In statistical physics, the fluctuation dissipation theorem states that if a thermodynamic system responds linearly to an external perturbation, then the amount by which it responds is simply related to the fluctuation properties of the thermodynamic system. Statistical physics, one of the fundamental theories of physics, uses methods of statistics in solving physical problems. ...

Molecular scale models (microscopic models) can be used to quantitatively predict material properties in the context of linear response theory. A basic premise or theorem of statistical thermodynamics on which such predictions are based is the fluctuation dissipation theorem. It proposes that there is an explicit relationship between molecular dynamics at thermal equilibrium, and the macroscopic response that is observed in a dynamic measurement. This theorem is based on fields that are weak relative to the potential of molecular interaction so that rates of relaxation are not affected by the applied field. The essence of fluctuation-dissipation theorem is that it relates equilibrium fluctuations to out-of-equilibrium quantities, like noise power is related to resistance. "Out-of-equilibrium" in the above sentence should be understood as close to equilibrium or stationary states. Model may refer to more than one thing : For models in society, art, fashion, and cosmetics, see; role model model (person) supermodel figure drawing modeling section In science and technology, a model (abstract) is understood as an abstract or theoretical representation of a phenomenon,see; geologic modeling model (economics) model... Statistical mechanics is the application of statistics, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ... Molecular dynamics (MD) simulation numerically solves Newtons equations of motion on an atomistic or similar model of a molecular system to obtain information about its time-dependent properties. ... In thermodynamics, a thermodynamic system is in thermodynamic equilibrium if its energy distribution equals a Maxwell-Boltzmann-distribution. ... Macroscopic means measurable and observable by the naked eye; describes existence as we perceive it. ...