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IV.A.4. (XIV.F.)

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
PM3
0.0 b
PM6 664.5 a
MNDOd
0.0 b
composite G1 511.6 a
0.0 b
G2MP2 508.8 a
0.0 b
G2 506.3 a
0.0 b
G3 499.1 a
0.0 b
G3B3 503.4 a
0.0 b
G3MP2 302.3 a
0.0 b
G4 501.6 a
0.0 b
CBS-Q 507.4 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                 NC               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
 
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
   
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

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

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
                             
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

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)     307.1 a
0.0 b
    307.1 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 III.C.1 List or set vibrational scaling factors to change the scale factors used here.
See section III.C.2 Calculate a vibrational scaling factor for a given set of molecules to determine the least squares best scaling factor.