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 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.

Investigation of cooperative effect exhibited by purely C-H—O hydrogen bonded (H-bonded) networks in linear and cyclic clusters of (1,3-cyclohexanedione)n (n = 2 to 6) has been carried out using density functional theoretical calculations. Linear clusters were found to show anti-cooperative behavior, while the cyclic clusters showed positive cooperativity. H-bond strengths and binding energies per bimolecular interaction were found to decrease with increasing cluster size for the linear clusters whereas their cyclic counterparts showed opposite trends. The extent of cooperativity has been found to show monotonic behavior for both linear and cyclic clusters and was found to reach an asymptotic limit with increasing cluster size. Natural bond orbital (NBO) analysis and atoms in molecule (AIM) calculations were found to corroborate the obtained results.

Histidine (an imidazole-based amino acid) is a promising building block for short aromatic peptides containing a proton donor/acceptor moiety. Previous studies have shown that polyalanine helical peptides substituted at regular intervals with histidine residues exhibit both structural stability as well as high proton affinity and high conductivity. Here, we present first-principle calculations of non-aqueous histidine-containing 310-,  and -helices and show that they are able to form hydrogen-bonded networks mimicking proton wires that have the ability to shuttle protons via the Grotthuss shuttling mechanism. The formation of these wires enhances the stability of the helices, and our structural characterizations confirm that the secondary structures are conserved despite distortions of the backbones. In all cases, the helices exhibit high proton affinity and proton transfer barriers on the order of 1~4 kcal/mol. Zero-point energy calculations suggest that for these systems, ground state vibrational energy can provide enough energy to cross the proton transport energy barrier. Additionally, ab initio molecular dynamics results suggests that the protons are transported unidirectionally through the wire at a rate of approximately 2 Å every 20 fs. These results demonstrate that efficient deprotonation-controlled proton wires can be formed using non-aqueous histidine-containing helical peptides.

The rapid and successful strides in quantum chemistry in the past decades can be largely credited to a conspicuous synergy between theoretical and computational advancements. However, the architectural computer archetype that enabled such a progress is approaching a state of more stagnant development. One of the most promising technological avenues for the continuing progress of quantum chemistry is the emerging quantum computing paradigm. This revolutionary proposal comes with several challenges, which span a wide array of disciplines. In chemistry, it implies, among other things, a need to reformulate some of its long established cornerstones in order to adjust to the operational demands and constraints of quantum computers. Due to its relatively recent emergence, much of quantum computing may still seem fairly nebulous and largely unknown to most chemists. It is in this context that here we review and illustrate the basic aspects of quantum information and their relation to quantum computing insofar as enabling simulations of quantum chemistry. We consider some of the most relevant developments in light of these aspects and discuss the current landscape when of relevance to quantum chemical simulations in quantum computers.

Mechanism of the oxidative nonpolar inversion reaction catalyzed by N-heterocyclic carbenes (NHCs) to achieve benzoxazoles was investigated in very details. The reaction was revealed to occur through five processes, and for oxidation in the second process, two successive tautomerizations followed by oxidation were demonstrated to be more energetically favorable than the other two pathways. The rate-determining step was disclosed to be the oxidation by 3,3’-5,5’-tetra-tert-butyl-4,4’-diphenoquinone (DQ). Afterwards, mechanism calculations to the non-catalyzed reaction was conducted and it was revealed that the excessive exothermic property of the initial step should be the main reason for the extremely high barrier in the following step. While with participation of NHC, this unfavorable transformation can be deftly prevented according to the specific sequence and amount of reagents addition, and therefore to enable the reaction to occur under mild conditions.

The structure, energetic and quantum chemical descriptors of Cs+ complexes of calix[4]arene-crown-6 (C4C6) and substituted C4C6 i.e 1,3 alternate-diethoxy C4C6 are reported here based on the analysis of results using density functional theory. Substitution of benzo group to both C4C6 and 1,3 alternate-diethoxy C4C6 resulted in reduction of binding energy (BE). Further substitution on benzo group with methyl, methoxy and amino groups leads to increase in BE and nitro substitution leads to decrease in BE for C4C6, whereas in the case of 1,3 alternate-diethoxy calix[4]arenebenzocrown-6, methoxy substitution leads to highest BE compared to other complexes. The calculated Gibbs free energy, ΔGgas also followed the same order as BE in the case of 1,3 alternate-diethoxy C4C6 and their substituted ligands. Furthermore, the ΔG of complexation were computed using thermodynamic cycle with conductor like screening model (COSMO) in different solvents: toluene, chloroform, octanol and nitrobenzene. The values of ΔGext are found to be increased with increase in the dielectric constant of the solvent and found to be highest in the nitrobenzene. The Atoms in Molecule (AIM) analysis reveals partial ionic character in Cs-O bond. Among all the studied complexes, 1,3 alternate-diethoxy calix[4]arene 3’-methoxy benzo crown-6 displays highest ΔGext in nitrobenzene. The calculated value of ∆∆Gext (∆∆G= ∆GCs+-∆GNa+) is found to be -41.82 kcal/mol with 1,3 alternate-diethoxy calix[4]arene 3’-methoxy benzocrown-6 which is higher than that obtained with calix [4] bis-crown-6 (-5.24 kcal/mol). The newly designed ligand might be suitable for the selective extraction of Cs+ over Na+ in the reprocessing of nuclear waste and thus invites the experimentalists for testing this DFT finding in the laboratory.

We studied the ring opening of propylene oxide (PO) by salen-M coordinated OH- group [M = Al(Ⅲ), Sc(Ⅲ), Cr(Ⅲ), Mn(Ⅲ), Fe(Ⅲ), Co(Ⅱ), Co(Ⅲ), Ni(Ⅱ), Cu(Ⅱ), Zn(Ⅱ), Ru(Ⅲ) and Rh(Ⅲ)]. The results show that the ring opening energy barriers for M(II) complexes are much lower than those with M(III) complexes in the gas phase, and the barriers correlate linearly with the negative charges on the OH- group, the Fukui function condensed on the OH- group. The nucleophilicity ordering in gas phase can be rationalized by the ratio of formal positive charges/radius of M cations. Solvent effect greatly increases the barriers of M(II) complexes, but slightly changes the results of M(III) ones, making the barriers similar. Analysis indicates that the reaction heats are linearly proportional to the reverse reaction barriers. The relationships established here can be used to estimate the ring opening barriers and to screen epoxide ring opening catalysts.

The preparation of hydrogen by photocatalytic principle is an important subject in the future energy direction. This article intends to design the catalytic structure of a crystalline (amorphous) TiO2/two-dimensional MoS2 sandwich structure supporting a single-atom, and explore the effect of this special structure on the photocatalytic reaction.Calculating the effective mass, electrostatic potential, light absorption spectrum and other related properties by DFT method, the analysis shows that the sandwich structure catalyst has good carrier transfer ability and electron-hole separation ability. Except for the Pt@Amorphousr-TiO2/MoS2 sandwich structure single-atom catalyst, which only has an excellent effect on the oxygen evolution of water, the rest of the interlayer catalysts have the two characteristics of photocatalytic hydrogen evolution and oxygen evolution.The new catalyst designed in this paper has innovative design ideas and high-efficiency research and development value.

Density functional calculations have been carried out to investigate the possibility of trapping of noble gas dimers by cyclo[18]carbon dimer. Parallel-displaced conformation of the cyclo[18]carbon dimer is found to be the minimum energy structure. Non-covalent interaction is found to hold the noble gas dimers. The lighter noble gases (He, Ne) posses repulsive interactions, the heavier one (Ar, Kr) are held by attractive interactions forming genuine bonds. Each of the noble gas atoms in turn forms non-covalent interaction with the cyclo[18]carbon monomers. The bond dissociation energy of the noble gas dimers dramatically increases inside the cyclo[18]carbon dimer. Energy decomposition analysis reveals that dispersion plays the major role towards the stabilization energy.

R\’enyi complexity ratio of two density functions is introduced for three and multidimensional quantum systems. Localization property of several density functions are defined and five theorems about near continuous property of R\’enyi complexity ratio are proved by Lebesgue measure. Some properties of R\’enyi complexity ratio are demonstrated and investigated for different quantum systems. Exact analytical forms of R\’enyi entropy, R\’enyi complexity ratio, statistical complexities based on R\’enyi entropy for integral order have been presented for solutions of pseudoharmonic and a family of isospectral potentials. Some properties of R\’enyi complexity ratio are verified for six diatomic molecules (CO, NO, N$_2$, CH, H$_2$, and ScH) and for other quantum systems.

In order to elucidate the temperature-dependent valence state of Ce ion and the occupation number of Ce 4f electrons in cerium mononitride (CeN), we perform an ab initio calculation on CeN by using a many-body scheme combing density functional theory (DFT) with dynamical mean field theory (DMFT), taking into account the spin-orbit coupling (SOC) interaction and on-site Coulomb repulsion between Ce 4f electrons. Results demonstrate that Ce 4f j=5/2 and j=7/2 manifolds undergo insulating-metallic transition with the increasing of temperature. Ce 4f-conduction electrons hybridization, f-f correlation, SOC interaction and final state effects yield a complicated spectrum function in CeN. Ce 4f atomic configuration transition and hybridization might be responsible for the temperature-dependent occupancy number of Ce 4f electrons and the mixed-valence state in CeN. A fact that localization of Ce 4f electrons, i.e., 4f1 configuration or Ce3+ valence, increases with the increasing of temperature could account for the experimentally observed lattice constant versus temperature data. Finally, the so-called quasiparticle band structure is also discussed for comparison with experimental angle-resolved photoemission spectrum (ARPES).

It has been a challenge in automated analysis of medical and chemical knowledge to extract represent quantitative structure–activity relationship (QSAR) using intelligent computing in drug discovery. One of many domain-specific bottlenecks in drug discovery is robust conformation search in three-dimensional (3D) space for flexible drug candidates. The process involves researchers and machines working together to achieve their own strengths for greater outcome. The present study has been developing a method for conformational sampling conformers in the class of 4-anilinoquinazoline derivatives for epidermal growth factor receptor (EGFR) tyrosine kinases inhibitors (TKIs). We use AG-1478 to demonstrate how the new intelligent computing method helps to quantum mechanically determine 22 target drug conformer clusters and their properties from conformational sampling, based on density functional theory (DFT) method, time-dependent (TD)-DFT in solvents and clustering analysis (CA). The UV-vis spectra of the preferred conformers agree well with earlier experimental measurements in which the conformer dependent UV-Vis spectral shift of AG-1478 can be as large as approximately 15 nm. We are further developing this method to study and design new 4-anilinoquinazoline derivatives of EGFR TKIs.

The aromaticity of boron-nitrogen clusters has been revisited through a systematic analysis using magnetic criteria. The results obtained through Ring Current Strength (RCS) measurements indicate that B2N2 has a strongly antiaromatic character, even the bond pattern analysis reveals that this system is doubly antiaromatic presenting two σ- and two π-orbitals of 4c-2e, according to the Adaptive Natural Density Partitioning bond pattern analysis (AdNDP) and z-component of the dissected Nucleus Independent Chemical Shift (NICSzz) isolines. B4N4 and B6N6 are marginally antiaromatic according to RCS and the bond pattern suggest four and six 8c-2e and 12c-2e delocalized π-orbitals respectively. B3N3 and B5N5 are slightly aromatic, with a bond pattern of three and five 6c-2e and 10c-2e π-orbitals respectively. All rest of the systems (x = 7 – 11) are non-aromatic. The results show some discrepancies with results based on the classical nucleus independent chemical shift, which can be attributed to tensor in-plane and core electron contributions. Finally, presented results reveal the need to be careful with the interpretations given by this index, so it will be necessary the use of 1D, 2D or 3D derived methodologies for a complete and correct analysis of (anti)aromaticity.

The defected carbon materials as a metal-free catalyst shown superior stability and catalytic performance in the acetylene hydrochlorination reaction. Through DFT calculation, for the first time several different defected configurations comprising mono, di-vacancies, and Stone Wales defect on single-walled carbon nanotubes (SWCNTs) have been used as a direct catalyst for acetylene hydrochlorination reaction. These defective sites on SWCNTs are the most active site for acetylene hydrochlorination reaction compared to pristine SWCNT. The different configuration of defects have different electronic structure, which specify that mono-vacancy defect, have more states adjecent to the Fermi level. The reactant acetylene (C2H2) adsorbed strongly than hydrogen chloride (HCl) and expected to be the initial step of the reaction Acetylene adsorbed strongly at mono-vacancy defected SWCNT compared to other investigated defects. The reaction pathways analysis revealed that mono- and di-vacancy defected SWCNT has a minimum energy barriers and shows extraordinary performance towards acetylene hydrochlorination. This work suggests the potential of metal-free defected carbon to catalyze acetylene hydrochlorination and provide a solid base for future developments in acetylene hydrochlorination.

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.

Polynomial graph invariants have been confirmed to have important applications in quantum chemistry and biological information. One of the famous polynomial graph invariants is the Tutte polynomial which gives multifarious interesting information about the graph structure. In this paper, we first give a simpler and more efficient method to get the Tutte polynomials of alternating polycyclic chains. Then we obtain the explicit expressions for the Tutte polynomials and the number of spanning trees of phenylene systems with given number of branching hexagons. Moreover, we determine the extremal values of the number of spanning trees among the phenylene systems with given one or two branching hexagons, and the corresponding extremal phenylene systems are characterized, respectively.

ABSTRACT2-{3-[2-(4-dimethylaminophenyl)vinyl]-5,5-dimethylcyclohex-2-enylidene}-malonitrile (DAT2) is a potential candidate for generating Terahertz radiation in the range 0.1-3 THz. In the present work, we synthesized DAT2 compound and confirmed it’s molecular structure by proton NMR. Good quality single crystals of DAT2 of size 1.2×0.5× 0.2 cm3 are grown for the first time, using solvent evaporation technique. The grown crystals are tested for crystalline perfection using powder XRD study and the crystal structure is determined to be monoclinic with centrosymmetric space group P 2/C. The electronic band structure was studied by Density Functional Theory and the theoretical band gap was compared with experimental bandgap 1.6 eV. Further,using DFT the dielectric constants [εr (ω ) andεi (ω )], reflectivityR (ω ), refractive index n (ω ), extinction coefficient K (ω ), optical conductivity σ (ω ) and energy loss function L (ω ) for DAT2 crystal has been calculated. The results are discussed in detailIndex terms: nonlinear optical material. organic compound. crystal growth DFT study. dielectric constant. refractive indexINTRODUCTIONOrganic nonlinear compounds are found to be very attractive for ultrafast photonic applications such as optical switching, second harmonic generation and terahertz (THz) wave generation oweing to their high nonlinearities and ultrafast response times1. Organic NLO crystals like DAST,DSTMS, BNA and OH1 etc., possessing very high second order nonlinear coefficients, are presently extensively studied for generation of Terahertz between 0.1-10 THz . 2-{3-[2-(4-dimethylaminophenyl)vinyl]-5,5-dimethylcyclohex-2-enylidene}-malonitrile (DAT2) is an organic nonlinear optical material studied for terahertz generation (THz) in the region 0.1 – 3 THz1,2. Many explosives like RDX, TNT etc., have their finger prints in this region and hence DAT2 can be used as a suitable candidate for detection of hidden explosives 3. DAT2 has a molecular formula of C21H23N3. It has very high electro-optic coefficient of r 12 = 56 pm/V2.The reason of high NLO response in DAT2 arises from the electron donor in dialkylamino group and the electron acceptor is a dicyanomethylidene, >C—-C(CN)2 group connected by a π-conjugated hexatriene bridge. Compared with other organic crystals, DAT2 posesses high thermal stability and good SHG efficiency. Crystal growth DAT2 by melt and vapour growth methods produced only few millimeter sized crystals, which makes it unsuitable for fabrication of optical devices. Hence, the authors are motivated in the developing large size DAT2 single crystals suitable for Terahertz applications.The computational chemistry is an easy way to study the molecular level properties of complicated structures, their bonding interactions, electronic and optical properties etc.,(Shoba et al. 2014, )5. It is important to know the physical properties such as material’s bandgap, dielectric constant, refractive index, conductivity,reflectivity etc.,to evaluate the performance related to optolectronic applications6,7, Also, no quantum chemical calculations were reported for DAT2 molecule so far. Hence, the authors are interested to study the important properties such as electronic band structure, dielectric constant and linear optical properties of DAT2 crystal. In the present work, the structural, electronic and optical properties of DAT2 crystal are determined by the ab initio pseudopotential density functional method. The results are presented and discussed in detail.II Material Synthesis and Crystal Growth : The raw materials 4-dimethyl aminobenzaldehyde, (3,5,5-trimethylcyclohex-2-enylidene) malononitrile, acetonitrile and other chemicals were purchased from Sigma-Aldrich (99.99% purity) and used for synthesis. DAT2 was synthesized by procedure8 described in Fig. 1. 4-dimethyl aminobenzaldehyde (0.1 mol) and (3,5,5-trimethylcyclohex -2- enylidene) malononitrile (0.1 mol) were dissolved in acetonitrile (100 ml) in a round-bottomed flask. To this mixture piperidine (0.01 mol) was added and the solution was stirred at 40̊ C for 24 h. The product formed was confirmed by TLC plate. The resulting solution was roto-evaporated and dried. The product was purified by column chromatography using n-hexane and ethyl acetate mixture (99.99/1). The yield obtained was 37%. DAT2 was dissolved in deutrated chloroform (CDCl3) and the proton NMR spectrum was recorded using Bruker instrument operating at 500MHz. 1H NMR (400 MHz, CDCl3): δ = 7.38 (d, J = 8.9 Hz, 2H), 7.01 (d, J = 16 Hz, 1H), 6.76 (d, J = 16 Hz, 1H), 6.73 (s, 1H), 6.64 (d, J = 8.9 Hz, 2H), 3.12 (s, 6H), 2.74 (s, 2H), 2.65 (s, 2H), 1.06 (s, 6H).13C NMR (100 MHz, CDCl3): δ = 169.2, 155.3, 151.2, 138.3, 129.5,129.4, 124.4, 121.4,114.1, 113.4, 112.3, 75.7, 42.9, 40.3, 39.2, 31.8, 28.1.For growing crystals of DAT2, the as synthesized salt was recrystallized twice from methanol to increase it’s purity. In the present work, we attempted to grow DAT2 single crystals using methanol. But, it yielded only small sized needle type crystals. Next, the solubility of DAT2 in acetone was determined. At room temperature the solubility was experimentally determined to be 5.2 g/100ml. Saturated DAT2 solution was prepared at 40̊ C and allowed to cool down to room temperature by slow evaporation of the solvent. Dark-red coloured plate like DAT2 crystal of dimension 1.2 ×0.5 × 0.2 cm3 was obtained after two weeks as shown in Fig. 2aIII Crystal structure : To identify the crystal structure and to calculate the lattice parameters of our as grown DAT2 crystals, powder X-ray diffraction analysis was carried out using Rigaku Ultimata III X-ray diffractometer. Cu Kα radiation of wavelength, 1.5405 Å was used as source for diffraction. The glancing angles were varied from 5 to 80◦ at the scan rate of 2° per minute. Fig. 2b shows the Bragg’s diffraction peaks obtained for powdered DAT2 sample. The experimental peaks were compared with Crystallographic Open Database (COD no: 96-710-1371). Using hkl values, the lattice parameters were calculated a = 6.1305Å, b = 7.424 Å, c = 20.258 Å,α = 90 ̵̊, β = 96̊ γ = 90̊. he crystal structure DAT2 belongs to monoclinic with space group P 2/c.