The bond-dissociation energy (BDE) workflow computes the energy of homolytically breaking a bond (i.e. where the electrons in a bond are split equally between both fragments). It first optimizes the starting molecule according to the desired mode and computing the energy of the starting molecule. It then iterates over all bonds to be broken and generates the fragments. Each fragment is optimized (except in "Reckless" mode) and a single point energy is taken. The BDE is then the difference in energy between the fragments and the intact molecule, with a correction factor to account for enthalpy effects.
| Mode | Inital Optimization | Final Optimization | Single Point | Optimizes Fragments? |
|---|---|---|---|---|
| Reckless | GFN-FF | GFN2-xTB | no | |
| Rapid | GFN2-xTB | r²SCAN-3c | yes | |
| Careful | r²SCAN-3c | ωB97X-3c | yes | |
| Meticulous | r²SCAN-3c | ωB97X-3c | ωB97M-D3BJ/def2-TZVPPD | yes |
Correction factors (BDE = a * ΔE + b):
| Mode | a | b |
|---|---|---|
| Reckless | 0.717441 | 0.0115402 |
| Rapid | 0.94478 | 0.00497265 |
| Careful | 0.896723 | 0.00642359 |
| Meticulous | 0.92756 | 0.00240908 |
"Rapid" is recommended for most work.