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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XVII.C.1. (III.D.6.)

Calculated Ionization Energy for C₄ (Carbon tetramer)

Experimental Ionization Energy is 12.54 ± 0.35 eV
Please note! These calculated ionizataion energies have the vibrational zero-point energy (zpe) included, but the zpe has NOT been scaled. Click on an entry for more details, including the ionization energy with a scaled zpe.

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Ionization Energies in eV

Methods with predefined basis sets

composite	G2	10.804
	G3	10.908
	G3B3	10.898
	G4	336884.515
	CBS-Q	10.914

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Ionization Energies in eV

Methods with standard basis sets

		STO-3G	3-21G	3-21G*	6-31G	6-31G*	6-31G**	6-31+G**	6-311G*	6-311G**	6-31G(2df,p)	6-311+G(3df,2p)	TZVP	cc-pVDZ	cc-pVTZ	cc-pVQZ	aug-cc-pVDZ	aug-cc-pVTZ	aug-cc-pVQZ	daug-cc-pVTZ
hartree fock	HF	7.777	10.349	10.349	10.187	10.292	10.292	10.447	10.476	10.476	10.336		10.500	10.443	10.483	10.492	10.476	10.493	10.493	10.490
density functional	BLYP	8.748	10.802	10.802										10.831
	B1B95	9.008	11.054	11.054	10.893	10.944	10.944	11.126	11.138	11.138	10.986			11.089	11.150
	B3LYP	9.001	11.081	11.081	10.926	10.966	10.966	11.186	11.203	11.203	11.012		11.255	11.124	11.224	11.242		11.246	11.247
	B3LYPultrafine					10.966												11.246
	B3PW91	9.149	11.261	11.261	11.066	11.111	11.111	11.280	11.309	11.309	11.146			11.250	11.315
	mPW1PW91	9.133	11.259	11.259	11.064	11.114	11.114	11.288	11.303	11.303	11.147			11.250	11.315
	M06-2X			11.175		11.118						11.379
	PBEPBE	9.450	11.385	11.385	11.216	11.283	11.283	11.516	11.483	11.483	11.305			11.441	11.488
	PBE1PBE					11.093
	HSEh1PBE		11.220			11.083		11.262							11.297
	TPSSh					10.991		11.158			11.022				11.194
	wB97X-D			11.188		11.041		11.219		11.245			11.278	11.341	11.240			11.256
	B97D3		11.024												10.986
		STO-3G	3-21G	3-21G*	6-31G	6-31G*	6-31G**	6-31+G**	6-311G*	6-311G**	6-31G(2df,p)	6-311+G(3df,2p)	TZVP	cc-pVDZ	cc-pVTZ	cc-pVQZ	aug-cc-pVDZ	aug-cc-pVTZ	aug-cc-pVQZ	daug-cc-pVTZ
Moller Plesset perturbation	MP2	7.638	10.315	10.315		10.519	10.518	10.749	10.812	10.812	10.784			10.752	11.010			11.063
	MP2=FULL	7.637	10.319	10.319		10.533	10.533	10.764	10.824	10.824	10.809			10.758	11.048			11.105
	MP3					10.467
	MP3=FULL					10.482		10.697
	MP4		10.099			10.308				10.601					10.843
	B2PLYP					10.873									11.475
	B2PLYP=FULLultrafine					10.912								10.958	11.289			11.336
Configuration interaction	CID		10.222	10.222		10.426
	CISD		10.231	10.231		10.425			10.684
		STO-3G	3-21G	3-21G*	6-31G	6-31G*	6-31G**	6-31+G**	6-311G*	6-311G**	6-31G(2df,p)	6-311+G(3df,2p)	TZVP	cc-pVDZ	cc-pVTZ	cc-pVQZ	aug-cc-pVDZ	aug-cc-pVTZ	aug-cc-pVQZ	daug-cc-pVTZ
Quadratic configuration interaction	QCISD		10.047	10.047		10.311	10.311	10.524	10.597	10.597	10.613			10.531	10.818
Coupled Cluster	CCD		10.052	10.052		10.311	10.311	10.524	10.598	10.598	10.613			10.541	10.819			10.866
	CCSD					10.316
	CCSD(T)													10.492				10.858
	CCSD(T)=FULL					10.284
		STO-3G	3-21G	3-21G*	6-31G	6-31G*	6-31G**	6-31+G**	6-311G*	6-311G**	6-31G(2df,p)	6-311+G(3df,2p)	TZVP	cc-pVDZ	cc-pVTZ	cc-pVQZ	aug-cc-pVDZ	aug-cc-pVTZ	aug-cc-pVQZ	daug-cc-pVTZ

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Ionization Energies in eV

Methods with effective core potentials (select basis sets)

		CEP-31G	CEP-31G*	CEP-121G	CEP-121G*	LANL2DZ	SDD	cc-pVTZ-PP	aug-cc-pVTZ-PP	Def2TZVPP
hartree fock	HF	10.205	10.317	10.275	10.434	10.310	10.309			10.498
density functional	B3LYP	10.920	10.953	10.993	11.066	11.143	11.125			11.243
	PBEPBE									11.500
Moller Plesset perturbation	MP2		10.567		10.725	10.443	10.445			11.040

For descriptions of the methods (AM1, HF, MP2, ...) and basis sets (3-21G, 3-21G*, 6-31G, ...) see the glossary in section I.C. Predefined means the basis set used is determined by the method.