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Effects of van der Waals Interactions in the Adsorption of Isooctane and Ethanol on Fe(100) Surfaces.

Bedolla PO, Feldbauer G, Wolloch M, Eder SJ, Dörr N, Mohn P, Redinger J, Vernes A - J Phys Chem C Nanomater Interfaces (2014)

Bottom Line: van der Waals (vdW) forces play a fundamental role in the structure and behavior of diverse systems.Nevertheless, they do not influence the spatial configuration of the adsorbed molecules.Their effect on the electronic density is a nonisotropic, delocalized accumulation of charge between the molecule and the slab.

View Article: PubMed Central - PubMed

Affiliation: Institute of Applied Physics, Vienna University of Technology , Wiedner Hauptstraße 8-10/134, 1040 Vienna, Austria ; Austrian Center of Competence for Tribology (AC2T Research GmbH), Viktor-Kaplan-Straße 2, 2700 Wiener Neustadt, Austria.

ABSTRACT
van der Waals (vdW) forces play a fundamental role in the structure and behavior of diverse systems. Because of development of functionals that include nonlocal correlation, it is possible to study the effects of vdW interactions in systems of industrial and tribological interest. Here we simulated within the framework of density functional theory (DFT) the adsorption of isooctane (2,2,4-trimethylpentane) and ethanol on an Fe(100) surface, employing various exchange-correlation functionals to take vdW forces into account. In particular, this paper discusses the effect of vdW forces on the magnitude of adsorption energies, equilibrium geometries, and their role in the binding mechanism. According to our calculations, vdW interactions increase the adsorption energies and reduce the equilibrium distances. Nevertheless, they do not influence the spatial configuration of the adsorbed molecules. Their effect on the electronic density is a nonisotropic, delocalized accumulation of charge between the molecule and the slab. In conclusion, vdW forces are essential for the adsorption of isooctane and ethanol on a bcc Fe(100) surface.

No MeSH data available.


Equilibrium adsorptiongeometry of an isooctane molecule on a bccFe(100) surface. The top, bridge, and hollow positions are indicatedby a circle, triangle, and square, respectively.
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fig1: Equilibrium adsorptiongeometry of an isooctane molecule on a bccFe(100) surface. The top, bridge, and hollow positions are indicatedby a circle, triangle, and square, respectively.

Mentions: Neither theorientation nor the adsorption site of isooctane andethanol is influenced by the nonlocal correlation. Initially, thepreferred adsorption configurations were calculated within the GGAaproximation. After inclusion of nonlocal interactions in our calculationsvia the optB86b-vdW functional, a second relaxation did not significantlychange the geometry of this configuration. The largest variationsin bond lengths were of the order of 10–3 Å,and in angles, the variations were of the order of 10–3 degree. In the most energetically favorable orientation, the carbonatoms of the isooctane molecule are close to the top and hollow sitesof the iron slab (Figure 1). The energies ofseveral other orientations differ by only around 20 meV per supercell,and for this reason no orientation is particularly favored at roomtemperature, where thermal energy kBT = 25 meV. Similarly, in the adsorption of ethanol severalorientations of the molecule are possible. In this case, however,the hydroxyl group always orients itself toward the slab in all low-energyconfigurations (Figure 2). The plotted geometrydiffers from the one reported by Tereshchuk and Da Silva56 for ethanol adsorbed on the Fe(110) surfaceonly by the C–C bond, which is almost perpendicular to thesurface. Our calculated small energy difference of 3 meV between thesetwo configurations indicates that both can coexist at room temperatureand that the surface termination does not influence the orientationof the adsorbed molecule. The energy hierarchy of all PBE structuresdid not change when it was recalculated with optB86b-vdW to take nonlocalforces into account.


Effects of van der Waals Interactions in the Adsorption of Isooctane and Ethanol on Fe(100) Surfaces.

Bedolla PO, Feldbauer G, Wolloch M, Eder SJ, Dörr N, Mohn P, Redinger J, Vernes A - J Phys Chem C Nanomater Interfaces (2014)

Equilibrium adsorptiongeometry of an isooctane molecule on a bccFe(100) surface. The top, bridge, and hollow positions are indicatedby a circle, triangle, and square, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126734&req=5

fig1: Equilibrium adsorptiongeometry of an isooctane molecule on a bccFe(100) surface. The top, bridge, and hollow positions are indicatedby a circle, triangle, and square, respectively.
Mentions: Neither theorientation nor the adsorption site of isooctane andethanol is influenced by the nonlocal correlation. Initially, thepreferred adsorption configurations were calculated within the GGAaproximation. After inclusion of nonlocal interactions in our calculationsvia the optB86b-vdW functional, a second relaxation did not significantlychange the geometry of this configuration. The largest variationsin bond lengths were of the order of 10–3 Å,and in angles, the variations were of the order of 10–3 degree. In the most energetically favorable orientation, the carbonatoms of the isooctane molecule are close to the top and hollow sitesof the iron slab (Figure 1). The energies ofseveral other orientations differ by only around 20 meV per supercell,and for this reason no orientation is particularly favored at roomtemperature, where thermal energy kBT = 25 meV. Similarly, in the adsorption of ethanol severalorientations of the molecule are possible. In this case, however,the hydroxyl group always orients itself toward the slab in all low-energyconfigurations (Figure 2). The plotted geometrydiffers from the one reported by Tereshchuk and Da Silva56 for ethanol adsorbed on the Fe(110) surfaceonly by the C–C bond, which is almost perpendicular to thesurface. Our calculated small energy difference of 3 meV between thesetwo configurations indicates that both can coexist at room temperatureand that the surface termination does not influence the orientationof the adsorbed molecule. The energy hierarchy of all PBE structuresdid not change when it was recalculated with optB86b-vdW to take nonlocalforces into account.

Bottom Line: van der Waals (vdW) forces play a fundamental role in the structure and behavior of diverse systems.Nevertheless, they do not influence the spatial configuration of the adsorbed molecules.Their effect on the electronic density is a nonisotropic, delocalized accumulation of charge between the molecule and the slab.

View Article: PubMed Central - PubMed

Affiliation: Institute of Applied Physics, Vienna University of Technology , Wiedner Hauptstraße 8-10/134, 1040 Vienna, Austria ; Austrian Center of Competence for Tribology (AC2T Research GmbH), Viktor-Kaplan-Straße 2, 2700 Wiener Neustadt, Austria.

ABSTRACT
van der Waals (vdW) forces play a fundamental role in the structure and behavior of diverse systems. Because of development of functionals that include nonlocal correlation, it is possible to study the effects of vdW interactions in systems of industrial and tribological interest. Here we simulated within the framework of density functional theory (DFT) the adsorption of isooctane (2,2,4-trimethylpentane) and ethanol on an Fe(100) surface, employing various exchange-correlation functionals to take vdW forces into account. In particular, this paper discusses the effect of vdW forces on the magnitude of adsorption energies, equilibrium geometries, and their role in the binding mechanism. According to our calculations, vdW interactions increase the adsorption energies and reduce the equilibrium distances. Nevertheless, they do not influence the spatial configuration of the adsorbed molecules. Their effect on the electronic density is a nonisotropic, delocalized accumulation of charge between the molecule and the slab. In conclusion, vdW forces are essential for the adsorption of isooctane and ethanol on a bcc Fe(100) surface.

No MeSH data available.