Discussion
In this study we mainly concentrated on the calculation of the Self consistent field calculation for Cr atom where the expected configuration is different from the observed one. As is already explained in the text the observed ground term and the expected ones are7S and 5D respectively. The total energy values for these representations determine the relative position of the states of one configuration to those of another. It is obvious from the table 1 that all calculations suggest the 7S representation should lie lowest which represents a deviation from Madelung’s rule.
The interaction between the nd orbitals and the core-electron orbitals might be the reason for this exception, the shells are seems to be filled according to the hydrogenic rule rather than the first part of Madelung’s rule, when there are more than four ad-shell electrons the quantum number n might have the dominant role.
Cr atom’s electron configuration that is different than the Madelung’s rule might be not only due to the Hund rules, but also with rhe phenomena known as ‘spin correlation’. This effect should not be considered with itself, it should be taken into account with the Hund’s first rule which states that the lowest energy atomic state is the one that maximizes the total spin quantum number for the electrons in the open subshell.