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Relative enthalpies of isomers - Comparison of 298.15K enthalpies (kJ mol-1)

Isomers of C2H2

index Species CAS number Name Relative experimental enthalpy (kJ mol-1) sketch
a CCH2 2143693 vinylidene   sketch of vinylidene
b C2H2 74862 Acetylene 0.0 sketch of Acetylene
The calculated enthalpies include the calculated and scaled vibrational zero-point energy.
Methods with predefined basis sets
semi-empirical AM1
0.0 b
PM6 602.9 a
MNDOd
0.0 b
composite G1 451.1 a
0.0 b
G2MP2 448.3 a
0.0 b
G2 445.8 a
0.0 b
G3 438.6 a
0.0 b
G3B3 438.1 a
0.0 b
G3MP2 241.8 a
0.0 b
G4 436.8 a
0.0 b
CBS-Q 438.7 a
0.0 b
molecular mechanics MM3
0.0 b

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 cc-pV(T+d)Z cc-pCVDZ cc-pCVTZ
hartree fock HF
0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b
 
0.0 b

0.0 b

0.0 b
140.2 a
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
208.6 a
0.0 b
   
ROHF                                   NC    
density functional LSDA
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b

0.0 b
 
0.0 b
   
0.0 b
   
BLYP
0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b

0.0 b
 
0.0 b
    238.0 a
0.0 b
   
B1B95
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b

0.0 b
 
0.0 b
    240.1 a
0.0 b
   
B3LYP
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
239.2 a
0.0 b
   
B3LYPultrafine        
0.0 b
                             
B3PW91
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b

0.0 b
 
0.0 b
    243.1 a
0.0 b
   
mPW1PW91
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b

0.0 b
 
0.0 b
    240.8 a
0.0 b
   
PBEPBE
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b

0.0 b
  245.2 a
0.0 b
   
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 cc-pV(T+d)Z cc-pCVDZ cc-pCVTZ
Moller Plesset perturbation MP2
0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b
   
0.0 b

0.0 b
 
0.0 b

0.0 b
 
0.0 b

0.0 b
  279.9 a
0.0 b
201.3 a
0.0 b
211.6 a
0.0 b
MP2=FULL  
0.0 b
   
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
   
0.0 b

0.0 b
 
0.0 b
    286.1 a
0.0 b
201.8 a
0.0 b
212.8 a
0.0 b
MP3        
0.0 b
                             
MP4        
0.0 b
   
0.0 b
                       
Configuration interaction CID        
0.0 b
   
0.0 b
                       
CISD        
0.0 b
                             
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 cc-pV(T+d)Z cc-pCVDZ cc-pCVTZ
Quadratic configuration interaction QCISD  
0.0 b
   
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
   
0.0 b
            a    
QCISD(T)        
0.0 b
   
0.0 b
                       
Coupled Cluster CCD        
0.0 b
   
0.0 b
     
0.0 b
          NC    
CCSD        
0.0 b
   
0.0 b
                       
CCSD(T)        
0.0 b

0.0 b
 
0.0 b
     
0.0 b

0.0 b
 
0.0 b

0.0 b
  179.0 a
0.0 b
167.5 a
0.0 b
179.2 a
0.0 b
CCSD(T)=FULL        
0.0 b
           
0.0 b

0.0 b
 
0.0 b

0.0 b
  185.8 a
0.0 b
168.4 a
0.0 b
181.2 a
0.0 b
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 cc-pV(T+d)Z cc-pCVDZ cc-pCVTZ

Methods with effective core potentials (select basis sets)
CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD
hartree fock HF
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
density functional B1B95 165.0 a
0.0 b
150.7 a
0.0 b
       
B3LYP
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
Moller Plesset perturbation MP2
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

Single point energy calculations (select basis sets)
6-311+G(3df,2p) cc-pVDZ cc-pVTZ aug-cc-pVDZ aug-cc-pVTZ cc-pV(T+d)Z
Moller Plesset perturbation MP2FC// HF/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
MP2FC// B3LYP/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
MP2FC// MP2FC/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b
MP4// HF/6-31G*
0.0 b
 
0.0 b
   
0.0 b
MP4// B3LYP/6-31G*  
0.0 b

0.0 b
   
0.0 b
MP4// MP2/6-31G*
0.0 b
 
0.0 b
   
0.0 b
Coupled Cluster CCSD// HF/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
CCSD(T)// HF/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b

0.0 b

0.0 b
CCSD// B3LYP/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b
CCSD(T)// B3LYP/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b
CCSD(T)//B3LYP/6-31G(2df,p)     242.3 a
0.0 b
    242.3 a
0.0 b
CCSD// MP2FC/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b
CCSD(T)// MP2FC/6-31G*
0.0 b

0.0 b

0.0 b

0.0 b
 
0.0 b
NC = not calculated
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.
gaw refers to the group additivity method implemeted in the NIST Chemistry Webbook.
See section Calculated; Vibrations; Scale Factors; Scale factors to list vibrational scaling factors.
See section Calculated; Vibrations; Scale Factors; Calculate a scale factor to calculate a vibrational scaling factor for a given set of molecules.