Harmonic spring approximation

The Harmonic spring (also known as the Hookean spring) approximation assumes that the spring obeys 'Hookes Law, i.e.

${\mathbf {F} }=-k{\mathbf {x} }$

where F is the force, x is the extension of the spring, and k is the spring constant.

This approximation is often used for chemical-bond stretching terms in various force fields:

Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle \Phi _{str}(r_{12})={\frac {1}{2}}K_{str}(r_{12}-b_{0})^{2}}