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III.G.1.a.

Comparison of levels of theory for Mg-Mg


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 3.9498
3
PM3 2.3424
2
PM6 1.6648
4
composite G2 3.0260
4
G3 5.2639
4
G3B3 3.7798
4
G4 3.2270
3
CBS-Q 3.0260
4

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 cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ
hartree fock HF 2.6781
2
3.0806
4
2.9633
4
3.0811
4
3.0503
5
3.0260
4
2.9857
4
5.2613
4
4.6684
3
3.0287
4
4.7035
2
5.3574
4
4.8439
3
4.8277
3
4.8158
3
4.8119
3
4.8026
3
5.0329
3
density functional LSDA 2.5916
3
3.0991
4
3.0587
4
3.2312
4
3.2080
4
3.2080
4
3.3051
4
3.2054
4
3.2054
4
3.1880
4
  3.4108
1
3.2113
4
3.2011
4
3.2447
2
3.3094
4
3.2717
3
3.2194
2
SVWN   3.1735
4
    3.2081
4
3.3810
1
3.2176
4
3.3772
1
3.3772
1
3.3554
1
    3.3852
1
3.3707
1
  3.3846
1
3.3725
1
 
BLYP 2.6223
2
3.8778
4
3.4099
4
3.8774
4
3.7586
4
3.7586
4
3.6528
4
3.7371
4
3.7375
4
3.6765
4
  8.9135
1
3.7113
3
3.6677
3
  3.8641
2
   
B1B95 2.6456
3
3.5532
4
3.3181
4
3.5942
4
3.5390
4
3.5328
4
3.6376
3
3.5354
4
3.5354
4
3.5089
4
  4.1167
1
3.5348
4
3.5339
4
3.3439
2
3.5032
4
3.4507
3
3.3211
2
B3LYP 2.6196
2
3.8722
4
3.3868
4
3.8519
4
3.7151
4
3.7151
4
3.6580
4
3.7034
4
3.6290
3
3.6494
4
3.9018
2
5.8192
4
3.7088
4
3.6125
3
3.6847
4
3.5775
3
3.6638
4
3.6687
4
B3LYPultrafine         3.7151
4
            9.8524
1
3.9299
1
3.9367
1
  3.9189
1
2.8952
2
 
B3PW91 2.6030
2
3.5681
4
3.3138
4
3.5486
4
3.4987
4
3.4987
4
3.4602
4
3.4935
4
3.4554
3
3.4799
4
  3.8018
1
3.4601
3
3.4409
3
  3.6026
2
   
mPW1PW91 2.9236
3
3.5525
4
3.2920
3
3.5336
4
3.4839
4
3.4839
4
3.4475
4
3.4800
4
3.4809
4
3.4702
4
  3.7747
1
3.4447
3
3.4300
3
  3.5905
2
3.5997
1
 
M06-2X 2.7370
1
3.9690
1
3.4402
1
3.8165
1
3.4632
4
3.7823
1
3.7834
1
3.7851
1
3.7851
1
3.7487
1
  4.2000
1
3.7881
1
3.7963
1
  3.7874
1
3.7974
1
 
PBEPBE 2.5964
2
3.4591
4
3.2654
3
3.4653
3
3.4526
4
3.4526
4
3.4047
4
3.4437
4
3.4437
4
3.4323
4
3.4923
2
3.5907
1
3.4499
4
3.4346
4
3.3452
2
3.4974
1
3.5022
1
3.3160
2
PBEPBEultrafine         3.5001
2
            3.5912
1
3.5011
1
3.5031
1
  3.4987
1
3.5031
1
 
PBE1PBE 2.6998
1
3.3471
1
3.3471
1
3.6404
1
3.4752
4
3.5766
1
3.5770
1
3.5825
1
3.5825
1
3.5615
1
  3.7434
1
3.5769
1
3.5843
1
  3.5757
1
3.5854
1
 
HSEh1PBE 2.7024
1
3.6415
1
3.3384
1
3.6336
1
3.3372
4
3.5704
1
3.5705
1
3.5756
1
3.5756
1
3.5523
1
  3.7379
1
3.5723
1
3.5760
1
  3.5706
1
3.5773
1
 
TPSSh   3.7046
1
3.3590
1
3.6287
1
2.9234
3
3.5543
1
2.9292
3
3.5552
1
      3.7630
1
3.5499
1
2.9257
3
  3.5479
1
3.5513
1
 
Moller Plesset perturbation MP2 2.6671
2
3.0845
4
3.6070
4
3.0790
4
2.9711
4
2.9711
4
3.8791
4
3.8833
4
3.8833
4
2.9685
4
  4.5142
4
3.9983
4
3.6131
3
3.7343
4
3.7241
3
3.7376
4
3.7274
4
MP2=FULL 2.6507
2
3.0828
4
3.3989
3
4.1227
3
3.8701
4
3.8687
4
2.9188
4
3.8381
4
3.6802
3
3.4551
3
  6.0381
1
3.2138
3
3.1672
3
3.6627
4
3.6863
2
2.9588
1
3.5713
3
MP3         3.7919
4
  2.9191
3
        5.8128
1
4.4465
1
4.0134
1
       
MP3=FULL         2.9159
3
  3.4433
3
        5.7622
1
4.4352
1
3.7586
1
       
MP4   4.0944
3
    2.9957
4
    4.2287
2
3.6236
3
    5.7632
1
4.4981
1
3.6345
4
  4.2729
1
3.9612
1
 
MP4=FULL   5.0289
1
    4.1549
1
      4.1648
1
      4.4862
1
3.7053
1
  4.2433
1
3.6628
1
 
B2PLYP         3.4965
3
                2.9379
3
       
Configuration interaction CID   4.1364
3
3.6474
3
4.3259
3
3.8308
3
    4.0772
4
                   
CISD   4.1293
3
3.6632
3
4.3188
3
3.8356
3
    3.8526
3
                   
Quadratic configuration interaction QCISD   3.1457
4
3.7137
3
4.3803
3
2.9691
4
4.0133
3
4.2707
4
4.2651
4
3.9587
3
3.7645
3
  5.8397
1
4.3679
4
3.9541
4
  5.0092
1
4.5240
1
 
QCISD(T)         3.8039
3
    4.5367
1
      5.7833
1
3.8560
3
3.5645
3
  3.7230
3
3.5565
3
 
Coupled Cluster CCD   4.1751
3
3.7019
3
4.3984
3
2.9572
4
3.9956
3
3.9238
3
4.2419
4
3.9400
3
3.7395
3
  5.7927
1
4.3523
4
3.7285
3
4.3990
1
3.8766
3
3.7131
3
4.4020
1
CCSD         2.9682
4
    5.1750
2
      5.8422
1
5.4034
1
4.5772
1
4.4473
1
5.0084
1
4.5360
1
4.4442
1
CCSD=FULL         5.1600
1
            5.7940
1
5.2894
1
4.0109
1
4.1422
1
4.8704
1
3.9142
1
4.1107
1
CCSD(T)         4.7609
2
3.6844
2
  4.5354
2
    4.0177
2
5.7775
1
4.1282
4
3.6892
4
3.9753
1
3.9257
4
3.6824
4
3.9775
1
CCSD(T)=FULL         3.7525
3
            5.7282
1
4.8850
1
  3.8203
1
4.4702
1
3.6969
1
3.7980
1

average calculated bond lengths (Å)
Methods with effective core potentials (select basis sets)
CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD
hartree fock HF 4.6282
4
4.8368
3
4.8862
3
4.8220
3
4.8689
3
5.0138
4
density functional B1B95 3.8294
2
3.7383
1
       
B3LYP 3.7472
3
3.6493
3
3.7249
3
3.6260
3
3.6452
3
3.4138
3
Moller Plesset perturbation MP2 4.1748
3
3.7508
3
4.3741
4
3.8296
4
4.4105
4
3.7764
3
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.