Question

Explain features in the Schrodingger equation that led to the "electron correlation problem." Explain the approximations that led to the introduction of effective nuclear charge(Zeff) and define effective nuclear charge. Explain its role and physical significance of the screening/shielding constant.

Answer 1

Electronic correlation is the interaction between electrons in the electronic structure of a quantum system. In all electronic systems , the principal difficulty is the treatment of the correlation between the motions of the many electrons, arising from their mutual repulsion. In Schrodinger equation, which describes how the quantum state of a quantum system changes with time, there is no term for the repulsonic energy that arises from two electron's repulsion. Hence, there is a huge error in the energy calculation of the system.

There were a few approximations used for calculate of effective nuclear charge (Z_eff). First approximation, electrons in larger shells do not affect Z_eff. Effective nuclear charge is defined as the net positive charge experienced by an electron in a multi-electron atom. The term "effective" is used because the shielding effect of negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge by the repelling effect of inner-layer electrons.