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  • 1
    Electronic Resource
    Electronic Resource
    Dynamical fluctuating charge force fields: Application to liquid water (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6141-6156 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new molecular dynamics model in which the point charges on atomic sites are allowed to fluctuate in response to the environment is developed and applied to water. The idea for treating charges as variables is based on the concept of electronegativity equalization according to which: (a) the electronegativity of an atomic site is dependent on the atom's type and charge and is perturbed by the electrostatic potential it experiences from its neighbors and (b) charge is transferred between atomic sites in such a way that electronegativities are equalized. The charges are treated as dynamical variables using an extended Lagrangian method in which the charges are given a fictitious mass, velocities, and kinetic energy and then propagated according to Newtonian mechanics along with the atomic degrees of freedom. Models for water with fluctuating charges are developed using the geometries of two common fixed-charge water potentials: the simple point charge (SPC) and the four-point transferable intermolecular potential (TIP4P). Both fluctuating charge models give accurate predictions for gas-phase and liquid state properties, including radial distribution functions, the dielectric constant, and the diffusion constant. The method does not introduce any new intermolecular interactions beyond those already present in the fixed charge models and increases the computer time by only a factor of 1.1, making this method tractable for large systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468398
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  • 2
    Electronic Resource
    Electronic Resource
    The absorption spectrum of the solvated electron in fluid helium by maximum entropy inversion of imaginary time correlation functions from path integral Monte Carlo simulations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9909-9918 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dipole absorption spectrum of an electron in fluid helium is calculated by the maximum entropy method (MEM) numerical inversion of quantum Monte Carlo data obtained from a path integral Monte Carlo (PIMC) simulation at 309 K at the reduced densities ρ*=0.1, 0.3, 0.5, 0.7, and 0.9. Our results agree with the RISM-polaron theory results of Nichols and Chandler [A. L. Nichols III and D. Chandler, J. Chem. Phys. 87, 6671 (1987)] and the grid wave function calculation of Coker and Berne [D. F. Coker and B. J. Berne, J. Chem. Phys. 89, 2128 (1988)]. The method generated the expected long high frequency tail and the low density zero-frequency intensity caused by high conductivity. The method has also been tested by comparing the MEM absorption spectrum to the analytical spectrum of an electron confined in a spherical cavity of fluctuating radius, a model for a solvated electron in a localized state. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467892
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  • 3
    Electronic Resource
    Electronic Resource
    Erratum: Theory and simulation of polar and nonpolar polarizable fluids [J. Chem. Phys. 99, 6998 (1993)] (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4720-4721 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467284
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum and classical relaxation rates from classical simulations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8359-8366 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time correlation function for a harmonic quantum mechanical system can be related to the time correlation function for a corresponding classical system. Although straightforward to derive and well known in other contexts, this relationship has been unappreciated in the context of vibrational relaxation, where time correlation functions obtained from classical molecular dynamics have been used to predict relaxation rates for a quantum solute in a classical solvent. This inconsistent treatment—quantum solute, classical solvent—predicts a relaxation rate which is slower than if the entire system, both solute and solvent, were treated classically. We demonstrate that if the classical time correlation functions are rescaled to account for the ratio of quantum to classical fluctuations, providing a quantum mechanical treatment for the solute and the solvent, the relaxation rates and the entire absorption spectrum are the same as for a purely classical treatment. Our conclusions are valid when the solute and solvent can be described by a set of effective harmonic normal modes, and can also be valid when anharmonicities are present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466780
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  • 5
    Electronic Resource
    Electronic Resource
    Equilibrium components of tubulin preparations (1977)
    s.l. : American Chemical Society
    Biochemistry 16 (1977), S. 5781-5785 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00645a021
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of heterogeneous solutions using laser light scattering: study of the tubulin system (1977)
    s.l. : American Chemical Society
    Biochemistry 16 (1977), S. 5776-5781 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00645a020
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  • 7
    Electronic Resource
    Electronic Resource
    A Born–Oppenheimer approximation for path integrals with an application to electron solvation in polarizable fluids (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2902-2916 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Born–Oppenheimer approximation is introduced into the path integral expression for the canonical partition function. It is difficult to apply this to simulations. We devise a new adiabatic expression which we call the free energy Born–Oppenheimer approximation which is much easier to simulate. It is shown that this approximation deviates from the exact path-integral expression by no more than does the standard Born–Oppenheimer approximation and we apply it to the problem of an excess electron dissolved in a polarizable fluid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465198
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  • 8
    Electronic Resource
    Electronic Resource
    Theory and simulation of polar and nonpolar polarizable fluids (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6998-7011 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The theory of polarizable fluids is developed on the basis of a model fluid consisting of anisotropic Drude oscillators with embedded permanent dipoles. A matrix Monte Carlo method is used to simulate these fluids and to compare their dielectric properties with the predictions of the mean spherical approximation (MSA) theory. Simple identities are used in conjunction with the matrix expressions to derive mean spherical approximations to the screening functions for charges and permanent multipoles in polarizable fluids. This is useful in the theory of the solvated electron.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465446
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  • 9
    Electronic Resource
    Electronic Resource
    Vibrational relaxation in simple fluids: Comparison of theory and simulation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7301-7318 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: General theoretical expressions for the dephasing and energy relaxation times of a stiff oscillator in simple fluids are derived from the GLE and a critical discussion of the dynamic processes in these systems is given. In addition new methodological aspects of stochastic and full molecular dynamics simulations are discussed. The new reversible integrator based on the Trotter factorization of the classical propagator is used to directly simulate the vibrational energy and phase relaxation of a stiff classical oscillator dissolved in a Lennard-Jones bath. We compare the "real'' relaxation from full MD simulations with that predicted by Kubo theory and by the generalized Langevin equation (GLE) with memory friction determined from the full molecular dynamics. It is found that the GLE gives very good agreement with MD for the vibrational energy relaxation, even for nonlinear oscillators far from equilibrium. The dephasing relaxation is also well approximated by the GLE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464723
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  • 10
    Electronic Resource
    Electronic Resource
    Efficient molecular dynamics and hybrid Monte Carlo algorithms for path integrals (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2796-2808 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: New path integral molecular dynamics (PIMD) and path integral hybrid Monte Carlo (PIHMC) algorithms are developed. It is shown that the use of a simple noncanonical change of variables that naturally divides the quadratic part of the action into long and short wavelength modes and multiple time scale integration techniques results in very efficient algorithms. The PIMD method also employs a constant temperature MD technique that has been shown to give canonical averages even for stiff systems. The new methods are applied to the simple quantum mechanical harmonic oscillator and to electron solvation in fluid helium and xenon. Comparisons are made with PIMC and the more basic PIMD and PIHMC methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465188
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