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Computational study of structural and dynamical properties of formamide-water mixtures
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10.1063/1.2364896
/content/aip/journal/jcp/125/18/10.1063/1.2364896
http://aip.metastore.ingenta.com/content/aip/journal/jcp/125/18/10.1063/1.2364896

Figures

Image of FIG. 1.
FIG. 1.

Formamide-formamide site-site radial distributions for and atom pairs pertaining to distinct molecules.

Image of FIG. 2.
FIG. 2.

Water-water site-site radial distributions for O–O, O–H, and H–H atom pairs. Note different scales on axes.

Image of FIG. 3.
FIG. 3.

Formamide-water site-site radial distributions for , , and site pairs.

Image of FIG. 4.
FIG. 4.

(a) Local mole fractions of FA (, solid lines) and water (, dot-dashed lines) as a function of , for the mixtures studied. The thickest and thinnest lines correspond to and , respectively; the intermediate lines correspond to intermediate compositions. The horizontal dashed lines at , 0.4, 0.6, and 0.8 are plotted for comparison. (b) Parameter obtained for the compositions studied.

Image of FIG. 5.
FIG. 5.

Pair energy probability distributions, considering only the four nearest neighbors of a given molecule, for (a) FA-FA pairs, (b) W-W pairs, (c) FA surrounded by closest W neighbors, and (d) W surrounded by closest four FA molecules.

Image of FIG. 6.
FIG. 6.

Distribution of the tetrahedral order parameter, , for (a) FA-FA pairs, (b) W-W pairs, (c) FA with respect to the closest four W neighbors, and (d) W with respect to its closest FA molecules. The inset in panel (b) shows computed for the water molecules that have all four nearest neighbors inside the first coordination shell, that is, . The area under each curve is normalized to unity.

Image of FIG. 7.
FIG. 7.

Distribution of tetrahedral order parameter, : comparison between SPC/E and TIP4P/2005 potential models for water, for (a) W-W pairs and (b) FA-W pairs. The curves corresponding to FA mole fractions , 0.4, 0.2, and 0.0 have been offset vertically by , , , and , respectively.

Image of FIG. 8.
FIG. 8.

Top scheme: H-bond definition (see text). (a) represents the fraction of FA molecules participating in H bonds with FA, (b) the fraction of water molecules forming H bonds with water, (c) the fraction of FA molecules forming H bonds with water, and (d) the fraction of water molecules participating in H bonds with FA. The different symbols correspond to different FA mole fractions, as indicated.

Image of FIG. 9.
FIG. 9.

Average number of H bonds between W-W (black squares) and W-FA (gray squares) per water molecule; and between FA-FA (black circles) and FA-W (gray circles) per FA molecule, as a function of FA mole fraction, . The curves with white symbols correspond to the total average number of H bonds per water (squares) and FA molecules (circles).

Image of FIG. 10.
FIG. 10.

Self-diffusion coefficients for FA (circles) and water (squares) as a function of FA mole fraction. The white circles are experimental data taken from Ref. 52. Black and gray symbols correspond to SPC/E and TIP4P/2005 potential models for water.

Image of FIG. 11.
FIG. 11.

TCF of the total angular velocity, , for (a) water and (b) formamide molecules, for the studied mixtures.

Image of FIG. 12.
FIG. 12.

(a) Short-time behavior of the water single dipole TCF, . The inset shows the decay of , corresponding to FA molecules, on a longer time scale. Panel (b) shows the water librational spectra, , for the compositions studied.

Image of FIG. 13.
FIG. 13.

Single-molecule orientational relaxation times for FA (dipole vector, left panel) and water (HH vector, right panel) as functions of composition, for SPC/E and TIP4P/2005 potential models. Experimental estimates for FA and water according to NMR measurements are taken from Ref. 58 and drawn with white symbols. The lines are just guides to the eye.

Image of FIG. 14.
FIG. 14.

Logarithm of H-bond lifetime autocorrelation functions, (a) and (b), for hydrogen bonds between FA-FA, W-W, and unlike FA-W molecules. The curves for W-W and FA-W have been shifted vertically by and for clarity. The different line types correspond to different FA mole fractions, as indicated. Note the different time scales in panels (a) and (b).

Tables

Generic image for table
Table I.

Intermolecular potential parameters and molecular geometry. Lennard-Jones parameters and are equal to zero for the three reported force fields.

Generic image for table
Table II.

Total and partial number densities for the solutions studied, box length employed in each MD trajectory average temperature and excess internal energies of mixing obtained from simulations, along with experimental excess enthalpies. Energies are given in kJ/mol.

Generic image for table
Table III.

Mean lifetimes obtained for H bonds between species of the same and different kinds in FA-water mixtures, computed from the TCF of the occupation numbers, .

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/content/aip/journal/jcp/125/18/10.1063/1.2364896
2006-11-13
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Computational study of structural and dynamical properties of formamide-water mixtures
http://aip.metastore.ingenta.com/content/aip/journal/jcp/125/18/10.1063/1.2364896
10.1063/1.2364896
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