Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
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Calc. vs exp. Bad Vib. HF vs MP2 Bad scale factors Low excited states Oddities NaCN Is not linear FAQ Help Units Choose Units Energy Bond length Rotational Constant Moment of Inertia Dipole and Quadrupole Polarizability Explanations Hartree cm-1 Debye Credits Just show me Show me a calculated geometry Summary Using older interface Limit Basis sets Method options List Recent molecules Choose a few Molecules Number of atoms By heavy atoms Diatomics InChI Deuterated Dimers Geometry Point group Point group count Bonds types Isodesmic reactions Bad point group Multiple conformers, states Vibrations Big anharmonicity Energy Enthalpy at 0 Kelvin Similar molecules Similar Isomers Cis/trans Tautomers Multiple conformers, states Ions, Dipoles, etc. List Ions Ionization changes point group Dipole Quadrupole Polarizability Proton Affinities Index of CCCBDB Feedback Error form Wants
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

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

• 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. Exception: 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.