Table 1.
Comparison of three methods (DFT, CCSD, and CCSD(T)) for five interaction types (cation-π; π-π staking; hydrogen-π; hydrogen bond; and metallic cation-coordinate interaction
| Interaction pair | Molecule |
B3LYP/6-31+G(d,p) |
CCSD/6-31+G(d,p) |
||
|---|---|---|---|---|---|
| Eint(kcal/mol) | R(Å) | Eint-kcal/mol) | R(Å) | ||
|
a π-π stack |
C6H6-C6H6 |
+0.100 |
7.874 |
−1.883 |
4.262 |
|
b H-π |
C6H5CH6-Imid |
−2.444 |
3.616 |
−5.897 |
3.324 |
|
c H-b |
NMA-NMA |
−5.827 |
2.186 |
−6.023 |
2.022 |
| Coordinate |
Imid-Na+ |
−38.045 |
2.267 |
−36.788 |
2.317 |
|
d Cation-π |
C6H6CH3-H3O+ |
Eint(kcal/mol) |
R(Å) |
CPU time |
|
| B3LYP/6-31+G(d,p) |
|
−17.791 |
2.781 |
1.08 hours |
|
| CCSD/6-31+G(d,p) |
|
−18.147 |
2.781 |
50 days |
|
| CCSD(T) /6-31+G(d,p) | −18.872 | 2.781 | 86 days | ||
a DFT method B3LYP/6-31+G(d,p) cannot yield attractive interaction energy for C6H6-C6H6 π-π stacking interaction, failing in describing the dispersion dominated π-π stacking interactions.
b ‘H-π’ indicates the interaction between polar hydrogen atom with aromatic molecule in ‘T’ orientation, in which the dispersion energy contributes more than 50%. The energy difference between CCSD and DFT calculations is defined as the dispersion contribution.
c ‘H-b’ indicates the common hydrogen bond interaction, which is the MO-coordinated and charge dominated interaction.
d In the cation-π interactions the electrostatic interactions and MO orbital coordinate interactions make the main contributions, and the dispersion contribution is less than 10%.