Calculated Dipole Moments Research Articles

The effect of intermolecular actions on the nematic phase range of tolane-liquid crystals

ABSTRACTAn approach to understand the effect of intermolecular actions on the nematic stability, a series of tolane compounds nH containing intermolecular π–π stacking, dipole–dipole and hydrogen bond interactions, are developed and investigated. Their mesophase behaviour were measured by differential scanning calorimetry (DSC) and polarising optical microscopy (POM), the results show that carboxylic acids nH exhibit high melting points and narrow nematic phase intervals, which are attributed to the too strong intermolecular actions. By disrupting the intermolecular hydrogen bond, their corresponding methyl esters nC have been designed and synthesised. It is interesting to note that these compounds exhibit broad nematic mesophase intervals and low melting points. The above results demonstrate that the interruption of intermolecular actions is an effective way to improve the nematic stability. In addition, the effects of the terminal alkyl chains and the terminal polar groups on the nematic stability were also discussed. Finally, DFT calculations of molecular conformation and dipole moment were conducted to better understanding of the molecular structure–mesomorphic property relationship.

Low energy electron-impact study of AlO using the R-matrix method

This comprehensive study reports the electron-impact on the open shell AlO molecule at low energy (less than 10 eV) using the R-matrix method. We present the elastic (integrated and differential), momentum-transfer, electronic excitation and ionisation cross sections; along with effective collision frequency over a wide electron temperature range (1000–100 000 K). Correlations via a configuration interaction technique are used to represent the target states. Calculations are performed in the static-exchange and 24-target states close-coupling approximation at the experimental bond length of 1.6178 A. We have used different basis sets 6-311G*, double zeta, polarization (DZP), cc-pCVTZ to represent our target states. We have chosen the Gaussian Type Orbitals (GTOs) basis set DZP to represent the atomic orbitals which gave the best one-electron properties of the molecule. The calculated dipole moment (1.713 au), rotational constant (0.641399 cm-1) and the vertical excitation energies are in concurrence with the best available data. The continuum electron is also represented by GTOs and is placed at the center of mass of the molecule. Resonance analysis is carried out to assign the resonance parameters and the parentage of detected resonances by fitting the eigenphase sums to the Breit–Wigner profile. Our study has detected three core-excited shape resonances in the 24-state model. We detect a stable bound state of AlO- of 1 A 1 symmetry having configuration 1σ 2 … 7σ 21π 42π 4 with a vertical electronic affinity value of 2.59 eV which is in good accord with the experimental value of 2.6 ± (0.01) eV. The ionisation cross sections are calculated using the Binary-Encounter-Bethe Model in which Hartree–Fock molecular orbitals at self-consistent level are used to calculate kinetic and binding energies of the occupied molecular orbitals. We include partial waves up to g-wave beyond which Born closure method is employed to obtain converged cross sections.

Restoring the Pauli principle in the random phase approximation ground state

Random phase approximation ground state contains electronic configurations where two (and more) identical electrons can occupy the same molecular spin-orbital violating the Pauli exclusion principle. This overcounting of electronic configurations happens due to quasiboson approximation in the treatment of electron-hole pair operators. We describe the method to restore the Pauli principle in the RPA wavefunction. The proposed theory is illustrated by the calculations of molecular dipole moments and electronic kinetic energies. The Hartree–Fock based RPA, which is corrected for the Pauli principle, gives the results of comparable accuracy with Møller-Plesset second order perturbation theory and coupled-cluster singles and doubles method.

New quaternary alkali metal cadmium selenites, A2Cd(SeO3)2 (A = K, Rb, and Cs) and Li2Cd3(SeO3)4

A series of new alkali metal cadmium selenites, A2Cd(SeO3)2 (A = K, Rb, and Cs) and Li2Cd3(SeO3)4 have been synthesized in phase pure forms through hydrothermal and solid-state reactions. Structural analyses using single crystal X-ray diffraction indicate that while A2Cd(SeO3)2 and Li2Cd3(SeO3)4 reveal layered structures consisting of CdO6 and SeO3 polyhedra, their symmetry, bonding modes, and the orientation of lone pairs on Se4+ cations are different. A closer examination suggests that the observed structural variations found in the reported materials are attributed to the structure-directing effect of alkali metal cations with different sizes. Scanning electron microscopy/energy dispersive analysis by X-ray, thermogravimetric analysis, Infrared and UV–vis diffuse reflectance spectroscopy, transformation reactions under hydrothermal conditions, and local dipole moment calculations for the reported materials are also reported.

Lattice calculation of electric dipole moments and form factors of the nucleon

We analyze commonly used expressions for computing the nucleon electric dipole form factors (EDFF) $F_3$ and moments (EDM) on a lattice and find that they lead to spurious contributions from the Pauli form factor $F_2$ due to inadequate definition of these form factors when parity mixing of lattice nucleon fields is involved. Using chirally symmetric domain wall fermions, we calculate the proton and the neutron EDFF induced by the CP-violating quark chromo-EDM interaction using the corrected expression. In addition, we calculate the electric dipole moment of the neutron using background electric field that respects time translation invariance and boundary conditions, and find that it decidedly agrees with the new formula but not the old formula for $F_3$. Finally, we analyze some selected lattice results for the nucleon EDM and observe that after the correction is applied, they either agree with zero or are substantially reduced in magnitude, thus reconciling their difference from phenomenological estimates of the nucleon EDM.

Theoretical electronic structure with dipole moment and rovibrational calculation of the low-lying electronic states of the HgF molecule

With the lack of evitable data about the electronic structure of the low-lying states of the HgF molecule unlike its counter parts of mercury monohalides, spectroscopic study of eighteen low-lying doublet and quartet electronic states in the representation 2s+1Λ(+\\-) of this molecule is conducted. Adiabatic potential energy curves of those states are investigated using the complete active space self consistent field (CASSCF) calculation with multi-reference configuration interaction (MRCI) method including single and double excitations with Davidson correction (+Q). The spectroscopic constants as Re, ωe, ωexe, Be, αe, Te and μe are calculated for the bound states. The dissociation energy D00 and the percentage ionic character fionic are also computed. The transition dipole moment μTDM between some doublet low-lying states is studied and some emission coefficients as the Einstein spontaneous coefficients A21, the spontaneous radiative lifetime τspon, and the oscillator strength f21 are thus determined. A rovibrational study has been done to investigate the vibrational levels of the low-lying bound states and the vibrational constants Ev, Bv, Dv, Rmin and Rmax are reported. The Franck–Condon factors have also been calculated for the most probable transitions between the excited states and the ground state. The comparison between the values of the present work and those short information available in the literature shows good accordance.

Calculation of the atomic electric dipole moment of Pb2+ induced by nuclear Schiff moment

We report the atomic electric dipole moment induced by the P, T violating interactions in the nuclear/sub-nuclear level, for 207Pb2+ and 207Pb, owing to the recent interest in the ferroelectric crystal PbTiO3 as one of the candidates for investigating macroscopic P, T-odd effects. In this paper, we calculate the atomic electric dipole moments of 207Pb and Pb2+, parametrized in terms of the P, T-odd coupling parameter, the nuclear Schiff moment (NSM), S, in the frame-work of the coupled-perturbed Hartree–Fock theory. We estimate the Schiff moment of Pb2+ using the experimental result of a system, which is electronically similar to the Pb2+ ion. We present the dominant contributions of the electric dipole moment (EDM) matrix elements and the important correlation effects contributing to the atomic EDM of Pb2+. Our results provide the first ever calculated EDM of the Pb2+ ion, and an estimate of its NSM from which the P, T-odd energy shift in a PbTiO3 crystal can be evaluated.

Spectroscopic and chemical reactivity analysis of D-Myo-Inositol using quantum chemical approach and its experimental verification

This paper describes the spectroscopic ( $$^1\hbox {H}$$ and $$^{13}\hbox {C}$$ NMR, FT-IR and UV–Visible), chemical, nonlinear optical and thermodynamic properties of D-Myo-Inositol using quantum chemical technique and its experimental verification. The structural parameters of the compound are determined from the optimized geometry by B3LYP method with $$6\text {-}311{+}{+}\hbox {G}$$ (d,p) basis set. It was found that the optimized parameters thus obtained are almost in agreement with the experimental ones. A detailed interpretation of the infrared spectra of D-Myo-Inositol is also reported in the present work. After optimization, the proton and carbon NMR chemical shifts of the studied compound are calculated using GIAO and $$6\text {-}311{+}{+}\hbox {G}$$ (d,p) basis set. The search of organic materials with improved charge transfer properties requires precise quantum chemical calculations of space-charge density distribution, state and transition dipole moments and HOMO–LUMO states. The nature of the transitions in the observed UV–Visible spectrum of the compound has been studied by the time-dependent density functional theory (TD-DFT). The global reactivity descriptors like chemical potential, electronegativity, hardness, softness and electrophilicity index, have been calculated using DFT. The thermodynamic calculation related to the title compound was also performed at B3LYP $$/$$ $$6\text {-}311{+}{+}\hbox {G}$$ (d,p) level of theory. The standard statistical thermodynamic functions like heat capacity at constant pressure, entropy and enthalpy change were obtained from the theoretical harmonic frequencies of the optimized molecule. It is observed that the values of heat capacity, entropy and enthalpy increase with increase in temperature from 100 to 1000 K, which is attributed to the enhancement of molecular vibration with the increase in temperature.

Calculations of molecular multipole electric moments of a series of exo-insaturated four-membered heterocycles, Y = CCH2CH2X

ABSTRACTThe influence of ring puckering angle on the multipole moments of sixteen four-membered heterocycles (1-16) was theoretically estimated using MP2 and different DFTs in combination with the 6-31+G(d,p) basis set. To obtain an accurate evaluation, CCSD/cc-pVDZ level and, the MP2 and PBE1PBE methods in combination with the aug-cc-pVDZ and aug-cc-pVTZ basis sets were performed on the planar geometries of 1-16. In general, the DFT and MP2 approaches provided an identical dependence of the electrical properties with the puckering angle for 1-16. Quantitatively, the quality of the level of theory and basis sets affects significant the predictions of the multipole moments, in particular for the heterocycles containing C=O and C=S bonds. Convergence basis sets within the MP2 and PBE1PBE approximations are reached in the dipole moment calculations when the aug-cc-pVTZ basis set is used, while the quadrupole and octupole moment computations require a larger basis set than aug-cc-pVTZ. On the other hand, the multipole moments showed a strong dependence with the molecular geometry and the nature of the carbon-heteroatom bonds. Specifically, the C-X bond determines the behavior of the μ(ϕ), θ(ϕ) and Ώ(ϕ) functions, while the C=Y bond plays an important role in the magnitude of the studied properties.

Effects of Changing Substituents on the Non-Linear Optical Properties of Two Coumarin Derivatives

In this article, we study the electric properties of two coumarin derivatives whose difference stems from the change of substituents at 3-position of the pendant benzene ring ( C 18 H 15 NO 3 ) and ( C 18 H 15 NO 4 ). We use the supermolecule approach to deal with the molecules under the effect of the crystalline environment to calculate dipole moment, linear polarizability, and second-order hyperpolarizability, for the isolated and embedded molecules, including the static and dynamic cases and the presence of solvents. The (hyper) polarizabilities were derived from an iterative process and an ab initio computational procedure. In addition, we also calculated the HOMO-LUMO energies; at this point, the objective is to verify the effect of the exchange of substituents on the Band-Gap energy, an important parameter related to the excitation properties of coumarin compounds.

Electronic Structure and Dipole Moment Calculations of the Electronic States of the Molecule BeCl

The electronic structure of the molecule BeCl have been investigated by using the Complete Active Space Self Consistent Field (CASSCF) with Multireference Configuration Interaction MRCI+Q (singly and doubly excitation with Davidson corrections). The potential energy curves, in terms of the internuclear distance R, have been calculated for 13 doublet and 14 quartet electronic states in the representation 2s+1Λ(+/-) of the molecule BeCl. The internuclear distance at equilibrium Re, the electronic energy with respect to the ground state Te, the harmonic frequency we, the rotational constants Be and the permanent dipole moment have been calculated for the bound electronic states. The Franck-Condon factor is calculated for the electronic transition between the two electronic states X2S+-(1)2P. Since there is limited data are published in literature, twenty-two new electronic states have been investigated here for the first time for the molecule BeCl. The comparison between our calculated values and those available in the literature shows a very good good agreement.

Microwave spectrum, molecular structure, dipole moment, and quantum chemical calculations of s-trans-(E)-2-methyl-2-propenal oxime

The spectroscopic constants of s-trans-(E)-2-methyl-2-propenal oxime (methacryl- aldehyde oxime) of normal, H2CC(CH3)CHNOH, and its deuterated species, H2CC(CH3)CHNOD, were determined by observing their microwave spectra in the frequency range of 8 to 40GHz in the ground vibrational state. The rotational constants were A=8321.38(82), B=2076.09(1), and C=1678.60(1) MHz for normal species and A=8283.7(16), B=1998.63(2), and C=1626.21(2) MHz for deuterated species, respectively. The inertial defects (ΔI=Ic−Ia−Ib) of normal and deuterated species were determined to be −3.09(2) and −3.10(3)uÅ2, respectively. The dipole moments were determined as μa=0.53(2), μb=0.27(2), and μtotal=0.60(5) D. The 14N nuclear quadrupole coupling constants were determined as χaa=3.62(12), χbb=−5.1(14), and χcc=1.48(26)MHz. The comparison of the observed spectroscopic parameters with the calculated ones led to the conclusion that the assigned spectrum was due to s-trans-(E) form. The rs coordinates of the hydrogen atom in a hydroxyl group were determined and the OH bond was found to be at the trans position with respect to the CN double bond. The structural parameters of r(C2C3), r(C2C6), ∠C2C3N and ∠C6C2C3, for s-trans-syn form were adjusted to the four observed rotational constants (B and C). The observed rotational constants for s-trans-(E) form were in good agreement with those calculated using the MP2/6-31G (d,p) level of theory.

Nematic compounds and mixtures with high negative dielectric anisotropy

ABSTRACTSyntheses, mesogenic and dielectric properties of three-ring alkylcyclohexyl, alkoxy and alkylphenyl benzoates substituted with four fluorine atoms or with two fluorine atoms and simultaneously a cyano group or two cyano groups are described. Their properties are compared with analogous three-ring phenyl tolanes. Conformation analysis and the calculation of dipole moments with the quantum chemistry method are performed to explain the experimental results. Several four fluorine-substituted two-ring tolanes and biphenyls are also prepared, which are used as a solvent decreasing viscosity, melting point and clearing point of the formulated mixtures. Examples of mixtures prepared from the esters and tolanes with high dielectric anisotropy are given. Curiosity is observed that 4ʹ-(4-ethoxyphenyl)-4-pentyloxy-2,2ʹ,3,3ʹ-tetrafluorotolane is not the mesogenic compound, while analogous ester 4ʹ-ethoxy-2,3-difluorobiphenyl-4-yl 2,3-difluoro-4-pentyloxybenzoate exhibits a broad temperature range of the nematic phase.

Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation

The current status of electric dipole moments of diamagnetic atoms which involves the synergy between atomic experiments and three different theoretical areas -- particle, nuclear and atomic is reviewed. Various models of particle physics that predict CP violation, which is necessary for the existence of such electric dipole moments, are presented. These include the standard model of particle physics and various extensions of it. Effective hadron level combined charge conjugation (C) and parity (P) symmetry violating interactions are derived taking into consideration different ways in which a nucleon interacts with other nucleons as well as with electrons. Nuclear structure calculations of the CP-odd nuclear Schiff moment are discussed using the shell model and other theoretical approaches. Results of the calculations of atomic electric dipole moments due to the interaction of the nuclear Schiff moment with the electrons and the P and time-reversal (T) symmetry violating tensor-pseudotensor electron-nucleus are elucidated using different relativistic many-body theories. The principles of the measurement of the electric dipole moments of diamagnetic atoms are outlined. Upper limits for the nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained combining the results of atomic experiments and relativistic many-body theories. The coefficients for the different sources of CP violation have been estimated at the elementary particle level for all the diamagnetic atoms of current experimental interest and their implications for physics beyond the standard model is discussed. Possible improvements of the current results of the measurements as well as quantum chromodynamics, nuclear and atomic calculations are suggested.

New vanadium tellurites: Syntheses, structures, optical properties of noncentrosymmetric VTeO4(OH), centrosymmetric Ba2V4O8(Te3O10)

Two new vanadium tellurites, VTeO4(OH) (1) and Ba2V4O8(Te3O10) (2), have been synthesized successfully with the use of hydrothermal reactions. The crystal structures of the two compounds were determined by single-crystal X-ray diffraction. Compound 1 crystallizes in the polar space group Pca21 (No. 29) while compound 2 crystallizes in the centrosymmetric space group C2/c (No. 15). The topography of compound 1 reveals a two-dimensional, layered structure comprised of VO6 octahedral chains and TeO3(OH) zig-zag chains. Compound 2, on the contrary, features a three-dimensional [V4O8(Te3O10)]4- anionic framework with Ba2+ ions filled into the 10-member ring helical tunnels. The [V4O8(Te3O10)]4- anionic network is the first 3D vanadium tellurite framework to be discovered in the alkaline-earth vanadium tellurite system. Powder second harmonic generation (SHG) measurements indicate that compound 1 shows a weak SHG response of about 0.3×KDP (KH2PO4) under 1064nm laser radiation. Infrared spectroscopy, elemental analysis, thermal analysis, and dipole moment calculations have also been carried out.

Truncated pyramidal-shaped InAs/GaAs quantum dots in the presence of a vertical magnetic field: An investigation of THz wave emission and absorption

The authors report on the calculation of energy eigenvalues, transition energies, and transition dipole moments (TDMs) of truncated pyramidal-shaped InAs/GaAs quantum dots (QDs) coupled to their wetting layers (WL) under a varying and vertical magnetic field. The aim of this work is to explore a tunable source for terahertz (THz) emission and absorption through the change in dimensions and magnetic field. Through the solving the Schrodinger equation in the single-band effective mass approximation for QDs, seven initial states were extracted and the corresponding envelope functions and their changes under a magnetic field were inspected. Two groups of QDs were considered: group A of QDs, in which the height length was taken to be constant as 5nm and the base length was varied from 10 to 30nm, and group B of QDs, in which the base length was taken to be constant as 25nm and the height length was varied from 1 to 6nm. The results showed that the transition frequencies of group B of QDs lay dominantly in the terahertz region and are shifted towards lower frequencies with decreasing the height and/or increasing the magnetic field. With applying a varied magnetic field up to 25 T, a ~6THz shift in s-to-pX transition frequency was seen. Also, the polarizations of pronounced transitions were also investigated. The s-to-px, s-to-pY, and pY-to-dXY transitions were shown to be all in-plan-polarized transitions. The s-to-dXY transition is not an allowed transition.

Expectation values of single-particle operators in the random phase approximation ground state.

We developed a method for computing matrix elements of single-particle operators in the correlated random phase approximation ground state. Working with the explicit random phase approximation ground state wavefunction, we derived a practically useful and simple expression for a molecular property in terms of random phase approximation amplitudes. The theory is illustrated by the calculation of molecular dipole moments for a set of representative molecules.

Electronic structure with rovibrational and dipole moment calculation of the diatomic molecules AsBr and AsI

CASSCF/MRCI calculations have been performed for the ground and the low-lying singlet and triplet excited electronic states, in the representation 2s+1Λ(+/−) of the diatomic molecules AsBr and AsI. Twenty and seventeen excited electronic states have been investigated respectively for AsBr AsI molecules. The potential energy curves, the electronic energy with respect to the ground state Te, the harmonic frequency ωe, the internuclear distance Re, the rotational constant Be, and the static and transition dipole moment have been investigated for the considered electronic states. The comparison between these constants of the four As-halides has been done along with the energy levels Te for the different electronic states. By using the canonical functions approach, the eigenvalue Ev, the rotational constant Bv, and the abscissas of the turning points Rmin and Rmax have been calculated for the considered electronic states up to the vibrational level v=100. The comparison between the values of the present work with the experimental data available in the literature shows a very good agreement. This study represents the first theoretical investigation of the electronic structure of both AsBr and AsI molecules.

Precise Access to the Molecular-Frame Complex Recombination Dipole through High-Harmonic Spectroscopy.

We report on spectral intensity and group delay measurements of the highest-occupied molecular-orbital (HOMO) recombination dipole moment of N_{2} in the molecular-frame using high harmonic spectroscopy. We take advantage of the long-wavelength 1.3 μm driving laser to isolate the HOMO in the near threshold region, 19-67eV. The precision of our group delay measurements reveals previously unseen angle-resolved spectral features associated with autoionizing resonances, and allows quantitative comparison with cutting-edge correlated 8-channel photoionization dipole moment calculations.

The theoretical interpretation of the Linear/circularly polarized light-induced molecular orientation of the azo group-containing trans-Achiral Schiff base dinuclear complex composite material

We have investigated linearly polarized UV and circularly polarized UV light-induced molecular orientation, namely increasing optical anisotropy of newly synthesized AZ containing chiral Schiff base Ni (II), Cu (II) and Zn (II) complexes, as organic/inorganic hybrid materials in polymethylmethacrylate (PMMA) cast films. The driving force and reason for polarized UV light-induced molecular orientation of AZ is so-called Weigert effect. The increase of the dichroic was measured with polarized absorption electronic spectra. In addition, we study on newly synthesized composites of AZ containing chiral Schiff base metal complexes with AZ to irradiate with not only linearly but also circularly polarized UV light (Wavelength selective (260, 318(π-π* of AZ) and 380 nm) and continuous wavelength). In addition, we comparison between simulated by TD-DFT and experimental spectra of electronic and CD spectra, and we calculated dipole moments by TD-DFT. Furthermore, we are using the CD spectrum after circularly polarized light UV irradiation, tried to observation change of supramolecular chiral order of the complexes.