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| {{Stub-general}}
| | In the '''united-atom model''' the <math>CH_2</math> and <math>CH_3</math> units |
| In the '''united-atom model''' the <math>CH_2</math>, <math>CH_3</math> and <math>CH_4</math> units | | are treated as one point, i.e. the hydrogen atoms are incorporated within |
| are treated as one unified interaction site (hence ''united-atom''), i.e. the hydrogen atoms are incorporated within | | the carbon atoms and are not expressed explicitly. |
| the carbon atoms and are not expressed explicitly. Many [[force fields]] | |
| make use of this approximation in order to reduce the computational
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| overheads. For example, ''n''-hexane consists of 6 carbon atoms and
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| 14 hydrogen atoms. A fully-atomistic model of ''n''-hexane would
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| require 20 interaction sites. Using the united-atom approximation, this reduces to
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| two <math>CH_3</math> sites and four <math>CH_2</math> sites, a significant reduction. The interaction sites are usually parametrised [[Lennard-Jones model | Lennard-Jones potentials]].
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| ==Justification==
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| ==Parameters==
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| ==References== | | ==References== |
| <references/>
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| ;Related reading
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| *[http://dx.doi.org/10.1080/00268978800101181 Rolf Lustig and William A. Steele "On the thermodynamics of liquid propane", Molecular Physics '''65''' pp. 475-486 (1988)]
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| *[http://dx.doi.org/10.1063/1.454894 Sumnesh Gupta, Jia-an Yang and Neil R. Kestner "Computer modeling of liquid propane using three-site potential models", Journal of Chemical Physics '''89''' pp. 3733-3741 (1988)]
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| *[http://dx.doi.org/10.1063/1.456853 Søren Toxvaerd "Molecular dynamics calculation of the equation of state of liquid propane", Journal of Chemical Physics '''91''' pp. 3716-3720 (1989)]
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| *[http://dx.doi.org/10.1063/1.458709 Søren Toxvaerd "Molecular dynamics calculation of the equation of state of alkanes", Journal of Chemical Physics '''93''' pp. 4290-4295 (1990)]
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| *[http://dx.doi.org/10.1063/1.4983406 Richard A. Messerly, Thomas A. Knotts IV, and W. Vincent Wilding "Uncertainty quantification and propagation of errors of the Lennard-Jones 12-6 parameters for n-alkanes", Journal of Chemical Physics '''146''' 194110 (2017)]
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| [[Category: Models]] | | [[Category: Models]] |