Electrochemical ammonia synthesis is being actively studied as a low temperature, low pressure alternative to the Haber-Bosch process. This work studied iridium as the electrochemical catalyst, following a previous study of adsorption characteristics on platinum. The characteristics studied include bond energies, bond lengths, spin densities, and free and adsorbed vibrational frequencies for the molecules N2, N, NH, NH2, and NH3. Overall, these descriptive characteristics explore the use of dispersion-corrected Density Functional Theory methods that can model N2 adsorption – the key reactant for electrochemical ammonia synthesis via transition metal catalysis. Specifically, three methods were tested: hybrid B3LYP, a dispersion-corrected form B3LYP-D3, and semi-empirical B97-D3. The latter semi-empirical method was explored to increase the accuracy obtained in vibrational analysis as well as reduce computational time. Two lattice surfaces, (111) and (100), were compared. The adsorption energies are stronger on (100) and follow the trend EB3LYP > EB3LYP-D3 > EB97-D3 on both surfaces.
The internal disorder of the two-dimensional confined hydrogenic atom is numerically studied in terms of the confinement radius for the 1_s_, 2_s_, 2_p_ and 3_d_ quantum states by means of the statistical Crámer-Rao complexity measure. First, the confinement dependence of the variance and the Fisher information of the position and momentum spreading of its electron distribution are computed and discussed. Then, the Crámer-Rao complexity measure (which quantifies the combined balance of the charge concentration around the mean value and the gradient content of the electron distribution) is investigated in position and momentum spaces. We found that confinement does disentangle complexity of the system for all quantum states by means of this two component measure.
In this study, three novel sensitizers with the donor-acceptor-π-spacer-acceptor D-A’-π-A) structure were designed based on the benzothiadiazole (BTD) surrounded by two thiophenes in each side (T4) mono-functionalized by an acid phosphonic (A) T4BTD-A dye by insertion of vinyl and cyanide CN electron-withdrawing moiety in a different position. Their geometrical, electronic and photovoltaic parameters were predicted using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, via the functional BHandH in combination with the Poples basis set 6-311G(d) for small atoms and pseudo-potential basis set LANL2DZ for Titanium atom at the chloroform solvent medium via the implicit CPCM model. Results showed that the inclusion of the C=C and the CN moieties exhibits a decrease in the HOMO–LUMO gap, and a redshift in the absorption spectra. The photoelectric conversion efficiency (PCE) for the T4BTD-A dye was estimated to be about 6.57 % under the standard AM 1.5G solar radiation, which is in excellent agreement with its measured value of 6.40 %, suggesting that our calculations scheme is consistent. Moreover, the predicted PCE value after elongation of T4BTD-A by C=C and CN has increased to 7.11 % and (7.82 %, 8.09 %) respectively. Our results revealed that the addition of CN electron-withdrawing moiety enhances the PCE of the studied dyes, while the position of CN moiety has a slight effect on the PCE of the studied dyes. Additionally, our calculation suggests that the CCCN1 and CCCN2 are good candidates as efficient sensitizers for dye-sensitized solar cell DSSCs applications.
The current study investigates the correlation between biological activity and physicochemical properties of a few specific estradiol isomers. Theoretical studies on the physicochemical properties of estradiol isomers were performed using different quantum mechanical methods. The computational methods used in this study include the Density Functional Theory (DFT) method, the Hartree-Fock (HF) method and Semi-empirical (AM1) method. Some physicochemical properties such as dipole moment, molecular weight, the energy of the highest occupied molecular orbital (E HOMO), the energy of the lowest unoccupied molecular orbital (E LUMO), polarizability, the octanol-water partition coefficient (Log P), polar surface area (PSA) the number of hydrogen bond donors (HBDs) and the number of hydrogen bond acceptors (HBAs), the surface area, volume of the molecule, and ovality are calculated for the isomers. However, only dipole moment values are suitable to identify a correlation of experimental biological activity of estradiol isomers. To the best of our knowledge, this is the first report on the relationships between dipole moment and biological activities of estradiol isomers. It is observed that the active compound has a significantly higher dipole moment value compared to the inactive compound. We have also analyzed the geometrical and graphical models of these isomers and related compounds to evaluate the differences in the molecular charge distributions.
Dirac relativistic partial wave analysis has been employed to analyze the angular distributions and critical minima along with maximum spin polarization for the elastic scattering of electrons from copper atoms over the energy range 1 - 2000 eV. Integrated elastic, inelastic, total and momentum transfer cross sections have also been calculated. This work uses a complex electron-atom optical potential that includes static, exchange, correlation-polarization and absorption potentials. Comparison of our calculations with the available experimental data and other theoretical calculations show a satisfactory agreement. As far as we are concern, critical minima and corresponding maximum spin polarization points have not yet been reported in literature.
The Shannon entropy (S) and the Fisher Information (I) entropies are investigated for a generalized hyperbolic potential in position and momentum spaces. Firstly, the Schrodinger equation is solved exactly using the Nikiforov-Uvarov-Functional Analysis (NUFA) method to obtain the energy spectra and the corresponding wave function. By Fourier transforming the position space wave function, the corresponding momentum wave function was obtained for the low lying states corresponding to the ground and first excited state. The positions and momentum Shannon entropy and Fisher Information entropies were calculated numerically. Finally, the Bialynicki-Birula and Mycielski (BBM) and the Stam-Cramer-Rao inequalities for the Shannon entropy and Fisher Information entropies respectively were tested and was found to be satisfied for all cases considered
Atomically precise metallic clusters behaving as superatoms, are relevant building blocks towards new materials under the bottom-up approach. Here we discussed the plausible formation of the Cu10Ru cluster as a superatomic specie accounted its 1S2 1P6 1D10 shell order, with the aim of identification of particular clusters with enhanced stability. By stochastic structure search on Cu10Ru clusters, we found six low-lying cluster isomers with ΔE values from 0.0 to 4.7 kcal∙mol above the ground state denoting an endohedral motif with the Ru dopant inside the Cu10 cage, as the favored structures. By using molecular dynamics simulations we found a clear trend of encapsulation of the Ru atom at low temperatures, quantified by the Cu-Ru bonding distances during the annealing procedure. The 17-ve counterpart, Cu9Ru shows a large electron affinity, owing to the trend to achieve a electronic shell closing as a new superhalogen species. These results are useful for further rationalization and design of novel superatoms expanding the libraries of endohedral clusters.
Quantum-chemical “descriptors”, including atomic partial charges, orbitals, and electrostatic potentials are powerful tools for understanding chemical reactivity. Localized defects in graphene are a particular challenge for these tools, especially to model the adsorption processes and to predict the interactions of transition metals with these defects. Such defects often have little charge polarization and a combination of localized and delocalized states. Our orbital overlap distance D(r) measures the “size” of occupied orbital lobes about point r, distinguishing the hybridization state and compact vs. diffuse character of local electronic structure. Here we apply the overlap distance to graphene defects. We find that the overlap distance clearly distinguishes differential reactivities of different atoms at intrinsic defects. Combining the overlap distance and electrostatic potential provides a rich picture of extrinsic defect reactivity, including semiquantitative predictions of transition metal binding.
Minimum energy structures of neutral and radical cations of end substituted thia[n]helicenes (n=1-10) in DCM solvent are reported. For both neutral and radical cations of these helicenes, calculated structures are non-planar for n=3-10. Helical structures are obtained for higher helicenes and thiahelicene system has a helical structure with one complete turn. Equilibrium geometries are predicted applying B3LYP-D/6-311++G(d,p) method in conjunction with SMD solvent model. Single point energy calculations are also performed at MP2 level to improve certain energy parameters. Excited state calculations are performed using Time-Dependent Density Functional Theory (TDDFT) formalism to predict UV-Visible spectra of neutral and radical cations of thia[n]helicenes in DCM solvent. Thia[n]helicenes radical cation have strong absorption in the near IR region. Calculations also suggest that dimerization is not a favourable process in DCM solvent for the end substituted neutral and radical cation of thiahelicene. The present theoretical study examines the molecular and electronic properties of thia[n]helicenes in search of near infrared electronic devices.
In this theoretical study, we investigate the electronic potential energy curves, spectroscopic parameters, vibrational energy levels and transition dipole moments for the diatomic dications BeRb2+, BeCs2+ and SrRb2+. We consider an ab initio approach based on the use of non-empirical pseudopotentials and parameterized l dependent polarization potentials. Results show that 1-22Σ+ for BeRb2+, 1-52Σ+ for BeCs2+ and 1-32Σ+ for SrRb2+ are repulsive. While the 32Σ+ for BeRb2+, 42Σ+ for BeCs2+ and 42Σ+ for SrRb2+ are metastable states. These states can accommodate some vibrational energy levels. Interesting avoided crossings between some 2+ states are localized and examined. Until now no experimental and theoretical studies have been made for each system. Consequently, we discuss our results by comparing with some data of similar systems. Besides, the transition dipole moments of the ground state to a few excited states are computed and presented. The information associated with the electronic structures, spectroscopic parameters as well as the transition properties that provide in this paper is anticipated to serve as guidelines for further experimental and theoretical researches for each diatomic dication considered in this work.
The atomic structure, spin states of the interface based on iron-porphyrin and armchair graphene nanoribbon (FeP/AGNR) and potential energy surface of FeP atop of AGNR migration is investigated via DFT theory. The multiplicity of Fe ion in iron porphyrin for all possible types of coordination is determined as a triplet. It is estimated that FeP would place atop AGNR at the position where two Fe-N bonds are located above the C-C bond, another two are located above C atoms. The barrier of migration of iron porphyrin complex atop of graphene armchair nanoribbon is found to be smaller the temperature factor, making the heterostructure to be in temperature equilibrium between different types of coordination of the iron porphyrin atop of graphene nanoribbon
Unique superhalogen properties of Pt(CN)n complexes (n = 1–6) containing cyanide (CN) pseudohalogen moieties bound with platinum (Pt) atom have been investigated under the quantum chemical formalism. The study involves theoretical calculations for both neutral and anionic forms of Pt(CN)n using density functional theory (DFT) with the hybrid functional B3LYP. In order to improve the accuracy of calculations, 6–311+G(d) basis set was implemented for CN moieties, whereas, SDD basis set supplemented with Stuttgart/Dresden relativistic effective core potential was used for Pt atom. HOMO–LUMO energy band gaps, vibrational frequencies and dissociation energies of Pt(CN)n complexes have been calculated to investigate their relative stability as well as reactivity. Additionally, superhalogen properties and salt forming capability of Pt(CN)n complexes have also been analyzed. Focus of analysis is on the delocalization of charges over attached CN ligands in successive members of the Pt(CN)n species. Reliable low–cost investigations on superacidity properties of associated protonated species have also been carried out keeping their industrial applications in mind.
A semiclassical phase-space perspective of band- and topological-insulator regimes of 2D Dirac materials, and normal- and superradiant-phases of atom-field interacting models is given in terms of delocalization, entropies, and quantum correlation measures. From this point of view, the low-energy limit of tight-binding models describing the electronic band structure of topological 2D Dirac materials like phosphorene and silicene with tunable band gaps, share similarities with Rabi-Dicke and Jaynes-Cummings atom-field interaction models, respectively. In particular, the edge state of 2D Dirac materials in the topological insulator phase exhibits a Schr\”odinger cat structure similar to the ground state of two-level atoms in a cavity interacting with a one-mode radiation field in the superradiant phase. Delocalization seems to be a common feature of topological insulator and superradiant phases.
We have recently developed a computational methodology to separate the effects of size, composition, symmetry and fluxionality in explaining the experimental photoelectron spectra of mixed-metal clusters. This methodology was successfully applied first in explaining the observed differences between the spectra of Al13- and Al12Ni- and more recently to explain the measured spectra of AlnMo-, n=3-5,7 clusters. The combination of our approach and new synthesis techniques can be used to prepare cluster based materials with tunable properties. In this work we use the methodology to predict the spectrum of Al6Mo-. This system was chosen because its neutral counterpart is a perfect octahedron and it is distorted to a D3d symmetry and was not observed in the recent experiments. This high symmetry cluster bridges the less symmetric Al5Mo- and Al7Mo-structures. The measured spectra of Al5Mo- has well defined peaks, while that of Al7Mo-does not. This can be explained by the fluxionality of Al7Mo-, as at least 6 different structures lie within the range that can be reached by thermal effects. We predict that Al6Mo- has well defined peaks, but some broadening is expected as there are two low-lying isomers, one of D3d and the second of D3h symmetry that are only 0.052 eV apart.
Etherification mechanism of 4,5-dihydroxy-1,3-bis (hydroxymethyl) imidazolidin-2-one (DMDHEU) with primary alcohols in acidic and parched condition were investigated by using density functional theory combined with comparision and reference to results of experiment and spectral analysis. Geometry and energy of reactants, products, actived complexes and carbocation intermediate were optimized at B3LYP/6-311g(d,p) level. Energy level diagram is compatible with type of cation – molecule reaction. Reactants and products form actived complexes with H+ and water, in this state H+ is occupied by both alcohol and water or ether and water. This state has lower energy level compared to both of the following cases: H+ is only occupied by water; and H+ is only occupied by the product or reactant. Computational results indicate that the etherification reaction follows unimolecular nucleophilic substitution (SN1) mechanism; substituent group –R in primary alcohol R-CH2OH (-R = -H, -CH3, -CH2CH3, -Vinyl, -CH2NHCH3, -CH2OCH3, -CH2Cl) only affect to energy barrier of step releasing H3O+ Ec but no effect to energy barrier of activation step Ea = 12.8 kcal/mol; value of Ec is much higher than value of Ea which were verified and confirmed through experiment results.
The influences of the initial states of HCl on the stereodynamics properties of the Ca+HCl reaction are investigated by utilizing the method based on the quasi-classical trajectory (QCT) theory and the analytical potential energy surface (APES). The orientation and alignment behaviors for the rotational angular momentum of the product, along with the generalized differential cross-section (PDDCS) dependent polarization, are employed to explore the stereodynamics properties. The initial rotational states of the HCl molecule impose a remarkable affection on the vector correlation distributions, regardless of the orientation, alignment, or PDDCS. The obvious forward or backward scattering, as well as the weak sideway scattering phenomena, are found for the different initial rotational states of the HCl molecule. The initial higher rotational-excited state of j=3 results in more obvious stereodynamics effects.
The polyphenyl chains with $n$ hexagons are the special graphs of unbranched polycyclic aromatic hydrocarbons. The objective of this study is to find the expected values of the multiplicative version of the atomic-bond connectivity index and geometric-arithmetic index of this class of special hydrocarbons. The average values of these two indices with respect to the set of all polyphenyl chains have been determined. Finally, the comparisons between the expected values of the aforementioned indices in the random polyphenyl and spiro chains, have been outlined.
We calculate the concerted pathway of 1, 2-bromochloroethane monocation to C2H4+ and BrCl using the Minnesota density functional M06-2X and the def2-TZVP basis set. We also calculate the elimination channel of 1, 2-bromochloroethane monocation to C2H4 and BrCl+ for the reason that positive charge can be assigned to either moiety in the fragmentation process of 1,2-C2H4BrCl+. Our results demonstrate that the elimination channel of 1, 2-bromochloroethane monocation to C2H4+ and BrCl is preferred, and the singly charged 1,2-bromochloroethane ions surpass two energy barriers and then separate into C2H4+ + BrCl by an asynchronous concerted process. Experimentally, we confirm that this elimination channel is from the dissociative ionization process of 1,2-bromochloroethane monocation by dc-slice imaging technique. Besides, we can see in laser-induced time-of-flight mass spectra of 1,2-bromochloroethane that fragment ion C2H4+ occur at the laser intensity of 6.0×1013 W/cm2 while BrCl+ occur at a higher laser intensity, which is consistent with the theoretical results that appearance energy of ion C2H4+ should be lower than that of BrCl+, and this is the reason why the low-velocity component of ion BrCl+ is absent from our sliced images.