National Institute of Standards and Technology

Computational Chemistry Comparison and Benchmark DataBase
Release
NIST Standard Reference Database 101

I	Introduction
II	Experimental data
III	Calculated data
IV	Data comparisons
V	Cost comparisons
VI	Input and output files
VII	Tutorials and Units
VIII	Links to other sites
IX	Feedback
X	Older CCCBDB versions
XII	Geometries
XIII	Vibrations
XIV	Reaction data
XV	Entropy data
XVI	Bibliographic data
XVII	Ion data
XVIII	Bad calculations
XIX	Index of properties
XX	H-bond dimers
XXI	Oddities

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© 2013 copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved.

The National Institute of Standards and Technology (NIST) is an agency of the U.S. Department of Commerce.

Please send questions, comments, corrections, additions and suggestions to cccbdb@nist.gov.

IV.E.3.

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

• 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.

A list of species that match the formula criteria is returned and one or more may be selected.

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.