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
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IX	Feedback
X	Older CCCBDB versions
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 C₂H₂ (Acetylene)

Experimental Ionization Energy is 11.4 ± 0.002 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	G4	11.398
	CBS-Q	11.409

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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	cc-pV(T+d)Z	daug-cc-pVDZ	daug-cc-pVTZ
hartree fock	HF	8.637	10.026	10.026	9.812	9.628	9.622	9.754	9.770	9.779	9.590	9.776	9.802	9.703	9.755	9.762	9.736	9.760	9.762	9.755	9.725	9.757
density functional	BLYP	9.894	11.087	11.087	10.906	10.803	10.807	11.021	11.063	11.078	10.841	11.130	11.120	10.933	11.100		11.057	11.121		11.100	11.059	11.119
	B1B95	10.152	11.267	11.267	10.578	10.949	10.849	11.098	11.123	11.134	10.970	11.192	11.194	11.047	11.138		11.111	11.180		11.138		11.179
	B3LYP	10.078	11.282	11.282	11.087	10.969	10.971	11.153	11.200	11.215	10.994	11.250	11.245	11.085	11.226	11.242	11.180	11.240	11.245	11.226	11.180	11.238
	B3LYPultrafine		11.282			10.969	10.971	11.153	11.200		10.994	11.250	11.245	11.085	11.226		11.180	11.240			11.180	11.238
	B3PW91	10.157	11.363	11.363	11.134	11.009	11.011	11.149	11.198	11.210	11.023	11.226	11.226	11.104	11.206		11.162	11.214		11.206	11.156	11.213
	mPW1PW91	10.113	11.325	11.325	11.095	10.964	10.965	11.108	11.144	11.156	10.973	11.175	11.182	11.057	11.155		11.115	11.165		11.134	11.109	11.165
	M06-2X	10.187	11.364	11.364	11.175	11.027	11.023	11.165	11.228	11.239	11.065	11.268	11.244	11.122	11.251		11.187	11.257			11.182	11.255
	PBEPBE	10.093	11.296	11.296	11.094	10.980	10.983	11.160	11.191	11.204	11.004	11.243	11.243	11.094	11.220		11.184	11.238		11.220	11.182	11.237
	PBEPBEultrafine		11.296			10.981	10.983	11.160	11.191		11.004	11.243	11.243	11.094	11.220		11.184	11.238			11.182	11.237
	PBE1PBE	10.075	11.303	11.303	11.083	10.951	10.951	11.096	11.130	11.141	10.959	11.162	11.168	11.046	11.144		11.107	11.154			11.101	11.153
	HSEh1PBE	10.058	11.289	11.289	11.066	10.933	10.934	11.080	11.119	11.131	10.942	11.151	11.157	11.030	11.134		11.092	11.144			11.086	11.143
	TPSSh	10.038	11.222	11.222	11.003	10.869	10.871	11.016	11.053	11.063	10.886	11.086	11.095	10.958	11.073	11.086	11.021	11.086	11.089		11.016	11.086
	wB97X-D	10.073	11.340	11.340	11.094	10.962	10.967	11.106	11.156	11.168	10.972	11.178	11.177	11.062	11.146	11.165	11.118	11.155	11.168		11.111	11.154
	B97D3	10.004	11.202	11.202	10.996	10.872	10.875	11.044	11.072	11.086	10.892	11.119	11.124	10.986	11.094	11.113	11.065	11.110	11.116		11.059	11.110
		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	cc-pV(T+d)Z	daug-cc-pVDZ	daug-cc-pVTZ
Moller Plesset perturbation	MP2	9.558	11.088	11.088	10.919	10.968	11.009	11.159	11.207	11.260	11.225	11.467	11.266	11.162	11.446	11.531	11.303	11.490	11.552	11.446	11.298	11.489
	MP2=FULL	9.559	11.090	11.090	10.922	10.979	11.022	11.171	11.221	11.274	11.247	11.491	11.279	11.172	11.478	11.560	11.312	11.523	11.580	11.478	11.308	11.522
	MP3					10.662		10.872				11.134	10.941	10.849	11.118
	MP3=FULL					10.673		10.856
	MP4		10.982			10.861				11.149		11.360		11.041	11.340		11.205	11.380
	MP4=FULL		10.984			10.872				11.162		11.386		11.043	11.374		11.186	11.415
	B2PLYP	9.857	11.178	11.178	10.993	10.923	10.936	11.104	11.146		11.015	11.261	11.196	11.060	11.237		11.165	11.259			11.162	11.258
	B2PLYP=FULL	9.857	11.179	11.179	10.994	10.926	10.940	11.108	11.151	11.177	11.022	11.268	11.200	11.063	11.247		11.168	11.269			11.165	11.268
	B2PLYP=FULLultrafine					10.926												11.269			11.165	11.268
Configuration interaction	CID		10.743	10.743	10.557	10.527			10.730			10.921		10.683	10.905
	CISD			10.754	10.559	10.543			10.743			10.930		10.695	10.915
		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	cc-pV(T+d)Z	daug-cc-pVDZ	daug-cc-pVTZ
Quadratic configuration interaction	QCISD		10.910	10.910	10.726	10.730	10.769	10.901	10.938	10.988	10.944	11.153	10.999	10.893	11.138		11.003	11.169		11.138
	QCISD(T)					10.815			11.037			11.284	11.117	10.986	11.265		11.118	11.304
	QCISD(TQ)					10.793		10.971				11.253		10.965	11.235	11.309		11.273
Coupled Cluster	CCD		10.888	10.888	10.704	10.697	10.736	10.868	10.908	10.958	10.919	11.129	10.963	10.866	11.114		10.983	11.148
	CCSD					10.712	10.756	10.888	10.925	10.976	10.933	11.142	10.985	10.882	11.127		10.994	11.158
	CCSD=FULL					10.728					10.955	11.166	10.997	10.891	11.161	11.223	11.003	11.194
	CCSD(T)					10.810	10.851	10.990	11.032	11.084	11.052	11.280	11.110	10.981	11.261	11.337	11.114	11.300	11.352	11.261
	CCSD(T)=FULL					10.821						11.304	11.119	10.990	11.295	11.368	11.122	11.335	11.381	11.295
		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	cc-pV(T+d)Z	daug-cc-pVDZ	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	9.724	9.516	9.919	9.720	9.951	9.957			9.761
density functional	BLYP									11.109
	B1B95									11.178
	B3LYP	10.927	10.789	11.107	10.988	11.226	11.217			11.232
	B3LYPultrafine									11.232
	B3PW91									11.209
	mPW1PW91									11.162
	M06-2X									11.243
	PBEPBE									11.228
	PBEPBEultrafine									11.228
	PBE1PBE									11.149
	HSEh1PBE									11.138
	TPSSh									11.079
	wB97X-D	10.918	10.783	11.114	10.995	11.196	11.191			11.158
	B97D3									11.109
Moller Plesset perturbation	MP2	10.768	10.832	11.020	11.073	11.035	11.041			11.456
	MP2=FULL									11.477
	B2PLYP									11.244
	B2PLYP=FULL									11.251

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.