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  • 1
    Electronic Resource
    Electronic Resource
    Microscopic calculation of surface-induced second-harmonic generation in crystals of para-nitroaniline (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6757-6762 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Previous results for surface linear optical response in centrosymmetric para-nitroaniline crystals are combined with literature values for the molecular first hyperpolarizability to calculate the surface-induced quadratic response. The average surface quadratic susceptibilities for incident light at a wavelength of 803 nm are calculated to be 71 and 50×10−22 m2 V−1 for different surface terminations normal to the [001] direction, and 9 and 7×10−22 m2 V−1 for different surface terminations normal to the [101] direction (the natural cleavage plane). The latter values are three orders-of-magnitude below that determined by Kobayashi and Kotani, consistent with their evidence for bulk second-harmonic generation from a new phase at the surface. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481251
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  • 2
    Electronic Resource
    Electronic Resource
    Microscopic calculation of surface linear optical response in crystals of para-nitroaniline (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6749-6756 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Previous theoretical results for surface linear optical response in molecular crystals are extended to treat response to the external applied field, the bulk macroscopic field, and the surface macroscopic field. They are used to calculate planewise dipole sums, surface local electric fields, surface linear susceptibilities, and surface refractive indices for surfaces normal to the [001] and [101] directions of the centrosymmetric para-nitroaniline crystals. For each direction, two different terminations give different results. Surface effects are stronger normal to the surface for the [001] direction, and in the surface for the [101] direction. Surface effects decrease sharply into the bulk, being negligible beyond neighboring layers of molecules. The present results provide input for calculations of surface-induced quadratic nonlinear optical response, reported in the following article. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481250
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  • 3
    Electronic Resource
    Electronic Resource
    Microscopic calculations of linear and quadratic optical response in model Langmuir–Blodgett multilayers (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6763-6773 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microscopic calculations are reported of linear and quadratic nonlinear optical response in Langmuir–Blodgett films. The films are modeled as ordered layers of molecules that can tilt from the vertical and have a higher polarizability and first hyperpolarizability in the head than in the tail. The local electric field varies little after the first layer and negligibly after the second, which simplifies the analysis. Tilted two-layer Y-type films can have quadratic susceptibility components as large as X- or Z-type ones. Overall the results provide a systematic account of the linear and nonlinear optical properties as a function of molecular and film structure that should assist interpretation of experimental results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481238
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  • 4
    Electronic Resource
    Electronic Resource
    First-principles calculation of bulk susceptibility for second-harmonic generation in crystalline C60 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5975-5980 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hyperpolarizabilities for electric dipole second-harmonic generation (SHG) due to the bilinear combination of an electric field and either the electric-field gradient (μeeq) or the associated magnetic field (τeem), and for electric quadrupole SHG quadratic in the electric field (μqee) have been calculated for the C60 molecule at pump photon energies from 0.5 to 2.2 eV using the valence effective Hamiltonian method with a minimal STO-3G basis; magnetic dipole SHG quadratic in the electric field (τmee) is zero by symmetry in C60. The coefficients exhibit resonances at photon energies near 1.9 for μeeq, 1.4 for μqee, and 2.0 eV for τeem. They are combined with empirical local-field factors and a theoretical local field-gradient tensor to calculate the composite susceptibility χ(2) for SHG from crystalline C60 in the same energy range. The susceptibility shows several resonances that arise from those in μeeq, μqee, and τeem. The results are able to reproduce the magnitudes and signs reported experimentally, subject to a sensitive dependence on photon energy near resonances. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476009
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  • 5
    Electronic Resource
    Electronic Resource
    Microscopic calculation of the third-order nonlinear optical susceptibility of DEANST crystal (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7926-7933 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The linear and nonlinear optical response properties of crystalline DEANST, N,N-diethyl-4-(2-nitroethenyl) phenylamine, have been computed rigorously, using a large set of input data including modified neglect of differential overlap (MNDO) and ab initio theoretical estimates of molecular polarizability α and hyperpolarizabilities β and γ, and experimentally measured refractive indices. The currently available microscopic expression for the third-order susceptibility tensor χ(3) of a molecular crystal has been corrected to include all possible frequency combinations in the cascading term. Calculations of linear response based on theoretical polarizabilities α fail to reproduce the experimental refractive indices of the crystal, and hence an effective polarizability tensor has been derived from the measured refractive indices and used in the computation of the local electric field. The calculation of χ(3) based on the MNDO hyperpolarizabilities is in tolerable agreement with the experimental measurements of third-harmonic generation. Environmental effects on the molecular response play a key role in the accuracy of the calculation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475106
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  • 6
    Electronic Resource
    Electronic Resource
    Microscopic theory of molecular crystal surface second-harmonic generation (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 850-859 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Second-harmonic generation (SHG) is induced in molecular crystals by the variation through the surface region of the electric fields associated with the optical wave and with the permanent electric multipole moments of the molecules. It arises from the molecular first hyperpolarizability, whether permanent or induced by electric fields at noncentrosymmetric sites in the bulk crystal or at sites in the surface region where centrosymmetry is lost. Algebraic expressions suitable for iterative numerical evaluation are derived for the molecular response coefficients as affected by the multipole fields in the surface region. Detailed expressions are then derived for the surface second-harmonic generation in terms of the spatially varying molecular response and a microscopic expression that is derived for the variation of optical electric field through the surface region. The treatment does not require the introduction of a surface dielectric constant but incidentally yields a microscopic expression for it. The quadratic susceptibilities for surface SHG in anthracene and pyrene are roughly estimated as respectively 1/80 and 1/20 that in p-nitroaniline, reported to be 4 fm V−1; the coefficients could vary by one or two orders of magnitude among different surfaces. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470066
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  • 7
    Electronic Resource
    Electronic Resource
    Microscopic treatment of substrate effects on linear optical properties of model Langmuir–Blodgett films (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8159-8168 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An algebraic treatment is developed for the effect of a plane substrate with isotropic relative permittivity on the linear optical response of layers of molecules treated as sets of point submolecules so as to incorporate molecular elongation and orientation. Results are modified from those for free-standing films by planewise sums describing the field at a dipole due to its image in the substrate. Numerical calculations of refractive indices are performed for a monolayer of molecules initially packed in a tetragonal structure normal to the substrate and then tilted to yield monoclinic structures. The head-group polarizability is varied relative to that of the other submolecules, as is the spacing between the layer and the substrate. Substrate effects are largest when a very polarizable head group of a tilted molecule is adjacent and very close to the substrate; in extreme cases the refractive indices diverge. The results support the idea that first-layer effects on optical properties could be dielectric as well as structural in origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468201
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  • 8
    Electronic Resource
    Electronic Resource
    Theory of electronic transport in molecular crystals. II. Zeroth order states incorporating nonlocal linear electron–phonon coupling (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1843-1853 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A generalized transformation is applied to a model Hamiltonian incorporating both local and nonlocal exciton–phonon coupling. For the application of the usual transport theory, the difference between the transformed coupling and its thermal average over the free phonon ensemble must be small. This is achieved by a temperature-dependent set of transformation coefficients defined by a transcendental equation which is soluble numerically after some approximation. Nonlocal coupling increases both the exciton binding energy and the usual band narrowing, but it also changes the band shape in a way which may introduce new minima and band broadening. The exciton velocities are then no longer related to the exciton hopping and scattering rates in the same way as in local coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449372
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  • 9
    Electronic Resource
    Electronic Resource
    Microscopic theory of linear and nonlinear optical and dielectric response in polymer materials (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 5404-5414 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A self-consistent cavity model is introduced to calculate optical and dielectric properties of polymer materials from the microscopic structure and molecular response. The material is treated as discrete molecules inside a cavity (chosen as spherical for convenience) and as a continuum outside. The cavity radius is to be increased progressively until the calculated properties converge within a set precision. Linear response for an isotropic polymer material is treated for three types of molecular polarizability: (a) dipolar response that is local within molecules; (b) dipolar response that is nonlocal within and between molecules; and (c) distributed monopolar and dipolar response that is nonlocal within molecules but local between molecules. In each case a microscopic expression is derived for computing the effective polarizability that gives the exact linear susceptibility from the Lorentz expression. For a poled polymer material of axial symmetry with type (c) response, expressions are derived for the anisotropic effective polarizability, the effective dipole moments under their mutual polarizing influence, the resulting dipole energy, and the poling energy in an external electric field (including quadratic terms that arise from allowing molecules to be polarizable). Nonlinear optical susceptibilities are then derived for a polymer material of arbitrary structure with type (c) response generalized to include first and second hyperpolarizabilities. In algebraic form, the results resemble those for distributed response in molecular crystals, without obvious dependence on the choice of cavity shape. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1350638
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  • 10
    Electronic Resource
    Electronic Resource
    Role of the cavity field in nonlinear optical response in the condensed phase (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3105-3108 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Comparison between a rigorous molecular crystal treatment of nonlinear optical response and a cavity model approach to third harmonic generation shows that a cavity field should be included at the output frequency. The argument for omitting this cavity field, that there is zero macroscopic field at the output frequency, fails to take proper account of polarization at the output frequency outside the cavity. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1343082
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