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均匀电子气，表示某一微观体系的势能和相关参数（通常为原子坐标）之间的函数关系，是势能函数的图像。势能面用一个或更多的坐标去表示，当用一个坐标去表示时，势能面通常被称为“势能曲线”。

势能面概念被用在物理以及化学领域, 尤其是它们的理论研究分支。 势能面可以被用来从理论层面理解由原子组成的物质的性质, 例如：搜寻分子的最低能量构形或者计算化学反应速率。

势能面类似于对地形的描述：对于一个有两个自由度的体系（例如：一个键长、一个键角），体系的势能可以类比为地形的高度，两个自由度可以类比为描述某位置的坐标。通过这样的描述，体系势能随坐标的变化可以很直观地被表示出来。

水分子势能面: 势能最低点对应优化后的水分子结构， O-H 键长 0.0958nm， H-O-H尖角为 104.5°

A potential energy surface (PES) describes the energy of a system, especially a collection of atoms, in terms of certain parameters, normally the positions of the atoms. The surface might define the energy as a function of one or more coordinates; if there is only one coordinate, the surface is called a potential energy curve or energy profile. An example is the Morse/Long-range potential.

It is helpful to use the analogy of a landscape: for a system with two degrees of freedom (e.g. two bond lengths), the value of the energy (analogy: the height of the land) is a function of two bond lengths (analogy: the coordinates of the position on the ground).

The PES concept finds application in fields such as chemistry and physics, especially in the theoretical sub-branches of these subjects. It can be used to theoretically explore properties of structures composed of atoms, for example, finding the minimum energy shape of a molecule or computing the rates of a chemical reaction.