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
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IX	Feedback
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XII	Geometries
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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 CH₄ (Methane)

Experimental Ionization Energy is 12.61 ± 0.01 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	12.469
	G3	12.442
	G3B3	12.378
	G4	12.392
	CBS-Q	12.465

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Ionization Energies in eV

Methods with standard basis sets

		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	11.953	11.953	11.892	11.777	11.589	11.589	11.696	11.517	11.513		11.525	11.474	11.485	11.486	11.450	11.481	11.484	11.481
density functional	M06-2X										12.547
	TPSSh				12.495		12.429			12.333				12.370
	B97D3																		12.350
		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	12.437	12.437	12.397	12.399	12.386	12.408	12.422	12.416	12.442		12.409	12.331	12.545	12.601	12.394	12.566	12.610
	MP2=FULL	12.438	12.438	12.399	12.404	12.395	12.417	12.428	12.423	12.468			12.339	12.566	12.621			12.629
	MP3				12.368		12.419
	MP3=FULL				12.373		12.403
	MP4	12.462			12.407				12.440
	B2PLYP													12.480
	B2PLYP=FULLultrafine				12.489								12.348	12.486			12.492
Configuration interaction	CID	12.405	12.405	12.357	12.318			12.322
	CISD	12.397	12.397	12.352	12.323			12.328
		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	12.443	12.443	12.402	12.385	12.381	12.398	12.400	12.400	12.432			12.321	12.509
	QCISD(T)				12.396								12.340	12.546		12.412	12.568
Coupled Cluster	CCD	12.451	12.451	12.407	12.378	12.379	12.394	12.392	12.399	12.428			12.322	12.508		12.381	12.526
	CCSD(T)												12.339	12.545		12.411	12.567
	CCSD(T)=FULL				-2.776								12.347	12.568		12.419	12.591
		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	11.781	11.644	11.814	11.692	11.887	11.890			11.486
Moller Plesset perturbation	MP2	12.251	12.255	12.324	12.359	12.380	12.382			12.549

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.