ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Mobility and solvation of ions in channels (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9266-9280 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present some results from a simulation study of the mobility and solvation of ions and uncharged molecules in aqueous solution in smooth cylindrical channels at room temperature. This ideal system provides a reference system with which to compare the behavior of water and ions in real porous materials such as zeolites, bucky tubes, and biological channels. We find that in channels of radii between 2.5 and 5.5 A(ring) the water molecules form a cylindrical solvation shell inside the channel walls with some evidence of a second shell in the center of the largest channel. Not all protons are involved in hydrogen bonding and a number point toward the walls. We attribute this to the concavity of the surface. When a sodium ion is added it tends to lie in the center of the channel where it can form the most complete solvation shell. Its diffusion rate decreases in smaller channels until it moves too slowly in a channel of 2 A(ring) radius to be detected in our simulations. This decrease is only partly due to an increase in the mean square force on the ion. A range of ions of different sizes were studied in a channel with radius 3 A(ring). While the smaller of these ions (F−, Na+, and Ca++) lie preferentially in the center of the channel, larger ions (Cl−, I−, and Cs+) penetrate some way into the layer of water inside the wall and methane and ions with the charges turned off move next to the wall. Landau free energy analysis shows that this change is due to the balance between entropy and energy. The behavior in smooth channels is quite the opposite of what has been observed in experimental studies and simulations of Gramicidin (pore radius of 2 A(ring)), where Cs+ lies closer to the center of the channel and Na+ lies off the axis. This difference can be attributed to the specific molecular structure of the gramicidin pores (e.g., the presence of carbonyl groups). As in bulk solutions, the mobilities of the ions in smooth channels increase to a maximum with ion size and decrease with increasing magnitude of the charge on the ion, while uncharged species diffuse much more rapidly and show a monotonic decrease with size. This behavior is related to the characteristics of the fluctuations of the forces on the solute molecules. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472757
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of ionic mobility. I. Alkali metal cations in water at 25 °C (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6964-6974 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe a series of molecular dynamics simulations performed on model cation-water systems at 25 °C representing the behavior of Li+, Na+, K+, Rb+, and Cs+ in an electric field of 1.0 V/nm and in its absence. The TIP4P model was used for water and TIPS potentials were adapted for the ion-water interactions. The structure of the surrounding water molecules around the cations was found to be independent of the applied electric field. Some of the dynamic properties, such as the velocity and force autocorrelation functions of the cations, are also field independent. However, the mean-square displacements of the cations, their average drift velocities, and the distances traveled by them are field dependent. The mobilities of the cations calculated directly from the drift velocity or the distance traveled by the ion are in good agreement with each other and they are in satisfactory agreement with the mobilities determined from the mean-square displacement and the velocity autocorrelation function in the absence of the field. They also show the same trends with ionic radii that are observed experimentally; the magnitudes are, however, smaller than the experimental values in real water by almost a factor of 2. It is found that the water molecules in the first solvation shell around the small Li+ ion are stuck to the ion and move with it as an entity for about 190 ps, while the water molecules around the Na+ ion remain for 35 ps, and those around the large cations stay for 8–11 ps before significant exchange with the surroundings occurs. The picture emerging from this analysis is that of a solvated cation whose mobility is determined by its size as well as the static and dynamic properties of its solvation sheath and the surrounding water. The classical solventberg model describes the mobility of Li+ ions in water adequately but not those of the other ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468323
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Erratum: Chemical ion association and dipolar dumbbells in the mean spherical approximation [J. Chem. Phys. 86, 983 (1987)] (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2093-2093 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454764
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Erratum: The equilibrium properties of charged hard spheres with adhesive interactions between opposite charged ions [J. Chem. Phys. 83, 6396 (1987)] (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2093-2094 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454765
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Molecular dynamics study of a dipolar fluid between charged plates. II (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2383-2393 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Further molecular dynamics simulations of thin films of Stockmayer molecules between Lennard-Jones plates are discussed when the distance h between the plates ranges from 2.25 σ to 9.5 σ, where σ is the molecular diameter, and the electric field E ranges between 0 and 1010 V/m. The solvation force is calculated as a function of the plate separation h when E=0 and E=109 V/m and as a function of the field E when h=4.0 σ and 7.5 σ. We also study the system when h=2.25 σ and 4.0 σ with the field E ranging from 0 to 1010 V/m and find that the monolayer system (h=2.25 σ) seems to undergo changes of state as the temperature is lowered at zero field or if the field is changed at low temperature. While, in the absence of a field, the molecules tend to form loops and chain-like structures with the dipoles parallel to the wall, a strong external field orients the dipoles along the field so that the long-range repulsive interaction appears to induce a transition to an imperfect (two-dimensional) triangular lattice at low temperature. In between these states, at low temperatures and high fields, the molecules are packed in parallel chains with their moments perpendicular to the field and in "ferroelectric domains'' of opposite polarization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452086
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Chemical ion association and dipolar dumbbells in the mean spherical approximation (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 983-994 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The sticky electrolyte model (SEM) is solved analytically in the mean spherical approximation (MSA) for binding between oppositely charged ions of a symmetrical electrolyte at a distance L=σ/4 and σ/5, where σ is the atomic diameter, extending earlier analytic studies for L=σ, σ/2, and σ/3. The excess energy of a fluid of dipolar dumbbells of elongation L〈σ/2 is calculated in this approximation by considering the saturation limit when all the ions are associated to form dimers and steric hindrance prevents polymerization. The results are in good agreement with Monte Carlo simulations for dipolar dumbbells and compare favorably with the solutions to the MSA and the HNC approximation using the site–site Ornstein–Zernike equation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452246
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Molecular dynamics study of a dipolar fluid between charged plates (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5232-5237 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recent experiments and computer simulations of thin films have observed the segregation of nonpolar molecules into layers or sheets parallel to the confining walls. We discuss a molecular dynamics study of a thin film of Stockmayer molecules between Lennard-Jones plates and find that, in the absence of an electric field, the dipoles are mainly oriented parallel to the plates in each layer. The component of the dipole autocorrelation function in this plane decays to zero more slowly than the component perpendicular to the walls. The polarization density profile, with an electric field perpendicular to the plates, is also studied, and is found to oscillate from layer to layer, with a magnitude that is in excess of what is predicted by the Debye theory of dielectric saturation by a factor nearly equal to the ratio of the local density to the average bulk density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451663
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Ion association and dipolar dumbbells: Solutions of the HNC and HNC/MS approximations at L=σ/2 and σ/3 for the sticky electrolyte model (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 5870-5881 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We extend an earlier analytic study of a sticky electrolyte model (SEM) to the case L=σ/3, where L is the distance at which positive and negative ions bind to each other, using the hypernetted chain (HNC) approximation within the spherical core and the mean spherical approximation (MSA) outside. We also present numerical solutions to the HNC approximation alone for σ/3 ≤L≤σ/2. The average number of bonded pairs is found to be essentially the same for the two approximations but the ion–ion correlation functions are very different except at high concentrations when the shielding is large. Small amounts of tetramers are also observed in the HNC correlation functions for σ/3〈L≤σ/2, and trimers are found when L=σ/2. An expression for the excess free energy of the SEM electrolyte is derived by turning on the stickiness between oppositely charged ions. The excess energy of the system of dipolar dumbbells with charges at a distance L=σ/3 is obtained in the MSA and the atom–atom correlation functions are compared with the HNC approximation and with recent Monte Carlo simulations. The asymptotic form of the direct correlation functions defined through the Ornstein–Zernike equation is given for dipolar dumbbells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449617
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    The equilibrium properties of charged hard spheres with adhesive interactions between oppositely charged ions (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6396-6404 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equilibrium properties of charged hard spheres with adhesive interactions between oppositely charged ions are studied in the hypernetted chain/mean spherical (HNC/MS) approximation and in the Percus–Yevick/Mean spherical (PY/MS) approximation which are solved analytically. Numerical solutions to the hypernetted chain (HNC) approximation for this model are also compared with the HNC/MS approximation for a model 2–2 electrolyte in the preparative concentration range. The effect of adhesion on the low density phase transition of the primitive model electrolyte is found to be slight in contrast to the effect of charge on the phase separations at high densities of a two component mixture of hard spheres in which there is adhesion only between molecules of different species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449538
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    A model for association in electrolytes. Analytic solution of the hypernetted-chain/mean spherical approximation (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 317-325 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the structural and thermodynamic properties of electrolytes in which the association between oppositely charged ions (A++B−(arrow-right-and-left)AB) is represented by a sticky electrolyte model (SEM) which allows positive and negative ions of diameter σ to be bonded at a distance L≤σ/2. The model is solved for a 2–2 electrolyte at concentrations up to 2 M and for L=σ/2 using the hypernetted-chain (HNC) approximation for the correlation functions within the spherical core and the mean spherical (MS) approximation outside. The number of AB dimers at a separation L is found to increase with concentration while there is a reduction in the number of contact ion pairs below that predicted by the restricted primitive model (RPM) from which stickiness is absent. The structural and thermodynamic properties of the SEM and RPM prove to be significantly different and sufficiently interesting to justify future applications of the SEM to molten salts and molecular solvents, especially if the ion–ion interactions can be treated with greater accuracy. The equilibrium properties of the fully associated system of extended dipoles with charges separated at a distance L=σ/2 are also given in the mean spherical approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449772
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...