Coupled cluster investigation of the electric-field-gradient-induced birefringence of H2, N2, C2H2, and CH4

Dependence of the multipole moments, static polarizabilities, and static hyperpolarizabilities of the hydrogen molecule on the H-H separation in the ground singlet state

In this work, we provide values for the quadrupole moment Θ, the hexadecapole moment Φ, the dipole polarizability α, the quadrupole polarizability C, the dipole-octopole polarizability E, the second dipole hyperpolarizability γ, and the dipole-dipole-quadrupole hyperpolarizability B for the hydrogen molecule in the ground singlet state, evaluated by finite-field configuration interaction singles and doubles (CISD) and coupled-cluster singles and doubles (CCSD) methods for 26 different H-H separations r, ranging from 0.567 a.u. to 10.0 a.u. Results obtained with various large correlation-consistent basis sets are compared at the vibrationally averaged bond length r₀ in the ground state. Results over the full range of r values are presented at the CISD/d-aug-cc-pV6Z level for all of the independent components of the property tensors. In general, our values agree well with previous ab initio results of high accuracy for the ranges of H-H distances that have been treated in common. To our knowledge, for H₂ in the ground state, our results are the first to be reported in the literature for Φ for r > 7.0 a.u., γ and B for r > 6.0 a.u., and C and E for any H-H separation outside a narrow range around the potential minimum. Quantum Monte Carlo values of Θ have been given previously for H-H distances out to 10.0 a.u., but the statistical error is relatively large for r > 7.0 a.u. At the larger r values in this work, α_xx and α_zz show the expected functional forms, to leading order in r^-1. As r increases further, Θ and Φ vanish, while α, γ, and the components of B converge to twice the isolated-atom values. Components of C and E diverge as r increases. Vibrationally averaged values of the properties are reported for all of the bound states (vibrational quantum numbers υ = 0-14) with rotational quantum numbers J = 0-3.

Quantum-electrodynamical birefringence vanishing in a thermal relativistic pair plasma

Quantum electrodynamical (QED) birefringence in a thermal relativistic pair plasma with the presence of the strong crossed field: , is proposed and investigated. We clarify the coupling relationship and competition between the QED effect and the plasma collective effect and find the critical condition that makes the birefringence vanish. In a relative weak electromagnetic field, the birefringence is dominated by the coupling of the QED-effect, the collective effect and the drift effect. In a relative strong electromagnetic field, we obtain the formulations stating the competition between the QED effect and the collective effect and then the critical conditions so that they are canceled with each other and the birefringence vanishes. With our results, a new possible scheme is proposed to estimate the thickness of the magnetosphere in a millisecond pulsar and the plasma density of a pulsar, if the magnetic field is known beforehand.

Ultra-wideline27Al NMR Investigation of Three- and Five-Coordinate Aluminum Environments

Ultra-wideline 27Al NMR experiments are conducted on coordination compounds with 27Al nuclei possessing immense quadrupolar interactions that result from exceptionally nonspherical coordination environments. NMR spectra are acquired using a methodology involving frequency-stepped, piecewise acquisition of NMR spectra with Hahn-echo or quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences, which is applicable to any half-integer quadrupolar nucleus with extremely broad NMR powder patterns. Despite the large breadth of these central transition powder patterns, ranging from 250 to 700 kHz, the total experimental times are an order of magnitude less than previously reported experiments on analogous complexes with smaller quadrupolar interactions. The complexes examined feature three- or five-coordinate aluminum sites: trismesitylaluminum (AlMes3), tris(bis(trimethylsilyl)amino)aluminum (Al(NTMS2)3), bis[dimethyl tetrahydrofurfuryloxide aluminum] ([Me2-Al(mu-OTHF)]2), and bis[diethyl tetrahydrofurfuryloxide aluminum] ([Et2-Al(mu-OTHF)]2). We report some of the largest 27Al quadrupolar coupling constants measured to date, with values of C(Q)(27Al) of 48.2(1), 36.3(1), 19.9(1), and 19.6(2) MHz for AlMes3, Al(NTMS2)3, [Me2-Al(mu-OTHF)]2, and [Et2-Al(mu-OTHF)]2, respectively. X-ray crystallographic data and theoretical (Hartree-Fock and DFT) calculations of 27Al electric field gradient (EFG) tensors are utilized to examine the relationships between the quadrupolar interactions and molecular structure; in particular, the origin of the immense quadrupolar interaction in the three-coordinate species is studied via analyses of molecular orbitals.

A computational study of some electric and magnetic properties of gaseous BF3 and BCl3

We present the results of an extended computational study of the electric and magnetic properties connected to Cotton-Mouton birefringences, on the trifluoro- and trichloroborides in the gas phase. The electric dipole polarizabilities, magnetizabilities, quadrupole moments, and higher-order hypersusceptibilities--expressed as quadratic and cubic frequency-dependent response functions--are computed within Hartree-Fock, density-functional, and coupled-cluster response theories employing singly and doubly augmented correlation-consistent basis sets and London orbitals in the magnetic property calculations. The results, which illustrate the capability of time-dependent density-functional theory for electron-rich systems, are compared with available experimental data. Revised values of both experimentally derived quadrupole moment of BF3, 2.72 +/- 0.15 a.u., and magnetizability anisotropy of BCl3, -0.45 +/- 0.09 a.u., both obtained in birefringence experiments that neglect the effects of higher-order hypersusceptibilities, are presented. In the theoretical limit the traceless quadrupole moments of BF3 and BCl3 are determined to be 3.00 +/- 0.01 and 0.71 +/- 0.01 a.u., respectively.

Solid-State 93Nb and 13C NMR Investigations of Half-Sandwich Niobium(I) and Niobium(V) Cyclopentadienyl Complexes

Solid-state 93Nb and 13C NMR experiments, in combination with theoretical calculations of NMR tensors, and single-crystal and powder X-ray diffraction experiments, are applied for the comprehensive characterization of structure and dynamics in a series of organometallic niobium complexes. Half-sandwich niobium metallocenes of the forms Cp'Nb(I)(CO)4 and CpNb(V)Cl4 are investigated, where Cp = C5H5- and Cp' = C5H4R- with R = COMe, CO2Me, CO2Et, and COCH2Ph. Anisotropic quadrupolar and chemical shielding (CS) parameters are extracted from 93Nb MAS and static NMR spectra for seven different complexes. It is demonstrated that 93Nb NMR parameters are sensitive to changes in temperature and Cp' ring substitution in the Cp'Nb(I)(CO)4 complexes. There are dramatic differences in the 93Nb quadrupolar coupling constants (C(Q)) between the Nb(I) and Nb(V) complexes, with C(Q) between 1.0 and 12.0 MHz for Cp'Nb(CO)4 and C(Q) = 54.5 MHz for CpNbCl4. The quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) pulse sequence is applied to rapidly acquire, in a piecewise fashion, a high signal-to-noise ultra-wide-line 93Nb NMR spectrum of CpNbCl4, which has a breadth of ca. 400 kHz. Solid-state 93Nb and 13C NMR spectra and powder XRD data are used to identify a new metallocene adduct coordinated at the axial position of the metal site by a THF molecule: CpNb(V)Cl4.THF. 13C MAS and CP/MAS NMR experiments are used to assess the purity of samples, as well as for measuring carbon CS tensors and the rare instance of one-bond 93Nb, 13C J-coupling, 1J(93Nb,13C). Theoretically calculated CS and electric field gradient (EFG) tensors are utilized to determine relationships between tensor orientations, the principal components, and molecular structures.

Density-functional theory study of electric and magnetic properties of hexafluorobenzene in the vapor phase

A series of electric and magnetic properties of hexafluorobenzene have been calculated, including the electric dipole polarizability, magnetizability, electric quadrupole moment, and nonlinear mixed electric dipole-magnetic dipole-electric quadrupole hyperpolarizabilities needed to obtain estimates of the Kerr, Cotton-Mouton, Buckingham, Jones, and magnetoelectric birefringences in the vapor phase. Time-dependent density-functional theory was employed for the calculation of linear-, quadratic, and cubic response functions. A number of density functionals have been considered, along with Sadlej's triple-zeta basis set and the augmented correlation-consistent polarized valence double zeta and augmented correlation-consistent polarized valence triple zeta basis sets. Comparisons have been made with experiment where possible. The analysis of results allows for an assessment of the capability of time-dependent density-functional theory for high-order electromagnetic properties of an electron-rich system such as hexafluorobenzene.

Density-functional and electron correlated study of five linear birefringences—Kerr, Cotton–Mouton, Buckingham, Jones, and magnetoelectric—in gaseous benzene

We present the results of an extended study of five birefringences--Kerr, Cotton-Mouton, Buckingham, Jones, and Magnetoelectric--on benzene in the gas phase. The relevant molecular quantities--first-order properties, linear, quadratic, and cubic response functions--are computed employing the density-functional theory (DFT) response theory, with a choice of functionals. In some cases, different functionals are employed for the wave-function computational step and for the subsequent analytical response calculation to determine the combination yielding at the same time the optimal energy and energy derivative results. Augmented correlation consistent basis sets of double and triple zeta quality are used. The DFT results are compared to those obtained at the Hartree-Fock level and in some cases within a coupled cluster singles and doubles electronic structure model. The study tries to assess the ability of the DFT response theory to describe a wide range of properties in a system of rather large size and high complexity. The relative strength of the five birefringences for plausible experimental conditions is determined and, when possible, comparison is made with the results of the measurements.

Solid-state 25Mg QCPMG NMR of bis(cyclopentadienyl)magnesium

Application of the "quadrupolar Carr-Purcell Meiboom-Gill" (QCPMG) sequence permits the first natural abundance solid-state 25Mg NMR study of an organometallic magnesium compound, bis(cyclopentadienyl)magnesium. Analytical and numerical simulations of both static and magic-angle spinning QCPMG NMR spectra beget an axially symmetric 25Mg electric field gradient (EFG) tensor (quadrupolar asymmetry parameter, eta(Q)=0.01(1)) with a nuclear quadrupole coupling constant of C(Q)=5.80(5)MHz. Restricted Hartree-Fock and hybrid density functional theory (B3LYP) calculations are in good agreement with experimental EFG values and predict a chemical shielding anisotropy of about 40-50 ppm, which we attempt to elucidate by numerical simulations. The parameters and orientation of the 25Mg EFG tensor are rationalized from examination of the crystal structure and molecular symmetry. The NMR properties of the cyclopentadienyl rings are examined by 13C[1H] CPMAS NMR, RHF and hybrid-DFT (B3LYP) calculations, and simulations of the effects of chemical exchange on the 13C powder pattern.