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Geometry Comparison

Be2 (Beryllium diatomic)


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

Experimental bond length is 2.460  Å

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Calculated bond length in Å
Methods with predefined basis sets
semi-empirical AM1 1.754
PM3 1.714
PM6 1.621
composite G2 2.241
G3 2.241
G3B3 4.460
G4 1.939
CBS-Q 2.241

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 daug-cc-pVTZ
hartree fock HF 2.112 2.045 2.045 2.046 2.043 2.043 2.053 2.049 2.049 2.043 1.780 2.039 2.060 2.049 2.045 2.061 2.049 2.046     2.048
ROHF   2.045 2.045 2.046 2.043 2.043 2.053 2.049 2.049     2.039 2.060 2.049 2.045 2.061 2.049 2.046      
density functional LSDA 2.129 2.005 2.005 2.006 2.000 2.000 2.005 1.992 1.992 2.000   1.997 2.010 1.993   2.010 1.992        
BLYP 2.137 2.153 2.153 2.154 1.939 2.151 2.147 2.137 2.137 2.151   2.137 2.151 2.135   2.020          
B1B95 2.126 2.014 2.014 2.015 2.011 2.011 2.149 2.007 2.007 2.010   2.007 2.019 2.008   2.019 2.007        
B3LYP 2.124 2.010 2.010 2.012 2.007 2.007 2.012 2.003 2.003 2.007 2.481 2.006 2.014 2.004 2.000 2.014 2.003 2.000      
B3LYPultrafine         2.007             2.006 2.014 2.004   2.014 1.939        
B3PW91 2.128 2.020 2.020 2.020 2.015 2.015 2.019 2.012 2.012 2.015   2.009 2.023 2.011   2.023          
mPW1PW91 2.125 2.020 2.020 2.019 2.015 2.015 2.019 2.012 2.012 2.014   2.008 2.022 2.012   2.023 2.011        
M06-2X 2.131 2.008 2.009 2.014 2.008 2.008 2.015 2.007 2.007 2.009 2.006 2.010 2.018 2.008   2.017 2.008        
PBEPBE 2.139 2.166 2.166 2.165 2.163 2.163 2.158 2.150 2.150 2.162 2.427 2.143 2.162 2.148   2.159 2.147        
PBEPBEultrafine         2.163             2.143 2.162 2.148   2.159 2.147        
PBE1PBE 2.125 2.019 2.019 2.019 2.014 2.014 2.019 2.011 2.011 2.014   2.008 2.022 2.012   2.022 2.011        
HSEh1PBE 2.125 2.020 2.020 2.020 2.015 2.015 2.019 2.012 2.012 2.015   2.009 2.022 2.012   2.023 2.011        
TPSSh   2.036 2.036 2.035 1.939 2.031 1.939 2.028   1.939   2.021 2.038 1.939   2.038 2.026        
wB97X-D     1.939   1.939   1.939   1.939     1.939 1.939 1.939     1.939        
B97D3   1.939     1.939   1.939   1.939   1.939 2.038   1.939     2.037       2.037
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 daug-cc-pVTZ
Moller Plesset perturbation MP2 2.122 2.044 2.044 2.044 1.939 2.017 2.024 1.939 2.027 2.019   2.035 2.041 2.021 2.012 2.043 2.021 2.014 2.037 2.017  
MP2=FULL 2.121 2.042 2.042 2.043 2.013 2.013 2.020 2.024 2.024 2.006   2.034 2.037 1.999 1.992 2.039 2.004 1.995 2.032 2.009  
ROMP2 2.122 2.054 2.054 2.055 2.026 2.026 2.034 2.040 2.040 2.031   2.046 2.053 2.034   2.056          
MP3         2.011   1.939         2.036 2.036 2.016              
MP3=FULL         1.939   2.013         2.036 2.032 1.992              
MP4   2.051     2.011     1.803 2.024     2.040 2.037 2.017   2.041 2.017        
MP4=FULL   2.050     2.007       2.021       2.033 1.993   2.037 2.000        
B2PLYP 2.434 3.163 3.163 2.710 2.559 2.559 2.538 2.549 2.549 2.528   2.386 2.567 2.531   2.559 2.528        
B2PLYP=FULL 2.434 3.171 3.171 2.711 2.556 2.556 2.535 2.546 2.546 2.516   2.385 2.563 2.478   2.555 2.472        
B2PLYP=FULLultrafine         2.009               2.023 2.004     2.005        
Configuration interaction CID   2.051 2.051 2.053 2.012     2.023                          
CISD   2.059 2.059 2.062 2.021     2.033                          
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 daug-cc-pVTZ
Quadratic configuration interaction QCISD   2.060 2.060 2.063 2.021 2.021 2.028 2.034 2.034 2.024   2.052 2.048 2.027   2.051 2.027        
QCISD(T)         2.024             2.056 2.051 2.029   2.054 2.030        
QCISD(TQ)         2.534                 2.489     2.487 2.463      
QCISD(TQ)=FULL                           2.323 2.407   2.327 2.399      
Coupled Cluster CCD   2.050 2.050 2.052 2.011 2.011 2.018 2.022 2.022 2.015   2.040 2.035 2.016   2.039 2.016        
CCSD         2.020     1.801       2.051 2.047 2.026 2.018 2.050 2.026 2.019      
CCSD=FULL         2.016             2.050 2.043 2.002 1.997 2.046 2.008 1.999      
CCSD(T)         2.023 1.806   1.809     2.028 2.055 2.050 2.028 2.020 2.053 2.028 2.021 2.046 2.024  
CCSD(T)=FULL         2.018             2.055 2.046 2.003 1.998 2.049 2.010 2.001 2.042 2.018  
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 daug-cc-pVTZ

Calculated bond length in Å
Methods with effective core potentials (select basis sets)
CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD cc-pVTZ-PP aug-cc-pVTZ-PP Def2TZVPP
hartree fock HF 2.111 2.111 2.072 2.053 2.071 2.071     1.939
density functional B1B95 2.595                
B3LYP 2.092 2.092 2.043 2.026 2.028 2.032     1.939
PBEPBE                 1.939
Moller Plesset perturbation MP2 2.119 2.084 2.068 2.028 2.070 2.068     1.939
Values that are outliers may reflect incorrect atom numbering for different levels of theory.
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