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

Geometry Comparison

C2 (Carbon diatomic)


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

Experimental bond length is 1.243  Å

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Calculated bond length in Å
Methods with predefined basis sets
semi-empirical AM1 1.275
PM3 1.284
PM6 1.235
composite G2 1.292
G3 1.292
G3B3 1.311
G4 1.308
CBS-Q 1.296

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) TZVP cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ cc-pCVDZ cc-pCVTZ
hartree fock HF 1.298 1.308 1.308 1.312 1.292 1.292 1.292 1.291 1.291 1.291 1.240 1.284 1.299 1.288 1.286 1.300 1.288 1.286 1.298 1.287
ROHF 1.295 1.304 1.304 1.309 1.290 1.290 1.291 1.289 1.289 1.289     1.297 1.286   1.298 1.286      
density functional LSDA 1.336 1.323 1.323 1.328 1.313 1.313 1.313 1.306 1.306 1.311     1.318 1.303   1.318        
SVWN   1.314     1.313   1.308                          
BLYP 1.350 1.334 1.334 1.339 1.323 1.323 1.324 1.317 1.317 1.320     1.328 1.313   1.271        
B1B95 1.331 1.321 1.321 1.326 1.310 1.310 1.310 1.305 1.305 1.307     1.314 1.302 1.300 1.315 1.301 1.300    
B3LYP 1.334 1.322 1.322 1.327 1.311 1.311 1.311 1.306 1.306 1.308 1.247 1.296 1.316 1.302 1.300 1.316 1.301 1.300 1.315 1.301
B3LYPultrafine         1.311                       1.301      
B3PW91 1.332 1.323 1.323 1.327 1.311 1.311 1.311 1.306 1.306 1.309     1.316 1.303   1.261        
mPW1PW91 1.328 1.321 1.321 1.325 1.308 1.308 1.309 1.304 1.304 1.307     1.314 1.301   1.259        
M06-2X         1.304                              
PBEPBE 1.345 1.335 1.335 1.338 1.322 1.322 1.323 1.317 1.317 1.321 1.255   1.327 1.314 1.313   1.255 1.313    
PBEPBEultrafine         1.264                              
PBE1PBE         1.309                              
HSEh1PBE         1.254                              
TPSSh         1.316   1.316             1.308            
Moller Plesset perturbation MP2 1.350 1.341 1.341 1.347 1.323 1.323 1.323 1.324 1.324 1.319   1.308 1.335 1.317 1.313 1.336 1.317 1.313 1.334 1.315
MP2=FULL 1.350 1.341 1.341 1.347 1.321 1.321 1.322 1.323 1.323 1.316     1.334 1.311 1.309 1.335 1.310 1.309 1.333 1.313
ROMP2 1.358 1.349 1.349 1.355 1.328 1.328 1.328 1.329 1.329 1.324     1.340 1.321   1.341        
MP3         1.313   1.314                          
MP3=FULL         1.312   1.312                          
MP4   1.348     1.331     1.285 1.333         1.277            
B2PLYP         1.312                 1.310            
Configuration interaction CID   1.325 1.325 1.332 1.309     1.310                        
CISD   1.331 1.331 1.337 1.313     1.314                        
Quadratic configuration interaction QCISD   1.340 1.340 1.347 1.322 1.322 1.321 1.323 1.323 1.317     1.335 1.314            
QCISD(T)         1.328     1.261         1.341 1.322   1.343 1.321      
QCISD(TQ)         1.327                       1.321      
Coupled Cluster CCD   1.331 1.331 1.338 1.314 1.314 1.315 1.316 1.316 1.311     1.328 1.308   1.329 1.308      
CCSD         1.319     1.255                        
CCSD(T)   1.260     1.326 1.258 1.259 1.258 1.258   1.249   1.340 1.320 1.315 1.341 1.320 1.315 1.339 1.319
CCSD(T)=FULL         1.346               1.270 1.314   1.271 1.244   1.338 1.316

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 1.348 1.324 1.332 1.298 1.324 1.324
density functional B1B95 1.303 1.293        
B3LYP 1.369 1.348 1.352 1.322 1.343 1.343
Moller Plesset perturbation MP2 1.393 1.361 1.372 1.335 1.365 1.365
Values that are outliers may reflect incorrect atom numbering for different levels of theory.
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