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Configuration strings

Configurations are stored in the database using an unambiguous notation which should be familiar to most users. A configuration consists of a space-delimited list of sub-shells in standard order each having the form, $nlm$, where $nl$ is the sub-shell (standard order: 1s, 2s, 2p, 3s, ...) and $m$ is the occupation number. Note that the shorthand notation of omitting $m$ when unity is not used, e.g. 2s1 not 2s. Configuration strings obey the rules:

Some examples:

Using a list of occupation numbers as the configuration label was considered and ultimately rejected due to the impracticality of storing Rydberg levels. Consider the configuration, 1s 200p; whereas only 13 characters are needed to store this configuration in the form described above, nearly 40000 characters are required if using a list of occupation numbers.

To get the number of electrons of a configuration takes two steps; first you need to calculate the number of electrons in the core and then add up the occupation numbers of the visible sub-shells. To get the number of electrons in the core, $n_{core}$, take the principal quantum number, $n$, and the orbital angular momentum, $l$ of the first open sub-shell and apply the following expression:

\begin{displaymath}
n_{core} = \frac{1}{3} n (n-1) (2n-1) + 2l^2 .
\end{displaymath} (E.1)

For a configuration of 4p5 5s2 5p1 we have $n=4$ and $l=1$. The above expression yields $n_{core} = 30$ and the total occupation of the visible sub-shells is 8 so this configuration has 38 electrons.


next up previous contents
Next: Term strings Up: Level Labels Previous: Level Labels   Contents
Tim Kallman 2014-09-12