Approximate structures of MESX and MECI can be explored automatically by the ADDF method. ADDF is applied to the following model function *F*(*ξ*) called **seam model function (SMF)**, which consists of a mean energy term for the two target PESs, *E*^{X}(**Q**) and *E*^{Y}(**Q**), and a penalty function for their energy gap,

where **Q** is the atomic coordinates and *α* is a constant parameter (in default, *α* = 30 kJ/mol). Typically, *α* is set to ∼1/10 of the vertical excitation energy in the target system, and in general results are not very sensitive to the value of *α*. Minimization of *F*(**Q**) gives a geometry in which both the mean energy and the energy gap are small. Hence, local minima on *F*(**Q**) can be good guesses of MESXs and MECIs.

An example of input for an automated exploration of approximate S_{0}/T_{1} MESX structures is:

` # ADDF/UB3LYP/6-31+G** 0 1 C -0.450261277786 0.001229457926 -0.553082461345 O 0.054687651811 -0.003728650367 0.666230115529 H 0.197675109173 0.761833114909 -1.107795147264 H 0.197898516798 -0.759333922472 -1.108541506919 Options ModelF Second Input UB3LYP/6-31+G** 0 3 END MaxStepSize=0.1 Stable=Opt FirstOnly `

The ** ModelF** option is used together with the

**Note**: the initial structure in the above input is optimized local minimum on the model function SMF.

See Global reaction route mapping by ADDF.

Updated At:Aug. 4, 2020, 2:02 p.m.