Abstract: Approximation of independent electrons and single electrons play a fundamental role in

the formation of solid electronic theory，and the movement of single electrons in the periodic

potential field develops into energy band theory.One of the important achievements of

energy band theory is the successful prediction of the electrical conductivity of

crystals.However，its interpretation of the properties of transition metal oxides has been

encountered inconsistent results.Mott first pointed out the fundamental reason for this from a

physical point of view: the energy band theory based on the single-electron approximation

and ignores the correlation between electrons. This article aims to introduce the basic ideas

of the single-electron approximation and its achievements and shortcomings，then discusses the

importance of electronic correlation in the current frontier field of condensed matter

physics，such as superconductivity and magic angle graphene.Let students understand that electronic

correlation effect is the link be- tween the basic knowledge of solid physics and the frontier

science.Therefore，the explanation of electronic correla- tion effect and its role in the field of

frontier physics should be emphasized in teaching.

Key words: electron correlations, Mott insulators, Hubbard model, frontier physics