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Dipole

About: Dipole is a research topic. Over the lifetime, 52856 publications have been published within this topic receiving 1100945 citations.


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Journal ArticleDOI
TL;DR: In this paper, a new basis set, denoted 4-21, is presented for first-row atoms, which is nearly equivalent to the 4-31G set but requires less computational effort.
Abstract: Systematic ab initio gradient calculation of molecular geometries, force constants, and dipole moment derivatives is described. A new basis set, denoted 4-21, is presented for first-row atoms. It is nearly equivalent to the 4-31G set but requires less computational effort. Completely optimized Hartree-Fock geometries of 18 molecules are compared using several basis sets, with and without polarization functions. The question of the best representation of molecular force fields is discussed, and a set of standardized internal coordinates is suggested for future work. Quadratic and the most important cubic force constants and dipole moment derivatives of first-row hydrides are calculated using the 4-21 basis set, and the results are compared with those from other basis sets, including near-Hartree-Fock ones. Force-field calculations on larger molecules with the 4-21 basis are summarized. A general formulation of the rotational correction to dipole moment derivatives is given.

1,973 citations

Book
01 Jan 1984
TL;DR: Theoretical Aspects of molecular Rotation Microwave Transitions - Line Intensities and Shapes Diatomic Molecules Linear Polyatomic Molecules Symmetric-Top Molecules Asymmetric-top Molecules The Distortable Rotor Nuclear Hyperfine Structure in Molecular Rotational Spectra effects of Applied Electric Fields Effects of Applied Magnetic Fields Internal Motions Derivation of Molecular Structures Quadrupole Couplings, Dipole Moments, and the Chemical Bond Irreducible Tensor Methods for Calculation of Complex Spectra Appendixes Author Index Subject Index
Abstract: Introduction Theoretical Aspects of Molecular Rotation Microwave Transitions - Line Intensities and Shapes Diatomic Molecules Linear Polyatomic Molecules Symmetric-Top Molecules Asymmetric-Top Molecules The Distortable Rotor Nuclear Hyperfine Structure in Molecular Rotational Spectra Effects of Applied Electric Fields Effects of Applied Magnetic Fields Internal Motions Derivation of Molecular Structures Quadrupole Couplings, Dipole Moments, and the Chemical Bond Irreducible Tensor Methods for Calculation of Complex Spectra Appendixes Author Index Subject Index.

1,881 citations

Journal ArticleDOI
TL;DR: In this paper, King-Smith and Vanderbilt developed a complete theory in which the polarization difference between any two crystal states in a null electric field takes the form of a geometric quantum phase.
Abstract: The macroscopic electric polarization of a crystal is often defined as the dipole of a unit cell. In fact, such a dipole moment is ill defined, and the above definition is incorrect. Looking more closely, the quantity generally measured is differential polarization, defined with respect to a "reference state" of the same material. Such differential polarizations include either derivatives of the polarization (dielectric permittivity, Born effective charges, piezoelectricity, pyroelectricity) or finite differences (ferroelectricity). On the theoretical side, the differential concept is basic as well. Owing to continuity, a polarization difference is equivalent to a macroscopic current, which is directly accessible to the theory as a bulk property. Polarization is a quantum phenomenon and cannot be treated with a classical model, particularly whenever delocalized valence electrons are present in the dielectric. In a quantum picture, the current is basically a property of the phase of the wave functions, as opposed to the charge, which is a property of their modulus. An elegant and complete theory has recently been developed by King-Smith and Vanderbilt, in which the polarization difference between any two crystal states---in a null electric field---takes the form of a geometric quantum phase. The author gives a comprehensive account of this theory, which is relevant for dealing with transverse-optic phonons, piezoelectricity, and ferroelectricity. Its relation to the established concepts of linear-response theory is also discussed. Within the geometric phase approach, the relevant polarization difference occurs as the circuit integral of a Berry connection (or "vector potential"), while the corresponding curvature (or "magnetic field") provides the macroscopic linear response.

1,867 citations

Journal ArticleDOI
TL;DR: In this paper, a modified handling of the link atoms which are introduced to terminate the dangling bonds of the model system is presented, which allows the consistent combination of vibrational frequencies and the calculation of other molecular properties such as IR intensities, Raman intensities as well as dipole moments, polarizabilities, and hyperpolarizabilities.
Abstract: The IMOMM, IMOMO, and ONIOM methods have been proven to be powerful tools for the theoretical treatment of large molecular systems where different levels of theory are applied to different parts of a molecule. Within this framework we present a modified handling of the link atoms which are introduced to terminate the dangling bonds of the model system. Using this new scheme the definition of the combined energy gradient, the Hessian matrix, and the integration of higher derivatives of the energy with respect to nuclear coordinates and the electric field vector becomes straightforward. This allows for the first time the consistent combination of vibrational frequencies and the calculation of other molecular properties such as IR intensities, Raman intensities as well as dipole moments, polarizabilities, and hyperpolarizabilities. Test calculations for some typical as well as unusual examples and partitioning schemes are presented to demonstrate the power and limitations of the method and to provide guidelines for its applicability. Users of the method are strongly advised to test, calibrate and confirm for themselves the validity of the method combination and the model subsystem for the properties they want to calculate.

1,824 citations

Journal ArticleDOI
TL;DR: The discrete dipole approximation is used to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces.
Abstract: We use the discrete dipole approximation to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces. The results are used to determine what conditions are most favorable for producing enhancements large enough to observe single molecule surface enhanced Raman spectroscopy. Most of the calculations refer to triangular prisms, which exhibit distinct dipole and quadrupole resonances that can easily be controlled by varying particle size. In addition, for the dimer calculations we study the influence of dimer separation and orientation, especially for dimers that are separated by a few nanometers. We find that the largest /E/2 values for dimers are about a factor of 10 larger than those for all the monomers examined. For all particles and particle orientations, the plasmon resonances which lead to the largest E-fields are those with the longest wavelength dipolar excitation. The spacing of the particles in the dimer plays a crucial role, and we find that the spacing needed to achieve a given /E/2 is proportional to nanoparticle size for particles below 100 nm in size. Particle shape and curvature are of lesser importance, with a head to tail configuration of two triangles giving enhanced fields comparable to head to head, or rounded head to tail. The largest /E/2 values we have calculated for spacings of 2 nm or more is approximately 10(5).

1,778 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,608
20223,362
20211,414
20201,567
20191,639
20181,677