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IV.D.1. (XII.C.1.)

Geometry Comparison

C2H (Ethynyl radical)


distance is atom 1 (C) to atom 2 (C)

Experimental bond length is 1.217  Å

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Calculated bond length in Å
Methods with predefined basis sets
semi-empirical PM3 1.290
PM6 1.190
composite G2 1.215
G3 1.215
G3B3 1.226
G4 1.203
CBS-Q 1.218

Calculated bond length in Å
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) cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ
hartree fock HF 1.221 1.223 1.223 1.235 1.215 1.215 1.216 1.210 1.209 1.208 1.204 1.220 1.205 1.203 1.219 1.204 1.203
ROHF   1.189 1.189   1.185 1.185 1.187 1.182       1.191 1.179        
density functional LSDA 1.217 1.214 1.214 1.221 1.225 1.224 1.226 1.206 1.206 1.214   1.229 1.204   1.230    
SVWN   1.214     1.215   1.217                    
BLYP 1.224 1.225 1.225 1.247 1.255 1.255 1.258 1.241 1.238 1.249   1.259 1.235   1.260    
B1B95 1.209 1.208 1.208 1.215 1.207 1.209 1.210 1.202 1.202 1.203   1.213 1.199   1.212    
B3LYP 1.211 1.209 1.209 1.217 1.226 1.225 1.233 1.203   1.204 1.199 1.234 1.199 1.198 1.240 1.199 1.199
B3LYPultrafine         1.226                     1.199  
B3PW91   1.211 1.211 1.217 1.213 1.210 1.212 1.203   1.205   1.214 1.200   1.214    
mPW1PW91   1.209   1.215 1.208 1.208 1.210 1.202 1.201 1.203   1.212 1.199   1.212    
PBEPBE   1.220     1.243 1.242 1.245 1.227 1.221 1.236 1.220 1.246 1.220     1.220  
PBEPBEultrafine         1.243                        
PBE1PBE         1.208                        
TPSSh         1.212   1.214           1.203        
Moller Plesset perturbation MP2   1.187 1.187 1.195 1.181 1.181 1.184 1.179 1.178 1.174   1.191 1.174   1.191 1.174  
MP2=FULL   1.187     1.180 1.180 1.183 1.178       1.190 1.171   1.191    
MP3         1.183   1.176                    
MP3=FULL         1.174   1.177                    
MP4         1.189     1.188         1.183        
B2PLYP                         1.202        
Configuration interaction CID         1.187     1.185                  
CISD         1.200                        
Quadratic configuration interaction QCISD   1.226     1.218 1.218 1.220 1.216       1.229 1.209        
QCISD(T)         1.222     1.221                  
Coupled Cluster CCD         1.186     1.184       1.196          
CCSD         1.217     1.215                  
CCSD(T)         1.221 1.221   1.219         1.212        

Calculated bond length in Å
Methods with effective core potentials (select basis sets)
CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD
hartree fock HF 1.280 1.262 1.248 1.219 1.246 1.245
density functional B1B95   1.285        
B3LYP 1.256 1.250 1.237 1.262 1.229 1.229
Moller Plesset perturbation MP2 1.240 1.218 1.205 1.187 1.205 1.204
Values that are outliers may reflect incorrect atom numbering for different levels of theory.
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