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1.
Salam A 《The Journal of chemical physics》2005,122(4):44113
The matrix element for the resonant transfer of excitation between two molecules possessing electric and magnetic multipole moments of arbitrary order is calculated using quantum electrodynamical response theory. A prerequisite of the method is the functional form for the lth order linear electric and magnetic multipole dependent electric displacement and magnetic field operators in the neighborhood of a molecule, whose derivation is also given. The initially unexcited species is viewed as a test body accepting energy resonantly via coupling to the Maxwell fields of the excited multipole source molecule. The generalized electric-electric multipole contribution to the matrix element is shown to agree with an earlier calculation using time-dependent perturbation theory. As an application involving both electric and magnetic terms, the rate of excitation transfer between two chiral molecules is computed and found to depend on the handedness of each species. 相似文献
2.
Conventional nuclear magnetic resonance spectroscopy is unable to distinguish between the two mirror-image forms (enantiomers) of a chiral molecule. This is because the NMR spectrum is determined by the chemical shifts and spin–spin coupling constants which – in the absence of a chiral solvent – are identical for the two enantiomers. We discuss how chirality may nevertheless be directly detected in liquid-state NMR spectroscopy: In a chiral molecule, the rotating nuclear magnetic moment induces an electric dipole moment in the direction perpendicular to itself and to the permanent magnetic field of the spectrometer. We present computations of the precessing electric polarization following a π/2 pulse. Our estimates indicate that the electric polarization should be detectable in favourable cases. We also predict that application of an electrostatic field induces a chirally sensitive magnetization oscillating in the direction of the permanent magnetic field. We show that the electric-field-perturbed chemical shift tensor, the nuclear magnetic shielding polarizability, underlies these chiral NMR effects. 相似文献
3.
This paper is a straightforward generalization of Maierle-Harris proposal regarding parity implications on the superpositions of chiral states of a molecule. It is shown that the inclusion of electric quadrupole and magnetic dipole interactions removes several of restrictions on the preparation of superpositions of mid R:L and mid R:R states of a chiral molecule. It is also found that the dephasing of mid R:L and mid R:R superpositions, due to the spontaneous emission from the chiral molecule, has opposing contributions from electric quadrupole-magnetic dipole and electric dipole interactions. 相似文献
4.
The improved generator coordinate Hartree–Fock (GCHF) method is extended to molecular systems. The Griffin–Hill–Wheeler–HF
equations were solved by an integral discretization technique. The method is then implemented with the use of the GAMESS program
and applied to the H2, Li2, and LiH molecules. For these molecules, sequences of basis sets of atom-centred Gaussian-type functions are employed to
explore the accuracy achieved with our approach. For all systems studied, our ground-state HF total energies are better than
those obtained with basis sets generated with the original GCHF method for molecules and larger even-tempered basis sets.
For H2, Li2, and LiH, the differences between our best energies and the corresponding numerical HF results are about 2 × 10−2, 1, and 4 × 10−1 μhartree, respectively. The dipole, quadrupole, and octupole moments at the center of mass and electric field, the electric
field gradient, the electrostatic potential, and the electron density at the nuclei were evaluated and compared with results
reported in the literature.
Received: 4 May 1999 / Accepted: 22 July 1999 / Published online: 2 November 1999 相似文献
5.
The discrimination energy, giving the difference in the interaction of two leavo molecules and one laevo with one dextro, is calculated where the coupling involves permanent electric and magnetic moments. Fixed electric dipoles arranged helically on a lattice (simulating the electric effects of a helical polymer for example) give chiral fields producing large (≈kT) discriminations. For the pairwise interaction of fixed molecules realistic electric dipole and electric quadrupole moments can lead to discriminations of about 100 cal mole?1 at 0.5 nm separation. In the hypothetical case of molecules possessing permanent electric and magnetic moments it is four or more orders of magnitude less. In a freely rotating molecule pair the sequence is reversed and electric and magnetic dipoles give much the bigger averaged discrimination energy. 相似文献
6.
7.
V. Pavlínek O. Quadrat P. Sáha M. J. Beneš J. Trlica 《Colloid and polymer science》1998,276(8):690-697
Electrorheological behavior of silicone oil suspensions of macroporous poly[(glycidyl methacrylate)-co-(ethylene dimethacrylate)]) (0.60 : 0.40 w) hydrolyzed to various degrees was investigated. Polarizability of particles expressed
by the particle dipole coefficient and, consequently, pseudoplasticity of the system at low shear rates after application
of an external electric field steeply increased with the hydrolysis degree of the copolymer. As the size and shape of particles
remain unchanged during hydrolysis, a series of model suspensions with the same hydrodynamic properties (Newtonian or slightly
pseudoplastic when no electric field was applied) but with different intensity of the electrorheological effect could be prepared.
Under these conditions, the use of Mason number failed to correlate the apparent viscosity of suspensions of particles with
different polarizability in the electric field. On the other hand, when polarizability of particles of a suspension system
changes due to a higher temperature, a single curve in the plot of apparent viscosity vs. the Mason number could be obtained.
Received: 17 February 1998 Accepted: 8 May 1998 相似文献
8.
Parameters of the formalism [1–6] describing spin crossover in the solid state have been defined via molecular potentials in model systems of neutral and ionic complexes. In the first instance Lennard-Jones and electric dipole–dipole potentials have been used whereas in ionic systems Lennard-Jones and electric point-charge potentials have been used. Electric dipole–dipole interaction of neutral complexes brings about
a positive excess energy controlled by the difference of electric dipole moments of HS and LS molecules. Differences of the
order of Δμ = 1–2 D cause an abrupt spin crossover in systems with T1/2 = 100–150 K. Magnetic coupling contributes both to the excess energy and excess entropy, however the overall effect is equivalent
to a modest positive excess energy. Ionic systems in the absence of specific interactions are characterised by very small
excess energies corresponding to practically linear van’t Hoff plots. Detectable positive and negative excess energies in these systems may arise from interactions of ligands belonging
to neighbouring complexes. The HOMO–LUMO overlap in HS–LS pairs can bring about a nontrivial variation of the shape of transition
curves. Examples of regression analysis of experimental transition curves in terms of molecular potentials are given. 相似文献
9.
Summary. Parameters of the formalism [1–6] describing spin crossover in the solid state have been defined via molecular potentials in model systems of neutral and ionic complexes. In the first instance Lennard-Jones and electric dipole–dipole potentials have been used whereas in ionic systems Lennard-Jones and electric point-charge potentials have been used. Electric dipole–dipole interaction of neutral complexes brings about
a positive excess energy controlled by the difference of electric dipole moments of HS and LS molecules. Differences of the
order of Δμ = 1–2 D cause an abrupt spin crossover in systems with T1/2 = 100–150 K. Magnetic coupling contributes both to the excess energy and excess entropy, however the overall effect is equivalent
to a modest positive excess energy. Ionic systems in the absence of specific interactions are characterised by very small
excess energies corresponding to practically linear van’t Hoff plots. Detectable positive and negative excess energies in these systems may arise from interactions of ligands belonging
to neighbouring complexes. The HOMO–LUMO overlap in HS–LS pairs can bring about a nontrivial variation of the shape of transition
curves. Examples of regression analysis of experimental transition curves in terms of molecular potentials are given. 相似文献
10.
Celestino Angeli Renzo Cimiraglia Maurizio Persico 《Theoretical chemistry accounts》1998,100(5-6):324-328
Within the frame of multireference perturbation configuration interaction we have developed a fast algorithm, based on diagrammatic
techniques, for the calculation of the first-order correction to the one-particle density matrix. As an example of an application
we have chosen the evaluation of the dipole moment of the CO molecule, where utilization of the first-order density is shown
to corroborate the variational calculation.
Received: 4 August 1998 / Accepted: 21 September 1998 / Published online: 16 November 1998 相似文献
11.
Yukikazu Itikawa 《Theoretical chemistry accounts》2000,105(2):123-131
When the fixed-nuclei (FN) approximation is applied to the calculation of electron scattering from a polar molecule, the
resulting cross section diverges in the forward direction of scattering. This is due to the long-range nature of the interaction
between the electron and the molecular dipole. To avoid this difficulty, a hybrid method is proposed for the calculation of
the scattering amplitude. This method is based on the FN approximation for a close collision and the Born approximation for
a distant collision. The present paper describes the detailed formulation of the method for practical applications. Furthermore
the present approach is extended to other long-range interactions (due to quadrupole moment and/or polarization effect) and
to a dipole-allowed vibrational excitation. In these cases, while no divergence occurs, it is often difficult to confirm the
convergence of the partial-wave expansion. With the employment of the present approach, it is much easier to confirm the convergence
and hence to obtain reliable cross sections. The formulas are given for diatomic molecules as well as for polyatomic ones.
Received: 12 June 2000 / Accepted: 6 July 2000 / Published online: 24 October 2000 相似文献
12.
W. Liptay 《Angewandte Chemie (International ed. in English)》1969,8(3):177-188
The position and the intensity of electronic bands are influenced by an electric field. Pronounced changes in the position of absorption bands are mainly due to the dipole moment of the molecule in the ground state and the change in the dipole moment during the excitation process, and pronounced changes in intensity are due to the field dependence of the transition moment, which can be described by the transition polarizability. The effect of an external electric field on the optical absorption (electrochromism) of suitable molecules can be used to determine the dipole moment in the ground state, the change in dipole moment during the excitation process, the direction of the transition moment of the electronic band, and certain components of the transition polarizability tensor. These data largely determine the strong solvatochromism (solvent-dependence of the position and intensity of electronic bands), which is observed in particular with molecules having large dipole moments. Smaller contributions to solvatochromism result from dispersion interactions, which predominate in the case of nonpolar molecules. The models developed have been experimentally checked and verified by a combination of electro-optical absorption measurements (influence of an external electric field on absorption) and investigation of the solvent-dependence of the electronic bands. 相似文献
13.
Paul A. Rejto Djamal Bouzida Gennady M. Verkhivker 《Theoretical chemistry accounts》1999,101(1-3):138-142
Binding-energy landscapes are used to investigate the thermodynamics of molecular recognition for the pteridine ring, a recognition
anchor in binding with dihydrofolate reductase, and two molecules with the same shape but different heteroatom substitutions.
The relative importance of hydrogen bonding and hydrophobic interactions in this system is analyzed by comparing these three
different decorations of the pteridine scaffold.
Received: 5 May 1998 / Accepted: 3 September 1998 / Published online: 17 December 1998 相似文献
14.
The phase separation behavior of near-critical ionic sodium-dodecyl-sulfate (SDS) micellar solution under a sinusoidal electric
field was investigated by phase-contrast optical microscopy and by the small-angle dynamic light scattering method. The sinusoidal
electric field significantly deformed the concentration domains and shifted the phase separation temperature. The autocorrelation
function under a sinusoidal electric field was measured in the vicinity of a phase separation temperature range of 0.10 K < Tp – T < 0.97 K, where Tp – T is the temperature distance from the phase separation temperature in quiescent state Tp. The correlation function with an oscillatory part in the longer correlation time region was observed. The occurrence of
the oscillatory mode, which depended on both the applied field frequency and the ambient temperature, indicates deformation
of concentration fluctuation domains by dynamical coupling between the phase separation and the applied sinusoidal electric
field.
Received: 9 June 2000 Accepted: 31 August 2000 相似文献
15.
Explicitly correlated MBPT-R12 and coupled cluster [up to CCSD(T)-R12] methods have been used in calculations of various
(vibrationless) electrical properties for the LiH molecule, including the dipole and quadrupole moments, dipole and quadrupole
polarizability tensors, dipole hyperpolarizability tensors, and the second dipole hyperpolarizability tensors. Generally,
with extension of the basis set the R12 method did not lead to faster convergence for the calculated properties towards the
basis limit. Nevertheless, R12 calculations serve as useful indicators to judge the reliability of the results, and substantially
help in determining the accuracy. Results obtained with the 11s8p6d5f/9s8p6d5f basis and CCSD(T)-R12 calculated within this work should be close to the basis set limit.
Received: 8 June 1998 / Accepted: 23 July 1998 / Published online: 7 October 1998 相似文献
16.
Hisayoshi Matsushima Adriana Ispas Andreas Bund Waldfried Plieth Yasuhiro Fukunaka 《Journal of Solid State Electrochemistry》2007,11(6):737-743
The electrodeposition process of Co films in a sulfuric acid solution was examined in a magnetic field (0–5 T). The surface
morphology of Co films electrodeposited without a magnetic field was drastically modified with the variation of hydrogen gas
evolution rate. Crystalline α-Co was formed in the range of pH = 1.5–6.0, while β-Co was not observed. When the magnetic field
was superimposed perpendicular to the electric field in the acidic solution (pH = 1.5), the hydrogen evolution rate was promoted
by MHD convection, which enhanced the ionic mass transfer (H+ and Co2+) near the electrode surface. Moreover, crystalline β-Co was formed simultaneously with the appearance of the elongated ridge-shape
precipitates under a higher magnetic field (≥3 T).
Contribution to special issue “Magnetic field effects in Electrochemistry” 相似文献
17.
Under the particular situation of highly doped and almost compensated semiconductors, a new kind of bound state happens at
high external excitation levels, which is formed of a close donor–acceptor molecule and a neighboring second donor or acceptor.
The de-excitation behavior of such a bound state resembles characteristics known from Auger transitions and for this reason
it is called an Auger molecule. The existence region of Auger molecules is determined in silicon-doped Ga1−
x
Al
x
As by electron-beam excited luminescence measurements at low temperature. The main peak position and the luminescence intensity
of the donor–acceptor recombination channel turn out to be affected in a characteristic manner by the existence of Auger molecules
at high excitation levels. An analysis of corresponding rate coefficients for the reproduction of experimental results is
also presented.
Received: 14 September 1999 / Accepted: 3 February 2000 / Published online: 21 June 2000 相似文献
18.
A hybrid quantum mechanical and molecular mechanical potential is used in Monte Carlo simulations to examine the solvent
effects on the electronic excitation energy for the n→π* transition of pyrimidine in aqueous solution. In the present study,
the pyrimidine molecule is described by the semi-empirical AM1 model, while the solvent molecules are treated classically.
Two sets of calculations are performed: the first involves the use of the pairwise three-point charge TIP3P model for water,
and the second computation employs a polarizable many-body potential for the solvent. The latter calculation takes into account
the effect of solvent polarization following the solute electronic excitation, and makes a correction to the energies determined
using pairwise potentials, which neglects such fast polarization effects and overestimates the solute-solvent interactions
on the Franck-Condon excited states. Our simulation studies of pyrimidine in water indicate that the solvent charge redistribution
following the solute electronic excitation makes modest corrections (about −130␣cm−1) to the energy predicted by using pairwise potentials. Specific hydrogen bonding interactions between pyrimidine and water
are important for the prediction of solvatochromic shifts for pyrimidine. The computed n→π* blue shift is 2275±110 cm−1, which may be compared with the experimental value (2700 cm−1) from isooctane to water.
Received: 14 January 1997 / Accepted: 21 February 1997 相似文献
19.
We present in this paper a modification of the selection procedure, within the CIPSI algorithm, specifically intended for
the calculation of one-electron properties. In this new procedure the determinants are selected following their contribution
to a certain one-electron property. As test cases we report the calculation of the electric dipole of carbon monoxide and
of the hyperfine coupling constants of the CH3 radical.
Received: 20 August 2000 / Accepted: 2 October 2000 / Published online: 21 December 2000 相似文献
20.
Ma Meizhong Xu Guoliang Xie Andong Chen Xiaojun Zhang Yongbin Zhu Zhenghe 《化学物理学报(中文版)》2005,18(1):64-68
The ground states of dimethyl siloxane under different intense electric fields ranging from - 0. 04 to 0. 04 a. u. are optimized using density functional theory DFT / B3P86 at 6-311 ++ G(d,p)level. The excitation energies and oscillator strengths under the same intense applied electric fields are calculated employing the revised hybrid CIS-DFT method. The result shows that the electronic state,molecular geometry,total energy,dipole moment and excitation energy are strongly dependent on the field strength and behave asymmetry to the direction of the applied electric field. As the electric field changes from - 0. 04 to 0. 04 a. u. ,the bond length of Si-O increases whereas the bond length of Si-C decreases because of the charge transfer induced by the applied electric field. The dipole moment of the ground state decreases linearly with the applied field strength. However,the dipole moment of molecule changes from positive to negative as the inverse electric field increase to - 0. 03 a. u. Further increase of the inverse electric field results in an increase of the total energy of the molecule. The dependence of the calculated excitation energies on the applied electric field strength is fitting well to the relationship proposed by Grozema. The excitation energies of the first five excited states of dimethyl siloxane decrease as the applied electric filed increases because the energy gap between the HOMO and LUMO become close with the field,which shows that the molecule is easy to be excited under electric field and hence can be easily dissociated. 相似文献