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

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
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    
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      
SVWN   2.005     2.000 2.000 2.005 1.992 1.992 2.000     2.010 1.993   2.010 1.992      
BLYP 2.137 2.153 2.153 2.154 2.151 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 2.008 2.014 2.008 2.008 2.015 2.007 2.007 2.009   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       2.021 2.038 1.939   2.038 2.026      
Moller Plesset perturbation MP2 2.122 2.044 2.044 2.044 2.017 2.017 2.024 2.027 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      
Configuration interaction CID   2.051 2.051 2.053 2.012     2.023                        
CISD   2.059 2.059 2.062 2.021     2.033                        
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

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 2.111 2.111 2.072 2.053 2.071 2.071
density functional B1B95 2.595          
B3LYP 2.092 2.092 2.043 2.026 2.028 2.032
Moller Plesset perturbation MP2 2.119 2.084 2.068 2.028 2.070 2.068
Values that are outliers may reflect incorrect atom numbering for different levels of theory.
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