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

---

NIST policy on privacy, security, and accessibility.

---

© 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 [email protected].

III.F.4. (XVIII.D.1.)

Negative orbital occupation numbers

A negative orbital occupation number indicates that the electronic ground state may not be well represented by a single electronic configuration.

Results for HN₃ (hydrogen azide)

The following table lists the minimum orbital occupation numbers

---

Methods with standard basis sets

		3-21G	6-31G*	cc-pVTZ
		3-21G	6-31G*	cc-pVTZ
Moller Plesset perturbation	MP2	-0.00192	-0.00022	-0.00029
	MP2=FULL		-0.00021
Coupled Cluster	CCD		0.00008
		3-21G	6-31G*	cc-pVTZ

The following table lists the T1 diagnostic

---

Methods with standard basis sets

		6-31G*
Coupled Cluster	CCSD	0.02072
		6-31G*