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Comparison of levels of theory for Be-Be


Click on an entry for a histogram of the values.
The subscript refers to how many bonds of that type have been calculated.
average calculated bond lengths (Å)
Methods with predefined basis sets
semi-empirical AM1 1.9311
2
PM3 1.9595
2
PM6 1.3994
4
composite G2 2.4486
2
G3 2.4486
2
G3B3 3.0096
2
G4 2.2351
4
CBS-Q 2.4475
2

average calculated bond lengths (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 Def2TZVPP cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ cc-pCVDZ cc-pCVTZ
hartree fock HF 2.8209
2
3.5025
2
3.5025
2
3.3394
2
2.8325
4
3.3293
2
4.0483
2
4.2192
2
4.2192
2
3.2776
2
1.7800
1
2.8904
4
2.1318
4
4.2255
2
4.4854
2
4.4826
2
4.4916
2
4.4847
2
4.4828
2
   
ROHF   2.0452
1
2.0452
1
2.0456
1
2.1423
2
2.0434
1
2.0532
1
2.0490
1
2.0490
1
    2.0386
1
  2.0598
1
2.0493
1
2.0449
1
2.0609
1
2.0485
1
2.0456
1
   
density functional LSDA 2.2028
3
2.2124
2
2.2124
2
2.2033
3
2.1979
3
2.2003
2
2.1989
2
2.1859
3
2.1868
2
2.1940
2
  2.1484
2
  2.2041
2
2.1874
2
  2.2038
2
2.1871
2
     
BLYP 2.2471
2
2.3187
2
2.3187
2
2.3124
2
2.0894
4
2.3032
2
2.2953
2
2.2843
2
2.2843
2
2.2951
2
  2.2412
2
  2.3002
2
2.2791
2
           
B1B95 2.2742
2
2.3343
2
2.3343
2
2.2969
2
2.2822
2
2.2822
2
2.3444
2
2.2771
2
2.2771
2
2.2706
2
  2.2004
2
  2.2842
2
2.2749
2
  2.2820
2
2.2734
2
     
B3LYP 2.2588
2
2.2944
2
2.2944
2
2.2765
2
2.2602
2
2.2602
2
2.2547
2
2.2477
2
2.2477
2
2.2501
2
2.4807
1
2.1852
4
2.0903
4
2.2613
2
2.2435
2
2.2412
2
2.2585
2
2.2426
2
2.2411
2
   
B3LYPultrafine         2.2603
2
            2.1842
2
  2.2614
2
2.2435
2
  2.2586
2
2.2340
4
     
B3PW91 2.2563
2
2.2973
2
2.2973
2
2.2766
2
2.2636
2
2.2636
2
2.2597
2
2.2558
2
2.2558
2
2.2574
2
  2.1811
2
  2.2642
2
2.2505
2
  2.0228
1
       
mPW1PW91 2.2589
2
2.3077
2
2.3077
2
2.2840
2
2.2699
2
2.2699
2
2.2652
2
2.2641
2
2.2641
2
2.2636
2
  2.1845
2
  2.2707
2
2.2583
2
  2.2697
2
2.2582
2
     
M06-2X 2.3300
2
2.4605
2
2.1304
4
2.4073
2
2.3128
4
2.3872
2
2.3815
2
2.3771
2
2.3771
2
2.3697
2
  2.2427
2
  2.3935
2
2.3782
2
  2.3856
2
2.3754
2
     
PBEPBE 2.2400
2
2.3195
2
2.3195
2
2.3116
2
2.3051
2
2.3051
2
2.2982
2
2.2920
2
2.2920
2
2.2999
2
2.4272
1
2.2404
2
2.0884
4
2.3023
2
2.2866
2
  2.2998
2
2.2860
2
     
PBEPBEultrafine         2.3050
2
            2.2402
2
  2.3022
2
2.2864
2
  2.2997
2
2.2858
2
     
PBE1PBE 2.2566
2
2.3007
2
2.3007
2
2.2801
2
2.2468
4
2.2669
2
2.2626
2
2.2604
2
2.2604
2
2.2605
2
  2.1856
2
  2.2680
2
2.2559
2
  2.2671
2
2.2555
2
     
HSEh1PBE 2.2556
2
2.1276
4
2.2960
2
2.2763
2
2.2449
4
2.2636
2
2.2452
4
2.2566
2
2.2566
2
2.2573
2
  2.1843
2
  2.2648
2
2.1179
4
  2.2639
2
2.2523
2
     
TPSSh   2.3078
2
2.3078
2
2.2749
2
2.0941
4
2.2591
2
2.0947
4
2.2554
2
  2.0934
4
  2.1814
2
  2.2606
2
2.0939
4
  2.2603
2
2.2472
2
     
wB97X-D     2.1157
4
  2.1100
4
  2.1118
4
  2.1103
4
    2.0902
4
  2.1118
4
2.1099
4
    2.1112
4
     
B97D3   2.1140
4
    2.1079
4
  2.1077
4
  2.1066
4
  2.1052
4
      2.1059
4
    2.1445
4
     
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 Def2TZVPP cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ cc-pCVDZ cc-pCVTZ
Moller Plesset perturbation MP2 2.8703
2
3.1334
2
3.1334
2
3.1055
2
2.0885
4
2.9728
2
3.1434
2
2.0979
4
3.0504
2
2.3619
2
  2.2455
4
2.1012
4
3.1399
2
2.4052
2
2.3727
2
2.9836
2
2.4006
2
2.3700
2
2.0367
1
2.0170
1
MP2=FULL 2.8690
2
3.1268
2
3.1268
2
3.0974
2
2.9572
2
2.9572
2
3.1207
2
2.4704
2
2.4704
2
2.3150
2
  2.2741
2
  3.1255
2
2.2319
2
2.3075
2
2.7199
3
2.2654
3
2.3016
2
2.0316
1
2.0091
1
ROMP2 2.1222
1
2.0543
1
2.0543
1
2.0555
1
2.0261
1
2.0261
1
2.0338
1
2.0396
1
2.0396
1
2.0311
1
  2.0460
1
  2.0533
1
2.0337
1
  2.0561
1
       
MP3         3.0132
2
  2.0822
4
        2.2639
2
  2.3985
2
2.3399
2
           
MP3=FULL         2.0808
4
  2.3051
4
        2.2617
2
  2.3826
2
2.1967
2
           
MP4   3.2224
2
    2.3072
2
    1.8031
1
2.3234
2
    2.2568
2
  2.3361
2
2.2553
4
  2.3420
2
2.2924
2
     
MP4=FULL   3.2148
2
    2.2932
2
      2.3130
2
        2.3252
2
2.1775
2
  2.3298
2
2.1816
2
     
B2PLYP 2.4342
1
3.1629
1
3.1629
1
2.7096
1
2.3299
3
2.5589
1
2.5383
1
2.5494
1
2.5494
1
2.5278
1
  2.3857
1
  2.5666
1
2.3388
3
  2.5585
1
2.5284
1
     
B2PLYP=FULL 2.4338
1
3.1705
1
3.1705
1
2.7111
1
2.5558
1
2.5558
1
2.5355
1
2.5462
1
2.5462
1
2.5157
1
  2.3851
1
  2.5630
1
2.4776
1
  2.5547
1
2.4722
1
     
Configuration interaction CID   3.3285
2
3.3285
2
3.3329
2
3.2328
2
    3.3930
2
                         
CISD   3.3161
2
3.3160
2
3.3233
2
3.2311
2
    3.4255
2
                         
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 Def2TZVPP cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ cc-pCVDZ cc-pCVTZ
Quadratic configuration interaction QCISD   3.3940
2
3.3940
2
3.4097
2
3.3325
2
3.3325
2
3.5999
2
3.5633
2
3.5633
2
2.3538
2
  3.4565
2
  3.5182
2
3.5465
2
  3.3635
2
3.2748
2
     
QCISD(T)         2.3172
2
            2.2934
2
  2.3300
2
2.2746
2
  2.3325
2
2.2734
2
     
QCISD(TQ)         2.5344
1
                  2.4888
1
    2.4867
1
2.4632
1
   
QCISD(TQ)=FULL                             2.3230
1
2.4073
1
  2.3268
1
2.3992
1
   
Coupled Cluster CCD   3.4299
2
3.4299
2
3.4346
2
3.3497
2
3.3497
2
3.5437
2
3.5319
2
3.5319
2
3.0733
2
  3.4417
2
  3.4897
2
3.3025
2
  3.3118
2
3.1971
2
     
CCSD         3.4862
2
    1.8014
1
      3.4533
2
  3.5075
2
3.3795
2
3.2836
2
3.3573
2
3.2697
2
3.2502
2
   
CCSD=FULL         3.4658
2
            3.4485
2
  3.4823
2
2.2070
2
2.3082
2
3.3167
2
2.2071
2
2.3018
2
   
CCSD(T)         3.2286
2
1.8056
1
  1.8095
1
      2.3016
2
  2.3423
2
2.2820
2
2.2604
2
2.3444
2
2.2803
2
2.2610
2
   
CCSD(T)=FULL         2.3126
2
            2.2946
2
  2.3287
2
2.1717
2
2.2171
2
2.3294
2
2.1763
2
2.2139
2
   
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 Def2TZVPP cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ cc-pCVDZ cc-pCVTZ

average calculated bond lengths (Å)
Methods with effective core potentials (select basis sets)
daug-cc-pVDZ daug-cc-pVTZ daug-cc-pVQZ Sadlej_pVTZ CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD
hartree fock HF         4.5206
2
4.5201
2
4.5014
2
4.4874
2
4.5010
2
4.5009
2
density functional B1B95         2.5947
1
         
B3LYP         2.3596
2
2.3417
2
2.3253
2
2.2938
2
2.2896
2
2.2940
2
Moller Plesset perturbation MP2         3.4806
2
3.1846
2
3.3969
2
2.4912
2
3.3773
2
3.3694
2
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.