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  • 1
    Electronic Resource
    Electronic Resource
    Hydrophobic effect on chain folding. The trans to gauche isomerization of n-butane in water (1982)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 104 (1982), S. 7647-7649 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00390a043
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular Dynamics Calculation of the Effect of Solvent Polarizability on the Hydrophobic Interaction (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 7172-7179 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00132a017
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  • 3
    Electronic Resource
    Electronic Resource
    The Aqueous Solvation of Water: A Comparison of Continuum Methods with Molecular Dynamics (1994)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 3949-3954 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00088a034
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  • 4
    Electronic Resource
    Electronic Resource
    Low-temperature variational approximation for the Feynman quantum propagator and its application to the simulation of quantum systems (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7531-7539 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The low-temperature propagator of Mak and Andersen [J. Chem. Phys. 92, 2953 (1990)] allows for much more rapid convergence of Feynman path integral computer simulations of quantum systems. The effectiveness of this propagator is very sensitive to the choice of an effective frequency and the choice of this made by Mak and Andersen, although good, is not optimum. In this paper a harmonic reference system is used together with a variation principle to compute this effective frequency. Simulations show that when this is used in the low temperature propagator, the results converge much more rapidly than for other choices of the frequency. Moreover, an energy estimator is derived, which allows this effective potential to be used for the determination of the energy of the quantum system. In addition, using a cumulant expansion of the centroid density in the free particle reference system, an effective potential along with a corresponding energy estimator is derived and compared to the above.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458189
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  • 5
    Electronic Resource
    Electronic Resource
    Path integral Monte Carlo studies of the behavior of excess electrons in simple fluids (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5689-5702 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The behavior of an excess electron in helium (at T=309 K) and xenon (at T=309 K and T=248 K) is studied over a range of fluid densities (ρ*=ρσ3=0.1–0.9). A path integral Monte Carlo technique is used to model the "quantum'' electron which interacts through pseudopotentials with the "classical'' solvent particles. In helium, the electron becomes confined in a cavity in the solvent and behaves like a particle in a spherical box. We observe contrasting behavior in the more polarizable xenon solvent where the electron exists in a "quasifree'' state. A variety of equilibrium properties of the electron and the solvent are presented to characterize the structure of the different systems. The anomolous density dependence of the experimental electron mobility along the coexistence curve in xenon can be understood qualitatively in terms of the equilibrium structures we observe at the different solvent densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452495
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  • 6
    Electronic Resource
    Electronic Resource
    Path integral Monte Carlo study of the hydrated electron (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6404-6418 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of an excess electron in water at room temperature is investigated using the Feynman path integral technique. The interaction potential between the electron and water is modeled by an effective potential, made up of three terms: a static potential, a repulsive potential, and a polarization potential. The polarization part is treated in two different ways: approximated as pairwise additive, and exactly with the many body polarization effects treated self-consistently. It is shown that the excess electron forms a cavity with the radius of the electron being 2.24 A(ring) for pairwise additive polarization and 2.11 A(ring) for the self-consistent treatment of the polarization. There is no sharp geometrical coordination number of water molecules around the electron. The water molecules within a distance of about 3.5 A(ring) from the center of the electronic change distribution point their OH bonds towards the electron, and form only three hydrogen bonds. It is also found that the pair correlation function of the solvent molecules close to the electron are considerably different from the corresponding quantities calculated in the bulk. The electron, therefore, is shown to modify the local density to a large extent. There are important structural differences between the many body polarization model and the two body polarization model. It is concluded that for a quantitative description of the structure of the hydrated electron, the self-consistent treatment of the long range (many body) polarization effects are important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452429
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  • 7
    Electronic Resource
    Electronic Resource
    Monte Carlo methods for accelerating barrier crossing: Anti-force-bias and variable step algorithms (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1980-1985 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For computer simulations of systems in which particles must cross large potential energy barriers, slow convergence is a problem. Basically there are two very disparate time scales: one characterizing motion in the potential wells and one characterizing the rare jumps from one stable well to another. Multiple time scale problems like this sorely test computer resources, and stand in the way of progress on simulations of chain folding, glass transitions, nucleation phenomena, activated barrier crossing, and quantum tunneling processes. Here several new methods are developed and tested on classical and quantum barrier crossings in double well problems. These new methods, called the anti-force-bias and variable step methods, lead to much faster convergence than standard methods. Convergence is tested by studying the deviation in the mean of the cumulative spatial distribution function from the exact distribution function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458029
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  • 8
    Electronic Resource
    Electronic Resource
    Excess electronic states in fluid helium (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2128-2137 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the nature of the excess electronic states in fluid helium by calculating the excess electron energies and wave functions for a set of configurations of solvent atoms taken from path integral Monte Carlo calculations on the solvated electron system. The eigenvalues and eigenfunctions for the different configurations of the solvent are used to calculate the inhomogeneously broadened density of states and absorption line shape of the excess electron over a range of fluid densities. The predictions of a simple theory of the excess electronic states in fluid helium due to Springett et al. [B. E. Springett, M. H. Cohen, and J. Jortner, Phys. Rev. 159, 183 (1967)] are found to agree quite well with our computer simulation results. This simple theory, however, predicts an inhomogeneously broadened elecronic absorption linewidth which is much narrower than that obtained from simulation. It is found that the RISM-polaron theory of Nichols and Chandler [A. L. Nichols III and D. Chandler, J. Chem. Phys. 87, 6671 (1987)] gives an absorption line shape which is in better agreement with our simulations. We observe a transition from lower energy states in which the electron is bound to density fluctuations in the fluid to the situation where the excess electron scatters through the fluid in continuum states at higher energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455057
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  • 9
    Electronic Resource
    Electronic Resource
    Dynamic friction on rigid and flexible bonds (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5084-5095 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A wide variety of problems involving molecular motion in liquids can be formulated in terms of the generalized Langevin equation (GLE). The friction coefficient on a molecular bond or on some more complicated reaction coordinate is then required. An often used approximation is to set the dynamic friction constant equal to the autocorrelation function of the fluctuating force exerted on the frozen bond by the remaining unfrozen coordinates. The true friction involves projection operators and should differ from this approximation. In this paper we derive various identities and show that the rigid bond approximation is the high frequency limit of the true dynamic friction coefficient. We compute the "true'' dynamic friction and the friction approximated on the basis of the rigid or frozen bond and show that the asymptotic limit is very accurate even for frequencies not much larger than the peak frequency of the solvent spectral density. Two different dynamical systems are studied using MD simulations with our newly devised NAPA integrator for systems with disparate time scales. In one the molecule is not allowed to rotate and in the other it is allowed to rotate. Interestingly, even for very long rotational reorientation times, small but significant differences in the long time decay of the bond dynamic friction are observed for rotational and nonrotational molecules—differences, however, that do not produce large differences in the static friction constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458647
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  • 10
    Electronic Resource
    Electronic Resource
    Combined fluctuating charge and polarizable dipole models: Application to a five-site water potential function (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 2237-2251 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a general formalism for polarizable electrostatics based on fluctuating bond-charge increments and polarizable dipoles and its application to a five-site model for water. The parametrization is based largely on quantum-chemical calculations and should be easily transferable to other molecules. To examine basis-set effects we parametrized two models from two sets of quantum calculations, using the aug-cc-pVTZ and aug-cc-pVQZ basis sets. We computed several gas-phase and condensed-phase properties and compared with experiment or ab initio calculations as available. The models are quite similar and give condensed-phase properties at ambient conditions that are in reasonable accord with experiment, but evince errors consistent with a liquid-state dipole moment that is slightly too large. The model fit to the aug-cc-pVTZ basis set has a smaller liquid-phase dipole moment and thus gives a somewhat better description of liquid water at ambient conditions. This model also performs well away from room temperature, deviating less than 2% from the experimental density from 0 to 100 °C, and showing good agreement with experimental radial distribution functions, although the temperature of maximum density (∼20 °C) is slightly too high and the model somewhat underpredicts the persistence of the hydrogen-bond network at elevated temperatures. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1376165
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