Table 3. Comparison of Different Approximations to the Dispersion Energy for Several van der Waals Systemsa.
| method/system | (N2)2 | (HF)2 | (H2O)2 | (CO)2 | CO–H2O | Ne–Ar |
|---|---|---|---|---|---|---|
| Edisp(20) | –0.7463 | –2.5564 | –3.1163 | –0.9945 | –0.9976 | –0.2439 |
| Edisp(2)(TDHF) | –0.6784 | –2.6731 | –3.2003 | –0.9599 | –0.9608 | –0.2359 |
| Edisp(2)(SAPT2) | –0.7282 | –3.1486 | –3.6265 | –1.0855 | –1.1296 | –0.2634 |
| Edisp(2)(TDDFT) | –0.7142 | –3.0704 | –3.5410 | –1.0846 | –1.061 | –0.2590 |
| Edisp(2)(CCD+ST(CCD)) | –0.7095 | –3.0987 | –3.5658 | –1.0356 | –1.0803 | –0.2638 |
| Edisp(2)(DF-CCSD(3)) | –0.7303 | –3.1796 | –3.6532 | –1.0802 | –1.1008 | –0.2670 |
| Edisp(2)(CCPP2(T)) | -0.7189 | -3.1655 | -3.6279 | -1.0586 | -1.1199 | -0.2661 |
| Edisp(2)(T) | –0.1218 | –0.4919 | –0.5815 | –0.2086 | –0.2015 | –0.0371 |
a
The test set was taken from ref (23). The DF-CCSD(3) dispersion corresponds to the density-fitted CCSD response function, accurate to the third order in the correlation operator. The energy unit is milihartree.