||Computational Chemistry Comparison and Benchmark DataBase
Release 22 (May 2022) Standard Reference Database 101
National Institute of Standards and Technology
You are here: Comparisons > Ion > Compare Ionzation energy > Koopman IE for a few molecules
Koopmans' Theorem Comparison of Ionization Energy for a set of species
Select a species by entering a chemical formula.
or choose by chemical groups.
Rules for chemical formula
- Enter a sequence of element symbols followed by numbers
to specify the amounts of desired elements (e.g., C6H6).
- Elements may be in any order.
- If only one of a given atom is desired, you may omit
the number after the element symbol.
- Parentheses may be used to group atoms.
- Multiple specifications for an atom will be added.
This means that CH3(CH2)4CH3 will be
treated the same as C6H14.
- A comma delimited list of several species may be entered.
- Ions are indicated by placing + or - at the end of the formula (CH3+, BF4-, CO3--)
Species in the CCCBDB
A list of species that match the formula criteria is returned and one or more may be selected.
- Mostly atoms with atomic number less than than 36 (Krypton), except for most of the transition metals.
See section I.B.1 for a periodic table view.
- Six or fewer heavy atoms and twenty or fewer total atoms.
Versions 8 and higher have a few substituted benzenes with more than six heavy atoms.
Versions 12 and higher have bromine-containing molecules.
Going to the group selection page allows the selection of molecules with certain chemical groups,
such as C=O bonds or NH2 groups.
A list of species that match the group criteria is returned and one or more may be selected.
Caution! Choosing a long list may take a long time to to load.
For example: 150 species takes about a minute.