Ab Initio Quantum Chemical Calculations Research Articles

Introducing a New Potential Figure of Merit for Evaluating Microstructure Stability in Photovoltaic Polymer-Fullerene Blends

A theoretical understanding of the microstructure of organic semiconducting polymers and blends is vital to further advance the optoelectronic device performance of organic electronics. We outline the theoretical framework of a combined numerical approach based on polymeric solution theory to study the microstructure of polymer:small molecule blends. We feed the results of ab initio density functional theory quantum chemistry calculations into an artificial neural network for the determination of solubility parameters. These solubility parameters are used to calculate Flory–Huggings intermolecular parameters. We further show that the theoretical values are in line with experimentally determined data. On the basis of the Flory–Huggings parameters, we establish a figure of merit as a relative metric for assessing the phase diagrams of organic semiconducting blends in thin films. This is demonstrated for polymer:fullerene blend films on the basis of the prototypical polymers poly(3-hexylthiophene-2,5-diyl) (...

From Square‐Planar [ICl4]− to Novel Chloroiodates(III)? A Systematic Experimental and Theoretical Investigation of Their Ionic Liquids

A systematic investigation on the existence of chloroiodates formed by reaction of Cl- with I2 Cl6 , apart from the well-known [ICl4 ]- , namely [I2 Cl7 ]- and [I3 Cl10 ]- , was undertaken by employing theoretical as well as experimental methods. The thermodynamic stability in terms of the complexation enthalpies and Gibbs energies, and also the decomposition of the iodine(III) polyinterhalogen anions through dichlorine elimination to form iodine (I) compounds, was studied by means of DFT and ab initio quantum-chemical calculations up to an extrapolated CCSD(T)/A'QZ level. On the experimental side, mixtures of [HMIM]Cl ([HMIM]+ =1-hexyl-3-methylimidazolium), [BMP]Cl ([BMP]+ =1-butyl-1-methylpyrrolidinium chloride) and [NEt4 ]Cl with 0.5, 1.0, and 1.5 equivalents of I2 Cl6 were investigated by single-crystal XRD, ion chromatography, NMR- and Raman spectroscopy. The reactions with 0.5 equivalents of I2 Cl6 resulted in the compounds [HMIM][ICl4 ], [BMP][ICl4 ], and [NEt4 ][ICl4 ], of which crystal structures were determined. The mixtures with 1.0 or 1.5 equivalents of I2 Cl6 yielded dark red liquids or suspensions of a dark red liquid with an orange solid, respectively. Both mixtures were studied by NMR-spectroscopy for the organic cation part and ion chromatography and Raman spectroscopy for the polyinterhalogen anions. The discussion of the experimental Raman spectra is supplemented with computed spectra based on the structures obtained from RI-MP2/def2-TZVPP structure optimisations. Overall [I2 Cl7 ]- appears to be the predominating anionic species in mixtures with 1.0 equivalents I2 Cl6 , while mixtures with 1.5 equivalents of I2 Cl6 are suspensions of I2 Cl6 in a liquid phase containing mixed anionic interhalogen complexes.

J1−J2 square lattice antiferromagnetism in the orbitally quenched insulator MoOPO4

We report magnetic and thermodynamic properties of a $4{d}^{1}$ (${\mathrm{Mo}}^{5+}$) magnetic insulator ${\mathrm{MoOPO}}_{4}$ single crystal, which realizes a ${J}_{1}\ensuremath{-}{J}_{2}$ Heisenberg spin-$1/2$ model on a stacked square lattice. The specific-heat measurements show a magnetic transition at 16 K which is also confirmed by magnetic susceptibility, ESR, and neutron diffraction measurements. Magnetic entropy deduced from the specific heat corresponds to a two-level degree of freedom per ${\mathrm{Mo}}^{5+}$ ion, and the effective moment from the susceptibility corresponds to the spin-only value. Using ab initio quantum chemistry calculations, we demonstrate that the ${\mathrm{Mo}}^{5+}$ ion hosts a purely spin-$1/2$ magnetic moment, indicating negligible effects of spin-orbit interaction. The quenched orbital moments originate from the large displacement of Mo ions inside the ${\mathrm{MoO}}_{6}$ octahedra along the apical direction. The ground state is shown by neutron diffraction to support a collinear N\'eel-type magnetic order, and a spin-flop transition is observed around an applied magnetic field of 3.5 T. The magnetic phase diagram is reproduced by a mean-field calculation assuming a small easy-axis anisotropy in the exchange interactions. Our results suggest $4d$ molybdates as an alternative playground to search for model quantum magnets.

Theoretical study of spin-forbidden cooling transitions of indium hydride using ab initio methods**Project supported by the National Natural Science Foundation of China (Grant Nos. 11104217 and 11402199) and the Program for New Scientific and Technological Star of Shaanxi Province, China (Grant No. 2012KJXX-39).

The feasibility of spin-forbidden cooling of the InH molecule is investigated based on ab initio quantum chemistry calculations. The potential energy curves for the , , , , , , , and states of InH are obtained based on multi-reference configuration interaction plus the Davidson corrections method. The calculated spectroscopic constants are in good agreement with the available experimental data. In addition, the influences of the active space and spin–orbit coupling effects on the potential energy curves and spectroscopic constants are also studied. For of , , , and states, the error from large active space is small. The potential energy curve of the state is not smooth for small active space. The spin–orbit coupling effects have great influences on the potential well depth and equilibrium internuclear distance of the state. The Franck–Condon factors and radiative lifetimes are obtained on the basis of the transition dipole moments of the , , and transitions. Our calculation indicates that the transition provides a highly diagonally distributed Franck–Condon factor and a short radiative lifetime for the state, which can ensure rapid and efficient laser cooling of InH. The proposed laser drives transitions by using three wavelengths.

Hydrogen migration within a water molecule: formation of HD+ upon irradiation of HOD with intense, ultrashort laser pulses

We have carried out velocity map imaging experiments on HOD molecules irradiated by 10 fs long pulses of intense (∼1 PW cm−2) laser light (800 nm). We have detected HD+ ions as a signature of unimolecular hydrogen migration within the water molecule; ion momentum maps measured at different laser polarizations yield evidence that such hydrogen migration occurs on ultrafast timescales. We have been able to utilize the momentum maps to deduce that (i) the HD+ ion that is formed is vibrationally excited, and (ii) that the electronic state of the precursor HOD2+ dication has an essentially linear geometrical structure with elongated O–H and O–D bonds. Our results are in agreement with expectations from ab initio quantum chemical computations of potential energy surfaces of the lowest-energy states of HOD, HOD+ and HOD2+.

Mixing energies (interaction parameters) and decomposition temperatures in solid solutions of monazites of rare earth elements with structure La1–x Ln x PO4

The mixing energies (interaction parameters) of solid solutions in orthophosphates La1–x Ln x PO4 of rare earth elements (REE) with monazite structure are calculated within the framework of the crystal energy theory of isomorphous replacement. Their values and contributions to the mixing energy depending on the size of replaceable structural units and the degree of ionicity of the chemical bond within the row of lanthanides from Ce to Dy expectedly increase. Accordingly, there is an increase in critical temperatures of solid solution decomposition (stability). This agrees with the previous results of ab initio quantum chemical calculations.

Ab initio study of fast small-amplitude vibrations as functions of slow large-amplitude motions in CD3OH and comparison to CH3OH

Ab initio quantum chemical calculations generating a two-dimensional map of the energy surface and vibrational frequencies have been carried out for CD3OH and CH3OH over ranges of the torsional angle γ and the OH bend angle ρ. We have explored the frequency variation of the fast small-amplitude asymmetric ν2 and ν9 CD and CH stretching modes of E parentage as functions of the slow large-amplitude γ and ρ coordinates associated with the torsional and OH-bending modes that would form a degenerate e pair in the ρ=0° limit of COH linearity. The Gaussian09 program package was employed to calculate minimized energies, structures and Hessians on a grid of points with γ varying from 120° to 180° from the top to the bottom of the torsional potential barrier and ρ varying from 0° at linearity up to a 100° bend. The energies, average frequencies and frequency differences for each species have been fitted to a model combining Fourier expansions in the torsional angle with power-series in the OH-bend angle (Thapaliya et al., 2015) and the expansion constants are presented and compared for the two isotopologues. The conical intersection points of degeneracy between the ν2 and ν9 frequencies have been located for CD3OH, close to those known for CH3OH (Dawadi and Perry, 2014). For CD3OH, CD stretching frequencies calculated along the IRC torsional path from top to bottom of the barrier have been fitted to a high-order local mode model for comparison with earlier results for CH3OH (Xu, 2000), and A-E torsional splittings have been predicted for the three CD stretches.

Generalized Self-Energy Embedding Theory.

Ab initio quantum chemistry calculations for systems with large active spaces are notoriously difficult and cannot be successfully tackled by standard methods. We generalize a Green's function QM/QM embedding method called self-energy embedding theory (SEET) that has the potential to be successfully employed to treat large active spaces. In generalized SEET, active orbitals are grouped into intersecting groups of a few orbitals, allowing us to perform multiple parallel calculations yielding results comparable to the full active-space treatment. We examine generalized SEET on a series of examples and discuss a hierarchy of systematically improvable approximations.

Experimental scaling of plane-Born cross sections and ab initio assignments for electron-impact excitation and dissociation of XF4 (X = C, Si, and Ge) molecules.

Electron energy loss spectra of carbon tetrafluoride, silicon tetrafluoride, and germanium tetrafluoride molecules (CF4, SiF4, and GeF4) have been measured for incident electron energies of 50-360 eV at 1.5°-15.5° and for 30 eV and 30° scattering angle, while sweeping the energy loss over the range 9.0-20.0 eV. Low-lying valence excited triplet and singlet states are investigated by quantum chemical ab initio calculations. The Rydberg series converging to the (lowest) ionisation energy limits of XF4 (X = C, Si, Ge) are also identified and classified using the systematic behaviour according to the magnitude of the quantum defects. A generalized oscillator strength analysis is employed to derive oscillator strength f0 value and the apparent Born integral cross sections from the corresponding differential cross sections by using the Vriens formula for the optically allowed transitions. The f0 value is compared with the optical oscillator strength of the photoabsorption, pseudo-photon measurements, and theoretical values. The binary-encounter and f-scaled Born cross sections of the most intense optically allowed transitions have been also derived from the excitation threshold to the high energy region where the Born approximation is valid. Potential energy curves were obtained along the XF3 + F coordinate with two different basis sets to lend support on electron impact dissociation processes yielding radical formation. We found that in CF4, the lowest-lying dissociative character is due to intramolecular conversion from Rydberg 3s to valence character (σ*(C-F)), whereas in SiF4 and GeF4, an antibonding behaviour prevails.

First observation of the 3Πg3 state of C2: Born-Oppenheimer breakdown.

The 33Πg state of the dicarbon molecule, C2, has been identified for the first time by a combination of resonant ionization spectroscopy, mass spectrometry, and high-level ab initio quantum chemical calculations. This marks the discovery of the final valence triplet state of C2 spectroscopically accessible from the lowest triplet state. It is found to be vibronically coupled to the recently discovered 43Πg state, necessitating vibronic calculations beyond the Born-Oppenheimer approximation to reconcile calculated rotational constants with observations. The 33Πg state of C2 is observed to have a much shorter fluorescence lifetime than expected, possibly pointing to predissociation by coupling to the unbound d3Πg state.

The gas-phase structure of the asymmetric, trans-dinitrogen tetroxide (N2O4), formed by dimerization of nitrogen dioxide (NO2), from rotational spectroscopy and ab initio quantum chemistry.

We report the first experimental gas-phase observation of an asymmetric, trans-N2O4 formed by the dimerization of NO2. In additional to the dominant 14N216O4 species, rotational transitions have been observed for all species with single 15N and 18O substitutions as well as several multiply substituted isotopologues. These transitions were used to determine a complete substitution structure as well as an r0 structure from the fitted zero-point averaged rotational constants. The determined structure is found to be that of an ON-O-NO2 linkage with the shared oxygen atom closer to the NO2 than the NO (1.42 vs 1.61 Å). The structure is found to be nearly planar with a trans O-N-O-N linkage. From the spectra of the 14N15NO4 species, we were able to determine the nuclear quadrupole coupling constants for each specific nitrogen atom. The equilibrium structure determined by ab initio quantum chemistry calculations is in excellent agreement with the experimentally determined structure. No spectral evidence of the predicted asymmetric, cis-N2O4 was found in the spectra.

Energy Resonance Crossing Controls the Photoluminescence of Europium Antenna Probes.

The energy transfer pathways in lanthanide antenna probes cannot be comprehensively rationalized by the currently available models, and their elucidation remains to be a challenging task. On the basis of quantum-chemical ab initio calculations of representative europium antenna complexes, an innovative energy resonance model is proposed, which is controlled by an overall nonet-quintet intersystem crossing on the basis of spin-orbit coupling among the sublevels of the involved states.

The role of Li+ ions in the gas phase dehydrohalogenation and dehydration reactions of i-C3H7Br and i-C3H7OH molecules studied by radiofrequency-guided ion beam techniques and ab initio methods.

Gas phase reactive collisions between lithium ions and i-C3H7X (X = Br, OH) molecules have been studied under single collision conditions in the center of mass (CM) 0.01-10.00 eV energy range using a radiofrequency-guided ion beam apparatus. Mass spectrometry analysis of the products did show the presence of [C3H6-Li]+, [HX-Li]+, C3H7+, and C2H3+ as well as of the [Li-i-C3H7Br]+ adduct while [Li-i-C3H7OH]+ was hardly detected. For all these reactive processes, the corresponding cross sections have been measured in absolute units as a function of the CM collision energy. Quantum chemistry ab initio calculations done at the second order Möller Plesset level have provided relevant information on the topology of the potential energy surfaces (PESs) where a reaction takes place allowing the characterization of the stationary points on the respective PESs along their reaction pathways. The connectivity of the different stationary points localized on the PESs was ensured by using the intrinsic reaction coordinate (IRC) method, confirming the adiabatic character of the reactions. The main topology features of the reactive PESs, in the absence of dynamical calculations, were used to interpret at the qualitative level the behavior of the experimental excitations functions, evidencing the role played by the potential energy barriers on the experimental dynamics of the reactions. Reaction rate constants at 303.2 K for different reactions have been calculated from measured excitation functions.

FTIR and Ab Initio Studies of Diisopropylsulfoxide and its Solutions

Fourier transform infrared (FTIR) measurements, ab initio quantum chemical calculations at the restricted Hartree–Fock (RHF) level and density functional theory (DFT) calculations have been performed to study molecular interactions in pure diisopropylsulfoxide (DiPSO) and the binary mixtures DiPSO/CCl4 and DiPSO/water. The optimized molecular geometry, vibrational wavenumbers, dipole moments and several thermodynamic parameters of free DiPSO and DiPSO/water 1:1 complex in the ground state were calculated using the RHF and B3LYP methods with the 6-31G(d) basis set. A fitting procedure has been performed for both SO and CH stretching regions and a detailed spectral interpretation has been done based on the data obtained from ab initio calculations, infrared spectra and band deconvolution analysis.

Ground State Properties of the Polar Alkali-Metal-Ytterbium and Alkaline-Earth-Metal-Ytterbium Molecules: A Comparative Study.

The accurate knowledge of electronic properties is important for creating and manufacturing ultracold molecules. We report here the ab initio quantum chemistry calculations on the properties of alkali-metal-ytterbium AM-Yb (AM = Li, Na, K, Rb, Cs) and alkaline-earth-metal-ytterbium AEM-Yb (AEM = Be, Mg, Ca, Sr, Ba) molecules for their electronic ground state. The potential energy curves (PECs) and permanent dipole moments (PDMs) are calculated on the basis of the multireference configuration interaction (MRCI) level of theory, where the core-valence correlations and scalar relativistic effects are included. The related spectroscopic constants are also determined. The results demonstrate that the dissociation energies and PDMs of AEM-Yb are smaller than those of AM-Yb molecules, and an interesting trend of the dissociation energy has been observed. This work provides favorable information for the experimental study of forming ultracold molecules via photoassociation technique.

Synthesis, crystal and molecular-electronic structure, and kinetic investigation of two new sterically hindered isomeric forms of the dimethyl[methyl(phenylsulfonyl)amino]benzenesulfonyl chloride

Two new structural isomers – 2,4-dimethyl-5-[methyl(phenylsulfonyl)amino]benzenesulfonyl chloride (1) and 2,4-dimethyl-3-[methyl(phenylsulfonyl)amino]benzenesulfonyl chloride (2) were synthesized by interaction of N-(2,4-dimethylphenyl)-N-methyl-benzenesulfonamide or N-(2,6-dimethylphenyl)-N-methylbenzenesulfonamide with chlorosulfonic acid. Both compounds have been structurally characterized by X-ray single crystal diffraction at 100 K. The crystals of 1 are triclinic: space group P1¯, a = 8.1542(2), b = 11.0728(3), c = 11.2680(3) Å, α = 116.557(3), β = 95.155(2), γ = 108.258(2)°, V = 831.97(4) Å3, Z = 2, R = 0.0251 for 2429 reflections; the crystals of 2 are monoclinic: space group P21/c, a = 11.7428(2), b = 11.3518(2), c = 12.5886(2) Å, β = 93.659(2)°, V = 1674.66(5) Å3, Z = 4, R = 0.0269 for 2622 reflections. The structure of both isomers is organized as molecular crystals. These sterically hindered organic molecules are cross-linked into framework by means of hydrogen bonds of CH⋯O type (H⋯O distances are in range 2.27(2)–2.76(2) Å). The ab initio quantum-chemical calculations of an electronic structure of the isomeric molecules of 1 and 2 have been performed using the restricted Hartree-Fock method with a 6-31G* basis set. The calculated values of charge density concentrated on the electronegative atoms of the sterically hindered molecules are in good agreement with parameters of the intramolecular hydrogen bonds. The obtained data of the kinetic investigations of the substitution reactions in aqueous solution well correlate with stereo-chemical characteristics of the both molecules of the dimethyl[methyl(phenylsulfonyl)amino]-benzenesulfonyl chloride.

Temperature-Dependent Rate Coefficients for the Reaction of CH2OO with Hydrogen Sulfide.

The reaction of the simplest Criegee intermediate CH2OO with hydrogen sulfide was measured with transient UV absorption spectroscopy in a temperature-controlled flow reactor, and bimolecular rate coefficients were obtained from 278 to 318 K and from 100 to 500 Torr. The average rate coefficient at 298 K and 100 Torr was (1.7 ± 0.2) × 10-13 cm3 s-1. The reaction was found to be independent of pressure and exhibited a weak negative temperature dependence. Ab initio quantum chemistry calculations of the temperature-dependent reaction rate coefficient at the QCISD(T)/CBS level are in reasonable agreement with the experiment. The reaction of CH2OO with H2S is 2-3 orders of magnitude faster than the reaction with H2O monomer. Though rates of CH2OO scavenging by water vapor under atmospheric conditions are primarily controlled by the reaction with water dimer, the H2S loss pathway will be dominated by the reaction with monomer. The agreement between experiment and theory for the CH2OO + H2S reaction lends credence to theoretical descriptions of other Criegee intermediate reactions that cannot easily be probed experimentally.

Nitrogen non-stoichiometric stabilization of UN2

Ab initio quantum chemical calculations are employed to investigate the electronic, mechanical, elastic and thermodynamic properties of UN2. The influence of nitrogen non-stoichiometry on the electronic, structural and dynamical properties of cubic uranium dinitride (UN2) is evaluated. The equilibrium lattice parameters, electronic band structure, density of state (DOS), elastic properties and phonon frequencies for the UN2−x (where x=0, 0.125, 0.25, 0.5) compounds are determined and analyzed in comparison with available experimental data. The introduction of nitrogen vacancies in UN2 structure is accompanied by pronounced DOS changes due to the shifting of the various electronic orbitals as well as the appearance of novel vacancy states in the near-Fermi region. We find that UN1.75, which is a 12.5% nitrogen deficient structure, is observed to be dynamically and elastically stable in good agreement with experimental observations.

Network-Forming Nanoclusters in Binary As\u2013S/Se Glasses: From Ab Initio Quantum Chemical Modeling to Experimental Evidences

Network-forming As2(S/Se)m nanoclusters are employed to recognize expected variations in a vicinity of some remarkable compositions in binary As–Se/S glassy systems accepted as signatures of optimally constrained intermediate topological phases in earlier temperature-modulated differential scanning calorimetry experiments. The ab initio quantum chemical calculations performed using the cation-interlinking network cluster approach show similar oscillating character in tendency to local chemical decomposition but obvious step-like behavior in preference to global phase separation on boundary chemical compounds (pure chalcogen and stoichiometric arsenic chalcogenides). The onsets of stability are defined for chalcogen-rich glasses, these being connected with As2Se5 (Z = 2.29) and As2S6 (Z = 2.25) nanoclusters for As–Se and As–S glasses, respectively. The physical aging effects result preferentially from global phase separation in As–S glass system due to high localization of covalent bonding and local demixing on neighboring As2Sem+1 and As2Sem−1 nanoclusters in As–Se system. These nanoclusters well explain the lower limits of reversibility windows in temperature-modulated differential scanning calorimetry, but they cannot be accepted as signatures of topological phase transitions in respect to the rigidity theory.

Dissociation of cyclopropane in double ionization continuum.

Dissociative double photoionization of cyclopropane is studied in the inner-valence region using tunable synchrotron radiation. With the aid of ab initio quantum chemical calculations the energies of dication states and their favoured fragmentation pathways are determined. These are compared to the experimental appearance energies of two-body fragmentation processes and to the kinetic energy released upon dissociation. Photon energy dependent state-selective dissociation in the 25-35 eV range is found. Calculations of dissociation pathways suggest that cyclopropane ring-deformation is selectively triggered at certain photon energies. The calculations suggest that initial ring deformation essentially determines the population of different dication states that function as gateways for particular dissociation channels. The measurements show that stepwise ionization processes populate dissociative 3e'-2 states via ring-opening and Jahn-Teller active states at photon energies below the double-ionization threshold. For energies above the double-ionization threshold the kinematics indicate that double ionization takes place predominantly within the Franck-Condon region populating 3e'-1 1e''-1 states.