Double hybrids: recommendations for accurate thermochemistry & kinetics

Double hybrids especially excel in thermochemistry, kinetics, transition metal chemistry, and the description of strained organic systems. They often provide improvements over the best performing, dispersion-corrected hybrid functionals.

With the recent efficient MP2 implementation in ADF (SOS-AO-PARI-MP2 [1]), it is now possible to run double hybrid calculations on very large systems.

Example double hybrids
Examples of double hybrids which can be comfortably run on a modern desktop:(H2O)142 water cluster, DNA segment (4 A-T base pairs), a capped gold nanocluster

Many double hybrids are now available in ADF. The implementation is especially efficient for the very accurate class of DOD-double-hybrid functionals, providing double hybrid energies at the computational cost of hybrids.

To provide recommendations to the user, the accuracy of 60 density functional approximations has been assessed on a large variety of chemical applications [2].

General recommendations for double hybrids in ADF

  • Basis set: all-electron TZ2P (QZ4P may not be numerically stable)
  • Accuracy: Normal (good or very good is usually not necessary)
  • Dispersion corrections: D4 or D3(BJ)
  • Use scalar ZORA, especially for transition metals and heavy elements
  • Use a DOD functional if you can (much faster!)

Specific recommendations per application type

1) reaction energies: B2T-PLYP-D3(BJ), or the faster revDOD-BLYP-D3(BJ).

2) activation energies: revDOD-PBEP86-D3(BJ); alternatives: more computationally demanding B2K-PLYP for transition metal complexes, metahybrid M08-HX for organic systems.

3) difficult isomerizations: revDOD-PBE-D4 or revDOD-PBEP86-D4. Fullerenes should not be calculated with double hybrids.

For some applications, double hybrids do not improve much over hybrids or GGAs with dispersion corrections.

4) simple isomerizations: B97-D4:

  libxc B97
  Dispersion Grimme4 s6=1.0000 s8=0.87854260 a1=0.29319126 a2=4.51647719 

5) non-covalently bound complexes: GGA+D, e.g. BLYP-D3(BJ). D4 is generally preferred over D3(BJ).

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[1] Arno Förster, Mirko Franchini, Erik van Lenthe, Lucas Visscher, A Quadratic Pair Atomic Resolution of the Identity Based SOS-AO-MP2 Algorithm Using Slater Type Orbitals, J. Chem. Theory Comput. <16>, 875-891 (2020).

[2] Arno Förster, Lucas Visscher, Double Hybrid DFT Calculations with Slater Type Orbitals, J. Comput Chem. 2020; 1-25.

Key concepts