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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

From: The multiple roles of histidine in protein interactions

Interaction pair

Molecule

B3LYP/6-31+G(d,p)

CCSD/6-31+G(d,p)

Eint(kcal/mol)

R(Ã…)

Eint-kcal/mol)

R(Ã…)

a π-π stack

C6H6-C6H6

+0.100

7.874

−1.883

4.262

b H-Ï€

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-Ï€

C6H6CH3-H3O+

Eint(kcal/mol)

R(Ã…)

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

 
  1. 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.
  2. 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.
  3. c ‘H-b’ indicates the common hydrogen bond interaction, which is the MO-coordinated and charge dominated interaction.
  4. d In the cation-Ï€ interactions the electrostatic interactions and MO orbital coordinate interactions make the main contributions, and the dispersion contribution is less than 10%.