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  • 1
    Electronic Resource
    Electronic Resource
    Companion equations for branes (2000)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 41 (2000), S. 4284-4292 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The quantum mechanical transition between a free particle Lagrangian and the Klein–Gordon field description of a free particle (particle-wave duality) is conjectured to extend to an analogous construction of relativistically invariant wave equations associated with strings and branes. Electromagnetic interactions in the two systems are discussed. It is emphasized that all integrable free field theories, including those of Dirac–Born–Infeld type, are associated with Lagrangians equivalent to divergences on the space of solutions of the equations of motion. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.533342
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  • 2
    Electronic Resource
    Electronic Resource
    Moyal–Nahm equations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 40 (1999), S. 2539-2548 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Various aspects of the Nahm equations in three and seven dimensions are investigated. The residues of the variables at simple poles in the seven-dimensional case form an algebra. A large class of matrix representations of this algebra is constructed. The large N limit of these equations is taken by replacing the commutators by Moyal brackets, and a set of nontrivial solutions in a generalized form of Wigner distribution functions is obtained. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.532713
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  • 3
    Electronic Resource
    Electronic Resource
    Assessment of the Handy–Cohen optimized exchange density functional for organic reactions (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 1441-1449 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated the performance of the new optimized exchange functional (OPTX) developed by Handy and Cohen [Mol. Phys. 99, 403 (2001)] for predicting geometries, heats of reaction, and barrier heights for twelve organic reactions (six closed-shell and six radical). OPTX has been used in conjunction with, among others, the well-known Lee–Yang–Parr (LYP) correlational functional to form two new functionals, OLYP and O3LYP. These are similar to the well-established BLYP and B3LYP functionals, respectively, with OPTX replacing the standard Becke exchange functional, B88. Our results strongly support claims made by their developers that OLYP is superior to BLYP, and essentially renders it obsolete. The computed OLYP heats of reaction, barrier heights, and even molecular geometries (with larger basis sets), are comparable with, if not better than, the corresponding B3LYP values. The O3LYP functional is overall better than B3LYP, albeit not by much. Both OLYP and O3LYP are among the best functionals currently available; the performance of OLYP in particular is noteworthy given that this functional includes no exact exchange. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1485723
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  • 4
    Electronic Resource
    Electronic Resource
    Electric field induced instabilities at liquid/liquid interfaces (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 2377-2381 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: External electric fields were used to amplify thermal fluctuations at the interface between two thin liquid films. Similar to the results shown previously for the enhancement of fluctuations at the polymer/air interface, interfacial fluctuations having a well-defined wavelength were enhanced with a characteristic growth rate. A simple theoretical framework to describe the experimental observations is presented. Both experiment and model calculation show a substantial reduction in feature size as a result of the change in surface/interfacial energy when going from the thin film to the bilayer case. Experimentally, features develop nearly 50 times faster for the bilayers in comparison to the polymer/air case. These results point to a simple route by which the nanoscopic feature can be easily and rapidly produced or replicated. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1338125
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  • 5
    Electronic Resource
    Electronic Resource
    Geometry optimization of large biomolecules in redundant internal coordinates (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6566-6572 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an improved version of our recent algorithm [B. Paizs, G. Fogarasi, and P. Pulay, J. Chem. Phys. 109, 6571 (1998)] for optimizing the geometries of large molecules. The approximate Cholesky factorization technique has been generalized to the case of redundant coordinates, and an alternative approach involving use of the B†B matrix in the iterative coordinate back transformation is described. The generalized full Cholesky factors of B†B are very sparse and the corresponding force and geometry transformations are fast and numerically stable, permitting us to apply this technique for internal coordinate geometry optimization of molecules containing thousands of atoms. As an example we present optimization data on alpha-helical alanine polypeptides, and various globular proteins. Results for the alanine polypeptides indicates that internal coordinate optimization is clearly superior to the first-order Cartesian optimization techniques generally used in force field calculations. The largest system investigated is alpha-helical Ac-(Ala)999-NH2 containing 9999 atoms, which was successfully optimized using less than a megaword of memory. Optimization of various globular proteins shows that our procedure can easily deal with highly redundant (including full primitive) coordinate sets. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1308551
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  • 6
    Electronic Resource
    Electronic Resource
    Erratum: "Polarization around an ion in a dielectric continuum with truncated electrostatic interactions" [J. Chem. Phys. 110, 10679 (1999)] (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 2510-2511 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An error was made in the derivation of Eq. (25) for the integrated electric field. The error is corrected and the modified results reported. In general, the various truncation schemes show improved agreement with the Born model for solvent polarization. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.482073
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  • 7
    Electronic Resource
    Electronic Resource
    Hyperfine and Zeeman quantum beats in the B 2Π1/2 state of NO (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3968-3976 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum beat signals have been observed in v=0, 1, 2, and 3 of the B 2Π1/2 state of NO for the first time and are used to carry out Doppler free spectroscopy in these levels. Beat signals are observed at zero magnetic field in all four vibrational levels between different hyperfine components for J=3/2 and J=5/2, and are analyzed to derive accurate hyperfine constants and quadrupole coupling parameters. Although from their magnetic tuning rates the beats between the different hyperfine levels can be assigned to particular F'↔F separations, the energy ordering of the F levels and the parity assignment remain to be determined. Independently of this exact assignment a small variation in the hyperfine parameters with vibrational state is observed which is irregular in v=3 indicating the presence of an interaction with another electronic state. When a small magnetic field is applied much more intense beat signals are observed which occur between the Zeeman split components of a single hyperfine level. The B 2Π1/2 state is nominally nonmagnetic in the Hund's case (a) limit and so the effective g values vary rapidly with J due to spin–orbit uncoupling. The relative intensities of these beat signals and their variation with both magnetic field and vibrational level is accurately predicted using the known spectroscopic constants and a fitted value of gr. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468525
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  • 8
    Electronic Resource
    Electronic Resource
    A two-color (1+1′)+1 multiphoton ionization study of CS2 in the 61 000–65 600 cm−1 energy region (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4847-4854 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The (1+1′)+1 resonance enhanced multiphoton ionization (REMPI) spectrum of jet-cooled CS2 has been recorded in the 61 000–65 600 cm−1 excitation energy range. Four prominent band groups are observed that can be assigned to Δν2=−1 and Δν2=1 sequences of the two-photon electronically forbidden 4p 1,3Δu←X˜ 1Σ+g transitions. Weak bands to higher energy appear to be associated with the 310, 230 and 110210 bands and corresponding sequence bands. The results show that the upper states are not 3d Rydberg states as has been previously supposed, and are consistent with a recent reinvestigation of the corresponding (3+1) REMPI spectrum. Further experimental information is obtained on the anomalous vibrational band structure of transitions to the 3Δu state. The 201 and 212 bands of the 4p 1Πu←X˜ 1Σ+g transition are also observed, but are much weaker, suggesting that vibronic interactions are less important in this state compared to the 4p 1,3Δu states. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470620
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  • 9
    Electronic Resource
    Electronic Resource
    Disorder induced enhancement of the third order optical nonlinearity in a conjugated polymer (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2295-2301 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on the relationship between material disorder and nonlinear optical response for a conjugated polymer. Inverse Raman scattering, the technique used here, is sensitive to the transition cross sections of both the purely electronic (Sv=01↔Sv=00) and vibronic (Sv=01↔Sv=10) transitions accessed, and both of these quantities are related to the extent of disorder in the polymer backbone. We have verified these morphology dependencies using crystalline and amorphous samples of the polydiacetylene poly(4BCMU). The magnitude of the nonlinear response per backbone repeat unit in the amorphous material is comparable to that of the crystalline form because of the large potential well displacement between the ground and excited electronic states characteristic of the disordered material. This increased potential well displacement compensates for the nonlinear response lost to the reduced macroscopic polymer alignment associated with the two-dimensionally isotropic spin cast film. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468717
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  • 10
    Electronic Resource
    Electronic Resource
    A study of some organic reactions using density functional theory (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2063-2079 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Twelve organic reactions (six closed shell and six radical) were studied using semiempirical, traditional ab initio and density functional methodologies. Full geometry optimizations of all species, both minima and transition states, were performed, and calculated geometries and barrier heights compared with experimental data. Our results demonstrate that although currently available density functionals tend to underestimate barrier heights, especially for radical reactions—in some cases reactions with low barriers are predicted to be essentially barrier free—they provide a significant improvement over standard methods. The adiabatic connection method recently proposed by Becke [J. Chem. Phys. 98, 5648 (1993)], in which a portion of the exact Hartree–Fock exchange is mixed in to the density functional, looks very promising. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468728
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