# MECP Screening

(Semi-automated) Screening of benzene MECPs with GFN2-xTB

## (Semi-automated) Screening of benzene MECPs with GFN2-xTB

An extension of the minimum energy crossing point optimization, is the metadynamics-based screening (analogously to conformational sampling). It can be called *via* the new **input file reader** . Again, for the GFN2-xTB *S*_{0}/*T*_{1} MECPs of benzene:

`crest --input input.toml`

```
12
C 1.3830400000 -0.2213700000 0.0054100000
C 0.8812100000 1.0799600000 0.0137400000
C -0.4965300000 1.2961400000 0.0106300000
C -1.3728900000 0.2109800000 -0.0044700000
C -0.8710300000 -1.0904600000 -0.0146100000
C 0.5067700000 -1.3067000000 -0.0079300000
H 2.4566500000 -0.3899700000 0.0090900000
H 1.5639800000 1.9254500000 0.0228700000
H -0.8876100000 2.3099700000 0.0197800000
H -2.4463500000 0.3796100000 -0.0082500000
H -1.5536800000 -1.9359000000 -0.0272900000
H 0.8977800000 -2.3206600000 -0.0132700000
```

```
#This is a CREST input file
input = 'struc.xyz'
runtype='mecp_search' # MECP sampling runtype
#parallelization
threads = 10
#calculation data
[calculation]
eprint = true
elog="energies.log"
[[calculation.mecp]] # This block automatically sets up a uhf=0 and uhf=2 calculation with xtb
method = "xtb"
binary = "xtb"
flags = "--gfn 2 --grad"
[[calculation.constraints]]
gapdiff2 = [7.5, 0.005, 0.25]
#molecular dynamics data, required for MECP sampling runtype
[dynamics]
length = 10.0
tstep = 2.5
dump = 100.0
hmass = 4
```

The sampling algorithm will run in parallel several (*i.e.*, ten) metadynamics simulations *on the mixed PES including the gap potential* and MECP-optimize the output trajectories. While the metadynamics bias potentials are set up automatically, **the user is responsible for setting the MD parameters**, such as the simulation lengths in *ps*. Some benzene MECPs that can be found with this method are shown below (in comparison with FOMO-CASCI(6,5) structures in transparent blue).