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

Geometry Comparison

Al2 (Aluminum diatomic)


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

Experimental bond length is 2.701  Å

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Calculated bond length in Å
Methods with predefined basis sets
semi-empirical AM1 2.498
PM3 2.571
PM6 2.591
composite G2 2.991
G3 2.991
G3B3 3.065
G4 3.031
CBS-Q 2.991

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-pV(T+d)Z cc-pCVDZ cc-pCVTZ
hartree fock HF 2.510 3.193 2.984 3.133 2.991 2.991 2.979 3.020 3.020 2.999 2.256 2.591 3.040 3.010 2.999 3.015 3.000 2.995      
ROHF         2.544                                
density functional LSDA 2.582 3.029 3.029 3.113 3.045 3.045 3.036 3.058 3.058 3.029     3.068 3.037   3.049 3.029        
SVWN   2.909         2.909                            
BLYP 2.614 3.231 3.104 3.204 3.125 3.125 3.111 3.148 3.148 3.104     3.144 3.115   2.806          
B1B95 2.565 3.017 3.017 3.113 3.028 3.028 3.018 3.052 3.052 3.019     3.055 3.030 3.021 3.034 3.022 3.017      
B3LYP 2.582 3.187 3.045 3.153 3.065 3.065 3.052 3.085 3.085 3.051 2.502 2.591 3.089 3.060 3.052 3.066 3.050 3.046      
B3LYPultrafine         3.065                       3.030        
B3PW91 2.572 3.168 3.026 3.125 3.038 3.038 3.032 3.062 3.062 3.031     3.066 3.040   2.750          
mPW1PW91 2.564 3.158 3.014 3.115 3.027 3.027 3.020 3.051 3.051 3.021     3.056 3.030   2.744          
M06-2X         2.906                                
PBEPBE 2.597 3.194 3.069 3.161 3.084 3.084 3.074 3.107 3.107 3.070 2.489   3.106 3.080 3.075 3.086 3.071 3.071      
PBEPBEultrafine         2.497                                
PBE1PBE         2.362                                
HSEh1PBE         2.909                                
TPSSh         2.909   2.909             2.909              
Moller Plesset perturbation MP2 2.537 3.249 2.954 3.198 2.966 2.966 2.954 2.991 2.991 2.991   2.591 3.040 2.997 2.463 3.019 2.991 2.463   2.744 2.718
MP2=FULL 2.535 3.251 2.949 3.199 2.960 2.960 2.950 2.991 2.991 2.960     3.034 2.975 2.396 3.013 2.958     2.738 2.708
MP3         2.965   2.888                            
MP3=FULL         2.883   2.877                            
MP4   3.310     2.971     2.475 2.994                        
B2PLYP         2.908                 2.909              
Configuration interaction CID   3.280 2.948 3.236 2.965     2.986                          
CISD   3.285 2.951 3.240 2.968     2.991                          
Quadratic configuration interaction QCISD   3.321 2.941 3.281 2.962 2.962 2.950 2.983 2.983 2.974     3.039 2.977              
QCISD(T)         2.965     2.307         3.048 2.983   3.026 2.978        
Coupled Cluster CCD   3.309 2.937 3.270 2.957 2.957 2.945 2.976 2.976 2.971     3.033 2.974   3.011 2.969        
CCSD         2.961     2.285                          
CCSD(T)         2.964 2.491   2.302     2.717   3.047 2.983 2.969 3.026 2.977   2.722 2.759 2.723
CCSD(T)=FULL         2.957               2.752 2.706 2.953 2.757 2.694     2.753 2.716

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 3.096 3.001 3.105 3.000 3.165 3.260
density functional B1B95 2.835 2.532        
B3LYP 3.162 3.078 3.159 3.072 3.216 3.257
Moller Plesset perturbation MP2 3.164 2.983 3.172 2.985 3.228 3.295
Values that are outliers may reflect incorrect atom numbering for different levels of theory.
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