFT- based approaches, which allows applying a fragmentation scheme in the analysis of the most probable sensitization pathway via antenna effect. The photophysical properties of all the complexes and antennas were carefully analyzed, and the most probable energy transfer pathways were elucidated. Rate constants for photophysical processes involved in the mechanism were calculated, showing a significant contribution of the vibronic coupling in all cases and the predominant intersystem-crossing between S1 and T1 states was demonstrated from the analysis of the nature of the wave function of those states. The energy transfer process described herein demonstrates the possibility of Eu(III) and Nd(III) sensitization by the studied ligands. The proposed methodology gives a complete picture of the antenna excited state dynamics.
Herein, we report the mechanism of Ir(III)-catalyzed intermolecular branch-selective allylic C−H amidation, including the influence of substituent effect on yield and regioselectivity. The sequence of amidation reaction is alkene coordination, allylic C−H activation, oxidative addition of methyl dioxazolone, reductive elimination of allyl-Ir-nitrenoid complex, amine protonation and proto-demetallation. The apparent activation energy of amidation between hexene and methyl dioxazolone is 17.8 kcal/mol, and the energy difference between two transition state for formation amide is only 2.8 kcal/mol. The introduction of more electron-deficient groups at the allyl terminal increases the apparent activation energy, conversely, the introduction of electron-donating groups significantly reduces the apparent activation energy. Among them, the apparent activation energy of the reaction between aniline group substituted allyl and methyl dioxazolone is only 13.8 kcal/mol, which further improves the reaction yield. In addition, the introduction of more electron-withdrawing groups on dioxazolone can significantly improve the regioselectivity. When 3,4,5,-trifluorophenyl substituted dioxazolone and hexene occur C−N bond coupling reaction, the energy difference of the two transition states is as high as 9.0 kcal/mol, indicating that the regioselectivity is greatly improved. The mechanism explanation of allylic C−H amidation will provide strong theoretical support for streamlined synthesis of allyl branched amides.
The installation of quantum chemistry software packages is commonly done manually and can be a time-consuming and complicated process. An update of the underlying Linux system requires a reinstallation in many cases and can quietly break software installed on the system. In this paper, we present an approach that allows for an easy installation of quantum chemistry software packages, which is also independent of operating system updates. The use of the Nix package manager allows building software in a reproducible manner, which allows for a reconstruction of the software for later reproduction of scientific results. The build recipes that are provided can be readily used by anyone to avoid complex installation procedures.
Quantum chemical calculations were carried out to establish the half-sandwich structural behaviour between heavier group-14 elements (Si-Pb) and neutral Be3 ring. The proposed complexes are found to be global minima on the potential energy surface. Quantum chemical investigation revealed that the complexes found possess high bond dissociation energy and also favorable thermodynamics of their formation. The complexes were also found to possess significant aromatic behaviour. In addition, the half-sandwich complexes were found to possess promising chemical properties to be useful for potential H2 storage material under reversible conditions.