View source for Interaction energy

{{Short description|Contribution to the total energy caused by interactions between entities present in the system}}
{{More citations needed|date=February 2022}}
In [[physics]], '''interaction energy''' is the contribution to the total [[energy]] that is caused by an [[Fundamental interaction|interaction]] between the objects being considered.

The interaction energy usually depends on the relative position of the objects. For example, <math>Q_1 Q_2 / (4 \pi \varepsilon_0 \Delta r)</math> is the [[electrostatics|electrostatic]] interaction energy between two objects with charges <math>Q_1</math>, <math>Q_2</math>.

==Interaction energy==
A straightforward approach for evaluating the interaction energy is to calculate the difference between the objects' combined energy and all of their isolated energies. In the case of two objects, ''A'' and ''B'', the interaction energy can be written as:
<ref>Theoretical and Computational Chemistry, 1999, Ideas of Quantum Chemistry, 2007 and Quantum Magnetic Resonance Imaging Diagnostics of Human Brain Disorders, 2010</ref>
<math display="block">\Delta E_\text{int} = E(A,B) - \left( E(A) + E(B) \right),</math>
where <math>E(A)</math> and <math>E(B)</math> are the energies of the isolated objects (monomers), and <math>E(A,B)</math> the energy of their interacting assembly (dimer).

For larger system, consisting of ''N'' objects, this procedure can be generalized to provide a total many-body interaction energy:

<math display="block">\Delta E_\text{int} = E(A_{1}, A_{2}, \dots, A_{N}) - \sum_{i=1}^{N} E(A_{i}).</math>

By calculating the energies for monomers, dimers, trimers, etc., in an N-object system, a complete set of two-, three-, and up to N-body interaction energies can be derived.

The supermolecular approach has an important disadvantage in that the final interaction energy is usually much smaller than the total energies from which it is calculated, and therefore contains a much larger relative uncertainty. In the case where energies are derived from quantum chemical calculations using finite atom-centered basis functions, [[basis set superposition error]]s can also contribute some degree of artificial stabilization.

==See also==
* [[Energy]]
* [[Force]]
* [[Fundamental interaction|Interaction]]
* [[Ideal solution]]
* [[Perturbation theory (quantum mechanics)]]
* [[Potential]]

== References ==
<references/>

{{DEFAULTSORT:Interaction Energy}}
[[Category:Statistical mechanics]]
[[Category:Energy (physics)]]


{{statisticalmechanics-stub}}
{{energy-stub}}