Kirkwood approximation in statistical mechanics

E200731

The Kirkwood approximation in statistical mechanics is a method for approximating many-particle correlation functions by expressing higher-order correlations in terms of lower-order ones, simplifying the description of interacting particle systems.

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Predicate Object
instanceOf approximation method in statistical mechanics
closure approximation
appliesTo classical fluids
equilibrium systems
interacting particle systems
assumption higher-order correlations are weakly dependent beyond pair level
many-body effects can be captured approximately by products of lower-order functions
category many-body approximation
statistical mechanical closure scheme
contrastWith Bogoliubov–Born–Green–Kirkwood–Yvon hierarchy
surface form: exact BBGKY hierarchy

full many-body correlation treatment
coreIdea approximate expression of three-body correlations via products of pair correlations
factorization of higher-order correlation functions
field liquid-state theory
many-body physics
statistical mechanics
goal to obtain tractable equations for pair correlations
historicalContext introduced in mid-20th century liquid-state theory
influenced later closure approximations in liquid-state theory
involves reduction of the hierarchy of correlation equations
limitation accuracy decreases for strongly correlated or highly dense systems
neglects genuine many-body correlations beyond products of pair terms
mathematicalNature nonlinear factorization ansatz for correlation functions
namedAfter John Gamble Kirkwood
surface form: John G. Kirkwood
purpose to approximate many-particle correlation functions
to express higher-order correlations in terms of lower-order ones
to simplify the description of interacting particle systems
relatedTo Bogoliubov–Born–Green–Kirkwood–Yvon hierarchy
surface form: BBGKY hierarchy

Ornstein–Zernike equation
closure relations in liquid-state theory
cluster expansion
pair distribution function
triplet distribution function
typicalApplication approximate computation of radial distribution functions
calculation of structural properties of liquids
typicalForm g^{(3)}(1,2,3) ≈ g^{(2)}(1,2) g^{(2)}(1,3) g^{(2)}(2,3)
usedIn approximate evaluation of thermodynamic properties
modeling of correlation effects in fluids
theory of dense gases
theory of simple liquids
usesConcept n-particle correlation function
pair correlation function
triplet correlation function

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James Kirkwood (multiple individuals) notableWork Kirkwood approximation in statistical mechanics
subject surface form: James Kirkwood (mathematician)