mecp_1.md

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default	MECP Optimization	MECP Calculations	Examples and Guides	1	false	Optimization of a benzene MECP with GFN2-xTB	/page/examples/mecp/mecp_opt.html

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CREST 3.0

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Optimization of a benzene MECP with GFN2-xTB

A specialized new feature of CREST 3 is the mixing of two potential energy surfaces with an additional bias potential to find minimum energy crossing points, as described in DOI: 10.1021/acs.jctc.2c00578. It can be called via the new input file reader {{site.data.icons.book}}, e.g., for the GFN2-xTB S₀/T₁ MECP of benzene: {: .text-justify }

{{ site.data.icons.code }} command {{ site.data.icons.codefile }} struc.xyz {{ site.data. icons.codefile }} input.toml

{% include command.html cmd="crest --input input.toml" %}

{% capture struc_file %} 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 {% endcapture %} {% include codecell.html content=struc_file style="font-size:10px" %}

{% capture toml_file %} #This is a CREST input file input = 'struc.xyz' runtype='ancopt'

#parallelization threads = 4

#calculation data [calculation] type = -1 # specify energy & gradient from [calculation.level] to be used # -1 is for MECPs eprint = true elog="energies.log"

[[calculation.level]] method = "xtb" binary = "xtb" uhf = 0 # GFN2-xTB S0 state flags = "--gfn 2 --grad" dir = 's0'

[[calculation.level]] method = "xtb" binary = "xtb" uhf = 2 # GFN2-xTB T1 state dir = 's1' flags = "--gfn 2 --grad"

[[calculation.constraints]] gapdiff2 = [10.0, 0.005, 0.25] #bias parameter to minimize the gap, [10, 0.005, 0.25] is ok for most molecules {% endcapture %} {% include codecell.html content=toml_file style="font-size:10px" %}

{% include defaulttab.html id="open-1" %}

The optimization trajectory (written to crestopt.log) will look like something in the following. Notice that the gap minimization between the two states (shown in red) is the initial driving force of the procedure. {: .text-justify }

{% include image.html file="example-mecp-1.png" alt="Benzene MECP optimization" caption="Optimization of the GFN2-xTB S₀/T₁ MECP for benzene, starting from the ground state structure." max-width=700%}