Temperature dependence of interactions of an ion pair in water: A molecular dynamics study

Journal Article · Sat Aug 01 00:00:00 EDT 1992 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.463128· OSTI ID:7205867

Dang, L X ^[1]

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1. Molecular Theory, Modeling and Simulation, Molecular Science Research Center, Pacific Northwest Laboratory, P. O. Box 999, Richland, Washington 99352 (United States)

We present a comparative study of the potentials of mean force (PMF) and the related thermodynamic properties for Na{sup +}--Cl{sup {minus}} ion pair using a rigid simple point charge (SPC/E) water model at two different temperatures, 298 and 373 K. The PMFs were calculated using the thermodynamic perturbation theory and the long-range interactions were evaluated using an Ewald summation technique. The PMFs for both temperatures display two minima corresponding to the contact and solvent-separated ion pairs; however, they are different in details. At room temperature, the solvent separated region is favored over the contact region. On the other hand, the calculated PMF at higher temperature indicate that the contact ion pair is more favorable. These observations are in general agreement with a recent Raman study of salt solutions of the similar systems. We also carried out a calculation at room temperature using the spherical truncation technique. The calculated PMF using this technique is somewhat more repulsive compared to the calculated PMF using an Ewald summation technique. However, these PMFs have similar characteristics. When comparing the present calculations with those reported in previous works on the same systems, our calculated PMF at room temperature is identical to the results of simulations using a flexible water model. This result suggests that the more stable solvent-separated ion pair at room temperature may not be due to the inclusion of the internal motions of water molecules. It is probably due to the balancing of the intermolecular forces.

• DOE Contract Number: AC06-76RL01830
• OSTI ID: 7205867
• Journal Information: Journal of Chemical Physics; (United States), Vol. 97:3; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
CHLORINE IONS
THERMODYNAMIC PROPERTIES
ION PAIRS
SODIUM IONS
WATER
ANIONS
CATIONS
DYNAMICS
INTERMOLECULAR FORCES
MOLECULES
PERTURBATION THEORY
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0273-0400 K
CHARGED PARTICLES
HYDROGEN COMPOUNDS
IONS
MECHANICS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
TEMPERATURE RANGE
664100* - Theory of Electronic Structure of Atoms & Molecules- (1992-)