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Computational Chemistry Comparison and Benchmark DataBase
Release 22May 2022
NIST Standard Reference Database 101
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XXH-bond dimers

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

Diagnostics on calculations

Species with negative natural orbital occupation numbers

This diagnostic indicates that a given molecule's electronic ground state may not be well represented by a single electronic configuration.
See: "A natural orbital diagnostic for multiconfigurational character in correlated wave functions" M. S. Gordon et al., J. Chem. Phys. 110(9), 4199, 1999
Click on "neg" for model chemistries and occupation eigenvalues.

With larger basis sets (such as aug-cc-pVTZ) many molecules have small negative occupation numbers. To provide a more useful diagnostic the following list is limited to orbital occupation numbers less than -0.001

Species Name Minimum Occupation Number
LiH Lithium Hydride neg
CH2- methylene anion neg
CH3- methyl anion neg
NH- Imidogen anion neg
NH2- amino anion neg
OH- hydroxide anion neg
H2O- water anion neg
NaH sodium hydride neg
HCl- hydrogen chloride anion neg
Cu Copper atom neg
Li2- lithium diatomic anion neg
B2 Boron diatomic neg
BC- boron monocarbide anion neg
BC+ boron monocarbide cation neg
C2 Carbon diatomic neg
C2+ carbon diatomic cation neg
C2H Ethynyl radical neg
C2H3 vinyl neg
BeN Beryllium mononitride neg
BeN- Beryllium mononitride anion neg
BN- boron nitride anion neg
BN boron nitride neg
BN+ boron nitride cation neg
CN Cyano radical neg
CN- cyanide anion neg
CN+ Cyano cation neg
HCN+ hydrogen cyanide cation neg
N2- nitrogen diatomic anion neg
NNH Dinitrogen monohydride neg
LiO- lithium oxide anion neg
LiOH lithium hydroxide neg
BeO beryllium oxide neg
BeO- Beryllium monoxide anion neg
BO boron monoxide neg
BO+ boron monoxide cation neg
CO+ carbon monoxide cation neg
HCO Formyl radical neg
NO Nitric oxide neg
NO- nitric oxide anion neg
HNO+ Nitrosyl hydride cation neg
O2- oxygen diatomic anion neg
HO2- Hydroperoxy anion neg
HO2+ Hydroperoxy cation neg
LiF lithium fluoride neg
BF- Boron monofluoride anion neg
FO- flourine oxide anion neg
F2- flourine diatomic anion neg
NaLi- lithium sodium anion neg
Na2- sodium diatomic anion neg
NaO sodium monoxide neg
NaO- sodium oxide anion neg
NaOH sodium hydroxide neg
NaF sodium fluoride neg
Mg2- magnesium diatomic anion neg
MgO magnesium oxide neg
MgO- magnesium oxide anion neg
MgOH magnesium hydroxide neg
MgF+ magnesium fluoride cation neg
AlN- aluminum mononitride anion neg
AlO Aluminum monoxide neg
AlO- Aluminum monoxide anion neg
AlO+ aluminum monoxide cation neg
SiC- silicon monocarbide anion neg
SiC+ silicon monocarbide cation neg
SiN Silicon nitride neg
SiN- silicon mononitride anion neg
SiN+ silicon mononitride cation neg
SiO- silicon monoxide anion neg
SiO+ silicon monoxide cation neg
CP Carbon monophosphide neg
CP- carbon monophosphide anion neg
CP+ carbon monophosphide cation neg
PN- phosphorus nitride anion neg
PN+ phosphorus nitride cation neg
P2- phosphorus diatomic anion neg
PO Phosphorus monoxide neg
BeS beryllium sulfide neg
BS boron sulfide neg
BS- boron monosulfide anion neg
BS+ boron monosulfide cation neg
CS- carbon monosulfide anion neg
CS+ carbon monosulfide cation neg
HCS Thioformyl radical neg
NS Mononitrogen monosulfide neg
SO Sulfur monoxide neg
SO- sulfur monoxide anion neg
MgS magnesium sulfide neg
AlS Aluminum sulfide neg
SiS- silicon monosulfide anion neg
PS phosphorus sulfide neg
BCl- boron monochloride anion neg
NCl- nitrogen monochloride anion neg
NCl+ nitrogen monochloride cation neg
ClO Monochlorine monoxide neg
ClO- chlorine monoxide anion neg
ClF- clorine monofluoride anion neg
SCl sulfur monochloride neg
CaO Calcium monoxide neg
CuO Copper Monoxide neg
CuF Copper monofluoride neg
CuCl Copper monochloride neg
CSe- Carbon monoselenide anion neg
SeO Selenium monoxide neg
SeO- selenium monoxide anion neg
BrF- bromine fluoride anion neg
C3H3 Propargyl radical neg
C3H5 Allyl radical neg
HN3 hydrogen azide neg
Li2O dilithium oxide neg
HCCO ketenyl radical neg
BO2 Boron dioxide neg
N2O+ Nitrous oxide cation neg
CO2+ Carbon dioxide cation neg
CH3CO Acetyl radical neg
NO2- Nitrogen dioxide anion neg
O3 Ozone neg
FOO Dioxygen monofluoride radical neg
NF2+ Difluoroamino cation neg
SiO2 silicon dioxide neg
PO2 Phosphorus dioxide neg
SO2 Sulfur dioxide neg
CS2+ Carbon disulfide cation neg
SSO Disulfur monoxide neg
ClOO chloroperoxy radical neg
OClO Chlorine dioxide neg
SeO2 Selenium dioxide neg
C4 Carbon tetramer neg
AlF3 Aluminum trifluoride neg
SOCl2 thionyl chloride neg
ClFO3 Perchloryl fluoride neg
SO2Cl2 Sulfuryl chloride neg
C6H5 phenyl neg
C3H4O2S 2H-Thiete-1,1-dioxide neg
C6H5CH2 benzyl radical neg