Impurity effects on the electronic structure of square quantum dots : A full configuration-interaction study

We perform a full configuration-interaction study on a square quantum dot containing several electrons in the presence of an attractive impurity. The magnetic ordering in the dot is analyzed using appropriate pair-correlation functions. We find that a change in the size of the quantum dot can change the nature of the impurity from nonmagnetic to magnetic. In the low-density regime, the impurity traps one electron and the magnetic moment on the localized peaks outside the impurity fluctuates from negative to positive going through zero as a function of number of electrons. We also observe that the impurity changes the charge densities of excited states of two-electron quantum dot significantly, which in the absence of the impurity are almost similar. Our study also shows that in the strongly correlated regime the configuration-interaction approach yields ~20% more localization than density-functional theory. It has also been observed that only a small fraction of the total number of Slater determinants are required to produce ~99% of the converged charge density.