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 I₂ (Iodine diatomic)

Experimental Ionization Energy is 9.3074 ± 0.0002 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

semi-empirical	AM1
	PM3

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Ionization Energies in eV

Methods with standard basis sets

		3-21G	3-21G*	6-311G*
hartree fock	HF	9.611	8.973	9.258
density functional	BLYP	9.187	8.975	9.218
	B1B95			9.543
	B3LYP	9.598	9.252	9.569
	B3PW91	9.715	9.333	9.601
	mPW1PW91	9.749	9.344	9.614
	M06-2X		9.575
	PBEPBE	9.377	9.063	9.358
	wB97X-D		9.357
	B97D3	9.333
		3-21G	3-21G*	6-311G*
Moller Plesset perturbation	MP2	9.104	9.156	9.401
	MP2=FULL	9.096	9.149	9.385
	MP3			9.394
	MP4	9.138		9.325
Configuration interaction	CID	9.256	9.144	9.407
	CISD	9.240	9.128	9.396
		3-21G	3-21G*	6-311G*
Quadratic configuration interaction	QCISD	9.209	9.156	9.401
	QCISD(T)			9.336
Coupled Cluster	CCD	9.230	9.183	9.430
	CCSD(T)			9.340
	CCSD(T)=FULL			9.325
		3-21G	3-21G*	6-311G*

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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	9.724		9.724		9.837	9.808	9.098		9.057
	ROHF							9.270		9.231
density functional	LSDA							9.915		9.884
	BLYP							9.108		9.095
	B1B95							9.367		9.336
	B3LYP	9.873		9.873		9.942	9.966	9.456		9.431
	B3LYPultrafine							9.456		9.431
	B3PW91							9.486		9.449
	mPW1PW91							9.493		9.461
	M06-2X							9.690		9.651
	PBEPBE							9.234		9.216
	PBEPBEultrafine									9.216
	PBE1PBE							9.459		9.429
	HSEh1PBE							9.445		9.413
	TPSSh							9.390		9.362
	wB97X-D							9.499		9.454
	B97D3							9.229		9.206
Moller Plesset perturbation	MP2	9.297		9.297		9.337	9.334	9.507		9.513
	MP2=FULL							9.500		9.511
	ROMP2							9.408		9.394
	MP3							9.521		9.472
	MP3=FULL							9.510		9.463
	MP4							9.480		9.463
	MP4=FULL							9.472		9.457
	B2PLYP							9.430		9.413
	B2PLYP=FULL							9.428		9.412
Configuration interaction	CID							9.452		9.378
	CISD							9.437		9.370
Quadratic configuration interaction	QCISD							9.520		9.492
	QCISD(T)							9.481		9.452
	QCISD(T)=FULL									9.446
Coupled Cluster	CCD							9.556		9.532
	CCSD							9.524		9.498
	CCSD=FULL									9.491
	CCSD(T)							9.484		9.456
	CCSD(T)=FULL							9.476		9.450

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.