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  • 1
    Electronic Resource
    Electronic Resource
    Reverse Monte Carlo Simulation of a Heteronuclear Molecular Liquid: Structural Study of Acetonitrile (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 5994-6002 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100074a028
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  • 2
    Electronic Resource
    Electronic Resource
    Reverse Monte Carlo analysis of neutron diffraction results: Water around its critical point (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2391-2398 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reverse Monte Carlo method in its molecular version, is used to analyze neutron diffraction data for water in two thermodynamic states around its critical point. At the lower density we find that the oxygen–oxygen and the oxygen–hydrogen partial radial distribution functions cannot be reproduced simultaneously in a satisfactory way. At the higher density the first peak of the oxygen–hydrogen partial radial distribution function, which gives a measure of the number of hydrogen bonded neighbors, turns out to be unreproducible. To understand the possible origin of these discrepancies the reverse Monte Carlo method is applied to the analysis of the radial distribution functions which are obtained directly by Fourier transforming the measured structure factors. This procedure reveals that at the lower density the total radial distribution function measured in light water can be responsible for the apparent deviations between simulated and experimental curves. At the higher density the experimental inaccuracy in the measurements of both light and half-deuterated water structure factors is found to affect the evaluation of the partial radial distribution functions. The results of the present work demonstrate that reverse Monte Carlo is a valuable method for revealing experimental inaccuracies, and therefore its use in the data reduction process is suggested. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472106
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  • 3
    Electronic Resource
    Electronic Resource
    The local structure of various hydrogen bonded liquids: Voronoi polyhedra analysis of water, methanol, and HF (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 9113-9121 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The local structure of three hydrogen bonded liquids comprising clusters of markedly different topology: water, methanol, and HF are investigated by analyzing the properties of the Voronoi polyhedra (VP) of the molecules in configurations obtained from Monte Carlo computer simulations. For comparisons, the properties of argon as a nonassociating reference liquid are also calculated. It is found that in liquid HF the fluctuation of the local density is much larger than in the other three liquids, and hence, besides the dense regions, this liquid contains numerous large voids as well. The size of the largest of these voids is found to be commensurate with a cluster of 11 HF molecules, whereas the number of voids as large as one molecule is in the order of the number of molecules. It is found that the number of the hydrogen-bonded neighbors of the HF molecules located at the boundary of such voids does not differ considerably from that of the other molecules, and thus they do not have any specific topological position (e.g., chain terminal) in the hydrogen bonded chains of the molecules. The shape of the VP is found to reflect the arrangement of the nearest neighbors of the molecules. Thus, the VP are considerably less spherical and their topological properties are distributed in a wider range in the associated liquids than in argon. Similarly, in the hydrogen bonded liquids considerably more geometric neighbors are found than the number of molecules belonging to the first coordination shell. On the other hand, in liquid argon, which is a closely packed system, the two values are found to be close to each other. The inhomogeneities of the local density of liquid HF are also reflected in the shape of the VP. The molecules located at the boundary of the large voids are found to have more spherical VP with more and larger faces than the other ones. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319617
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  • 4
    Electronic Resource
    Electronic Resource
    Grand canonical ensemble Monte Carlo simulation of a lipid bilayer using extension biased rotations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10770-10773 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The cavity-biased grand-canonical ensemble method was applied to the simulation of a lipid bilayer using an enhanced Monte Carlo sampling technique. The enhancements include controlling the torsion and molecular rotation step size based on the lipid's conformation and controlling the order of torsion change attempts. It was found that the proposed sampling technique significantly enhances the rate of sampling of the lipid conformations while the grand-canonical ensemble implementation ensures that the water can both penetrate and escape pockets in the bilayer. The latter will be particularly important for simulating bilayers with embedded molecules. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480442
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  • 5
    Electronic Resource
    Electronic Resource
    Voronoi polyhedra analysis of the local structure of water from ambient to supercritical conditions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5975-5985 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The changes of the local structure of water are investigated with increasing temperature and decreasing density from ambient conditions up to the critical point. The local structure around the molecules is analyzed in terms of the properties of the Voronoi polyhedra (VP) of the molecules. For reference, the entire analysis is also performed in liquid H2S. In this way, the effect of the hydrogen bonding on the local structure can also be studied. In determining the VP of the molecules an exact algorithm is used. In analyzing the local structure it is found that the decrease of the density not only leads to the increase of the free volume available for the molecules, but it also increases the volume of the voids present in the system. A linear relation is found between the average free volume of the molecules and the average volume of the vacancies, the latter being always about the double of the former. The comparison of the results concerning the shape of the VP of the molecules obtained for water at different thermodynamic state points and for liquid H2S clearly reveals that even above the critical point, hydrogen bonds are still playing a very important role in forming the molecular level structure of water. It is also found that the tetrahedral arrangement of the nearest-neighbor molecules, which is a characteristic feature of the water structure under ambient conditions, already disappears at temperatures well below the critical point, and the relative arrangement of the first four nearest-neighbor molecules becomes rather similar to that in liquid H2S. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479893
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  • 6
    Electronic Resource
    Electronic Resource
    Structural study of liquid methylene chloride with reverse Monte Carlo simulation (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 562-570 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reverse Monte Carlo simulation of liquid methylene chloride has been performed using five independent experimental datasets. The structure of the liquid has been analyzed in detail. Predictions for various total and partial structure factors of liquid methylene chloride has been made on the basis of the simulated configurations. Partial pair correlation functions, orientational correlations, and spatial distributions of the nearest neighbors have been analyzed. It is found that the nearest neighbors can be localized in three different positions around the central molecule. Preferences for both parallel and antiparallel orientations were found among these neighbors. The range of the orientational correlations between the molecules was found to be rather large, extending even to the second coordination shell of the molecules. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474416
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  • 7
    Electronic Resource
    Electronic Resource
    Computer simulation study of liquid CH2F2 with a new effective pair potential model (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2991-3002 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new effective pair potential model is proposed for computer simulations of liquid methylene fluoride and used in Monte Carlo simulations on the isothermal-isobaric ensemble at two different temperatures. The new model is able to reproduce the thermodynamic (internal energy, density, heat capacity, vapor-liquid equilibrium) and structural (neutron diffraction data) properties of liquid methylene fluoride with good accuracy. The structure of liquid methylene fluoride is analyzed in detail on the basis of the present simulation at 153 K. It is found that, unlike in liquid water, the preferential location of the nearest neighbors is in the direction of the face centers of the tetrahedron of the central molecule. However, the four nearest neighbors do not surround the central molecule in a highly tetrahedral arrangement: the obtained distribution of the tetrahedral angular order parameter is rather similar to that in liquid argon. Preferential head-to-tail type orientation is found for nearest neighbors, accompanied by a slight preference for antiparallel dipole–dipole arrangement. The orientational correlation of the molecules is found to be rather long ranged, extending over the first coordination shell. The observed preferential nearest neighbor arrangement is resulted from the competition of steric and electrostatic interactions. No evidence for C–H⋅⋅⋅⋅F type hydrogen bonding is found in liquid methylene fluoride. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477894
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  • 8
    Electronic Resource
    Electronic Resource
    Comparison of different water models from ambient to supercritical conditions: A Monte Carlo simulation and molecular Ornstein–Zernike study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8019-8031 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Structural, thermodynamic, and dielectric properties of three polarizable and two nonpolarizable water models are compared with experimental data at four different thermodynamic states from ambient to supercritical conditions. Pair-correlation functions and thermodynamic data are obtained from Monte Carlo simulations, performed both on the (N,V,T) and (N,p,T) ensembles. The dielectric constants are determined with the molecular Ornstein–Zernike theory. It is found that the polarizable models can reproduce the experimental structure considerably better than the nonpolarizable ones at the high-temperature states. In particular, the elongation of the hydrogen bonds with increasing temperature, which is observed by neutron diffraction measurements, in only seen in the simulations with the polarizable potential models. On the other hand, the polarizable models fail to describe the correct temperature dependence of the thermodynamic properties. Although at ambient conditions they overestimate both the density and the dielectric constant of the system, around the critical temperature they result in 10%–50% lower densities than the experimental values. The obtained magnitude of the internal energies as well as the dielectric constants are also considerably smaller than their experimental values at these thermodynamic state points. The results of this study point out the need of new polarizable water models which, besides the reasonable reproduction of the experimental pair-correlation functions, are also able to describe the dependence of the thermodynamic properties on the temperature and pressure. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478704
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  • 9
    Electronic Resource
    Electronic Resource
    Erratum: Reverse Monte Carlo analysis of neutron diffraction results: Water around its critical point [J. Chem. Phys. 105, 2391 (1996)] (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2988-2988 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473978
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  • 10
    Electronic Resource
    Electronic Resource
    Computer simulations of liquid HF by a newly developed polarizable potential model (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10166-10176 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new polarizable potential model of liquid HF is developed. The model is tested by comparing simulated thermodynamic and structural properties of liquid HF with experimental and ab initio molecular dynamics results. Properties of the isolated HF dimer obtained with this model are also compared with both ab initio and experimental data. It turns out that this model can describe the thermodynamic properties of liquid HF with a good accuracy in the entire temperature range of the liquid state at atmospheric pressure, and also give the energy and geometry of the isolated HF dimer in a good agreement with experimental and ab initio results. The obtained pair correlation functions of liquid HF agree also reasonably well with experimental and ab initio molecular dynamics findings, although the position of the peaks describing hydrogen bonding appears to be at 0.1–0.3 Å higher distances. Such a deviation is opposite to what has been observed with our previous nonpolarizable model, which resulted in peak positions generally at lower r values than the experimental and ab initio molecular dynamics data. This fact indicates that in spite of the still existing small deviations, the inclusion of the polarizability improves the potential model also from a structural point of view. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474152
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