National Institute of Standards and Technology

Computational Chemistry Comparison and Benchmark DataBase
Release 22	May 2022
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.

III.A.1.c.

Bond lengths, angles, or dihedrals given molecule at different levels of theory

The next several pages ask for
first - a molceule
second - a bond length, angle or dihedral, by choosing 2, 3 or 4 atoms in the molecule

Select species

Enter formula

The atom numbering does not line up between different methods for some species in the CCCBDB. This can lead to some erroneous geometry comparisons. We are working on correcting this.

Some experimental bond lengths are r_e values (bottom of well) and some are r₀ (vibrational zero point level). The calculations yield r_e values. For diatomics the experimental values are mostly r_e. For polyatomics usually r₀ is obtained from rotational spectra.

For polyatomics usually only a partial description of the geometry can be derived from the rotational constants, so assumptions are made in determining the geometry, such as all CH bonds in a methyl group have the same length.

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.