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, , where
is the sub-shell (standard order: 1s,
2s, 2p, 3s, ...) and
is the occupation number.
Note that the shorthand notation of omitting
when unity is not used, e.g.
2s1 not 2s.
Configuration strings obey the rules:
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 40 000 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, , take the principal
quantum number,
, and the orbital angular momentum,
of the first
open sub-shell and apply the following expression:
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